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The Influence of the Dispersed Phase on the Morphology, Mechanical and Thermal Properties of PLA/PE-LD and PLA/PE-HD Polymer Blends and their Nanocomposites with Ti[O.sub.2] and CaC[O.sub.3].

INTRODUCTION

Due to their specific properties, polymers have found application in various areas of human activity so nowadays they are considered the most important technical materials. However, as the application of polymer materials has recorded an increase, the amount of plastic waste also recorded an increase, which led to the problem of its disposal. One of the ways to mitigate this problem is to use biodegradable and biocompatible polymers and polymers whose degradation products are not environmentally harmful [1].

Among huge variety of polymers and polymer blends that have been investigated in the past decade scientists were particularly interested in polylactide (PLA) for its natural origin and biodegradability. Also, PLA is one of the most common polymers used in commercially available and generally accepted production technology of additive manufacturing known as the 3D printing.

PLA is a thermoplastic aliphatic polyester produced from renewable sources whose main disadvantage is its brittleness at room temperature. For the purpose of modifying PLA properties, several studies of PLA polymer blends with various polymers were conducted [2-5]. Also, to gain better mechanical properties, resistance to heat and stability, polymers and polymer blends are usually filled with inorganic nanofillers [6-9].

In general, mechanical and surface properties of polymer blends and polymer blends with fillers depend on several microstructural parameters such as properties of the matrix, distribution of the dispersed phase, properties and distribution of the filler as well as interfacial bonding. Previous studies have shown that the addition of the filler in small quantity can effectively modify the morphology of immiscible polymer blends (such as morphology refinement, coarsening, formation of irregularly shaped domains, promotion of co-continuity, and morphology stabilization), which impacts the mechanical properties of the blends [10]. In materials aimed for 3D printing, the addition of the filler improves mechanical properties of the polymer (e.g. stiffness) so the polymer (i.e. nanocomposite) will withstand stresses that occur during the 3D printing [11]. One of the most studied fillers, and the filler with the wide range of application, is Ti[O.sub.2] [12], However, more than 80% of the fillers used for thermoplastic polymers are based on calcium carbonate minerals [13] and CaC[O.sub.3] can be used in large quantities due to its availability and low price [14].

This research investigated morphology, mechanical, and thermal properties of PLA blended with low-density polyethylene (PE-LD) and high-density polyethylene (PE-HD) in 90/10 weight ratio prepared at different temperatures. Weight ratio of 90/10 was selected based on the desired properties of biodegradability and reduction of nonrenewable petrochemical waste. Also, previous research showed that hydrophobicity as an important surface property can be significantly modified on PLA/PE-LD polymer blend exactly in 90/10 ratio [15]. This polymer ratio was used to create the "island like" morphology on the surface and in that way increased hydrophobicity was obtained. Preparation temperatures of 160[degrees]C and 180[degrees]C were selected based on melting temperature of PLA which ranges between 160[degrees]C and 180[degrees]C.

Furthermore, the influence of Ti[O.sub.2] and CaC[O.sub.3] fillers on the mechanical properties and morphology of PLA/PE-LD and PLA/PE-HD 90/10 weight ratio was investigated. Impact of the filler particle size was examined by testing three types of Ti[O.sub.2] filler.

EXPERIMENTAL SECTION

Materials and Processing

Thermoplastic polymers used in the study were: polylactide (PLA), Ingeo[TM] Biopolymer 3251D produced by NatureWorks LLC, designed for injection molding applications; low-density polyethylene (PE-LD), DOW[TM] LDPE 780E produced by The Dow Chemical Company and high-density polyethylene (PEHD), 2004 TN 52 produced by Total Petrochemicals.

Fillers used in the study were precipitated calcium carbonate (CaC[O.sub.3]), Precarb 400 produced by Schaefer Kalk GmbH & Co. KG, powdered titanium dioxide with average particle size of 21 nm (Ti[O.sub.2] powder), AEROXIDE[R] Ti[O.sub.2] P25 produced by Evonik Resource Efficiency GmbH, granulated titanium dioxide with average particle size of 20 [micro]m (Ti[O.sub.2] granules), VP AEROPERL[R] P25/20 produced by Evonik Resource Efficiency GmbH, and fine powdered titanium dioxide with average particle size of 8 nm Ti[O.sub.2] (Ti[O.sub.2] fine powder), CristalACTiV[TM] PC500 produced by Millennium Inorganic Chemicals.

All polymer blends were prepared in a twin-screw extruder (Rondol 21 mm LAB TWIN) at a rotational frequency of 50 rpm. Influence of preparation temperature was examined at two sets of temperatures:

1. 150[degrees]C in the input zone / 160[degrees]C in working zones (further in text only 160[degrees]C will be indicated).

2. 160[degrees]C in the input zone / 180[degrees]C in working zones (further in text only 180[degrees]C will be indicated).

Preparation of the polymer blends with inorganic fillers was conducted under the conditions: frequency of 50 rpm and 180[degrees]C.

All components were premixed and introduced in the extruder at the same time. Prepared extruded blends were chopped up into granules and then hot pressed in 1-mm-thick sheets for mechanical and thermal testing. Hot pressing was performed at 190[degrees]C with preheating time 3-4 min and heating for 5 min on a Dake hydraulic press. A pressure of 11 MPa was applied. Cooling to the room temperature was performed on Fontune press. Polymer blends and polymer blends with fillers were prepared in weight ratios as shown in Table 1.

Characterization

After the preparation, mechanical properties of all samples were examined, while the thermal properties and morphology were examined only for the selected samples.

Mechanical properties were determined by tensile tests and Izod impact test. The tensile tests were carried out on the Zwick 1445 universal testing machine with the extension rate of 10 mm/min and gauge length of 50 mm. As the results of tensile tests, the values of Young's modulus, E (MPa), yield strength, [[sigma].sub.Y] (MPa), yield strain, [[epsilon].sub.Y] (%), strength at break, [[sigma].sub.B] (MPa), strain at break, [[epsilon].sub.B] (%), and the work to break, W (N m) were obtained. The impact strength, [a.sub.iU] (J/[mm.sup.2]), was measured by Izod testing according to ISO 180-2000.

Thermal properties of the selected samples were determined by the differential scanning calorimetry (DSC), on Mettler Toledo DSC 823c apparatus. All tests were conducted in an inert nitrogen stream flow of 50 mL/min. Two heating cycles that covered intervals from 20[degrees]C to 200[degrees]C, with the heating/cooling rate of 10[degrees]C/ min were applied. Heating and cooling regime consisted of:

* First heating cycle from 20[degrees]C to 200[degrees]C; stabilization on 200[degrees]C for 3 min;

* Cooling from 200[degrees]C to 20[degrees]C; stabilization on 20[degrees]C for 3 min;

* Second heating cycle from 20[degrees]C to 200[degrees]C; stabilization on 200[degrees]C for 3 min;

* Cooling from 200[degrees]C to 25[degrees]C.

Thermograms of the second heating were used to determine the values of the glass transition temperature, [T.sub.g] ([degrees]C), cold crystallization temperature, [T.sub.cc] ([degrees]C), melting temperature [T.sub.m] ([degrees]C), and enthalpies of cold crystallization, [DELTA][H.sub.cc] (J/g), and melting [DELTA][H.sub.m] (J/g).

Morphology was studied by the scanning electron microscopy (SEM) on the fracture surfaces of selected samples (after the tensile tests). For that purpose, VEGA 3 Tescan scanning electron microscope was used. All the samples were gold sputtered prior to SEM characterization.

RESULTS AND DISCUSSION

Influence of the Processing Temperature

DSC analysis includes monitoring of heat flow change in dependence on temperature regime. The resulting thermograms show the changes made in the polymer during different heating regimes. The first change on the PLA curve on Fig. 1 indicates a glass transition temperature ([T.sub.g]), further heating increases the motion of polymer macromolecules, which leads to restructuring with release of energy. This exothermic change on the thermogram represents the process of cold crystallization from which the crystallization temperature ([T.sub.cc]) is determined. Further heating results in the melting process, polymer absorbs the heat, and the molecules start to move freely. This change on the thermogram is shown as an endothermic transition, and the melting temperature ([T.sub.m]) can be determined as the peak of the endotherm.

Thermal properties of pure polymers and polymer blends determined by DSC are given in Table 2. Degree of crystallinity for polymer blends with PLA was calculated on the basis of melting enthalpy, according to the formula [16]:

[X.sub.C] = [[DELTA][H.sub.f,S]/[DELTA][H.sub.f,PLA] x (1 - w)] x 100% (1)

where:

[DELTA][H.sub.f,S]--measured melting enthalpy, in this case it corresponds to [DELTA][H.sub.m,PLA] as given in Table 2.

[DELTA][H.sub.f,PLA]--melting enthalpy of 100% crystal PLA, which is 93,6 [Jg.sup.-1] [16].

w--mass fraction of another polymer in polymer blend (PE-LD, PE-HD).

(1 -w)--mass fraction of PLA in the blend.

DSC thermograms of the second heating run of the initial PLA, PE-LD, PE-HD, and their blends in ratio 90/10 are presented in Figs. 1 and 2.

Thermograms in Fig. 1 and the data in Table 2 illustrate the clear glass transition of the initial PLA at [T.sub.g] (PLA) = 55.3[degrees]C and two peaks of cold crystallization at [T.sub.cc1] (PLA) = 95.7[degrees]C and [T.sub.cc2](PLA) = 153.8[degrees]C with a large melting peak at [T.sub.m](PLA) = 167.1 [degrees]C. Two crystallization peaks for PLA come from two crystalline modifications of PLA: orthorhombic ([beta]) and pseudoorthorhombic ([alpha]) structures [17]. Thermograms of pure PE-LD (Fig. 1) and PE-HD (Fig. 2) illustrate only the melting peaks at [T.sub.m](PE-LD) at 111. 1[degrees]C and [T.sub.m](PE-HD) at 136.8[degrees]C. Glass transition temperature of PE-LD and PE-HD were not determined because they were outside the measuring range of the device. The literature values of PE-LD and PE-HD glass transition temperature are [T.sub.g] (PE-LD) = -90[degrees]C and [T.sub.g](PE-HD) = -110[degrees]C, respectively [18].

For PLA/PE-LD and PLA/PE-HD polymer blends in weight ratio 90/10, it has been shown that they have a glass transition temperature near the value of PLA glass transition temperature so it can be concluded that the PLA polymer is not miscible with PE-LD or PE-HD in the 90/10 ratio. Furthermore, increase of preparation temperature did not increase miscibility of the polymer components.

This was also confirmed with the SEM images of fracture surface of PLA/PE-LD 90/10 and PLA/PE-HD 90/10 prepared at 160[degrees]C and at 180[degrees]C (Fig. 3). SEM micrographs have shown the existence of dispersed domains of PE-LD, as well as PE-HD, in the PLA matrix, which indicates immiscibility of the two phases. The size of the PE-LD domain ranges from 5 to 20 pm, while the uniformly dispersed spherical domains of PE-HD phase ranges from 5 to 10 pm. The fracture takes place at the interface of the phases, which can be attributed to the poor adhesion between the two polymers. For each blend (PLA/PE-LD and PLA/PE-HD), similar morphologies were observed at both preparation temperatures (160[degrees] C and at 180[degrees]C).

The relative degree of crystallinity in the PLA/PE-LD and PLA/PE-HD blends was calculated from the enthalpy of fusion, according to the Eq. 1. It has been calculated that the degree of pure PLA crystallinity is 38.9%, which corresponds to some previous investigations [15, 19]. Addition of 10% PE-LD and PEHD in the PLA did not change [T.sub.m] and [T.sub.g] but, it did slightly change the degree of crystallinity. It has been shown that the degree of crystallinity had increased with the addition of PE-LD and PE-HD when blend was prepared at 160[degrees]C, but the crystallization decreased when blend was prepared at 180[degrees]C. Available literature [20] also confirms that the presence of PE domains facilitate the mobility of PLA chains, which then results in better arrangement of the chains and in the increase of crystallinity of PLA. Decrease of crystallinity of the PLA in the blends prepared at 180[degrees]C can be a consequence of the stress induced by mixing of the polymers and the pressing of the samples [17], that is, the PLA chains are arranged into a less favorable way by the high stress during preparation, which prevented chains to crystallize in a folded-chain crystals.

Values of analyzed mechanical properties of pure PLA and PLA/PE-LD and PLA/PE-HD 90/10 polymer blends prepared at 160[degrees]C and 180[degrees]C are given in Table 3, and stress-strain curves are shown in Fig. 4.

The biodegradable, stiff, and brittle PLA showed extremely high strength at break and Young's modulus, as well as low value of the strain at break. Addition of PE-LD in 10% weight fraction caused a drastic reduction of strength at break as well as toughness and strain at break. This behavior good correlates with thermal properties that have already been described above (immiscible blend, high crystallization degree; Table 2) as well as SEM images that showed no interaction between the dispersed phase and the matrix (separation of phases and no interfacial adhesion between the phases; Fig. 3). The higher preparation temperature did not significantly affect the mechanical properties of pure PLA as well as PLA/PE-LD 90/10, which also complies the thermal properties and morphology. Therefore, retaining the originally high strength of PLA and achieving greater toughness cannot be achieved by the addition of PE-LD. Previous research [19] of surface and interfacial phenomena of the initial PLA and PE-LD polymers and their blends of different composition showed that surface free energies of both polymers are very similar and by measuring the contact angle of water droplet on pure polymers it has been shown that both polymers are predominantly hydrophobic. Also, by calculating the interfacial parameters of the PLA/PE-LD blend, it has been found that the interfacial energy between these two polymers is relatively low. This relatively low interfacial energy between PLA and PE-LD would suggest a good mixing of these two polymers, but further measurements showed negative value of the wetting coefficient, which was an indication of debonding at the interface in the immiscible blends. Those findings suggested the necessity of compatibilization by the addition of nanofiller [19]. According to the available literature, compatibilization and better mechanical properties (better toughness and impact strength) can also be gained with different copolymers [21-23] as well as other reactive compatibilizers [24-26].

In contrast to PE-LD, PE-HD has significantly higher values of the Young's modulus, strength at break, strain at break, and work to break due to the higher share of the crystal phase, that is, due to the lack of branched side groups in the basic macromolecular chain, which allows more tight structure of the chain segments [18]. Addition of PE-HD to PLA in 10% weight fraction showed that PLA/PE-HD 90/10 polymer blend retained high strength at break, but no increase in strain at break was achieved and significant decrease of impact strength occurred. This complies with thermal properties (immiscible blend, high crystallization degree; Table 2) as well as SEM images that showed separation of phases and no interfacial adhesion between the phases (Fig. 3). Compared to the PLA/PE-LD mixture of the same ratio 90/10 prepared at 160[degrees]C, PLA/PE-HD 90/10 blend showed a more regular form of dispersed domains, as well as a better domain size distribution of the PE-HD (5 [micro]m to 10 [micro]m) with the higher portion of larger domains in the PLA matrix. Such morphology resulted in better mechanical properties of the PE-HD blend compared to PE-LD blend. SEM micrographs of fracture surface of the PLA/PE-HD 90/10 blend prepared at 180[degrees]C (Fig. 3) have shown similar morphology as the SEM micrograph of the same blend prepared at a lower temperature, which complies to unchanged mechanical properties. The size of the dispersed domain was also between 5 and 10 pm, but a smaller portion of larger domains and better adhesion was noticed.

Mechanical properties showed the same trend at both preparation temperatures so it can be concluded that the higher preparation temperature does not significantly affect the mechanical properties of PLA/PE-HD 90/10 polymer blend.

Stress-strain diagram (Fig. 4) confirms the above discussion and findings that for both polymer blends, PLA/PE-LD 90/10 and PLA/PE-HD 90/10, no significant change in mechanical properties occurs with the increase of processing temperature.

Influence of the Fillers

As previously discussed, the poor mechanical properties of the polymer blends are caused by surface and interfacial phenomena that can be interpreted as the absence of adhesion or interaction between the polymers in the immiscible blends [19]. Also, SEM micrographs (Fig. 3) of fracture surface of PLA/PE-LD 90/10 and PLA/PE-HD 90/10 blends showed immiscibility of its components and formation of two separate phases inside the material and poor adhesion between PLA and PE-LD, that is, PLA and PE-HD are observed. The addition of nanofillers to polymer blends could increase interactions on the interface of the phases and thus act as a compatibilizer or reinforcement of the system [19]. So, for the purpose of improving the adhesion, and consequently the mechanical properties of polymer blends, fillers are used as potential compatibilizers.

Nofar et al. [27] performed the extensive analysis of many studies that have investigated PLA-based blend nanocomposites and concluded that not only the final morphology of the blend, but also the thermodynamics and interfacial properties would determine the final features of the product.

In this study, the effect of fillers on the morphology, mechanical, and thermal properties of polymer blends PLA/PE-LD and PLA/PE-HD was examined on samples of 90/10 weight ratio prepared in extruder at 180[degrees]C. CaC[O.sub.3] and three types of Ti[O.sub.2] were used as fillers and they were added to the polymer blends in a 5% mass fraction. The impact of particle size of the filler was examined by using three types of Ti[O.sub.2]: powdered Ti[O.sub.2] (average particle size of 21 nm, Ti[O.sub.2] powder), granulated Ti[O.sub.2] (average particle size of 20 pm, Ti[O.sub.2] granules) and fine powdered Ti[O.sub.2] (average particle size of 8 nm, Ti[O.sub.2] fine powder). Fine powdered Ti[O.sub.2] filler was also added in 10% weight ratio.

The effects of filler addition on the DSC thermograms are visible in Figs. 5 and 6, and the thermal properties are given in Table 4.

The DSC thermogram of the PLA/PE-LD 90/10 blend with the CaC[O.sub.3] filler (Fig. 5) indicated that the PE-LD component signal has additionally decreased and the PLA melting signal has increased compared to the nonfilled blend. The addition of CaC[O.sub.3] did not significantly affect the glass transition temperature and the melting temperature compared to the nonfilled blend. However, the filler addition has increased the degree of crystallinity, from [X.sub.c] =30.2% for nonfilled blend to [X.sub.c] =47.1%. The addition of CaC[O.sub.3] filler to the PLA/PE-HD 90/10 blend (Table 4) caused a slight increase of glass transition temperature. Also, there was a slight decrease in the cold crystallization enthalpy, [DELTA][H.sub.cc1] and [DELTA][H.sub.cc2], as well as the increase of the crystallization temperature of the less stable PLA structure. Furthermore, the melting temperature of the components in the composite has slightly shifted toward the lower values. However, all these differences are pretty small and can be attributed to the interpretation errors or the inhomogeneity of the samples. As well as for the PLA/PE-LD 90/10 sample, the filler addition in PLA/PE-HD has increased the degree of crystallinity, from [X.sub.c] = 51.6% for nonfilled blend to [X.sub.c] = 56.6%. According to the literature [13, 28], CaC[O.sub.3] as the filler changes the crystallinity of the system in which is added. Filler particles influence the degree of nucleation and the growth of the spherulites causing an increase in the degree of crystallinity. Thus, CaC[O.sub.3] nanoparticles act as additional nucleation centers in the polymer matrix in the way that they stimulate the formation and growth of crystalline nuclei, as well as they increase the crystallization rate. In this way, the filler increases the crystallinity of the system.

DSC thermogram of samples with the addition of Ti[O.sub.2] as a filler (Fig. 6) showed that the addition of 5% of the fillers to pure PLA did not have a significant impact on the glass transition temperature or on the cold crystallization temperature but it increased the degree of crystallinity compared to the pure PLA. Degree of crystallinity was maximized with the addition of powdered titanium dioxide. The resultant higher crystallinity might be a consequence of a favored nucleation [29] and regular arrangement of PLA chains [9].

Similar thermal properties showed the PLA/PE-LD 90/10 blend and its nanocomposites with the Ti[O.sub.2] filler. The exceptions were observed for the addition of 5% of titanium dioxide in fine powder form, where a significant decrease of the glass transition temperature was achieved. In this case, the filler prevented the formation of crystal domains so the more of the amorphous phase exists in the blend (the degree of crystallinity is 38,5%, i.e., it is the lowest among the samples with 5% of titanium dioxide in fine powder form) causing the chain movement at lower temperatures. The degree of crystallinity was also maximized ([X.sub.c] = 51,2%) with the addition of powdered titanium dioxide. PLA/PE-HD 90/10 blend and its nanocomposites with 5% of fillers have also shown no significant changes in glass transition temperature, enthalpies, and temperatures of cold crystallization and melting. The highest degree of crystallization was achieved with 5% of powdered titanium dioxide. Also, it was observed that the addition of fine powdered Ti[O.sub.2] resulted in lower degree of crystallization, compared to unfilled blend, which can be a consequence of the polymer chains reorganization in the blend [30].

Furthermore, it is important to notice that the addition of 10% of fine powdered Ti[O.sub.2] has caused significant changes in the thermal properties ([T.sub.g], [T.sub.cc1] and [T.sub.m,PLA]) (Table 4) of all nanocomposites. Lower glass transition temperature in these nanocomposites can be attributed to the better miscibility of the phases [31] as well as a consequence of the reduction of the crystal phase, which leads to increase in amount of amorphous phase and higher mobility of polymeric chains in the amorphous phase. The degree of crystallinity was also minimal when this amount of the fine powdered filler was added to the pure PLA component as well as the PLA/PE-LD and PLA/PE-HD blends. It is generally accepted that the presence of nonmiscible and amorphous polymers leads to the formation of smaller crystals and a reduction in total crystallinity. It can therefore be assumed that the addition of 10% of fine powdered Ti[O.sub.2] caused the destruction of the crystalline structure of the initial polymer and polymer blends and that is why amorphousness has increased.

Values of analyzed mechanical properties of nonfilled and filled PLA/PE-LD and PLA/PE-HD 90/10 polymer blends are given in Table 5.

Results for PLA/PE-LD 90/10 polymer blend showed that the addition of the fillers improved mechanical properties as expected. Addition of the fillers resulted in an increase of the stiffness, and the highest stiffness was obtained with the 5% of CaC[O.sub.3] (E = 1,230 MPa). Strength at break, [[sigma].sub.b], and the strain at break, [[epsilon].sub.b], showed the same trend and the highest increase was obtained with the addition of 5% CaC[O.sub.3]. When SEM micrographs of PLA/PE-LD/CaC[O.sub.3] composite with 5% added nanoparticles (Fig. 7) was analyzed, the phase separation was still observed. The dispersed phase had more regular form than in the nonfilled blend and the dispersed phase size ranges from 5 to 15 [micro]m. It would be expected that the filler was placed at the interface of the two polymer phases, but instead it was noticed that the filler was mainly placed in the PLA phase. So, such better and expected results of mechanical tests (significant increase of strength at break and toughness, as well as increase of Young's modulus and stiffness) can be addressed to the better distribution of the dispersed phase in the matrix and the phase reinforcement due to the increase of viscosity caused by CaC[O.sub.3] settlement in one of the phases. Increased crystallinity of PLA also contributes to the improved tensile strength and Young's modulus [32].

Work to break, which is a direct measure of toughness, has also increased with the addition of all the fillers. The greatest increase was achieved with the addition of 5% Ti[O.sub.2] powder (from initial W = 0.05 N m to W= 0.24 N m).

Strength at break, [[sigma].sub.b], and the strain at break, [[epsilon].sub.b], showed the same trend. The lowest values were obtained for the nonfilled polymer blend ([[sigma].sub.b] = 9.2 MPa and [[epsilon].sub.b] = 1.4%) and the addition of fillers increased the values of those properties. The highest increase was obtained with the addition of 5% CaC[O.sub.3] as already discussed but the similar increase was achieved with the 5% Ti[O.sub.2] powder and 5% Ti[O.sub.2] granules filler. SEM micrographs of PLA/PE-LD blend with the addition of 5% Ti[O.sub.2] powder has also shown the presence of two separate phases with the clearly visible phase border but also a very good dispersion of the filler was visible (Fig. 7)--the domains are of spherical shape, they are properly distributed within the matrix, and their size ranges from 2 to 8 pm. Interactions between the phases are also satisfactory. So, such improved mechanical properties of the polymer blend can be attributed to a very good dispersion of the filler and the smaller domain size in the matrix.

It is important to notice that the addition of larger amount of the Ti[O.sub.2] fine powder filler (i.e. 10% Ti[O.sub.2] fine powder) resulted in the decrease of the Young's modulus compared to the initial blend without the filler and no significant impact on strength at break, [[sigma].sub.b], and the strain at break, [[epsilon].sub.b], was achieved. Furthermore, work to break was the lowest when Ti[O.sub.2] as fine powder was added, regardless of the added quantities (5% or 10%). When SEM micrographs of PLA/PE-LD with 10% of Ti[O.sub.2] is analyzed (Fig. 7g and h), it can be seen that filler dispersion was also poor in this case and the filler agglomerates of up to 4 pm were visible at the surface. This phenomenon was expected because the mass fraction of the filler in this nanocomposite is twice as high as in previously analyzed (PLA/PE-LD with 5% Ti[O.sub.2]). Although elongated form of domain occurred the domains were mainly spherical and the size ranged from 10 to 40 [micro]m. Interactions between the phases are poorer than in nanocomposite with 5% of powdered Ti[O.sub.2]. Since the particle size of Ti[O.sub.2] fine powder filler (average particle size 8 nm) is much smaller than the Ti[O.sub.2] powder (average particle size 21 nm), it would be expected that the smaller filler provides a larger contact surface between the filler and the particles of the dispersed phase. However, in this case, it was just the opposite, the addition of Ti[O.sub.2] fine powder created larger domains than with the addition of Ti[O.sub.2] powder. This could be addressed to the placement of the fillers, but additional analyses are needed to confirm this.

Finally, according to the given results it can be concluded that the fillers act as compatibilizers increasing the polymer consistency and influencing the creation of a better structure inside the blend, which leads to the improvement of mechanical properties of an immiscible PLA/PE-LD 90/10 polymer blend. Among tested fillers, CaC[O.sub.3] and Ti[O.sub.2] in powder form have shown the best results for PLA/PE-LD 90/10 blend, and the worst results were achieved with Ti[O.sub.2] in a fine powder form.

As previously discussed, mechanical properties of the pure PLA have not been improved with the addition of 10% PE-HD, as well as with the addition of 10% PE-LD. However, unlike PELD, which drastically reduced Young's modulus (as well as work to break, strain at break and stress at break), PE-HD had the effect of reducing those values to a lesser extent. But, the addition of the fillers to the PLA/PE-HD 90/10 polymer blend did not improve the mechanical properties of the blend as expected. The maximum value of the Young's modulus, that is, the highest stiffness, was achieved with the addition of 5% CaC[O.sub.3] (E = 979 MPa), but the result is very close to the value of the Young's modulus measured for PLA/PE-HD without filler (E = 938 MPa). Also, the addition of the 5% Ti[O.sub.2] powder and 5% Ti[O.sub.2] granules obtained similar values of Young's modulus (E = 935 MPa for sample with Ti[O.sub.2] powder and E = 882 MPa for sample with Ti[O.sub.2] granules). Values of all other tested mechanical properties (work to break, strain at break and stress at break) decreased with the addition of each filler to the PLA/PE-HD 90/10 polymer blend. The greatest decrease was achieved with the addition of 5% Ti[O.sub.2] in a fine powder form, and the lowest decrease was measured for the sample with 5% CaC[O.sub.3] in a powder form.

When SEM micrographs of PLA/PE-HD/CaC[O.sub.3] composite with 5% added nanoparticles were analyzed (Fig. 8), dispersed spherical domains of PE-HD phase, size 5 to 10 pm, surrounded by a PLA matrix with a smooth fracture surface were noticed. It was also noticed that the filler is placed in one of the phases and aggregates of the filler occur in the system. Aggregates of the filler inside the blend create the weak spots that can cause the cracking of the material. It has been shown [33] that the filler aggregates cause the reduction of strength at break and deterioration of other mechanical properties. Furthermore, the tendency to form aggregates increases with the increased amount of filler.

SEM micrographs of PLA/PE-HD blend with the addition of 5% Ti[O.sub.2] powder and 5% of Ti[O.sub.2] fine powder (Fig. 8) have also shown the presence of two separate phases. Both nanocomposites exhibited poorer mechanical properties than the nonfilled polymer blend of PLA/PE-HD 90/10, but deterioration of the mechanical properties is much less expressed in nanocomposite with the Ti[O.sub.2] powder. SEM micrographs of PLA/PE-HD/Ti[O.sub.2] powder nanocomposite showed the domain size in the range of 5 to 15 [micro]m and more homogeneous domain distribution in the matrix compared to the PLA/PE-HD/Ti[O.sub.2] fine powder nanocomposite. The interactions inside the nanocomposite were also better compared to nanocomposite with the Ti[O.sub.2] fine powder.

The domains of the PLA/PE-HD/Ti[O.sub.2] fine powder nanocomposite have a size of 5 to 25 [micro]m, and their interactions are poor. The nanofiller was not well dispersed, and there were visible filler aggregates sized about 2 pm. Therefore, due to weak adhesion, wide particle size distribution and the presence of filler aggregates this nanocomposite showed poor mechanical properties.

Compared to the blend with PE-LD (Fig. 7), more homogeneous size distribution of the dispersed domains in the PLA matrix and the smaller domain size range are observed in the PEHD blend of the same ratio and the same mass fraction of the added filler. However, no significant improvement in the mechanical properties was achieved in the PE-HD composite compared to the PE-LD composite due to poor adhesion between the phases and the generation of aggregates.

Although the different blends were studied, previous researches have shown that Ti[O.sub.2] nanoparticles can be selectively localized on the interfacial surface surrounding the thermo plastic polyurethane (TPU) phase in the PLA/TPU polymer blend [8]. But also, Ti[O.sub.2] nanoparticles can be dispersed within the PLA matrix like it has been shown when PLA blend with poly([epsilon]-caprolactone) (PCL) was studied [34].

Finally, since the filler was not placed on the interface where it would act as a compatibilizer and increase the adhesion, deterioration of mechanical properties has occurred. Furthermore, bad dispersion of the filler and the presence of filler aggregates has caused the morphological coarsening of domains and induced the formation of a nonhomogeneous blend structure, which affected the mechanical properties. Among tested fillers, CaC[O.sub.3] has shown the best results for PLA/PE-HD 90/10 blend. The worst results were achieved with Ti[O.sub.2] in a fine powder form, which could be explained by the fact that Ti[O.sub.2] particles reduce the movement of PLA chains [35] and consequently influence the mechanical properties.

CONCLUSIONS

This research investigated morphology, mechanical, and thermal properties of PLA/PE-LD 90/10 and PLA/PE-HD 90/10 polymer blends prepared at 160[degrees]C and 180 [degrees]C. Furthermore, the influence of several types of Ti[O.sub.2] and CaC[O.sub.3] fillers on the morphology and mechanical properties of the blends was investigated. Impact of the particle size of the filler was examined with the Ti[O.sub.2] filler. The fillers were chosen because of their availability on the market and wide range of application but also because of their potential use as functional fillers--CaC[O.sub.3] can influence the hydrophobicity of the polymer and Ti[O.sub.2] can photo catalyze some reactions.

It has been shown that preparation temperature has no significant impact on the mechanical properties of pure PLA as well as PLA/PE-LD 90/10 and PLA/PE-HD 90/10 polymer blends.

Addition of the fillers to the PLA/PE-LD system has improved the mechanical properties as expected but has not improved the mechanical properties of the PLA/PE-HD 90/10 blend. Generally, among tested fillers CaC[O.sub.3] has shown the best results, and the worst results were achieved with Ti[O.sub.2] in a fine powder form.

It was expected that interaction between the phases will affect the mechanical behavior of the samples the most. However, from the obtained SEM micrographs and mechanical results, it was concluded that the domain size distribution of the dispersed phase within the matrix as well as dispersion of the filler have the greatest influence on mechanical properties. Better mechanical properties showed samples with a narrow size distribution of the dispersed phase domain (5 to 10 [micro]m) with the higher portion of larger domains that are uniformly distributed within the polymer matrix. To obtain satisfactory mechanical properties, the filler should be homogeneously dispersed and prevention of formation of the filler agglomerate should be ensured. Better phase interaction should contribute the most to the improvement of the mechanical properties of the material, but here it has been shown that it is not the crucial factor.

ACKNOWLEDGMENT

This work has been supported by Croatian Science Foundation under the project entitled "Development of materials for 3D printing of microreactors" (UIP-2014-09-3154).
NOMENCLATURE LIST

CaC[O.sub.3]           calcium carbonate
DSC                    differential scanning calorimetry
E                      Young's modulus (MPa)
[DELTA][H.sub.cc]      enthalpy of cold crystallization (J/g)
[DELTA][H.sub.m]       enthalpy of melting (J/g)
[DELTA][H.sub./f,s]    measured melting enthalpy
[DELTA][H.sub.f,PLA]   melting enthalpy of 100% crystal PLA
PCL                    poly([epsilon]-caprolactone)
PE-LD                  low-density polyethylene
PE-HD                  high-density polyethylene
PLA                    polylactide
SEM                    scanning electron microscopy
[T.sub.cc]             cold crystallization temperature ([degrees]C)
[T.sub.g]              glass transition temperature ([degrees]C)
[T.sub.m]              melting temperature ([degrees]C)
Ti[O.sub.2]            titanium dioxide
TPU                    thermo plastic polyurethane
W                      work to break (N m)
w                      mass fraction of another polymer in polymer
                         blend
[a.sub.iU]             impact strength (J/[mm.sup.2])
[[epsilon].sub.B]      strain at break (%)
[[epsilon].sub.Y]      yield strain (%)
[X.sub.c]              degree of crystallinity
[[sigma].sub.B]        strength at break (MPa)
[[sigma].sub.Y]        yield str/ength (MPa)


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Vedrana Lovincic Milovanovic [iD], (1) Ivana Hajdinjak, (2) Ivona Lovrisa, (2) Domagoj Vrsaljko [iD] (2)

(1) MAXICON d.o.o., Kruzna 22, Zagreb, Croatia

(2) Faculty of Chemical Engineering and Technology, University of Zagreb, Zagreb, Croatia

Correspondence to: V. L. Milovanovic; e-mail: vedrana.lovincic@maxicon.hr Contract grant sponsor: Croatian Science Foundation: contract grant number: UIP-2014-09-3154.

DOI 10.1002/pen. 25124

Caption: FIG. 1. DSC thermograms of the second heating run of the initial PLA, PE-LD, and PLA/PE-LD 90/10 prepared at different temperatures.

Caption: FIG. 2. DSC thermograms of the second heating run of the initial PLA, PE-HD, and PLA/PE-HD 90/10 prepared at different temperatures.

Caption: FIG. 3. SEM micrographs of PLA/PE-LD 90/10 and PLA/PE-HD 90/10 prepared at 160[degrees]C and 180[degrees]C: (a) PLA/PELD 90/10 at 160[degrees]C, magnification 500x; (b) PLA/PE-LD 90/10 at 160[degrees]C, magnification 2000x; (c) PLA/PE-LD 90/10 at 180[degrees]C, magnification 500x; (d) PLA/PE-LD 90/10 at 180[degrees]C, magnification 2000x; (e) PLA/PE-HD 90/10 at 160[degrees]C, magnification 500x; (f) PLA/PE-HD 90/10 at 160[degrees]C, magnification 2000x; (g) PLA/PE-HD 90/10 at 180[degrees]C, magnification 500x; (h) PLA/PE-HD 90/10 at I80[degrees]C, magnification 2000x.

Caption: FIG. 4. Stress-strain diagram for PLA/PE-LD 90/10 and PLA/PE-HD 90/10 polymer blends prepared at different temperatures.

Caption: FIG. 5. DSC thermograms of the second heating run of PLA/PE-LD 90/10 and PLA/PE-HD 90/10 with the addition of CaC[O.sub.3] filler.

Caption: FIG. 6. DSC thermograms of the second heating run of PLA/PE-LD 90/10 and PLA/PE-HD 90/10 with the addition of Ti[O.sub.2] fillers.

Caption: FIG. 7. SEM micrographs of PLA/PE-LD 90/10 filled with nanofillers: (a) PLA/PE-LD 90/10 without fillers, magnification 500x; (b) PLA/PE-LD 90/10 without fillers, magnification 2000x; (c) PLA/PE-LD 90/10 with 5% CaC[O.sub.3], magnification 500x; (d) PLA/PE-LD 90/10 with 5% CaC[O.sub.3], magnification 2000x; (e) PLA/PE-LD 90/10 with 5% Ti[O.sub.2] powdered, magnification 500x; (f) PLA/PE-LD 90/10 with 5% Ti[O.sub.2] powdered, magnification 2000x; (g) PLA/PE-LD 90/10 with 10% Ti[O.sub.2] fine powdered, magnification 500x; (h) PLA/PE-LD 90/10 with 10% Ti[O.sub.2] fine powdered, magnification 2000x.

Caption: FIG. 8. SEM micrographs of PLA/PE-HD 90/10 filled with nanofillers: (a) PLA/PE-HD 90/10 without fillers, magnification 500x; (b) PLA/PE-HD 90/10 without fillers, magnification 2000x; (c) PLA/PE-HD 90/10 with 5% CaC[O.sub.3], magnification 500x; (d) PLA/PE-HD 90/10 with 5% CaC[O.sub.3], magnification 2000x; (e) PLA/PE-HD 90/10 with 5% Ti[O.sub.2] powdered, magnification 500x; (f) PLA/PE-HD 90/10 with 5% Ti[O.sub.2] powdered, magnification 2000x; (g) PLA/PE-HD 90/10 with 5% Ti[O.sub.2] fine powdered, magnification 500x; (h) PLA/PE-HD 90/10 with 5% Ti[O.sub.2] fine powdered, magnification 2000x.
TABLE 1. Weight ratios of prepared samples.

                                      Mass fraction

                                      PLA             PE-LD   PE-HD

PLA                                   100%
PE-LD                                 100%
PE-HD                                 100%
PLA/PE-LD 90/10                       90%             10%
PLA/PE-HD 90/10                       90%                     10%
PLA               + 5% CaC[O.sub.3]   95%
PE-LD                                 95%
PE-HD                                 95%
PLA/PE-LD 90/10                       85.5%           9.5%
PLA/PE-HD 90/10                       85.5%                   9.5%
PLA               + 5% Ti[O.sub.2]    95%
PE-LD             P25 (powder)        95%
PE-HD                                 95%
PLA/PE-LD 90/10                       85.5%           9.5%
PLA/PE-HD 90/10                       85.5%                   9.5%
PLA               + 5% Ti[O.sub.2]    95%
PE-LD             P25/20              95%
PE-HD             (granules)          95%
PLA/PE-LD 90/10                       85.5%           9.5%
PLA/PE-HD 90/10                       85.5%                   9.5%
PLA               + 5% Ti[O.sub.2]    95%
PE-LD             PC 500              95%
PE-HD             (fine powder)       95%
PLA/PE-LD 90/10                       85.5%           9.5%
PLA/PE-HD 90/10                       85.5%                   9.5%
PLA               + 10% Ti[O.sub.2]   90%
PE-LD             PC 500              90%
PE-HD             (fine powder)       90%
PLA/PE-LD 90/10                       81%             9%
PLA/PE-HD 90/10                       81%                     9%

                                      Mass fraction

                                      CaC[O.sub.3]   Ti[O.sub.2]
                                                     P25

PLA
PE-LD
PE-HD
PLA/PE-LD 90/10
PLA/PE-HD 90/10
PLA               + 5% CaC[O.sub.3]   5%
PE-LD                                 5%
PE-HD                                 5%
PLA/PE-LD 90/10                       5%
PLA/PE-HD 90/10                       5%
PLA               + 5% Ti[O.sub.2]                   5%
PE-LD             P25 (powder)                       5%
PE-HD                                                5%
PLA/PE-LD 90/10                                      5%
PLA/PE-HD 90/10                                      5%
PLA               + 5% Ti[O.sub.2]
PE-LD             P25/20
PE-HD             (granules)
PLA/PE-LD 90/10
PLA/PE-HD 90/10
PLA               + 5% Ti[O.sub.2]
PE-LD             PC 500
PE-HD             (fine powder)
PLA/PE-LD 90/10
PLA/PE-HD 90/10
PLA               + 10% Ti[O.sub.2]
PE-LD             PC 500
PE-HD             (fine powder)
PLA/PE-LD 90/10
PLA/PE-HD 90/10

                                      Mass fraction

                                      Ti[O.sub.2]    Ti[O.sub.2]
                                      P25/20         PC500

PLA
PE-LD
PE-HD
PLA/PE-LD 90/10
PLA/PE-HD 90/10
PLA               + 5% CaC[O.sub.3]
PE-LD
PE-HD
PLA/PE-LD 90/10
PLA/PE-HD 90/10
PLA               + 5% Ti[O.sub.2]
PE-LD             P25 (powder)
PE-HD
PLA/PE-LD 90/10
PLA/PE-HD 90/10
PLA               + 5% Ti[O.sub.2]    5%
PE-LD             P25/20              5%
PE-HD             (granules)          5%
PLA/PE-LD 90/10                       5%
PLA/PE-HD 90/10                       5%
PLA               + 5% Ti[O.sub.2]                   5%
PE-LD             PC 500                             5%
PE-HD             (fine powder)                      5%
PLA/PE-LD 90/10                                      5%
PLA/PE-HD 90/10                                      5%
PLA               + 10% Ti[O.sub.2]                  10%
PE-LD             PC 500                             10%
PE-HD             (fine powder)                      10%
PLA/PE-LD 90/10                                      10%
PLA/PE-HD 90/10                                      10%

TABLE 2. Thermal properties of pure polymers and polymer blends
prepared at different temperatures.

                                            Cold crystallization
                            Glass
                         transition     [T.sub.ccl]      [DELTA]
Sample                   [T.sub.g]      ([degrees]C)   [H.sub.cc1]
                        ([degrees]C)                      (J/g)
160[degrees]C
PLA              100        55.3            95.7          26.50
PE-LD            100          -              -              -
PE-HD            100          -              -              -
PLA/PE-LD       90/10       55.1            95.4          25.30
PLA/PE-HD       90/10       54.8            94.1          21.70
180[degrees]C
PLA/PE-LD       90/10       55.2            98.6          13.90
PLA/PE-HD       90/10       56.7            94.8          22.30

                        [T.sub.cc2]     [DELTA]
Sample                  ([degrees]C)  [H.sub.cc2]
                                         (J/g)

160[degrees]C
PLA              100       153.8         2.80
PE-LD            100         -             -
PE-HD            100         -             -
PLA/PE-LD       90/10      153.5         1.80
PLA/PE-HD       90/10      153.1         2.00
180[degrees]C
PLA/PE-LD       90/10      154.5         1.80
PLA/PE-HD       90/10      153.5         3.10

                                Melting of PLA
                           [T.sub.m]        [DELTA]
                              PLA          [H.sub.m]
Sample                    ([degrees]C)     PLA (J/g)

160[degrees]C
PLA              100         167.1           36.40
PE-LD            100           -               -
PE-HD            100           -               -
PLA/PE-LD       90/10        167.1           36.60
PLA/PE-HD       90/10        166.8           38.30
180[degrees]C
PLA/PE-LD       90/10        167.5           22.00
PLA/PE-HD       90/10        166.8           36.20

                             Melting of PE-LD
                         [T.sub.m]      [DELTA]
                           PE-LD       [H.sub.m]
Sample                  ([degrees]C)     PE-LD
                                         (J/g)
160[degrees]C
PLA              100         -             -
PE-LD            100       111.1         79.00
PE-HD            100         -             -
PLA/PE-LD       90/10      110.4          2.60
PLA/PE-HD       90/10                      -
180[degrees]C
PLA/PE-LD       90/10      111.0         15.10
PLA/PE-HD       90/10        -             -

                             Melting of PE-HD
                         [T.sub.m]       [DELTA]       Degree of
                           PE-HD       [H.sub.m]     crystallinity
Sample                  ([degrees]C)   PE-HD (J/g)   [X.sub.c] (%)

160[degrees]C
PLA              100                                     38.9
PE-LD            100
PE-HD            100       136.8          200.1
PLA/PE-LD       90/10        -                           43.4
PLA/PE-HD       90/10      131.0          13.8           45.5
180[degrees]C
PLA/PE-LD       90/10        -                           26.1
PLA/PE-HD       90/10      130.8          14.0           43.0

TABLE 3. Mechanical properties of PLA/PE-LD and PLA/PE-HD
90/10 prepared at different temperatures.

Sample                  Young's modulus,          Yield
                             E (MPa)            strength,
                                             [[sigma].sub.y]
                                                   (MPa)
160[degrees]C
  PLA            100    1,357 [+ or -] 161           -
  PLA/PE-LD     90/10     918 [+ or -] 87            -
         PLA/PE-HD     90/10    965 [+ or -] 94             -
  PE-LD          100      261 [+ or -] 8      9.2 [+ or -] 0.1
  PE-HD          100     955 [+ or -] 35     25.3 [+ or -] 0.5
180[degrees]C
  PLA            100    1,538 [+ or -] 177           -
  PLA/PE-LD     90/10    782 [+ or -] 193            -
  PLA/PE-HD     90/10    938 [+ or -] 183            -
  PELD           100     431 [+ or -] 24             -
  PEHD           100     918 [+ or -] 87             -

Sample                    Yield strain,        Strength at
                        [[epsilon].sub.y]         break,
                               (%)           [[sigma].sub.b]
                                                   (MPa)
160[degrees]C
  PLA            100            -            52.1 [+ or -] 4.8
  PLA/PE-LD     90/10           -             9.5 [+ or -] 1.2
  PLA/PE-HD     90/10           -            44.2 [+ or -] 0.8
  PE-LD          100     20.2 [+ or -] 2.1    9.4 [+ or -] 0.1
  PE-HD          100     9.4 [+ or -] 0.4    25.4 [+ or -] 0.4
180[degrees]C
  PLA            100            -            53.8 [+ or -] 4.8
  PLA/PE-LD     90/10           -             9.2 [+ or -] 3.8
  PLA/PE-HD     90/10           -            33.2 [+ or -] 1.9
  PELD           100            -             5.1 [+ or -] 0.3
  PEHD           100            -             9.5 [+ or -] 1.2

Sample                    Strain at break,         Work to break,
                        [[epsilon].sub.b] (%)           W (nm)

160[degrees]C
  PLA            100         4.0 [+ or -] 0.2     0.53 [+ or -] 0.10
  PLA/PE-LD     90/10        1.3 [+ or -] 0.2     0.04 [+ or -] 0.01
  PLA/PE-HD     90/10        3.7 [+ or -] 0.0     0.43 [+ or -] 0.01
  PE-LD          100        41.4 [+ or -] 1.8     4.72 [+ or -] 1.43
  PE-HD          100     1,477.2 [+ or -] 94.3   98.49 [+ or -] 3.13
180[degrees]C
  PLA            100        4.0 [+ or -] 0.2      0.54 [+ or -] 0.10
  PLA/PE-LD     90/10       1.4 [+ or -] 0.3      0.05 [+ or -] 0.03
  PLA/PE-HD     90/10       2.8 [+ or -] 0.3      0.23 [+ or -] 0.03
  PELD           100        2.3 [+ or -] 0.2      0.06 [+ or -] 0.00
  PEHD           100        1.3 [+ or -] 0.2      0.04 [+ or -] 0.01

Sample                  Impact strength,
                           [a.sub.iU]
                         (J/[mm.sup.2])

160[degrees]C
  PLA            100    44.5 [+ or -] 4.6
  PLA/PE-LD     90/10   2.8 [+ or -] 1.3
  PLA/PE-HD     90/10   10.2 [+ or -] 6.0
  PE-LD          100           (N)
  PE-HD          100           (N)
180[degrees]C
  PLA            100    44.5 [+ or -] 4.6
  PLA/PE-LD     90/10   2.8 [+ or -] 1.0
  PLA/PE-HD     90/10   42.3 [+ or -] 2.8
  PELD           100           (N)
  PEHD           100           (N)

TABLE 4. Thermal properties of pure polymers and polymer blends
PLA/PE-LD 90/10 and PLA/PE-HD 90/10 with fillers.

                                               Glass
                                             transition
Sample                                       [T.sub.g]
                                            ([degrees]C)

PLA          100                                55.3
PLA/PE-LD   90/10                               55.2
PLA/PE-HD   90/10                               56.7
PLA/PE-LD   90/10     +5% CaC[O.sub.3]          58.1
PLA/PE-HD   90/10                               59.6
PLA          100     +5% Ti[O.sub.2]P25         55.4
PLA/PE-LD   90/10         (powder)              56.5
PLA/PE-HD   90/10                               59.6
PLA          100    +5% Ti[O.sub.2]P25/20       55.4
PLA/PE-LD   90/10        (granules)             55.4
PLA/PE-HD   90/10                                -
PLA          100    +5% Ti[O.sub.2]PC500        58.6
PLA/PE-LD   90/10       (fine powder)           50.5
PLA/PE-HD   90/10                               55.5
PLA          100            + 10%               48.7
PLA/PE-LD   90/10     Ti[O.sub.2]PC500          48.6
PLA/PE-HD   90/10       (fine powder)           45.7

                                             Cold crystallization

                                            [T.sub.cc1]      [DELTA]
Sample                                      ([degrees]C)   [H.sub.cc1]
                                                              (J/g)

PLA          100                                95.7          27.02
PLA/PE-LD   90/10                               98.6          15.07
PLA/PE-HD   90/10                               94.8          21.31
PLA/PE-LD   90/10     +5% CaC[O.sub.3]          98.6          19.50
PLA/PE-HD   90/10                               97.4          16.70
PLA          100     +5% Ti[O.sub.2]P25         93.6          27.02
PLA/PE-LD   90/10         (powder)              90.3          23.92
PLA/PE-HD   90/10                               96.3          17.14
PLA          100    +5% Ti[O.sub.2]P25/20       94.6          27.76
PLA/PE-LD   90/10        (granules)             91.8          22.83
PLA/PE-HD   90/10                               92.3          15.63
PLA          100    +5% Ti[O.sub.2]PC500        96.4          22.05
PLA/PE-LD   90/10       (fine powder)           88.9          16.90
PLA/PE-HD   90/10                               93.4          16.86
PLA          100            + 10%               83.9          12.21
PLA/PE-LD   90/10     Ti[O.sub.2]PC500          85.1          15.09
PLA/PE-HD   90/10       (fine powder)           80.6          3.91

                                            [T.sub.cc2]      [DELTA]
Sample                                      ([degrees]C)   [H.sub.cc2]
                                                              (J/g)

PLA          100                               153.8          3.24
PLA/PE-LD   90/10                              154.5          0.17
PLA/PE-HD   90/10                              153.5          0.22
PLA/PE-LD   90/10     +5% CaC[O.sub.3]         154.3          3.40
PLA/PE-HD   90/10                              148.8          1.70
PLA          100     +5% Ti[O.sub.2]P25        153.3          0.64
PLA/PE-LD   90/10         (powder)             148.5          1.15
PLA/PE-HD   90/10                              154.4          0.30
PLA          100    +5% Ti[O.sub.2]P25/20      149.8          0.99
PLA/PE-LD   90/10        (granules)            153.4          0.22
PLA/PE-HD   90/10                              149.0          0.40
PLA          100    +5% Ti[O.sub.2]PC500       153.4          1.30
PLA/PE-LD   90/10       (fine powder)          152.0          0.56
PLA/PE-HD   90/10                              152.6          1.25
PLA          100            + 10%              144.6          0.42
PLA/PE-LD   90/10     Ti[O.sub.2]PC500         152.6          0.81
PLA/PE-HD   90/10       (fine powder)          146.4          0.42

                                                 Melting of PLA

                                             [T.sub.m]
                                                PLA         [DELTA]
Sample                                      ([degrees]C)   [H.sub.m]
                                                           PLA (J/g)

PLA          100                               167.1         35.45
PLA/PE-LD   90/10                              167.5         25.48
PLA/PE-HD   90/10                              166.8         43.49
PLA/PE-LD   90/10     +5% CaC[O.sub.3]         167.8         37.70
PLA/PE-HD   90/10                              168.1         45.30
PLA          100     +5% Ti[O.sub.2]P25        167.0         45.10
PLA/PE-LD   90/10         (powder)             166.5         40.95
PLA/PE-HD   90/10                              168.7         42.21
PLA          100    +5% Ti[O.sub.2]P25/20      167.0         43.25
PLA/PE-LD   90/10        (granules)            166.1         40.45
PLA/PE-HD   90/10                              166.3         41.12
PLA          100    +5% Ti[O.sub.2]PC500       167.3         40.85
PLA/PE-LD   90/10       (fine powder)          163.8         30.83
PLA/PE-HD   90/10                              166.6         36.59
PLA          100            + 10%              161.4         27.34
PLA/PE-LD   90/10     Ti[O.sub.2]PC500         162.8         23.37
PLA/PE-HD   90/10       (fine powder)          161.1         21.50

                                                 Melting of PE-LD

                                             [T.sub.m]
                                               PE-LD         [DELTA]
Sample                                      ([degrees]C)   [H.sub.m]
                                                           PE-LD (J/g)

PLA          100                                 -              -
PLA/PE-LD   90/10                              111.0          13.55
PLA/PE-HD   90/10                                -              -
PLA/PE-LD   90/10     +5% CaC[O.sub.3]         110.1          2.70
PLA/PE-HD   90/10                                -              -
PLA          100     +5% Ti[O.sub.2]P25          -              -
PLA/PE-LD   90/10         (powder)             110.3          4.03
PLA/PE-HD   90/10                                -              -
PLA          100    +5% Ti[O.sub.2]P25/20        -              -
PLA/PE-LD   90/10        (granules)              -            3.18
PLA/PE-HD   90/10                                -              -
PLA          100    +5% Ti[O.sub.2]PC500         -              -
PLA/PE-LD   90/10       (fine powder)            -            0.81
PLA/PE-HD   90/10                                -              -
PLA          100            + 10%                -              -
PLA/PE-LD   90/10     Ti[O.sub.2]PC500         110.3          9.70
PLA/PE-HD   90/10       (fine powder)            -              -

                                                Melting of PE-HD

                                            [T.sub.m]
                                              PE-HD       [DELTA]
Sample                                         CC)       [H.sub.m]
                                                        PE-HD (J/g)

PLA          100                                             _
PLA/PE-LD   90/10                               -            -
PLA/PE-HD   90/10                             130.8        7.21
PLA/PE-LD   90/10     +5% CaC[O.sub.3]          -            -
PLA/PE-HD   90/10                             131.4        14.1
PLA          100     +5% Ti[O.sub.2]P25         -            -
PLA/PE-LD   90/10         (powder)              -            -
PLA/PE-HD   90/10                             132.4        26.92
PLA          100    +5% Ti[O.sub.2]P25/20       -            -
PLA/PE-LD   90/10        (granules)             -            -
PLA/PE-HD   90/10                             132.1        17.55
PLA          100    +5% Ti[O.sub.2]PC500        -            -
PLA/PE-LD   90/10       (fine powder)           -            -
PLA/PE-HD   90/10                             133.0        25.87
PLA          100            + 10%               -            -
PLA/PE-LD   90/10     Ti[O.sub.2]PC500          -            -
PLA/PE-HD   90/10       (fine powder)         132.1        21.92

                                              Degree of
                                            crystallinity
Sample                                      [X.sub.c] (%)

PLA          100                                 37.9
PLA/PE-LD   90/10                                30.2
PLA/PE-HD   90/10                                51.6
PLA/PE-LD   90/10     +5% CaC[O.sub.3]           47.1
PLA/PE-HD   90/10                                56.6
PLA          100     +5% Ti[O.sub.2]P25          50.7
PLA/PE-LD   90/10         (powder)               51.2
PLA/PE-HD   90/10                                52.7
PLA          100    +5% Ti[O.sub.2]P25/20        48.6
PLA/PE-LD   90/10        (granules)              50.5
PLA/PE-HD   90/10                                51.4
PLA          100    +5% Ti[O.sub.2]PC500         45.9
PLA/PE-LD   90/10       (fine powder)            38.5
PLA/PE-HD   90/10                                45.7
PLA          100            + 10%                32.5
PLA/PE-LD   90/10     Ti[O.sub.2]PC500           30.8
PLA/PE-HD   90/10       (fine powder)            28.4

TABLE 5. Mechanical properties of PLA/PE-LD 90/10 and
PLA/PE-HD 90/10 with fillers.

Sample                                        Young's modulus
                                                  E (MPa)

PLA/PELD   90/10   Without filler             782 [+ or -] 193
PLA/PEHD   90/10                              938 [+ or -] 183
PLA/PELD   90/10   +5% CaC[O.sub.3]          1,230 [+ or -] 115
PLA/PEHD   90/10                              979 [+ or -] 83
PLA/PELD   90/10   +5% Ti[O.sub.2]powder      855 [+ or -] 140
PLA/PEHD   90/10                              935 [+ or -] 170
PLA/PELD   90/10   +5% Ti[O.sub.2]granules    882 [+ or -] 121
PLA/PEHD   90/10                              853 [+ or -] 61
PLA/PELD   90/10   +5% Ti[O.sub.2]fine        871 [+ or -] 105
                   powder
PLA/PEHD   90/10                              686 [+ or -] 119
PLA/PELD   90/10   +10% Ti[O.sub.2]fine       746 [+ or -] 142
                   powder
PLA/PEHD   90/10                                     -

Sample                                       Yield strength,
                                             [[sigma].sub.y]
                                                  (MPa)

PLA/PELD   90/10   Without filler                   -
PLA/PEHD   90/10                                    -
PLA/PELD   90/10   +5% CaC[O.sub.3]                 -
PLA/PEHD   90/10                                    -
PLA/PELD   90/10   +5% Ti[O.sub.2]powder            -
PLA/PEHD   90/10                                    -
PLA/PELD   90/10   +5% Ti[O.sub.2]granules          -
PLA/PEHD   90/10                                    -
PLA/PELD   90/10   +5% Ti[O.sub.2]fine              -
                   powder
PLA/PEHD   90/10                                    -
PLA/PELD   90/10   +10% Ti[O.sub.2]fine             -
                   powder
PLA/PEHD   90/10                                    -

Sample                                         Yield strain,
                                             [[epsilon].sub.y]
                                                    (%)

PLA/PELD   90/10   Without filler
PLA/PEHD   90/10                                     -
PLA/PELD   90/10   +5% CaC[O.sub.3]                  -
PLA/PEHD   90/10                                     -
PLA/PELD   90/10   +5% Ti[O.sub.2]powder             -
PLA/PEHD   90/10                                     -
PLA/PELD   90/10   +5% Ti[O.sub.2]granules           -
PLA/PEHD   90/10                                     -
PLA/PELD   90/10   +5% Ti[O.sub.2]fine               -
                   powder
PLA/PEHD   90/10                                     -
PLA/PELD   90/10   +10% Ti[O.sub.2]fine              -
                   powder
PLA/PEHD   90/10                                     -

Sample                                         Strength at
                                                  break,
                                             [[sigma].sub.b]
                                                   (MPa)

PLA/PELD   90/10   Without filler             9.2 [+ or -]3.8
PLA/PEHD   90/10                             33.2 [+ or -] 1.9
PLA/PELD   90/10   +5% CaC[O.sub.3]          32.5 [+ or -] 4.3
PLA/PEHD   90/10                             32.8 [+ or -] 2.2
PLA/PELD   90/10   +5% Ti[O.sub.2]powder     32.0 [+ or -] 2.0
PLA/PEHD   90/10                             20.9 [+ or -] 1.5
PLA/PELD   90/10   +5% Ti[O.sub.2]granules   29.3 [+ or -] 3.0
PLA/PEHD   90/10                             28.2 [+ or -] 1.2
PLA/PELD   90/10   +5% Ti[O.sub.2]fine       20.5 [+ or -] 2.4
                   powder
PLA/PEHD   90/10                             21.8 [+ or -]2.8
PLA/PELD   90/10   +10% Ti[O.sub.2]fine      15.6 [+ or -] 1.8
                   powder
PLA/PEHD   90/10                                     -

Sample                                            Strain at
                                                    break,
                                             [[epsilon].sub.b] (%)

PLA/PELD   90/10   Without filler              1.4 [+ or -] 0.3
PLA/PEHD   90/10                               2.8 [+ or -] 0.3
PLA/PELD   90/10   +5% CaC[O.sub.3]            2.6 [+ or -] 0.3
PLA/PEHD   90/10                               2.8 [+ or -] 0.2
PLA/PELD   90/10   +5% Ti[O.sub.2]powder        3.1 [+ or -]0.4
PLA/PEHD   90/10                               2.7 [+ or -] 0.2
PLA/PELD   90/10   +5% Ti[O.sub.2]granules     2.4 [+ or -] 0.3
PLA/PEHD   90/10                                2.6 [+ or -]0.1
PLA/PELD   90/10   +5% Ti[O.sub.2]fine         2.0 [+ or -] 0.3
                   powder
PLA/PEHD   90/10                               2.0 [+ or -] 0.2
PLA/PELD   90/10   +10% Ti[O.sub.2]fine        1.7 [+ or -] 0.1
                   powder
PLA/PEHD   90/10                                       -

Sample                                        Work to break,
                                                   W(nm)

PLA/PELD   90/10   Without filler            0.05 [+ or -] 0.03
PLA/PEHD   90/10                             0.23 [+ or -] 0.03
PLA/PELD   90/10   +5% CaC[O.sub.3]          0.20 [+ or -] 0.04
PLA/PEHD   90/10                             0.21 [+ or -] 0.03
PLA/PELD   90/10   +5% Ti[O.sub.2]powder     0.24 [+ or -] 0.04
PLA/PEHD   90/10                             0.18 [+ or -] 0.02
PLA/PELD   90/10   +5% Ti[O.sub.2]granules   0.17 [+ or -]0.04
PLA/PEHD   90/10                             0.16 [+ or -]0.01
PLA/PELD   90/10   +5% Ti[O.sub.2]fine       0.10 [+ or -]0.04
                   powder
PLA/PEHD   90/10                             0.08 [+ or -] 0.03
PLA/PELD   90/10   +10% Ti[O.sub.2]fine      0.06 [+ or -] 0.01
                   powder
PLA/PEHD   90/10                                     -

Sample                                        Impact strength,
                                                [a.sub.iU]
                                               (J/[mm.sup.2])

PLA/PELD   90/10   Without filler              2.8 [+ or -] 1.0
PLA/PEHD   90/10                              42.3 [+ or -] 2.8
PLA/PELD   90/10   +5% CaC[O.sub.3]           32.2 [+ or -] 9,2
PLA/PEHD   90/10                              40.5 [+ or -] 2.8
PLA/PELD   90/10   +5% Ti[O.sub.2]powder     18.87 [+ or -] 10.60
PLA/PEHD   90/10                             14.25 [+ or -] 6.02
PLA/PELD   90/10   +5% Ti[O.sub.2]granules   8.90  [+ or -] 5.09
PLA/PEHD   90/10                             12.96 [+ or -] 6.46
PLA/PELD   90/10   +5% Ti[O.sub.2]fine        4.25 [+ or -] 2.87
                   powder
PLA/PEHD   90/10                              7.15 [+ or -] 2.35
PLA/PELD   90/10   +10% Ti[O.sub.2]fine       3.38 [+ or -] 1.47
                   powder
PLA/PEHD   90/10                                     -
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Author:Milovanovic, Vedrana Lovincic; Hajdinjak, Ivana; Lovrisa, Ivona; Vrsaljko, Domagoj
Publication:Polymer Engineering and Science
Article Type:Report
Date:Jul 1, 2019
Words:10819
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