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Efficiency of high energy electrons to produce polypropylene/natural rubber-based thermoplastic elastomer.

INTRODUCTION

A thermoplastic elastomer (TPE) (1), (2) belongs to the family of rubber-like materials. In contrast to conventional vulcanized rubbers a TPE can be processed and recycled like a thermoplastic. A thermoplastic polyolefin elastomer (TPO) is a blend of a polyolefin and a conventional rubber. Its elastomer phase has no or little crosslinking. A thermoplastic vulcanizate (TPV) is a blend of a thermoplastic polymer and a conventional rubber where the rubber phase is crosslinked by dynamic vulcanization.

A polypropylene and natural rubber (PP/NR) blend is a common and valued member of the TPE family. A thorough literature survey reveals that most of the study deals with PP/NR TPOs (3), (4) and TPVs (5), (6). Conventional crosslinking systems, like sulfur (7-10), peroxides (9-15), and phenolic resins (16), (17) have been used abundantly in comparison to high energy electrons to produce PP/NR TPVs. The use of high energy electrons for dynamic vulcanization is quite difficult and requires a special experimental setup as well as experimental data from the electron beam treatment at room temperature. Thus, the number of available literatures is scarce and rather recent. A few recent studies regarding the dynamic vulcanization by high energy electrons known as electron induced reactive processing (EIReP) have been published for PP/ethylene propylene diene rubber (18), (19) and PP/ethylene octane copolymer (20), (21) TPVs. However, there is no literature available regarding electron beam crosslinked PP/NR TPEs prepared at room temperature as far as our knowledge. In industry, electron beam technology is used to crosslink the final products like floor heating pipes, cable insulations, and so forth. Finally, it has proved its potential to abide by several principles from "The Twelve Principles of Green Chemistry" (22).

PP/NR blends have long been commercialized by Malaysian Rubber Producers' Research Association (23). However, most of the commercially available polymer blends lag behind due to inherent incompatibility of the blend components (7). Molecular level compatibility is not achieved for a PP/NR blend (24). So, many studies have been devoted to increase the compatibility of this system (24-27). In common practice, a third component, typically a copolymer, may be added as a compatibilizer or a chemical reaction can be induced to modify the interfacial adhesion in the two-phase polymer blend (26). High energy electrons are widely used to induce a chemical reaction in a polymer or a polymer compound. These chemical reactions can be controlled by the absorbed dose. In the case of PP/NR blend, we have to take into account that PP tends to degradation while NR tends to crosslinking during an electron treatment at room temperature. Further, a high absorbed dose is required to generate a satisfactory level of crosslinking in the NR phase (28) due to its high unsaturation in the backbone. This high absorbed dose leads to more degradation of PP and poses as a barrier for industrial scale processing as it requires higher energy and lowers the level of mechanical properties. Polyfunctional monomers (PFMs) are used as sensitizer or co-agent during the electron beam crosslinking of polymers. Thus, the degradation of PP and the level of absorbed dose for crosslinking can be reduced using a suitable PFM. The efficiency of PFM may vary depending on its reactivity and solubility toward the polymer to be crosslinked (29). Depending on chemical structure and functionality of the PFM they can form a network structure (for functionality higher than two) or a branched structure (for functionality equals to two) in polymer matrices.

In this article, electron beam technology has been used to induce chemical crosslinks in the NR of the PP/NR blend in presence and absence of a PFM. The properties of PP/NR blends have been evaluated to understand the influence of absorbed dose as well as to get experimental data to support our future study for EIReP of PP/NR TPVs. Various characterization methods have been used to understand the structure. Further, the mechanical properties were evaluated to prove the suitability of these TPEs for potential applications. The Charlesby--Pinner plot was drawn to determine the ratio of degradation to crosslinking for the prepared PP/NR blends. Differential scanning calorimetric study were performed to understand the influence of electron beam on the molecular arrangements of polymer components. A plausible mechanistic pathway was suggested to understand the ongoing underlined phenomenon behind enhanced properties.

EXPERIMENTAL

Materials

Standard Malaysian Rubber of low dirt content [Mooney viscosity, M[L.sub.1+4] (100[degrees]C): 78; dirt content (max. wt%): 0.03; plasticity retention index (max. wt%): (30) was kindly supplied by Tun Abdul Razak Research Centre, Brickendonbury, United Kingdom. Polypropylene H2150, Hostalen (density: 0.900 g [cm.sup.-3] at 23[degrees]C; MFI: 0.3 g per 10 min at 230[degrees]C and 2.16 kg) was obtained from LyondellBasell, Frankfurt, Germany. Dipropylene glycol diacrylate (DPGDA, density: 1.06 g [cm.sup.-3] at 25[degrees]C) was supplied by Cytec, Brussels, Belgium. Figure 1 shows the chemical structure of PP, NR, and DPGDA.

Dose Range for Crosslinking of NR

We have investigated the gel content of virgin NR as function of absorbed dose (Fig. 2) to determine the range of dose for the crosslinking of NR. No gel content was measured at an absorbed dose of 25 kGy. It increases to about 28 and 64% at an absorbed dose of 100 and 200 kGy, respectively. These experimental results show, that high absorbed doses (150-350 kGy) are required to get a high gel content for NR.

Content of Co-agent

Figure 3 shows the tensile stress of virgin and irradiated PP as function of tensile strain. As expected, a dose of 25 kGy strongly influences the elongation at break value of the high molecular weight PP to be used in this study. In accordance to the literature, PFMs can be used to lower the electron induced degradation of PP. The required amount of PFM was calculated in two steps. Based on the definition of the dose and its transfer to a polymer molecule, we calculated the average number of radicals ([N.sub.r]) of PP H2150 for an absorbed dose (D) of 300 kGy and an overall G-value of PP ([G.sub.t] of 1.65 radicals per 100 eV absorbed energy. According to Burton (30), the overall G-value characterizes the total number of molecules produced or destroyed per 100 eV of absorbed energy. In [E.sub.q]. I, [N.sub.A] represents the Avogadro constant and [E.sub.pol] is the average energy absorbed per polymer chain. [M.sub.n.sup.PP] represents the number averaged molecular mass of PP used in this study. It amounts to 500,000 g/mol.

D = E / m = [E.sub.pol] / [m.sub.pol] = [N.sub.r] * [N.sub.A] / [M.sub.n.sup.PP] * [G.sub.t] [??] [N.sub.r] = D * [M.sub.n.sup.PP] * [G.sub.t] / [N.sub.A]

At an absorbed dose of 300 kGy about 25 radicals are generated on the high molecular mass PP. All these radicals should react with one double bond of a DPGDA molecule to avoid the electron induced degradation of PP during the solid state irradiation. Based on this assumption, the weight percentage of DPGDA was calculated with Eq. 2, where [M.sub.n.sup.DPGDA] is the molecular mass of DPGDA (242 g/mol) and wt(PP) represents the weight percentage of PP. We got 0.6 wt% of DPGDA.

wt(DPGDA) = wt(PP) * [N.sub.r] * [M.sub.n.sup.DPGDA] / [M.sub.n.sup.PP](2)

Mastication Time of NR

Polymer blends may fail due to various reasons regarding the components. The viscosity mismatch is one of them and poses a serious threat towards prevention or delay in distribution of the components. In the case of PP/NR blend, differences in viscosity are expected. According to Varghese et al. (7) 10 min mastication of NR reduces its molecular weight and further mastication leads to degradation. In this study, the complex viscosity as function of frequency was determined for virgin PP, virgin NR, and NR subjected to mastication (10 and 20 min in a two-roll mill at room temperature under air) to evaluate the viscosity ratio of PP and NR as well as the required time for the mastication of NR. Figure 4 shows the complex viscosity versus frequency for pure PP and virgin NR as well as masticated NR (10 and 20 min).

In comparison to PP H2150, the complex viscosity of NR masticated for 10 min is less, but shows a similar trend. A higher viscosity for PP compared to NR is required to avoid a viscosity mismatch during melt mixing due to thermal and electron induced degradation of PP. Before making any decision on the time of mastication, we studied the influence of mastication time on the tensile properties of NR at different dose values (Fig. 5). The tensile strength of virgin and masticated NR increases with increasing dose. Nevertheless, virgin NR shows the highest values of tensile strength and elongation at break. In the case of 10 min mastication, we measured lower values of tensile strength. Within the experimental uncertainty, there was hardly any change in the elongation at break values. In contrast to this result, a mastication time of 20 min led to a further decrease of tensile strength as well as a significant reduction in the elongation at break values. This result is in agreement with Varghese et al. (7). Thus, the blend was prepared using NR masticated for 10 min at ambient temperature and PP as it was procured.

Preparation of PP/NR Blends and Their Electron Irradiation

Masticated NR and PP (50/50 wt%) were used to prepare the blends by a batch process in a Haake Rheomix internal mixing chamber, having a volume of 50 [cmsup.3], with a rotor speed of 90 rpm at an average temperature of 185[degrees]C in presence of nitrogen. The friction ratio was maintained at 1.5. The total time of mixing was kept at 11 min to minimize the thermal degradation of PP and NR at high temperature. DPGDA (0.6 wt%) was added during melt mixing for samples containing the PFM. After melt mixing the test samples were prepared by a compression molding machine (Rucks Maschinenbau, Glauchau, Germany) at 200[degrees]C, 6 min, and 88 bar pressure. Finally, the compression molded sheet of 2-mm thickness was placed on the pallet and passed through the irradiation zone of the electron accelerator by a conveyer system. The irradiation was done at room temperature and in nitrogen atmosphere.

Testing Methods

The complex viscosity measurements were carried out with an ARES rheometer (Rheometrics Scientific, New Castle, USA) within a torque range from 0.02 to 2000 gcm in parallel-plate geometry. The samples were prepared pared from the formerly compression molded plates. Their thickness amounted to 2 mm and their diameter was 25 mm. The measurements were done in [N.sub.2] atmosphere at a temperature of 190[degrees]C within a frequency range from 0.1 to 100 rad/sec.

Infrared spectra were recorded for all the samples in Equinox 55 (Bruker, Karlsruhe, Germany) Fourier transformed infrared spectrophotometer (FTIR). The samples were scanned from 4000 to 400 [cm.sup.-1] at a resolution of 4 [cm.sup.-1] in transmission mode. All the results given in this report are the averages of three measurements.

The gel content of the samples was measured by subjecting the samples for 8 h in boiling xylene at 140[degrees]C to completely remove the soluble fraction of PP and NR phase. After extraction, the samples were dried in a vacuum oven and weighed. The gel content ([X.sub.c]) was calculated as follows.

[X.sub.c] = ([W.sub.1]/[W.sub.0]) * 100 (3)

[W.sub.o] is the initial weight of the specimen and W1 represents the weight after xylene extraction.

Equilibrium solvent swelling measurements were performed to determine the crosslink density values. A circular piece of 2-mm thickness was made to swell in toluene for about 72 h to achieve equilibrium swelling and then dried for 24 h in an oven. Initial, swollen, and dried weights were measured using an analytical balance. In the case of PP/NR blend, PP and NR have formed a co-continuous morphology where the PP phase is much less swell-able. Thus, vulcanized NR phase swells against the compressive force of the PP phase. Finally, the overall crosslink density was calculated relative to the (NR + PP) phases and expressed as (v + PP). The latter was done to avoid the correction for the part of the PP phase, being extracted as amorphous PP. The modified Flory-Rehner equation [31] presented as Eq. 4 has been used to determine the crosslink density (v) values.

V = 1 / [V.sub.s] x ln(1 - [V.sub.r]) + [V.sub.r] + x[([V.sub.r]).sup.2]

In Eq. 4, Vs represents the molar volume of toluene: 106.2 [cm.sup.3]/mol, x characterizes the polymer solvent interaction parameter (Huggins interaction parameter), which in this case amounts to 0.393 (32), and [V.sub.r] is the volume fraction of NR in the swollen network, which is expressed by Eq. 5.

[V.sub.r] = 1 / [V.sub.r] + 1 = 1 / Q

In Eq. 5, [A.sub.r] is the ratio of the volume of absorbed toluene to that of NR after swelling. Q represents the degree of swelling. (4)

Differential scanning calorimetric measurements were performed in the DSC Q1000 (TA Instruments, New Castle, USA). The samples (~6 mg per sample) were tested in the temperature range of -80-200[degrees]C at a heating (scanning) rate of 10 K/min under [N.sub.2] atmosphere. The dumb-bell shaped specimens of the blends used for testing were die-cut from the compression molded sheet and the testing was done after 24 h of maturation at room temperature in accordance to ISO 527-2/S2/50 using a universal tensile testing machine Zwick 8195.04 (Ulm, Germany) at a constant cross-head speed of 50 mm [min.sup.-1]. The E modulus was determined between 0.05 and 0.25% of strain.

The morphology of the PP/NR blends was investigated using the scanning electron microscope SEM Ultra Plus (Carl Zeiss SMT, Jena, Germany). Before SEM imaging, all samples were placed over a sticky surface made by conductive carbon cement on a SEM sample holder and then coated with platinum (layer thickness 15 nm), using a sputter coater (BAL-TEC SCD 500 Sputter Coater, Leica, Wetzlar, Germany). Finally, the samples were prepared at -140[degrees]C by cutting (Ultra-microtome UC 7, Leica, Wetzlar, Germany), without staining or etching.

RESULTS AND DISCUSSION

Effect of Absorbed Dose on the Chemical Structure of the Blend Components

Melt mixing at high temperature and followed by high energy electron treatment at room temperature are supposed to bring considerable chemical changes in the overall structure of the polymer blend components. Functionalization of PP at elevated temperature is a known technique used for better interfacial adhesion and chemical bonding (33). Figure 6a and b show the infrared spectra of PP/NR blends without and with 0.6 wt% of DPGDA, respectively. Absorption bands at ~1740, 1710, 1660, and 1540 [cm.sup.-1] were observed for all samples regardless of DPGDA's presence and absorbed dose. The bands, like 1740 [cm.sup.-1] (lactones) can be attributed to PP only. Conversely, the bands like 1660 [cm.sup.-1] (C=C stretching) and 1540 [cm.sup.-1] (COO- for proteins and amino acids) can only be attributed to NR whereas the band 1710 [cm.sup.-1] (carbonyl) can be attributed to both of PP and NR degradation (33), (34).

The results clearly show that FTIR is not sensitive enough to detect the electron induced changes in both components of the blend with or without DPGDA even at an absorbed dose of 350 kGy in comparison to the control sample. A higher absorbed dose should have led to lower intensity of C=C stretching due to higher crosslinking of NR. But, the C=C content of NR is very high. At an absorbed dose of 350 kGy, about 0.5% of C=C bonds of NR are utilized and within the experimental uncertainty no change in C=C stretching intensity could be observed.

Cross/ink Density and Gel Conten

Figures 7 and 8 show graphs of crosslink density and gel content values, respectively. With higher absorbed dose a steady increase in crosslink density as well as gel content value was observed. At an absorbed dose of 150 kGy, the DPGDA did not lend any extra efficiency of improving the crosslink density, whereas a significant increase in gel content value was observed. At an absorbed dose of 250 kGy the same crosslink density and gel content values were achieved for both samples within the experimental uncertainty. In contrast to these results, a small increase in crosslink density values was found for the sample containing DPGDA at an absorbed dose of 350 kGy. At this value of absorbed dose, the gel content value was greater than 50%. In the case of the samples with DPGDA, it amounted to 63%. This high value of gel content may be attributed to graft linkage formation (5), (18). The results of the gel contents are corroborated by the plots relating the sol fraction, S, with the inverse of the absorbed dose (Fig. 9) in accordance to Eq. 6 (35). In this equation, [u.sub.1] is the initial number averaged degree of polymerization, [P.sub.0], fracture density per unit of dose in kGy, [q.sub.0], density of crosslinked units per unit of dose in kGy, and D the absorbed dose in kGy.

S + [S.sup.0.5] = [p.sub.0] / [q.sub.0] + 1 / [q.sub.0] * D * [u.sub.1] (6)

The Charlesby-Pinner plot is drawn in order to determine the ratio of chain scission to crosslinking ([p.sub.0]/[q.sub.0]) for the PP/NR blend. For PP, the G-value for crosslinking and scission are almost equal. Thus, PP tends to degradation. In the case of NR, the G-value for crosslinking is much higher than that of scission. That means NR tends to crosslinking. The experimental data of both blends suggest the favorability of crosslinking over scission. But, there is a small change in the ratio of chain scission to crosslinking ([p.sub.0]/[q.sub.0]) as well as in the slope of the Charlesby--Pinner plot. In the case of PP/NR blend with DPGDA, we got the minimum value for the ratio of chain scission to crosslinking (0.66) as well as for the slope of the Charlesby--Pinner plot (125 kGy). From these results, we concluded that the density of crosslinked units per unit of dose for the PP/NR blend slightly increased in the present of DPGDA. This is in agreement with the measured crosslink density at 350 kGy.

Differential Scanning Calorimetric Study

Differential scanning calorimetric study were performed to understand crystallization and melting behavior of the prepared blends. Table 1 shows the experimental data of glass transition temperatures of NR and PP ([T.sub.g]), melting temperature ([T.sub.m]), maximum crystallization temperature ([T.sub.c,m]), and melt enthalpy ([DELTA]H). Within the experimental uncertainty no significant change in [T.sub.g] is observed for both components of the blend, NR, and PP. The melt enthalpy of PP remained mostly unchanged up-to 250 kGy absorbed dose for blends without as well as with PFM. However, blends treated with an absorbed dose of 350 kGy showed a decrease of melt enthalpy. This decrease can mainly be attributed to high energy electron induced changes in the molecular structure of the PP generating defects in the PP crystalline structure. Both types of blend showed a decreasing trend of melting temperature with increasing dose. This trend was further enhanced by low molecular weight and low viscosity DPGDA for the blend having a PFM.

TABLE 1. Experimental data for glass transition
([T.sub.g]) of NR and PP. melting temperature
([T.sub.c,m]), maximum crystallization temperature
([T.sub.m]), and melt enthalpy ([DELTA][H) for all samples.

Sample              [T.sub.g] (a)  [T.sub.g] (a)  [T.sub.m] (a)
                             (NR)             PP        (second
                     [[degrees]C]   [[degrees]C]       healing)
                                                   [[degrees]C]

Blend_0 kGy                   -66             -5          159.6

Blend_150 kGy                 -65             -7          156.0

Blend_250 kGy                 -65             -7          151.0

Bk-nd_350 kGy                 -65             -9          153.0

Blend_DPGDA_0 kGy             -66             -7          159.9

blend_DPGDA_150kGy            -66             -6          156.0

blend_DPGDA_250kGy            -65             -7          153.0

blend_DPGDA_350kGy            -63             -5          147.8

Sample               [T.sub.c,m]  [DELTA][H.sup.b]
                      (a) (first  (second healing)
                        Cooling)             [J/g]
                    [[degrees]C]

Blend_0 kGy                112.9              47.2

Blend_150 kGy              111.0              47.6

Blend_250 kGy              109.5              45.9

Bk-nd_350 kGy              110.5              44.3

Blend_DPGDA_0 kGy          113.5              48.6

blend_DPGDA_150kGy         112.2              47.0

blend_DPGDA_250kGy         110.9              47.2

blend_DPGDA_350kGy         108.7              43.8

(a) Experimental uncertainty amounts to -[+ or -]1 K.

(b) Experimental uncertainty amounts to [+ or -] 0.5 J/g.


In comparison with pure PP ([T.sub.m] = 165[degrees]C), the decrease in melting temperature for the un-irradiated PP/NR blends can be attributed to the addition of amorphous NR, because of its negative effect on the normal crystallization process of PP (36). Further, there are common phenomena in the PP phase of the PP/NR blend during the electron treatment like the reduction of molecular weight, chain branching, and the incorporation of chemical groups like carbonyl and hydroperoxides (37). Finally, all the above competing processes influence the melting temperature and crystallinity of the blend.

Mechanical Properties

Simultaneous effects of absorbed dose and PFM are supposed to make a marked difference in the mechanical properties of PP/NR blends. The mechanical properties are the main criteria for most of the standards with addition to special properties for specific applications. The influence of absorbed dose and DPGDA on the tensile strength and the elongation at break values are shown in Figures 10 and 11, respectively. Table 2 contains the summary of mechanical data. In the case of the blend with 0.6 wt% of DPGDA, the maximum tensile strength was reached at an absorbed dose of 150 kGy. A similar value of tensile strength for the blend without DPGDA was obtained at an absorbed dose of about 250 kGy. Thus, the dose reduction effect of a PFM is observed as expected. This level of dose reduction was achieved by adding only 0.6 wt% of DPGDA, which gives the hope of the feasibility for an additive free production of PP/NR blends with crosslinked NR phase. At an absorbed dose of 350 kGy, the tensile strength value of both blends merges. A similar trend was also found in the case of elongation at break values. The blend with DPGDA reached the maximum value (350 [+ or -] 10%) at an absorbed dose of 150 kGy and the maximum value of the blend without DPGDA (310 [+ or -] 25%) was attained at an absorbed dose of 250 kGy. At 350 kGy a decrease of elongation at break values was observed for both blends. In the case of the blend with DPGDA, elongation at break decreased sharply indicating a higher crosslinking which in turn affects the elongation property negatively.

TABLE 2. Summary of mechanical data for all blends.

Samples                    Tensile   Elongation at             100%
                  [strength.sup.a]   [break.sup.a]  [Modulus.sup.a]
                             [MPa]             [%]            [MPa]

Blend_0 kGy       7.9 [+ or -] 0.3   77 [+ or -] 7               --

Blend_150 kGy    11.8 [+ or -] 1.8    250 [+ or -]    10.0 [+ or -]
                                                50              0.5

Blend_250 kGy    14.5 [+ or -] 0.5    310 [+ or -]    10.5 [+ or -]
                                                10              0.5

Blend_350 kGy    13.7 [+ or -] 3.4    280 [+ or -]    11.0 [+ or -]
                                                12              0.5

Blend_DPGDA_0     5.5 [+ or -] 0.5  46 [+ or -] 15               --
kGy

Blend_DPGDA_150  13.7 [+ or -] 2.1    350 [+ or -]    10.0 [+ or -]
kGy                                             10              0.5

Blend_DPGDA_250   6.9 [+ or -] 2.0  31 [+ or -] 25                -
kGy

Blend_DPGDA_350  13.7 [+ or -] 0.1    220 [+ or -]    11.0 [+ or -]
kGy                                             16              0.5

Samples                  Young's
                 [Modulus.sup.a]
                           [MPa]

Blend_0 kGy      231 [+ or -] 17

Blend_150 kGy     209 [+ or -] 4

Blend_250 kGy    243 [+ or -] 15

Blend_350 kGy    271 [+ or -] 33

Blend_DPGDA_0    204 [+ or -] 21
kGy

Blend_DPGDA_150   277 [+ or -] 2
kGy

Blend_DPGDA_250  219 [+ or -] 25
kGy

Blend_DPGDA_350  251 [+ or -] 26
kGy

(a) Average of three measurements.


All these observations are in good agreement with the data of the gel fraction study. More than 50% gel content value at higher absorbed dose (350 kGy), especially in presence of PFMs, suggest crosslinking of NR as well as PP/NR graft-link formation, which affects mechanical properties. Finally, we found that the maximum tensile properties of the 50/50 blend of PP/NR with DPGDA were reached at a gel content of 33%. In contrast, the maximum tensile properties of the 50/50 blend of PP/NR without DPGDA were reached at gel content of 50%.

Correlation Between Morphology and Technological Properties

A morphology study can give an insight picture of the polymer blends to understand how the materials may behave during test or application. In Figure 12, photomicrographs of blends with and without DPGDA are shown for the maximum tensile properties in comparison to the un-irradiated one. In these photomicrographs, graphs, co-continuous matrices are observed as expected from rubber-thermoplastic blend prepared by melt mixing (38), (39).

The electron treatment at room temperature had no influence on the morphology of the blends. This means, the blend morphology settled before vulcanization. This is contrary to the dynamic vulcanization or the EIReP where the vulcanization process takes place during melt mixing to finalize the morphology as dispersed crosslinked rubber particle in the thermoplastic matrix (39). Nevertheless, Fig. 12d shows a somewhat well-defined interface whereas others show co-continuous pictures tend to penetrating network. This might be due to the preferential migration of the low viscous DPGDA into the interface leading to higher graft-linkage of that region during irradiation compared to the bulk volume of NR (Fig. 13). Further investigations are required to prove this plausible mechanism to understand the better mechanical property of the blend containing 0.6% DPGDA and treated with an absorbed dose of 150 kGy.

For untreated samples the interfacial adhesion was of mainly physical nature and partially due to functionalization of PP at elevated temperature, whereas for Fig. 12c the crosslinking took place throughout the NR co-continuous phase without any preference in the interface. In contrast to a TPV, where the continuous thermoplastic matrix mainly contributes to the final mechanical property of the material (40), at a 50/50 blend ratio, the co-continuous phases of rubber and thermoplastic contribute almost equally.

Correspondence to: Uwe Oohs; e-mail: gohs@ipfdd.de

DOI 10.1002/pen.23414

Published online in Wiley Online Library (wileyonlinelibrary.com).

[c] 2012 Society of Plastics Engineers

CONCLUSIONS

(1.) A TPO based on PP and NR at 50/50 blend ratio was successfully developed using an electron treatment at room temperature. The electron beam technology shows its promising ability to develop advanced materials within existing technical boundaries.

(2.) The mastication of NR for minimization of viscosity mismatch is an essential step for the product development.

(3.) An electron treatment under nitrogen atmosphere with a maximum dose of 350 kGy did not influence the yield of functional groups of the blends with or without DPGDA.

(4.) The blend morphology showed a co-continuous phase of both components.

(5.) The use of a PFM resulted in an increased tensile property at a reduced dose level and helped in generating higher graft-linkage at the interface of PP and NR.

(6.) Depending on the application, there is plenty of scope for customization of final products.

(7.) There is hope for an additive free (no PFMs) crosslinking of NR in PP, as this study suggests that the judicious selection of raw materials, dose level, and crosslinking conditions (nitrogen atmosphere) can reduce the amount of PFMs. Based on the above summarized results, the EIReP of an additive free PP/NR blend might have the potential to produce a PP/NR TPV with improved mechanical properties. Further investigations are in preparation to evaluate the potential of EIReP for the production of PP/NR TPVs.

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Manas Mondal, (1), (2) Uwe Gohs, (1) Udo Wagenknecht, (1) Gert Heinrich (1), (2)

(1) Leibniz-Institut fur Polymerforschung Dresden e.V., Institut fur Polymerwerkstoffe, Hohe Strasse 6, 01069 Dresden, Germany

(2) Technische Universitat Dresden, Institut fur Werkstoffwissenschaft, 01069 Dresden, Germany
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Author:Mondal, Manas; Gohs, Uwe; Wagenknecht, Udo; Heinrich, Gert
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:4EUGE
Date:Aug 1, 2013
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