Biodegradable Polymer Blends of Poly(L-lactic acid) and Gelatinized Starch.
Gelatinized starches were prepared with various content of glycerol and were investigated in terms of the effect of the glycerol addition on characteristics of starch and its blends. Poly (L-lactic acid) (PTA) with various ratios of linear/star shaped PLA and starch gelatinized with various ratios of water/glycerol were melt-blended by using twin screw mixer. The blends were characterized by DSC thermal analysis, tensile test and morphological analysis. Gelatinization of starch was found to lead to destruction or diminution of hydrogen bonding in granules and a decrease of crystallinity of starch. DSC data showed that starch played a role as a nucleating agent and glycerol as plasticizer contributed to an improvement in crystallinity in PLA blends. When the content of starch increased, the size of spherulites in PLA blends was smaller and less regular. In the case of PLA/pure starch blends, the voids appeared, which were formed by the separation of starch particles from the matrix. But for PLA/gelainized sta rch blends, these voids were not observed. In the case of blends with linear PLA and starch gelatinized with water/glycerol ratio of 100/40, the greatest superiority of mechanical properties was shown and the toughness was improved compared with PLA/pure starch blends.
PLA possesses good mechanical properties and clarity besides its processability. But its brittleness is a major defect for many applications. Moreover, the relatively high price of the intermediate lactide lowers the possibility of commercialization. In order to modify various properties or to lower the price, studies on PLA blends with other polymers have been carried out. PLA was reported to be miscible with other stereoisomer such as Poly(DL-lactic acid). The blends of PLA and PDLLA had varying properties according to the mixing ratio (1, 2). It is also known that PLA is able to form miscible blends with various polymers such as poly (ethylene oxide) (3), poly (vinyl acetate) (4) and poly (ethylene glycol) (5).
Blending of starch and starch derivatives, both in granular and destructurized forms, with various polymers has been investigated. For the sake of giving some biodegradable characteristics to the thermoplastic polymer, they have been blended with common plastics such as polyethylene (6), poly (vinyl chloride) (7), poly (ethylene-co-vinyl alcohol) (8), and poly (ethylene-co-acrylic acid) (9). Moreover, starch is blended with other biodegradable polymers such as aliphatic polyesters and with non-biodegradable polymers in order to lower the cost of the finished product and enhance the biodegradable characteristics. The well-known examples are PCL/starch blend, poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/starch blend (10) and poly (vinyl alcohol) /starch blend (11).
In starch-based blend systems, one of important factors affecting mechanical properties is the interfacial affinity with the matrix polymer. Gelatinization of starch was a good method to enhance the interfacial affinity (12). Starch is gelatinized in order to disintegrate granules and overcome the strong crystalline intramolecular forces prior to mixing with other polymers (12). It is necessary that the water contained in gelatinized starch is removed thoroughly to blend with easily hydrolyzed polymers such as aliphatic polyesters. But during the removal of water, gelatinized starch easily re-forms the strong crystalline because of intramolecular hydrogen bonding. Glycerol as a plasticizer was used in this work in order to prevent this re-formation of the strong crystalline in starch.
In this work, blends of PLA and starch were prepared for the purpose of combining the good mechanical properties of PLA with the low cost of starch. Generally, star-shaped polymers can be processed at lower temperatures than their linear counterparts, which can be advantageous, especially in the procession of thermo-labile polymers like poly (lactide)s. Accordingly, we used star-shaped PLA and its blends with linear PLA and investigated the effect of star-shaped PLA on various properties of PLA/starch blends. In addition. to enhance the interfacial adhesion between PLA and starch, gelatinized starches were prepared with various contents of glycerol and were investigated in terms of the effect of the glycerol on characteristics of starch and its blends.
Star-shaped PLA with six arms (S-PLA) and linear PTA (L-PLA) used in this research were supplied by Korea Institute of Science and Technology, with weight average molecular weights of approximately 61,000 and 367,000, respectively. PLA was purified by reprecipitation using chloroform as the solvent and methanol as the precipitant. Corn starch (amylose content of 30% and granule size of 10 [sim] 12 [micro]m) was obtained from Samyang Xenex Co. PLA and starch were dried under vacuum at 40[degree]C for 48 h. Glycerol (GR-0725) was purchased from Tedia Chem. Co. and was used without purification.
The samples were prepared with various water/glycerol ratios shown in Table 1. Starch gelatinization was carried out in a flask with a condenser, with stirring at a speed of 60 rpm at 70[degrees]C for 30 min. Prepared samples were dried in a vacuum oven at 50[degrees]C for 12 h and then were pulverized by means of a crusher. The process of "dry and crush" was repeated two times, and the samples were stored for a week under vacuum. The final moisture content of pure starch was about 12%, but the contents for all the gelatinized starches were approximately 7%, which was determined using a moisture analyzer (MA 39, Sartorius Co., USA).
In the case of gelatinized starch in the presence of glycerol, the quantities of glycerol were determined by TGA analysis using a Perkin-Elmer TGA7 thermogravimetric system at a heating rate of 20[degrees]C/min between 50[degrees]C and 500[degrees]C. Because glycerol evaporated slowly at 150[degrees]C to 250[degrees]C and a thermal decomposition of starch occurred quickly at 350[degrees]C to 420[degrees]C, the content of residual glycerol in gelatinized starch could be easily obtained from TGA thermograms and 1st differential curves. Table 1 shows that the contents obtained by TGA thermograms were almost the same as calculated contents by input quantities. These results indicate that almost all the quantity of glycerol remained without vaporizing during drying and melt-blending.
All the blends were prepared using a Haake Reomix 600 at 180[degrees]C for 5 min. The ratios of L-PlA/S-PlA were 100/0, 70/30, 50/50, 70/30 and 0/100. Pure and gelatinized starch was added from 10 to 30 wt% in 10 wt% intervals that were calculated with weights of PLA and starch regardless of glycerol content After blending, all the samples were cooled to room temperature under air atmosphere.
For mechanical testing, films with a thickness of 0.2 mm were prepared using a hot press at 185[degrees]C, a hold pressure of 3000 psi and hold time of 30 sec. Prepared films were quenched in cold water, and dried under vacuum at room temperature for 48 h in order to remove water thoroughly, and stored in a desiccator with [P.sub.2][O.sub.5].
A Perkin-Elmer DSC 7 was used to investigate the thermal characteristics of the blends. The first scans were conducted at a heating rate of 10[degrees]C/min between 0[degrees]C and 200[degrees]C under a nitrogen atmosphere. Rapid cooling to 0[degrees]C allowed the samples to be frozen in an amorphous state. The actual measurement was performed during a second scanning at a heating rate of 10[degrees]C/min between 0[degrees]C and 200[degrees]C. A Mattson Alpha-Centauri FT-IR spectrophotometer was used by KBr palletizing method. X-ray diffractometer (Rigaku Denki, Japan, Ni-filtered CuK[alpha] radiation at 40kV, 40mA) was used at a scan speed of 5[degrees]/min with a 2[theta] range of 5[degrees] [sim] 40[degrees]. Nikon polarized light microscope (OPTIPOTO-POL) was used not only to observe the appearance of gelatinized starch but also to study the spherulitic morphology of the annealed blends at the desired crystallization temperature ([T.sub.c]) for 30 min. The fracture surfaces of the samples were observed u sing a SEM (Jeol JSM 35-CF, Japan). The tensile strength, Young's modulus and elongation at break were determined using an Instron testing machine (model 4465) at a crosshead speed of 10 mm/min. The testing samples were prepared into dogboneshaped films with a gauge length of 25 mm and a width of 5 mm, and were stored for one day with room conditions. An average of five test values was taken for each sample.
RESULTS AND DISCUSSION
Figure 1 shows FT-IR spectra of pure and gelatinized starch and the FT-IR assignments for starch are denoted in Table 2(13). The OH band of GO starch shown between 3000 and 3500 [cm.sup.-1] became narrow and shifted to a higher wavenumber in comparison with that of pure starch. The C-O-stretching band also shifted to 1020 [cm.sup.-1] from 1013 [cm.sup.-1] for pure starch. These shifts seem to indicate that a gelatinizalion of starch led to a diminution of hydrogen bonding in the granules. For gelatinized starches with glycerol, the shifts of the C-O- and the OH band were larger than those for GO starch as well as pure starch and increased with an increase of glycerol content. Especially for G3 starch, the C-O- band shifted very largely to 1034 [cm.sup.-1] in comparison with 1013 [cm.sup.-1] for pure PLA. In the case of the GO sample gelatinized in the absence of glycerol, it is highly probable that the hydrogen bonding between starch polymeric chains was destructured by hydration during gelatinization, but u nder the drying process, this bonding could be reformed owing to removal of the water molecules existing between starch polymeric chains. For starches gelatinized in the presence of glycerol, the introduction of glycerol may prevent this re-formation of hydrogen bonding because glycerol still remained and solvated between the starch polymeric chains, which led to larger shifts of the C-O- and the OH band than those for the GO starch.
The FT-IR pattern of glycerol is very similar to that of corn starch, and the characteristic peaks appear at almost the same location as starch. That is, the IR absorption of glycerol overlapped at almost all IR regions with that of starch. So we could not obtain information about the contribution or the existence of glycerol.
X-ray diffraction patterns of pure starch and various gelatinized starches are shown in Fig. 2. For pure starch, single peaks at 2[theta] of 14[degrees] 88' and 22[degrees] 54' and double peaks at 16[degrees] 86' and 17[degrees] 78' were observed. This pattern corresponded to the typical A-type X-ray diffraction pattern of corn starch. In the case of gelatinized starch, the areas of the peaks, which corresponded to the crystalline region, decreased in comparison with pure starch, which led to a decrease of crystallinity.
In the case of the G3 sample with glycerol content about 37%, the overall diffraction pattern shifted to a wide angle and was distinctly different from those of other samples, which was similar to the typical V-type diffraction pattern that appeared by a transformation from the A-type under extrusion at conditions of high temperature and high pressure (14).
Figure 3 shows optical micrographs of granules of pure starch and particles of gelatinized starch samples. For pure starch (a), sphere-shaped granules with diameters of about 10 [micro]m were observed. But in the case of G0 sample (b) gelatinized only with water, the shape of particles was not a granule form but a very irregular form, and the size was larger than that of a granule of pure starch. As mentioned above, during drying, amylose diffusing out of collapsed granules was re-aggregated and formed a large lump. G0 samples were obtained from pulverization of this lump using a crusher, which led to more irregular shapes and larger sizes than granules of pure starch. In the case of gelatinized starch containing glycerol ((c), (d)), the granule forms were observed but the size became slightly larger and the shape of the particles became rougher than those of the granules of pure starch. These results were due to swelling of granules through water or glycerol and diffusing of amylose out of the collapsed gra nules during gelatinization. The re-aggregation (which was observed for the G0 sample] was partially observed for the G1 sample, but entirely disappeared in the G2 sample. We thought that the introduction of glycerol contributed to a prevention of re-aggregation of starch particles because glycerol still remained and solvated between starch polymeric chains.
For G3 starch, the granular shape could not be observed using an optical microscope because the excessive glycerol strongly solvated the solvate starch and formed a large lump that could not be pulverized using a crusher owing to its high flexibility and stickiness.
Thermal Properties of PLA/Starch Blends
DSC characteristics of blends with L-PLA and various starch are denoted in Table 3. We investigated the effect of glycerol on the thermal properties of PLA. The introduction of glycerol led to a decrease of the glass transition temperature ([T.sub.g]), melting point ([T.sub.m]) and the temperature of crystallization ([T.sub.c]) of L-PLA. These results indicated that glycerol played a role as a plasticizer in L-PLA. In particular, a significant depression of [T.sub.g] (up to 9[degrees]C) was observed and found to increase with an increase in plasticizer content, which is a typical behavior for plasticized semi-crystalline polymers. The heat of fusion ([delta][H.sub.f]) and the exothermal heat of crystallization ([delta][H.sub.c]) of L-PLA were found to increase with an increase of glycerol content, indicating that addition of glycerol resulted in an increase of crystallinity. It has been reported for other polymers that plasticizers contribute to an improvement in crystallinity of polymers (15). Naturally funct ionalized oils have been found to improve the crystallization behavior of poly (ethlene terephthalate) (16). In the case of PLA, it has been reported that addition of citrate esters as plasticizers has led to increases in crystallinity, and enhanced molecular mobility due to the presence of plasticizer could cause an increase in crystallinity (17).
In the case of L-PLA/pure starch blends, [T.sub.m] and [T.sub.g] remained almost unchanged regardless of starch content, but [T.sub.c] shifted to a lower temperature and the width of exothermic peaks for crystallization became narrower than that of pure L-PLA. Additionally, [delta]H values for crystallization and melting became larger than that of pure L-PLA. These results would seem to indicate that starch played a role as a nucleating agent enhancing crystallization of L-PLA. This nucleating effect of starch was also observed for LPLA/gelatinized starch blends. But in the case of LPLA/GO blends, [delta][H.sub.c] values are somewhat smaller than those of L-PLA/pure starch blends. We thought that this result was due to a decrease in the nucleating effect of GO because the particle size was larger than that of pure starch.
For L-PLA/gelatinized starch blends containing glycerol, [T.sub.g] and [T.sub.m] decreased but [delta]H increased with an increase in glycerol content, owing to the plasticizing effect of glycerol.
Table 4 shows DSC characteristics of blends with L-/S-PLA and pure starch or G2 starch. The DSC thermogram of pure L-PLA showed a broad crystallization peak at 90[degrees]C to 150[degrees]C and a melting peak at 176.1[degrees]C. But pure S-PLA showed no exothermic peak for crystallization and no melting peak in the 2nd heating scan owing to its star shaped polymeric structure. Generally, this structure was difficult to produce chain folding or chain packing, leading to lower crystallinity and rate of crystallization than in a linear structure. [T.sub.g] and [T.sub.m] for pure L-PLA were observed at approximately 64[degrees]C and 176[degrees]C, respectively. With an increase In S-PLA concentration, the [T.sub.g] and [T.sub.m] decreased. This may be attributed to the lower [T.sub.g] and [T.sub.m] of S-PLA than those of L-PLA. Since branched and star-shaped polymeric structures have a higher number of end-groups and a smaller radius of gyration of the polymer chains in the melt at comparable molecular weights, It would be expected that they have lower [T.sub.g], [T.sub.m] and melt viscosity than linear polymers (18, 19).
A slight increment of [T.sub.c] and a significant decrement of the heat of fusion were observed and found to increase with an increase in S-PLA concentration, indicating lower crystallinity and rate of crystallization. In fact, crystallinity was [sim]29% for pure L-PLA ([delta][H.sub.f] for 100% crystalline L-PLA is 93.6 J/g), but at 30, 50 and 70 wt% S-PLA concentration, the crystallinity was 23, 14 and 8%, respectively.
At 10 wt% starch content, a decrease of [T.sub.m] and [T.sub.g] was shown and [T.sub.m] showed double peaks with an increase of S-PLA. Double or multiple melting peaks have been reported for several polymers or polymer blends, and various theories exist about the origin of multiple melting (20, 21). But the appearance for blend with star shaped polymer and linear polymer has never been reported.
For pure S-PLA/starch blends, melting and exothermic peak were observed, which was also due to the nucleating effect of starch. In the case of 10 wt% G2 starch blends, the decrement of [T.sub.m] and [T.sub.g] and the increment of [delta]H were larger than any other samples, due to both nucleating effect of starch and plasticizing effect of glycerol. At 30 wt% G2 content, though glycerol content increased, [T.sub.g], [T.sub.m] and [T.sub.c] differed little from blends with 10 wt% G2 content, but [delta]H was slightly decreased.
Figure 4 shows polarized optical micrographs of L-PLA and L-PLA/various gelatinized starch blends (ratio of 8:2) crystallized isothermally at each [T.sub.c] for 30 min. Spherulites of pure L-PLA (a) show a good fibril structure growing radially. The average radius of the spherulites is about 140 [micro]m for pure L-PLA. For L-PLA/pure starch blend (b), a large number of small spherulites growing between good dispersed granules were observed. But their sizes and shapes were much smaller and less regular than pure L-PLA. These results indicated that starch played a role as a nucleating agent, and sequentially the size and shape of the grown spherulites changed.
In the case of L-PLA/G0 blend (c), a large particle of G0 starch and very irregular spherulites were observed. The spherulite size was larger than that of L-PLA/pure starch. For L-PLA/G1 blend (d), the spherulite sizes had a wide distribution. This is due to a wide distribution of particle sizes of G1. For samples with high glycerol content, the spherulite sizes became smaller and had more regular distribution in comparison with the samples with low glycerol content. The optical micrograph of L-PLA/G2 blend(e) was similar to that of L-PLA/pure starch blend.
Figure 5 shows SEM photographs of fracture surface of L-PLA/starch blends. For L-PLA/starch blend (a), the voids appeared here and there and the size was much larger than the granule size. Because the SEM photos were taken after fracturing in liquid nitrogen, debonding under tension is not likely to result in such large voids. So we thought that several granules located in voids and a breakaway of the granules from the matrix after fracturing led to these large voids. This breakaway seems to be due to poor interfacial adhesion between the granule and PLA matrix.
For L-PLA/GO blend (b), a large particle of GO with the diameter of approximately 30 [sim] 50 [micro]m clung to the matrix. and the interfacial adhesion seems to be improved compared with L-PLA/pure starch blend, indicating that starch gelatinization contributed to improvement of interfacial adhesion between starch and L-PLA. The SEM photograph of L-PLA/G2 blend (c) shows a good dispersion of starch particles and irregular shape of particles. The void could not be observed at the fracture surfaces. Thus the interfacial adhesion between L-PLA/gelatinized starch with glycerol seemed to be superior to any other samples.
Mechanical Properties of PLA/Starch Blends
Mechanical data of L-PLA and various starch blends is reported in Table 5. We investigated an effect of glycerol addition on mechanical properties of L-PLA. The introduction of glycerol led to a decrease of tensile strength and modulus, but elongation at break slightly increased. Generally, one of the primary functions of a plasticizer is to improve the elongation at break and toughness. However, this has to be achieved at the expense of tensile strength and modulus. Therefore, this tendency is the same as a typical effect of plasticizer.
Generally, in the incompatible polymeric composite with particulates, significant decrements of all the mechanical properties are shown. Even at 10 wt% starch content, starch decreased the tensile strength by 40% and modulus by 60% in comparison with pure PLA. In the case of 30 wt% starch, the tensile strength did not come up to even 30% for L-PLA and the sample was very brittle. These results were due to the poor interfacial adhesion between L-PLA and starch, which were consistent with SEM analysis.
For L-PLA/G0 blends, most properties were superior to those of L-PLA/pure starch blends at 20 wt% starch contents and over. In particular, as starch content was larger, the superiority increased. Though the particle size of GO was larger than that of pure starch, the superiority to L-PLA/pure starch blends suggested that gelatinization of starch had an effect on the improvement of interfacial adhesion between L-PTA and starch.
In spite of the addition of plasticizer leading to decrease tensile strength and modulus, L-PLA/G1 and L-PLA/G2 blend showed superior properties to L-PTA/pure starch blends. Particularly for L-PTA/G2 blend, significant deterioration of tensile strength at 30 wt% starch was not appreared in comparison with L-PTA/starch blend. And at 20 wt% starch content, the elongation at break come up to that of pure L-PTA. That is, the toughness was improved compared with L-PTA/pure starch blends. These resulted from enhancement of interfacial adhesion between L-PTA and starch by starch gelatinization and a good dispersion state of starch particles due to the introduction of glycerol, which prevented their re-aggregation.
The modulus decreased with an increase in starch content owing to the effect of glycerol. In the case of L-PTA/G3 blends, because the glycerol content was too high, a dramatic deterioration of tensile strength and modulus was shown at 20 wt% starch content and above. Table 6 denotes mechanical properties of L-PTA/S-PLA blends and its blends with pure starch and G2 starch. L-PLA showed excellent the tensile strength of 72.5 MPa and modulus of 2154 Mpa, but the elongation at break did not attain to even 10%. For S-PLA, all the properties are lower than those of L-PTA owing to its lower molecular weight compared with L-PTA. For L-PTA/S-PLA blend, none of the properties show any significant deterioration when S-PLA concentration increases. At 30 wt% concentration, on the contrary. the mechanical properties increased, indicating a synergistic effect. We thought that the synergy effect was due to an increase in the entanglement of polymeric chains. In general, branched and star shaped macromolecules have a differe nt entanglement structure and possess a higher density of chain-ends than linear polymer. So, the addition of star shaped PLA may lead to increase in chain entanglement.
In samples with 10 wt% starch content, the properties were significantly deteriorated with an increase in S-PLA ratio and the synergy effect in samples without starch was not shown. Especially for pure S-PLA blends, it was so brittle that tensile testing could not be carried out. We thought that S-PLA with lower molecular weight than b-PLA was affected by thermal degradation or hydrolysis during melt-mixing in the presence of a small amount of water contained in starch.
At 30 wt% starch content, any significant change of properties is not shown at an S-PLA ratio up to 50%, but over 50%, tensile testing films could not be prepared.
In blends with G2 starch, most properties were superior to those of L-PLA/pure starch blends. In particular, at 10 wt% G2 content, the tensile strength showed over 40 MPa without deterioration increasing in S-PLA concentration to 50 wt%. This also resulted from enhancement of the interfacial adhesion due to gelatinization of starch and introduction of glycerol. But at 70 wt% S-PLA concentration, serious deterioration was observed, and for pure S-PLA blends, it was so brittle that testing films could not be prepared.
Gelatinization of starch destroyed of hydrogen bonding in granules and decreased crystallinity. The introduction of glycerol during gelatinization prevented re-formation of hydrogen bonding between the starch polymeric chains. The addition of starch lowered the crystallization temperature and increased the degree of crystallinity in PTL/starch blends. The starch acted as a nucleating agent. Glycerol was a plasticizer that improved crystallinity in the PLA blends.
Starch affected the size and shape of the spherulites. When the content of starch increased, the size became smaller and less regular. For PLA/pure starch blends, voids appeared, which were formed by the separation of starch particles from the matrix. The voids disappeared for PLA/gelainized starch blends, which indicated that starch gelatinization improved the interfacial adhesion between starch and PLA. When pure starch was added, the mechanical properties deteriorated. For PLA/gelatinized blends, most mechanical properties were superior to those for the PLA/pure starch blends. In particular, the b-PLA/G2 blends had the best mechanical properties, and the toughness was improved compared with the b-PLA/pure starch blends.
We are grateful to the Center for Advanced Functional Polymer, KAIST, for partial financial support, 1998.
(*.) Corresponding author.
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Gelatinization Conditions and Glycerol Contents Obtained by TGA. Sample Gelatinization Conditions No. Water (mI) Glycerol (g) Starch (g) Starch Content (wt%) G0 200 0 100 100 G1 180 20 100 83.3 G2 160 40 100 71.4 G3 140 60 100 62.5 L-PLA/G 1 -- -- -- 19.23 8/2 L-PLA/G2 -- -- -- 18.52 8/2 L-PLA/G3 -- -- -- 17.86 8/2 Sample Contents Obtained by TGA No. Glycerol Starch Glycerol Content (wt%) Content (wt%) Content (wt%) G0 -- 100 -- G1 16.7 83.9 16.1 G2 28.6 72.5 27.5 G3 37.5 63.2 36.8 L-PLA/G 1 3.85 20.34 3.01 8/2 L-PLA/G2 7.41 18.97 8.21 8/2 L-PLA/G3 10.71 18.23 10.28 8/2 FT-IR Assignments for Starch. Wavenumber ([cm.sup.-1]) Assignment 2850, 2920 C-H stretching 1640 [delta] (O-H) bend of absorpted water 1462 [CH.sub.2] bending 1445-1325 C-H bending and wagging 1243, 1205 O-H bending 960-1190 C-O streching DSC charateristics of L-PLA/Starch Blends. Sample Ratios of Content of Tg Tc No. PLA/Starch Glycrol (wt%) -- -- 64.2 129.0 L-PLA -- 5 58.9 89.3 113.6 [alpha] -- 10 56.9 89.6 106.8 [alpha] 90:10 0 60.8 106.2 L-PLA/Starch 80:20 0 60.5 99.8 70:30 0 61.1 107.2 90:10 0 61.1 110.5 L-PLA/G0 80:20 0 59.0 101.7 70:30 0 60.9 108.5 90:10 1.96 58.1 90.5 110.5 [alpha] L-PLA/G1 80:20 3.85 55.4 85.9 101.9 [alpha] 70:30 5.66 55.2 91.1 108.8 [alpha] 90:10 3.85 57.4 90.4 L-PLA/G2 80:20 7.41 55.2 88.5 70:30 10.71 57.2 91.4 90:10 5.66 56.9 89.2 L-PLA 80:20 10.71 55.3 91.7 70:30 15.25 56.8 92.7 Sample [delta]Hc Tm [delta][H.sub.f] No. 13.8 176.1 27.1 L-PLA 35.6 173.0 39.0 34.8 172.1 44.6 31.7 175.6 37.0 L-PLA/Starch 31.1 173.9 37.7 30.0 175.1 32.5 28.6 176.1 30.8 L-PLA/G0 30.5 172.4 38.4 29.3 174.7 31.5 29.9 172.5 37.4 L-PLA/G1 27.0 168.9 41.9 26.6 171.9 30.2 24.7 170.0 42.3 L-PLA/G2 27.8 166.2 45.6 25.7 169.6 41.0 19.5 168.5 39.6 L-PLA 27.9 168.2 46.3 26.5 167.4 44.0 ([alpha].)double peaks DSC Characteristics of L-/S-PLA /Starch Blends. Starch S-PLA Tg Tc [delta]Hc Content Content (wt%) ([degrees]C) ([degrees]C) (J/g) 0 64.2 129.1 13.8 30 63.9 136.3 10.0 50 61.4 136.2 5.7 70 61.3 137.2 4.1 100 54.3 -- -- starch 0 60.8 106.2 31.7 10 wt% 30 58.9 107.4 39.2 50 53.8 110.0 38.7 70 52.0 113.4 32.2 100 48.7 121.8 7.0 G2 0 57.4 90.4 24.7 10 wt% 30 49.3 98.0 38.3 50 48.5 102.4 38.9 70 46.4 106.0 28.1 100 42.3 109.6 16.8 starch 0 61.1 107.2 30.0 30 wt% 30 58.3 107.1 30.6 50 54.8 111.6 29.8 70 52.9 114.8 25.5 100 50.4 119.9 11.1 G2 30 wt% 0 57.2 91.4 25.7 30 52.6 99.4 23.2 50 52.6 88.9 103.1 [alpha] 24.5 70 47.2 107.5 24.4 100 46.8 114.4 9.7 Starch Tm [delta]Hm Content ([degrees]C) (J/g) 176.1 27.1 173.1 21.4 168.4 13.1 164.6 7.5 -- -- starch 175.6 37.0 10 wt% 160.1 170.5 [beta] 41.2 153.8 165.6 [beta] 39.1 148.0 159.7 [beta] 32.4 142.2 145.2 [beta] 7.6 G2 170.0 42.3 10 wt% 163.1 43.3 147.0 161.9 [beta] 39.0 133.0 153.9 [beta] 24.6 134.1 141.8 [beta] 17.6 starch 175.1 32.5 30 wt% 171.2 32.5 156.2 167.4 [beta] 31.1 150.3 162.9 [beta] 26.2 141.9 145.6 [beta] 11.3 G2 30 wt% 169.6 41.0 165.1 26.7 152.1 164.6 [beta] 32.4 134.1 158.3 [beta] 21.0 138.0 144.5 [beta] 9.8 ([alpha].)double peaks. ([beta].)double peaks. Mechanical properties of L-PLA/Starch Blends. Tensile Elongation Sample Ratios of Content of Strength Modulus at Break No. PLA/Starch Glycrol (wt%) (MPa) (MPa) (%) -- -- 75.2 2154 7.4 [+ or -] 0.4 L-PLA -- 5 63.3 1382 9.2 [+ or -] 0.6 -- 10 58.8 1217 10.7 [+ or -] 0.8 90:10 0 45.5 972 6.8 [+ or -] 0.1 L-PLA/Starch 80:20 0 31.6 1078 3.2 [+ or -] 0.2 70:30 0 16.8 817 3.3 [+ or -] 0.4 90:10 0 40.8 1113 4.7 [+ or -] 0.6 L-PLA/GO 80:20 0 35.8 1112 4.5 [+ or -] 0.5 70:30 0 23.0 912 4.0 [+ or -] 0.7 90:10 1.96 43.0 1031 6.5 [+ or -] 0.5 L-PLA/G1 80:20 3.85 32.5 1175 5.2 [+ or -] 0.4 70:30 5.66 26.6 1059 4.1 [+ or -] 0.2 90:10 3.85 47.6 1010 6.8 [+ or -] 0.6 L-PLA/G2 80:20 7.41 30.9 900 7.3 [+ or -] 0.8 70:30 10.71 27.8 747 5.7 [+ or -] 0.4 90:10 5.66 44.7 1143 6.7 [+ or -] 0.8 L-PLA/G3 80:20 10.71 23.8 818 8.4 [+ or -] 0.6 70:30 15.25 20.9 696 5.6 [+ or -] 0.2 Mechanical Properties of L-/S-PLA/Starch Blends. S-PLA Tensile Elongation Starch Content Strength Modulus at Break Content (wt%) (MPa) (MPa) (%) 0 75.2 2154 7.4 [+ or -] 0.4 30 80.4 2226 10.5 [+ or -] 0.7 50 74.9 2102 5.4 [+ or -] 0.5 70 70.5 1989 5.7 [+ or -] 0.7 100 45.9 1343 6.5 [+ or -] 0.4 0 45.5 972 6.8 [+ or -] 0.1 30 38.2 924 4.8 [+ or -] 0.3 starch 50 29.1 876 4.5 [+ or -] 0.6 10wt% 70 17.1 734 3.1 [+ or -] 0.2 100 -- -- -- G2 0 47.6 1010 6.8 [+ or -] 0.6 10wt% 30 40.3 987 5.8 [+ or -] 0.5 50 42.4 969 5.1 [+ or -] 0.2 70 17.6 848 3.5 [+ or -] 0.3 100 -- -- -- starch 0 16.8 817 3.3 [+ or -] 0.4 3Owt% 30 22.4 892 3.4 [+ or -] 0.2 50 13.8 764 2.8 [+ or -] 0.4 70 -- -- -- 100 -- -- -- G23Owt% 0 27.8 747 5.7 [+ or -] 0.4 30 28.9 752 4.1 [+ or -] 0.7 50 18.3 711 2.9 [+ or -] 0.4 70 10.4 702 3.1 [+ or -] 0.3 100 -- -- --
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|Author:||PARK, JUN WUK; SOON IM, SEUNG; HYUN KIM, SOO; HA KIM, YOUNG|
|Publication:||Polymer Engineering and Science|
|Article Type:||Statistical Data Included|
|Date:||Dec 1, 2000|
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