Vipul Davé

Biodegradable polymer blends of poly(lactic acid) and poly(ethylene glycol)

Poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were melt-blended and extruded into films in the PLA/PEG ratios of 100/0, 90/10, 70/30, 50/50, and 30/70. It was concluded from the differential scanning calorimetry and dynamic mechanical analysis results that PLA/PEG blends range from miscible to partially miscible, depending on the concentration. Below 50% PEG content the PEG plasticized the PLA, yielding higher elongations and lower modulus values. Above 50% PEG content the blend morphology was driven by the increasing crystallinity of PEG, resulting in an increase in modulus and a corresponding decrease in elongation at break. The tensile strength was found to decrease in a linear fashion with increasing PEG content. Results obtained from enzymatic degradation show that the weight loss for all of the blends was significantly greater than that for the pure PLA. When the PEG content was 30% or lower, weight loss was found to be primarily due to enzymatic degradation of the PLA. Above 30% PEG content, the weight loss was found to be mainly due to the dissolution of PEG. During hydrolytic degradation, for PLA/PEG blends up to 30% PEG, weight loss occurs as a combination of degradation of PLA and dissolution of PEG.

Citrate Esters as Plasticizers for Poly(Lactic Acid)

Citrate esters were used as plasticizers with poly(lactic acid) (PLA). Films were extruded using a single-screw extruder with plasticizer contents of 10, 20, and 30% by weight. All of the citrate esters investigated were found to be effective in reducing the glass transition temperature and improving the elongation at break. It was observed that the plasticizing efficiency was higher for the intermediate-molecular-weight plasticizers. Hydrolytic and enzymatic degradation tests were conducted on these films. It was found that the lower-molecular-weight citrates increased the enzymatic degradation rate of PLA and the higher-molecular-weight citrates decreased the degradation rate as compared with that of unplasticized PLA.

Miscibility and biodegradability of blends of poly(lactic acid) and poly(vinyl acetate)

Poly(lactic acid) (PLA) was melt blended with poly(vinyl acetate) (PVA) using a single-screw extruder. The extruded films obtained were characterized for miscibility, physical properties, degradation and surface morphology. Differential scanning calorimetry showed that all the as-extruded films were amorphous, and that the blends were compatible as only one glass transition temperature was observed. Results obtained from physical property testing indicated that the blends exhibit synergism in the range of 5 to 30% PVA, probably due to some interactions taking place in that region. Enzymatic degradation studies showed that there was a vast difference in the weight loss of pure PLA samples and the 95/5 PLA/PVA blend. Surface tension results showed that this was due to the vast difference in the surface tension of the pure PLA films and the 95/5 blend. Deaged-free blends showed the maximum degradation, followed by aged-extruded and then deaged-fixed. Scanning electron micrographs showed that the mode of degradation differs for the aged and deaged samples. A uniform degradation pattern was seen in the case of deaged samples while the aged samples showed a non-uniform pattern of degradation.

Effects of physical aging, crystallinity, and orientation on the enzymatic degradation of poly(lactic acid)

The effects of physical aging, degree of crystallinity, and orientation of poly(lactic acid) (PLA) were studied using differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The samples of PLA with 96% [L] and 4% [D] contents were prepared by injection molding. The physical aging of PLA strongly depended on time and temperature. The change of rate of physical aging was very fast initially and slowed down as time increased. The enzymatic degradation of PLA was carried out with proteinase K at 37°C at a pH value of 8.6 in a Tris/HCl buffer solution. The enzymatic degradation rate was found to decrease as a function of physical aging (i.e., excess enthalpy relaxation). The rate of enzymatic degradation of PLA decreased with the increase in crystallinity. A threshold was observed when the heat of fusion was less than 20 J/g. The weight loss of PLA with a low level of crystallinity had no apparent change during any period of testing time. The rates of enzymatic degradation of stretched and injection-molded specimens were comparable.

Liquid crystalline, rheological and thermal properties of konjac glucomannan

Konjac glucomannan (KGM) exhibited liquid crystalline (LC) behaviour in aqueous solutions above 7% (w/w) concentrations as was determined by polarized optical microscopy and circular dichroism. The rheological properties of the concentrated LC solutions of KGM exhibited pseudoplastic behaviour. The fibrous extrudates retained a significant degree of flow-induced orientation as was determined by wide angle X-ray scattering, thereby indicating potential applications of KGM as fibres and films. Differential scanning calorimetry experiments showed that a significant degree of interaction occurred between KGM and water and that the KGM gels produced in our study cannot be classified as thermoreversible.

Review of Konjac Glucomannan

The paper reviews the solution and gelling properties of konjac glucomannan (KGM) and its interactions with other hydrocolloids such as xanthan and carrageenan for food applications. Research activities in the area of KGM processing in environmentally friendly aqueous environments have been discussed for coatings and packaging applications.

Biodegradability of Cellulose Acetate Plasticized with Citrate Esters

Abstract Cellulose acetate (CA) was melt compounded with two different citric acid esters: triethyl citrate and acetyl triethyl citrate. It was observed, based on the glass transition temperatures, that both plasticizers were miscible with CA. The addition of plasticizer reduced the tensile modulus and increased the elongation of CA. The biodegradation rates increased dramatically with an increase in plasticizer content.