ABSTRACT:The solubility parameters of polylactide (PLA), poly(ethylene terephthalate) (PET), and various disperse dyes calculated according to the group contribution method were used to explain the low sorption of some disperse dyes on PLA but the high sorption of the same dyes on PET. It was found that the dyes with high sorption on PLA tended to have solubility parameters near that of PLA, which has a lower solubility parameter than that of PET. It was also found that the solubility parameter, which was calculated based on cohesive energy and molar volume at 25°C, was more appropriate for explaining dyeings at lower temperature, 100 and 110°C, than those at higher temperature, 130°C. Based on the finding that dyes with solubility parameters near that of PLA tend to have high sorption on PLA, general structures for disperse dye that may have high sorption on PLA were proposed.

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BACKGROUND: Some of the problems with electrospun zein fiber are that it has very low tenacities in the dry and wet states and that mats of the fiber become films when immersed in water. The fibers are therefore unusable for various applications despite their good biocompatibility and biodegradability. This research was conducted to overcome these problems by electrospinning novel fibers containing various concentrations of zein, citric acid (CA) and sodium hypophosphite monohydrate (SHP) and by crosslinking the zein with CA and with SHP serving as a catalyst. RESULTS:The CA-crosslinked electrospun zein fiber has as much as 10-fold greater wet tenacity and 15-fold greater dry tenacity than regular electrospun zein fiber. The average diameter of these fibers is 451 nm, which is the smallest diameter ever reported for zein-based electrospun fiber. A mat of this fiber retains its fibrous structure when immersed in water, and the fiber retains about 70% of its tenacity after 16 days at 50 • C and 90% relative humidity. CONCLUSION:The high dry and wet tenacities, good water stability and small diameter of the novel CAcrosslinked electrospun zein fiber make it attractive for biomedical and other applications that expose zein to water or that require high surface area.

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Molecular modeling is used to explain how the resistance of poly[(L‐lactide)‐co‐(D‐lactide)] to hydrolysis is affected by the percentages of L‐ and D‐lactide and their arrangements in blocks or random arrangements in the polymer. Previous studies on improving the hydrolysis resistance of PLA have involved forming either poly(L‐lactide)/poly(D‐lactide) (PLLA/PDLA) polyblends or copolymers of L‐ and D‐lactide. In this study, molecular modeling was used to study the hydrolysis resistance of PLA containing various arrangements of L‐ and D‐lactide in the polymers. PLA copolymers are found to have less resistance to hydrolysis than a PLLA/PDLA polyblend having the same percentages of L‐ and D‐lactide because a polyblend can form more stereocomplexes, which is the most stable structure PLA can form.

Grafting various groups onto cellulose is found to substantially increase acid hydrolysis of the b-(1,4)-glycosidic linkages. Molecular modeling is used to explain how various substituents such as esters and ethers cause this phenomenon. A substituent helps stabilize hydrolyzed cellulose by serving as an anchor to the end of the cleaved cellulose to which it is bonded, making it less mobile, and allowing it to have stronger interactions than those in pure hydrolyzed cellulose. Hydrolysis increases with increasing size of the substituent. Molecules sorbed but not grafted to cellulose do not increase hydrolysis. Hydrolysis mainly occurs at glucoses bonded to the substituent, and supporting experiments show that hydrolysis approaches equilibrium when no substituent remains on the cellulose fiber.

The ability of polylactide (PLA) to retain its mechanical properties after repeated cleanings at various pH levels, washing temperatures, and drying conditions has been studied. One of the problems with PLA is its poor resistance to hydrolysis, especially under alkaline conditions. In this study, PLA fabrics were sent through 50 cleaning cycles with different pH levels (8 or 10), washing temperatures (35 or 558C), and drying conditions (air dry at 218C/65% relative humidity or tumble dry at 50 or 708C). The retention percentages of the breaking tenacity, breaking elongation, and modulus of the PLA yarns were measured after every 10 cleaning cycles. A pH of 8 gave greater breaking tenacity, breaking elongation, and modulus retention than pH 10. Washing PLA at 358C and air drying it at 218C resulted in greater modulus retention than washing and drying at higher temperatures. Hydrolysis of the polymer was the main cause of the loss in mechanical properties. Equations were developed to predict the retention percentage of the breaking tenacity, breaking elongation, and modulus based on the pH, number of cleaning cycles, and washing and drying temperatures. Recommendations for appropriate conditions for the cleaning of PLA fabrics that result in greater mechanical property retention are given.