Ramaswamy Mani

Properties of injection moulded blends of starch and modified biodegradable polyesters

Abstract The properties of blends of starch and aliphatic biodegradable polyesters are presented in this paper. The aliphatic polyesters used include: polye-caprolactone, polybutylene succinate and a butanediol–adipate–terephthalate copolymer. To improve the compatibility between the starch and the synthetic polyester, a compatibilizer containing an anhydride functional group incorporated on to the polyester backbone was used. The blends were melt compounded using a twin-screw extruder. The concentration of the starch in the blend was varied from 10% to 70% by weight. The amylopectin content of the starches varied from 30% to 99%. The addition of a small amount of compatibilizer increased the strength significantly over the uncompatibilized blend. For the compatibilized blend, the tensile strength was invariant with starch content when compared to the original polyester, while it decreased with increase in starch content for the uncompatibilized blend. Blends displayed a sharp intake of water and those containing butanediol–adipate–terephthalate copolymer had a higher water absorption than those containing the other polyester. Each blend displayed two glass transition; one corresponding to the polyester and the other corresponding to starch. For compatibilized blends, the glass transition temperature of starch in the blend is lower than that observed for the uncompatibilized blend. For all polyester blends, those containing 99% amylopectin starch at 70% level had the lowest crystallinity which otherwise decreased with decreased amylopectin level in the starch. Blend morphology indicates that the starch phase become finer as the amylopectin in the blend increased. Also, a higher starch content led to greater melting of the starch granules and at 70% starch by weight, a cocontinuous phase between the starch and the synthetic polymer exists.

Functionalization of polyesters with maleic anhydride by reactive extrusion

Maleic anhydride (MAn) was grafted onto aliphatic and aromatic/aliphatic copolyesters by reactive extrusion in the presence of a free radical initiator using a twin-screw extruder. The grafting reaction was confirmed by spectroscopic analyses. The presence of succinic anhydride groups was shown by FT-IR spectroscopy, and NMR spectra indicate that the grafts consist of single succinic anhydride units. The 2D 1H-NMR spectra (COSY) indicate that grafting reactions take place at aliphatic dicarboxylic acid units of copolyesters. The graft content was determined by a nonaqueous titration method. The effects of concentration of initiator and monomer and reaction temperature on the graft content and intrinsic viscosity were studied. The low percentage grafting in poly(lactic acid) was observed due to the presence of limited free radical sites in the polymer backbone. Temperature and monomer and initiator concentrations affect the graft content, and the desired graft content with minimal degradation can be obtained by controlling these factors.

Synthesis and characterization of starch-graft-polycaprolactone as compatibilizer for starch/polycaprolactone blends

SUMMARY Polycaprolactone (PCL) was grafted onto starch through introduction of urethane linkages. The grafting reaction was carried out in two steps. The first step was the reaction of hydroxyl-terminated PCL with 2,4-tolylene diisocyanate. The isocyanate terminated PCL was then reacted with starch to obtain starchgrajl-polycaprolactone (starch-g-PCL). The grafting reaction was confirmed by FT-IR spectroscopy. The compatibility of the starch/PCL blend was enhanced with a compatibilizer, starch-g-PCL, whose amount was 3 wt.-% of the blend. The tensile strength and morphology of the compatibilized blend were determined. It was found that the compatibilized starch/PCL blend has finer phase domains and an improved interfacial adhesion. Mechanical properties of the compatibilized blend were found to be significantly higher than those of the corresponding uncompatibilized starcWCL blend.

Properties of injection moulded starch/synthetic polymer blends—IV. Thermal and morphological properties

Abstract The morphological properties of blends of corn starch and maleated polyolefins are presented in this paper. Four different starches were used: unmodified waxy maize, industrial corn, common corn and a high amylose starch. The concentration of starch in the blends was kept at 70% by weight. Three different synthetic polymers, ethylene-vinyl acetate, low density polyethylene and high density polyethylene were melt blended with the respective starches in a corotating twin screw extruder. A corresponding maleated synthetic polymer was added as a compatibilizer. Differential scanning calorimeter (DSC), dynamic mechanical analyzer (DMA), scanning (SEM) and transmission electron (TEM) microscope and optical microscopy (OM) were used to evaluate the phase morphology. DSC studies indicate that starch granules underwent melting with each subsequent processing step. This was also confirmed from the optical photomicrographs where the starch granule size decreased after each subsequent processing step. DMA studies showed that the blends exhibited two distinct glass transitions, one for each component and that the glass transition temperature of starch decreased as the amylose content increased in the starch blends. Microscopy studies indicated that the starch phase became finer as the amylopectin content in the starch increased. For blends containing waxy starch, a co-continuous phase with synthetic polymers was evident.