No abstract

Free-radical-initiated grafting of maleic anhydride (MA) onto poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable aliphatic-aromatic copolyester, was performed by reactive extrusion. 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane was used as the free-radical initiator. The peroxide concentration was varied between 0.0 and 0.5 wt % at 3.0 wt % MA concentration; the MA concentration was varied between 1.0 and 5.0 wt % at 0.5 wt % peroxide concentration. The reaction temperature was maintained at 185 degrees C for all experiments. Under these conditions, between 0.194% and 0.691% MA was grafted onto the polyester backbone. Size-exclusion chromatography, melt flow index, intrinsic viscosity measurements, thermal gravimetric analysis, and differential scanning calorimetry were used to characterize the maleated copolyester. Increasing the initiator concentration at a constant MA concentration of 3% resulted in an increase in the grafting of MA while decreasing the molecular weight of the resulting polymer. Increasing the feed MA concentration also increased the grafting percentage. The maleation of the polyester proved to be very efficient in promoting strong interfacial adhesion with high amylose cornstarch in starch foams as prepared by melt blending. Thus, the use of maleated copolyester as a compatibilizer between starch and PBAT allowed the reduction of the density of resulting starch foams to approximately 21 kg/m3 and improved the resilience from 84% to as high as 95%. Also, the resulting starch foams exhibited improved hydrophobic properties in terms of lower weight gain and higher dimensional stability on moisture sorption.

This article concerns the utilization of maleated thermoplastic starch (MTPS) in the reactive extrusion meltblending with poly(butylene adipate-co-terephthalate) (PBAT) in blown film applications. First, MTPS was prepared from cornstarch with glycerol (plasticizer) and maleic anhydride (MA; esterification agent). MTPS was then melt-blended with PBAT in a subsequent downstream extrusion operation. The effects of both polyester and MA contents were studied on the physicochemical parameters of melt-blends. For high polyester fractions (>60 wt%), PBAT-g-MTPS graft copolymers were obtained through transesterification reactions. They were promoted by the MA-derived acidic moieties grafted onto the starch backbone as shown by selective Soxhlet extraction experiments and FTIR analyses. At lower polyester content, no significant reaction occurred more likely due to an inversion in the phase morphology between both components. Tensile properties of PBATg-MTPS graft copolymer containing 70 wt% polyester were much higher as the TPS/PBAT melt-blend modified with MA. This can be explained by a finer morphology of the dispersed phase in the continuous PBAT matrix, and an increased interfacial area for the grafting reaction as attested by morphological studies.

Cylindrical starch foam shapes were produced on a small scale (ϳ11-12 kg/hr) Werner Pfleiderer ZSK-30 twin-screw extrusion (TSE) process using water, which functions as a plasticizer as well as a blowing agent. The properties of the starch foams depend on the type of starch used (hydroxypropylated high amylose corn starch, 70% amylose), the amount of water and additives (poly(hydroxyamino ether)) (PHAE) used, and extrusion conditions such as temperature and the screw configuration. PHAE offers the adhesion and durability of epoxy resins with the flexibility and processibility of thermoplastic resins. PHAE was successful in imparting mechanical strength and toughness, cell integrity, weather and water resistance to the foam structure. The purpose of this work was to study the effects of the extrusion (melt) temperature, amount of water added and the screw configuration on the density of starch foams. The water externally added was varied from 3% to 12%, while the PHAE content was varied from 3% to 15% of the starch used (on a wet basis). The foaming was carried out at melt temperatures in the range from 85 to 145°C. A match of material properties with process engineering conditions was achieved to facilitate the control of expansion to a structure with valuable commercial properties. The effects of processing conditions on the foaming process were studied using a Werner Pfleiderer ZSK-30 twin screw extruder. The optimum temperature, blowing agent content, and PHAE content were determined. The density of the cylindrical foam extrudates obtained was 22-25 kg/m 3 . The screw configuration, temperature and pressure profiles, and additives affected the morphology, expansion ratio (ER), resilience, and compressibility of the product. These results were then employed on an industrial scale (410 -420 kg/hr) twin-screw food extruder, a Wenger-80, to manufacture foam sheets. The density of the foam sheets was 27-30 kg/m 3 . The cushioning and insulation proper-ties were studied and are reported. POLYM. ENG. SCI., 46: -451, 2006.