Production of Starch Foams by Twin-Screw Extrusion:  Effect of Maleated Poly(butylene adipate-co-terephthalate) as a Compatibilizer

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.

Study of the compatibilizer effect in the properties of starch / polyester blends

“…In the study of the maize starch/PBAT foams using maleic anhydride in the maleatation of the polyester, Nabar et al [7] found that this process was efficient in promote a greater interfacial adhesion and no phases separation of the blends were observed. Raquéz et al [19] evaluated the utilization of MA as compatibilizer in starch/ PBAT blends and observed that the presence of MA improved the compatibility between the polymeric phases, provided by the grafting of anhydride in the starch and after promoting acid-catalyzed transesterification reactions.…”

“…Native starch is considered a non-plastic material, requiring thermal-mechanical processing, in the presence of plasticizers, with the aim to disrupt their semi-crystalline structure and result in an amorphous material, called thermoplastic starch (TPS) [3,4] . There are several current researches in order to use TPS as a biodegradable packaging material, however, this still have some disadvantages, as the elevated influence of the environmental conditions, defficient mechanical properties and difficulty in their stability and processability [5][6][7] . Among the proposals to improve the starch films properties, the production of blends of starch associated with syntetic polymers, as PBAT (poly (butylene adipate co-terephthalate)) have been broadly studied.…”

Novel High‐Performance Talc/Poly[(butylene adipate)‐co‐terephthalate] Hybrid Materials

“…This particular composition has already shown to retain enough melt-strength as well as sufficient grafting extent. [33] These MA-g-PBAT chains were then reactively melt-blended with talc via esterification reactions. Tin(II) octoate (Sn(Oct) 2 ) and 4-dimethylaminopyridine (DMAP) were studied as esterification catalysts.…”

“…[25] In practice, the reactive extrusion maleation of PBAT was carried out using 3 wt.-% MA, and 0.5 wt.-% 2,5-dimethyl-2,5-di(tert-butylperoxy) hexane (Luperox 101) as free-radical initiator in order to retain enough melt-strength as well as sufficient percentage grafting for the resulting MA-g-PBAT. [33] The maleation process was carried out at 185 8C, which was a temperature high enough to avoid the homopolymerization of MA. It is worth recalling that the temperature does not significantly affect the grafting percentage of MA onto the polyester backbone.…”

Preparation and characterization of maleated thermoplastic starch‐based nanocomposites

“…Because of its interesting thermal and mechanical properties, PBAT, as biodegradable aliphatic-aromatic copolyester, represents a promising candidate in the preparation of starch-based products with useful end applications, while maintaining the biodegradability of the overall composition. 31,32 In contrast to TPS, the low melt-viscosity of MTPS, together with its increased reactivity led, by melt-blending with PBAT, to the formation of stronger covalent bonds at the MTPS-polyester interface, and therefore a finer phase morphology for the resulting melt-blends. 30 However, compared with those of pristine PBAT, it was observed that the occurrence of acid-promoted hydrolysis, inter-and intramolecular transesterification reactions underwent by the polyester matrix.…”