| Starch-based biodegradable plastic is an important degradable polymer material.However, as starch macromolecules contain lots of hydroxyls, strong interaction among themleads to the degradation temperature below melting temperature. Therefore, native starch cannot be thermal processed. In addition, mechanical properties of pure starch materials areusually poor, and water-resistant ability is also low because of hydrophilic hydroxyl groups.Although these disadvantages can be improved by blending starch with conventional resinsuch as PE and PP, the composites are unable to be degraded, which is not conductive toenvironment. Consequently, issues about thermoplastic starch as well as blends containingbiodegradable polymers were focused in this paper, ensuring their biodegradability at thesame time.Firstly, processing characteristics and conditions for producing thermoplastic starch (TPS)were studied, and then two groups of co-plasticizers glycerol/formamide glycerol/urea wereused respectively to prepare TPS. The effects of different co-plasticizers and coupling agentson properties of TPS were investigated. Secondly, two kinds of biodegradable polyesterspoly(lactic acid)(PLA) and polycaprolactone(PCL) were blended with TPS, to form binaryblends TPS/PLA and ternary ones TPS/PLA/PCL which were both starch based. The impactof blending modification on TPS was discussed. Thirdly, PLA and PCL were grafted withmaleic anhydride (MAH) before blending with TPS. The subsequent TPS/PLA-g-MAH andTPS/PLA-g-MAH/PCL-g-MAH blends were then studied through tests on mechanicalproperties, water-resistance, rheological behaviors and biodegradation. FT-IR, SEM, DSC andXRD were also used for analysis. Meanwhile, the compatibilized composites were comparedwith TPS/PLA and TPS/PLA/PCL blends.The results showed that processing and applied properties of TPS were sensitive totemperature when it was prepared with small molecule plasticizers. The mixing temperatureshould be adjusted according to plasticizer content.10PHR increase of the plasticizer matched10℃decrease of the processing temperature. TPS plasticized by glycerol/urea with proportion of40/10had good integrated mechanical properties, for its impact strength was6.4%lower than one plasticized only by glycerol while tensile strength was20%higher.Water-resistance and rheological properties were also better than the latter. TPS can notcompatibilize with PLA and PCL, but polyesters grafted with MAH improved compatibilityof each component. As a result, compared with TPS/PLA and TPS/PLA/PCL blends, thetensile strength of TPS/PLA-g-MAH and TPS/PLA-g-MAH/PCL-g-MAH rose by1.8and2.6times, impact flexibility rose by57.9%and1.2times and water absorption fell8.1%and10.3%averagely. Biodegradation experiment indicated that weight loss of all thecompatibilize blends with various proportions was above70%after being buried in soil for90days, showing satisfactory biodegradability. |
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