PBAT/TPS Blends Based On Reactive Compatibilization, Elongational Extrusion And MCC Modification

The huge amount of plastic waste has caused serious environmental issues.To address these issues,one effective approach is to develop biodegradable polymer materials.To this end,poly(butylene adipate-co-terephthalate)(PBAT)holds tremendous potential not only due to its attractive biodegradable capability of aliphatic polyesters but also because of its good mechanical properties of aromatic polyesters.However,its practical application in large scale is still limited by the high production cost.By contrast,thermoplastic starch(TPS)is much cheaper and easier to obtain,although it is hard to process and exhibits poor mechanical properties.Thus,it may be rational to decrease the cost of PBAT and increase the performance of TPS by blending them.Unfortunately,the poor compatibility between the hydrophilic TPS and the hodrophobic PBAT generally results in poor mechanical properties which are far beyond the requirements for practical applications.In this thesis,a series of methods have been proposed to improve the mechanical properties of PBAT/TPS blends based on reactive compatibilization,elongational extrusion and modification of microcrystalline cellulose(MCC).First,reactive epoxy compatibilizer(REC)was used to improve the compatibility of PBAT/TPS blends.The epoxy functional group of REC could react with PBAT and TPS,producing the PBAT-REC-starch copolymer.Consequently,not only the compatibility between TPS and PBAT was greatly improved and the interfacial interaction was strengthened,but also the dispersion of rigid TPS in PBAT was improved,resulting in improved significantly impact strength and elastic modulus.In addition,the epoxy functional group of REC could also react with both carboxyl and hydroxyl groups of PBAT,thus effectively preventing the degradation of PBAT through chain extension.This provides an effective method for the preparation of high-performance PBAT/TPS blends with high TPS-loading.Second,to further improve the mechanical properties of compatibilized PBAT/TPS blends,a double-axis eccentric rotor extruder(ERE)with the elongation flow field was used for elongational extrusion processing of compatibilized PBAT/TPS blends.Unlike the conventional extrusion process,the compatibilized PBAT/TPS blends underwent a cyclic compression and release process during the tensile extrusion process,resulting in more adequate plasticization of TPS and more uniform dispersion in the PBAT matrix.In addition,the small aspect ratio of the eccentric rotor extruder leads to a shorter thermal history experienced by the material and less shear force in the tensile flow field,further avoiding degradation of PBAT.The compatibilized PBAT/TPS blends produced by the stretch extrusion process have better tensile properties and impact strength,providing a new way to manufacture compatibilized PBAT/TPS blends at low cost and high performance.Third,a two-step elongational extrusion processing was used to regulate the phase-separated structure of the compatibilized PBAT/TPS blends.The results showed that the phase structure of the compatibilized PBAT/TPS blends transformed from sea-island to bi-continuous phase by two-step elongational extrusion processing,and the material had better mechanical properties with tensile strength slightly lower than that of PBAT,elongation at break comparable to that of PBAT,and impact strength significantly higher than that of PBAT.This provides theoretical guidance for preparing PBAT/TPS blends with high mechanical properties.Last,to further enhance the mechanical properties of the compatibilized PBAT/TPS blend,MCC was introduced into the blends to prepare the PBAT/TPS/MCC composites.After the two-step elongational extrusion process,MCC was uniformly dispersed in the blend,which enhanced the crystallinity and thermal stability of the compatibilized PBAT/TPS blends.At the same time,the PBAT/TPS/MCC composites maintained a bi-continuous phase structure and the material had a high elastic modulus.This provides a new idea for preparing the biodegradable materials with high performance and low cost.