Preparation And Performance Investigation Of Biodegradable Poly (Butylene Adipate-co-Terephthalate) Blends And Films

Polymer materials have the merits of light weight,corrosion resistance,easy processing,low price,polymer materials have penetrated into every aspect of people’s life at present.However,polymer materials bring great convenience to people at the same time also produce a lot of problems,such as “white pollution” and energy crisis.In order to solve these problems,the development and utilization of biodegradable polymer materials instead of non-degradable polymer materials is the most effective method.Poly(butylene adipate-co-terephthalate)(PBAT)has many advantages,such as good flexibility,complete biodegradation,excellent thermal stability and biocompatibility,and is one of the most potential environmentally friendly materials to replace traditional polymers.However,PBAT has the shortcomings of poor barrier performance,low crystallinity,low strength and modulus,thus its application has been greatly limited.In view of these shortcomings of PBAT itself,two hard and brittle polymers,polyvinyl acetate(PVAc)and poly(L-lactide)(PLLA),were selected to be blended with PBAT to complement the shortcomings of the polymers,and poly(D-lactide)(PDLA)and glycidyl methacrylate-grafted poly(ethylene octene)(GPOE)were added,the effects of PDLA and GPOE on the properties of PBAT blends were studied.In addition,carbon dioxide-based thermoplastic polyurethane elastomer(PPCU)with better barrier properties was selected to blend with PBAT to improve the mechanics,rheological properties,crystallization properties and barrier properties of polymers,so as to obtain excellent comprehensive performance of PBAT composites.The main contents and conclusions of this dissertation are as follows:(1)A series of PBAT/PVAc blend systems with different contents of PVAc were prepared by melt blending process and the compatibility,phase morphology,thermal,rheological and mechanical properties of the blends were investigated.PBAT/PVAc blends were incompatible system with two respective glass transition temperatures(Tg),and the dispersed PVAc phase was uniformly dispersed in the PBAT matrix in small spheres.The addition of PVAc could act as heterogeneous nucleating agent,improve crystallization ability of PBAT,and increase degree of crystallinity and crystallization temperature.With the increase of PVAc content,the storage modulus and complex viscosity of PBAT/PVAc blends increased in the low frequency region,while the loss factor in the low frequency region of PBAT/PVAc blends decreased.The increase of complex viscosity is beneficial to the blowing process.The larger storage modulus and the smaller tanδ were,the better melt elasticity,the less viscosity dissipation,and the the foamability was improved.The addition of PVAc was beneficial to the film blowing and foaming process.When PVAc content was 30wt%,the Young’s modulus of PBAT increased from 203 MPa to 416 MPa,with an increase of 104.9%,and the yield strength increased from 7.5MPa to 11.5MPa,with an increase of 53.3%.The addition of PVAc effectively improved the mechanical properties of PBAT,which was conducive to the application of PBAT blends in films and foams.(2)PLLA was selected to melt blend with PBAT for melt blending,and PDLA was added in the blending process.The effects of PDLA content on the morphological evolution,crystallization behavior and crystallization kinetics,crystallization morphology,rheological behavior and mechanical properties of PLLA/PBAT blends were studied.The addition of PDLA caused the in situ formation of poly(lactide)stereocomplex crystals in the PLLA/PBAT blend system during the melting blending process,and with the increase of PDLA content,the content of poly(lactide)stereocomplex crystals also increased.The addition of PDLA increased the storage modulus,loss modulus and compound viscosity,and decreased the loss factor of PLLA/PBAT blends in the low frequency region,which indicating the elastic properties of the blends increased.With the increase of PDLA content,the particle size of the PBAT dispersed phase in the blend system gradually increased and the distribution became wider.The poly(lactide)stereocomplex crystals formed could act as a heterogeneous nucleating agent and increased Xc of PLLA in the blend,but excessive PDLA content could form poly(lactide)stereocomplex crystals network structure,inhibit the movement of molecular chains and reduce the degree of crystallinity.The addition of PDLA greatly shortened the crystallization time of PLLA in the blend,but did not affect the compatibility of PLLA and PBAT.In terms of mechanical properties,blending PBAT with PLLA could achieve complementary properties.The elongation at break of PLLA/PBAT blend was 238%,more than 60 times higher than that of pure PLLA,while the modulus and yield strength remained at 1025 and 43.2MPa,respectively.In addtion,with the increase of PDLA content,the elongation at break of the blend decreased while the modulus increased,but the blend still had good toughness.(3)The GPOE was selected as the compatibilizer for the blends of PLLA and PBAT,and the PLLA/PBAT/GPOE blends were prepared by melt blending and blown into thin films.The rheological properties,melt strength,thermal properties,crystallization properties,compatibility,phase structure,the mechanical properties,thermal stability and water vapor permeability of the blend and blend films were investigated.The addition of GPOE increased the storage modulus,loss modulus and complex viscosity of the blend in the low-frequency region and improved the melt strength,which was beneficial to the stability of the film bubble during the blowing process.The addition of GPOE could promote the movement ability of PLLA molecular chain,improve the crystallization ability,accelerate the crystallization speed,and increase the degree of crystallinity.With the addition of GPOE,the graft points generated between molecular chains in the blend could be used as heterogeneous nucleation agents of PLLA crystals,the spherulite size in the blend decreased and the number of spherulites increased.GPOE improved the compatibility between PLLA and PBAT and the glass transition temperature of PLLA and PBAT approached and the phase interface between PLLA and PBAT became blurred.The addition of GPOE reduced the Young’s modulus of the blend,increased the elongation at break of the blend and tear strength of the film.In addition,GPOE could effectively improve the water vapor barrier performance of the blend film.(4)PPCU was selected for blending with PBAT,and a small quantity of chain extender(ADR)containing epoxy group was added.PBAT/PPCU/ADR blends were prepared by melt blending method and blown into films.The rheology,thermal properties,mechanical properties,barrier properties,water vapor permeability,wettability,optical properties and biodegradability of the blends and films were studied.ADR could react with both PBAT and PPCU,and could play as compatibilizer in the blending system.With the increase of PPCU content,the storage modulus and complex viscosity of PBAT/PPCU/ADR blend in the low-frequency region were both improved.With the increase of PPCU content,the Tg of PBAT and PPCU gradually approached,and they had good compatibility.The addition of PPCU made the PBAT crystal more imperfect,reduced the melting point of PBAT,slowed down the crystallization of PBAT,and reduced the degree of crystallinity of PBAT.The elongation at break and tensile strength of the blend films first increased and then decreased with the increase of PPCU content.When the PPCU content was 30 phr,the maximum values were 968%(MD)/1665%(TD)and 66.6MPa(MD)/46.4MPa(TD).With the increase of PPCU content,the Young’s modulus gradually decreased,and the films became softer.The addition of PPCU improved the resistance to water vapor and carbon dioxide gas.In addition,the blend films had excellent optical properties and could be biodegraded in soil.