Preparation And Properties Of Biodegradable Flexible Transparent Poly(Lactic Acid) Films

Environmental concerns and a shortage of petroleum resources have driven efforts aimed at the bulk production of biodegradable materials.Poly(lactic acid)(PLA)is a kind of aliphatic polyester,which has a number of interesting properties including biodegradability,biocompatibility,good mechanical properties,and processability.But polylactide also has some shortcomings such as brittleness,low melt strength,which influences the properties of products and interrupts the widely used.In this study,polylactide(PLA)film was successfully prepared with PLA and tougheners,plasticizers,chain extenders by means of melt blending.The biodegradable PLA film manufactured by this study could be widely used as daily package film or bags.The paper can be divided into three parts:(1)In this paper,we studied toughening modification of PLA by means of melting blend with polyhydroxyalkanoate(PHA)copolymers,Poly(propylene-carbonate)(PPC),vinyl acetate-vinyl versatate-ethylene(VAc-W-E).The results showed that PHA,VAc-W-E and PPC have different degrees toughening effects on PLA.Elongation of the blends monotonically increased with toughener content.The results of DSC showed that PHA and PPC reduced the glass transition temperature(Tg)of PLA,but VAc-W-E increased the Tg of PLA.The three tougheners have different degrees improved the PLA's crystallinity.Compared with the PHA and VAc-W-E,the PPC was the best.Dynamic rheological properties study showed that the addition of tougheners led to the gradual reduce in the complex viscosity(?*),storage modulus(G ')and loss modulus(G'')of PLA blends.They exhibit good flowability and excellent optical properties.(2)The long-chain branched PLA was prepared with PLA and chain extender of T,F by means of melt grafting method in a mixing device,respectively.The existence of long chain branching were fully proved through linear rheology and extensional rheology.The r?*,G ' and G''increased with chain extenders content,which higher than that of neat PLA at low angular frequency(?).With 2.0 wt%of chain extender in PLA,the Newtonian plateau of LCB-PLA disappeared in the investigated frequency range and strain hardening in elongational experiments.LCB-PLAs exhibited high melt stength,which improves the blowing film ability substantially.Compared the rheology data of chain extender T and F,we found that with 2.0 wt%chain extender T in PLA showed the best result.(3)Adipates and plant-based plasticizer have different degrees plasticization effects on PLA/PPC blends.Compared the mechanical property of adipates and plant-based plasticizer,the results showed that adipates has the best plasticization effects on PLA/PPC blends.With 10wt%of adipates in PLA/PPC blends,we found that the elongation of the plasticized PLA/PPC blends increased to 304.1%,and the tear strength of the film dropped to 113.4KN/m.The results of DSC showed that the addition of plasticizers led to the gradual reduce in the Tf,the cooling crystallization temperature(Tc)and the melting temperature(Tm)of PLA/PPC blends,while increased the Xc.Adipates and plant-based plasticizer could decreased the ?*,G' and G'' of blends.Moreover,this research also studied the migration of adipates in four different simulation food media by gas chromatography.The results were showed that the values of those migrations were all below the EU standards.