Preparation And Properties Of Biodegradable Poly(L-lactide) Films

Polylactic acid?PLA?,is a thermoplastic,biocompatible,biodegradable polymer derived from renewable resources such as corn,starch and sugar.PLA has good biocompatibility,solvent resistance,mechanical properties and processability,which is non-toxic and non-irritating.It is accepted as an environmentally friendly material,which has been widely used in packaging materials,biomedical materials and other fields.However,the application of PLA is limited because of its brittleness,low thermal resistance,slow crystallization,low elongation at break,poor notch impact strength and hydrolysis properties.The alternative methods to improve the ductility and flexibility of PLA are to graft reactions,or to blend with other flexible polymers,or plasticizers,or nucleator.In this paper,three systems of PLA blends were designed,such as PLA,toughening agent and plasticizer system;PLA,toughening agent and elastomer system;PLA,elastomer and elastomer flexible material system.The main contents and conclusions are as follows:?1?The environmental-friendly diethylene glycol adipate?DGBEA?and poly?diethylene glycol adipate??PDEGA?,were employed as plasticizers.The content of the plasticizer was 8wt%,and the content of MBS was changed from 3wt%-12wt%.The mixture of the plasticizer and PLA/MBS were melt blended and blown film process.The rheological properties,thermal properties,crystallization behavior,mechanical properties,mechanical properties,optical properties and enzymatic degradation were studied.The results showed that when the plasticizer DGBEA or PDEGA was added to pure PLA,the fluidity changed little,while MBS changed the fluidity of the blends and enhanced the melting strength of the blends.In the whole frequency range,the storage modulus,complex viscosity and elasticity of the blends increased with the increase of MBS content,which indicated that the crosslinking between PLA and PMMA was formed.The plasticization of DGBEA and nucleation of MBS promoted the crystallization of PLA.With the addition of DGBEA,T_g and T_cc of PLA decreased by 17^oC and 20^oC respectively;with the addition of PDEGA,T_g and T_ccc of PLA decreased by 12^oC and 20^oC respectively.With the increase of MBS content,T_g and T_cc of PLA continued to decrease,and the crystallinity increased by 12%.It was observed by POM that the nucleation point of PLA increased,and the crystallized size of PLA decreased with the increase of MBS content.The mechanical properties of PLA/DGBEA/MBS or PLA/PDEGA/MBS blends and films were significantly improved under the plasticizing effect of DGBEA or PDEGA and the toughening effect of MBS.The elongation at break and impact strength of the blends increased significantly.The maximum elongation at break and impact strength of PLA/DGBEA/MBS blends were 380%and 72.4 kJ/m²,respectively.The maximum elongation at break and impact strength of PLA/PDEGA/MBS blends were 147%and90.3 kJ/m²,respectively.The elongation at break and tear strength of the films increased significantly.The maximum elongation at break of PLA/DGBEA/MBS films were289.5%?MD?and 286.8%?TD?,respectively.The maximum tear strength was 129kN/m?MD?and 127 kN/m?TD?.The maximum elongation at break of PLA/PDEGA/MBS films were 155.3%?MD?and 154.3%?TD?,and the maximum tear strength is 163.6 kN/m?MD?and 160.4 kN/m?TD?,respectively.PLA is a good biodegradable material.The addition of DGBEA or PDEGA and MBS would not affect the biodegradability of PLA by adjusting the proportion of materials.?2?Polylactide?PLA?,methyl methacrylate-butadiene-styrene copolymer?MBS?,and poly?propylene carbonate?polyurethane?PPCU?were blended and blown film process.In the experiment,the content of MBS was 10wt%,and the content of PPCU was changed.The rheological properties,thermal properties,crystallization behavior,mechanical properties,mechanical properties and toughening mechanism of the blends and films were studied.The results showed that the flexible ether bond in PPCU molecular chain could improve the movement of molecular chain,the toughness of blends and the mechanical properties of films.The complex viscosity of PLA/MBS/PPCU blends decreased with the increase of PPCU content from 5wt%to40wt%.The complex viscosity of the blends decreased significantly with PPCU content from 30%to 40%.The low frequency region?decreased from 55^o to 35^o in 60/10/30and 50/10/40 PLA/MBS/PPCU blends,which indicated that the elastic behavior had been enhanced.The enhanced elastic behavior will be beneficial to blowing film in the actual production process.DSC analysis revealed that MBS and PPCU enhanced the ability of crystallization for PLA;MBS made it by promoting nucleation while PPCU through plastic deformation.The mechanical test results showed that PLA could be obviously toughened by the addition of MBS and PPCU.The tensile strength of PLA/MBS/PPCU blends decreased from 45.9 MPa to 35.4 MPa.The elongation at break of PLA had been improved from 6.2%for neat PLA to 276.5%after addition of 40wt%PPCU.The impact strength was increased from 10.8 kJ/m²for neat PLA to 74.7 kJ/m² for PLA/MBS/PPCU 50/10/40,which displayed that the brittle-ductiletransitionoftheblendswasobtained when MBS and PPCU were added.The tensile strength of PLA/MBS/PPCU films decreased from 33.5 MPa?MD?and 28.2 MPa?TD?to 27.4 MPa?MD?and 24.2 MPa?TD?with the increase of PPCU content from 5wt%to 40wt%.The elongation at break increased from 139.3%?MD?and 65.7%?TD?to 271.1%?MD?and 222.2%?TD?,respectively.The tear strength of PLA/MBS/PPCU films was above 100 kN/m.The toughening mechanism investigation revealed that shear yielding of PLA matrix was triggered by the cavitation of MBS and the plasticizing deformation of PPCU.POM displayed the density of spherulite nucleation increased,the size of the crystalline particles decreased with the addition of MBS.With increasing PPCU content from 5wt%to 40wt%,the density of spherulite nucleation increases and the size of the crystalline particles decreases.The molten PPCU has the effect of melt,making the movement of PLA chains easier.As a result,this research suggested that PLA could be toughened synergistically by MBS and PPCU.In summary,the PLA/MBS/PPCU?50/10/40?blends and films had excellent properties,which would be widely used in the biodegradable packaging application.?3?Poly?lactic acid??PLA?,poly?butylene adipate-co-terephthalate??PBAT?and poly?propylene carbonate?polyurethane?PPCU?were blended by using a twin-screw extruder and then the PLA/PBAT/PPCU trinary blends were made into films via the blown film technique.The content of PLA was fixed,and the content of PPCU and PBAT were changed.The rheological properties,thermal properties,crystallization behavior,mechanical properties,optical properties and gas barrier properties of the blends were studied.DSC results indicated that T_g of PBAT was increased from-29.2to-12.3^oC,T_g of PPCU was increased from 43.5 to 45.6^oC and T_g of PLA was decreased from 53.6 to 51.8^oC with increasing PPCU content from 10%to 50%,which showed that the compatibility of PLA,PBAT and PPCU was enhanced.DSC and POM results showed that the amorphous PPCU together with non-crystalline PBAT and PLA could form a continuous amorphous phase with the crystalline PLA domains evenly dispersed in the films,which resulted in a smaller crystallite dimension of PLA/PBAT/PPCU films.Tensile and tear tests displayed all of the PLA/PBAT/PPCU films had high elongation at break decreased from 240%?MD?and 413%?TD?of 35/55/10PLA/PBAT/PPCU film to 226%?MD?and 353%?TD?of 35/15/50 PLA/PBAT/PPCU films,respectively;the tear strength of all the PLA/PBAT/PPCU films was high from134.7?MD?and 137.3 kN/m?TD?of 35/55/10 PLA/PBAT/PPCU film to 143.6?MD?and 147.8 kN/m?TD?of 35/15/50 PLA/PBAT/PPCU films.For the PLA/PBAT/PPCU films,PBAT could significantly enhance elongation at break,PLA and PPCU were conducive to improve the tensile strength and the Young's modulus,PPCU could improve the tear strength.The research suggested that all the PLA/PBAT/PPCU films had excellent mechanical properties,including higher tear strength,tensile strength and higher elongation at break,and relatively excellent barrier properties,which would be widely used in the biodegradable packaging fields.