Study On Properties And Foam Behaviors Of Polylactic Acid/Glass Fiber Composites

As a typical biodegradable material,the polylactic acid(PLA)is expected to replace petroleum-based plastics,to be the new plastic in the 21st century.PLA has been applied in garment,textiles,packaging,agroforestry,civil,medical supplies,daily necessities and other fields widely because its crystallizability,biodegradability,good properties for processing,optical transparency.However,the shortcomings of PLA,for example,heat stability is poor,and its melt strength is not strong enough,limit its application furtherly.In addition,the synthesis process of PLA is complicated,the production cost is high,so PLA foams arise at the historic moment.However,the melt strength of PLA is too low to get the complete cellular structure.Therefore,the modification of PLA has high guiding significance on the theory and practical application to enhance its performance and broaden its potential application fields.Glass fibers that own high strength,good heat resistance,transparency,electrical insulation,and low price,are be used as polymer reinforced materiasl widely.Aiming at the shortage of the PLA matrix,the paper mainly researched polylactic acid/glass fiber(PLA/GF)composites preparation,performance,annealing process and foaming behavior.In this study,PLA/GF composites were prepared with two screw extrusion technology and equipment,the mass ratio of PLA and GF was 95/5.90/10.85/15、80/20.And mechanical properties,thermal properties,crystallinity,rheological property was studied.The result showed that with the increase of GF,the mechanical properties of PLA/GF composites were improved obviously,for example,when the mass ratio of GF was 20%,the tensile strength,tensile modulus,bending strength,bending modulus,impact strength was increased by 86.41%,135.98%,42.61%,99.57%,166.61%.Also,with the increase of GF,the storage modulus increased and then decreased,the loss factor decrease,the result showed that small amounts of GF could improve the dynamic thermodynamic performance of PLA/GF composites.The heat resistance was improved and thermal stability wasn’t changed with the content of GF.Secondly,we analyzed the effects of GF on the crystallization properties of PLA and quantitative analyzed of the effect of GF on the crystallizing rate of PLA by Jeziory method.On this basis,we studied the effects of annealing conditions(annealing temperature and time)for the crystallinity and mechanical properties of PLA/GF by differential scanning calorimetry(DSC),X-ray diffraction(XRD)and universal testing machine.the result showed that the cold crystallization temperature tended to the lower temperature,the cold crystallization peak became sharper with the increase of GF,the performance indicated GF promoted PLA crystallization,speeded up the crystallizing rate of PLA.According to the result of XRD,all these PLA/GF samples were still formed the most common crystal modification(a-form).With the function of GF and annealing treatment,the crystallinity and mechanical properties of PLA/GF were enhanced.Finally,we studied the contents of GF and the technological parameters(foaming temperature and saturation pressure)on the influence of PLA/GF composite foaming behavior,revealed the internal relationship between the contents of GF,foaming temperature,saturation pressure and mean cell diameter,cell density,volume expansion rate of PLA/GF composite foam samples.The result showed that the viscoelasticity of PLA/GF composite was higher than pure PLA,so that the microcellular foam structure could remain integrated.The mean cell diameter first increased and then decreased and the cell density first decreased and then increased with the contents of GF.When the foaming temperature raised between 125-128℃,the mean cell diameter increased and the cell density decreased,the volume expansion rate first increased and then stayed the same.The maximum expansion rate could reach 13.5%,increased by 330.31%compared with pure PLA.When the increase of saturation pressure between 10MPa-16MPa,the mean cell diameter first decreased and then increased,finally decreased,and foam density first increased and then decrease,finally increased,the volume expansion rate always raised.