Study On The Poly(Lactic Acid) Modified By Multiscale Polyester Elastomer Particles

Poly(lactic acid)(PLA)is a polymer material with good biodegradability and biocompatibility,but its disadvantages of the slow crystallization rate and poor toughness have limited its further application.The melt-blending technology is an important and efficient method for modifying the PLA by using some elastomer particles.It is a remarkable fact that few studies were explored on the influence of the size of the elastomer particles on the properties of PLA.In this paper,we firstly prepared some kinds of biodegradable polyester elastomer particles(BEP)with different particle sizes,and then fabricated some PLA/BEP composites by using the simple melt-blended method.The effects of size and loading of the BEP on some properties of the PLA composites were investigated specially.1.Preparation of some PLA/BEP composites.Firstly,the unsaturated polyester was synthesized from aliphatic diol and dihydric acid(anhydride)by melt polycondensation.Then the unsaturated polyester was emulsified,irradiated and spray dried to prepare the some kinds of BEPs with the size of 50 nm,150 nm,300 nm,500 nm and 1 ?m respectively.Then the multiscale BEPs were melt-blended with PLA respectively to prepare some PLA/BEP composites.2.Study on mechanical properties of the PLA/BEP composites.Tensile test and impact test of PLA composites showed that the elongation at break of PLA composites increases with the increasing size and loading of the BEP,meanwhile the impact strength and storage modulus both increase as well.The BEP with the size of 1 ?m can increase the elongation at break from 2.8% of pure PLA does to 39.8%.The BEP with the size of500 nm can increase the notched impact strength from 2.79 k J/m2 of pure PLA does to4.99 k J/m2.The BEP with the composite particle size of 50 nm and 300 nm can increase the un-notched impact strength from 18.57 k J/m2 of pure PLA does to 52.60 k J/m2,which have the effect of synergistic modification on PLA composites.The classic percolation model theory is not applicable to explain the mechanism of the multiscale BEPs toughening PLA in this paper.SEM images showed that many craze and microvoids were founded on the impact and tensile fracture surfaces of the PLA composites,and thesesurfaces with roughness exhibited obvious plastic deformation.3.Study on the crystallization property of the PLA/BEP composites.The PLA/BEP composites were characterized by differential scanning calorimeter,X-ray diffractometer and polarizing microscope.The results showed that reducing the size of the BEPs or increasing their loadings can increase the crystallinity of the PLA composite,reduce the size of spherulite,increase the crystal density,reduce the crystallization temperature,shorten the half crystallization time and increase the crystallization rate obviously.The half melting crystallization time of the PLA/BEP composites with 5 phr loading of BEP(50 nm)was shortened from 10.20 min of pure PLA does to 8.12 min,and the half cooling crystallization time of the PLA/BEP composites with 10 phr loading of BEP(50nm)was shortened from 224 s of pure PLA does to 103 s.In addition,the multiscale BEPs can also reduce the Tg of PLA,and promote the formation of ?' crystal of the PLA composites.4.Study on degradability and cell compatibility of the PLA/BEP composites.The degradation experiments of PLA/BEP composites in the lipase solution,the water solutions with different p H values and the soil showed that the weight loss rate of PLA/BEP composites increased with the decrease of the particle size or the increase of the loading of the BEP.The weight loss rate of PLA/BEP composites with 10 phr loading of BEP(50 nm)in Na OH solution with p H=13 after degradation of 25 days was over98%,meanwhile the weight loss rate of the PLA/BEP composites was nearly 4 times that of pure PLA after degradation of 4 months in soil environment.The results of MTT test showed that the PLA composites modified by the multiscale BEPs have no obvious cytotoxicity,and have good cell compatibility.The L929 cells cultured in PLA and its composites leaching solution grew well,and their relative growth rates were all above75%.