Structures and Properties of the Blends of Modified Starches and Poly(lactic acid)
The biodegradable poly(lactic acid)(PLA)is a candidate for substituting the fossil-fuel-based polymers.The renewable starch-modified PLA is conducive to its widespread use.Three maleic anhydride(MAH)modified corn starches(CSM)were prepared by the wet process.PLA/CSM blends were prepared by mixing PLA and CSM.The structures and properties of CSM,the blends of PLA and various starches were studied.Infrared analysis shows that MAH could be grafted onto the starch granules by esterification.The degree of esterification for the corn starches modified by the addition of MAH solution is higher than that modified by the addition of MAH particles.The particle size analysis displays that the particle sizes of CSM dried by the lyophilization are smaller than these of CSM dried by heat.The results of differential scanning calorimetry(DSC)and X-ray diffraction(XRD)show that the blends of PLA with starches are easy to crystallize and have higher crystallinity.The crystallinity of the PLA film blended with the lyophilized modified starches is greater than that blended with hot-dried modified starches.However,the glass transition temperature of PLA decreases with the addition of starches,but it is still higher than 52℃.The results of scanning electron microscopy(SEM)show that there is a good interface compatibility between PLA and the modified starches.The results of thermogravimetry analysis(TG)indicate that the thermal stability of PLA drops with the addition of CMS,but the temperature of 5%weight loss is still over 220℃,and the char yield at600℃is over 3%.The wet process for MAH-grafted starches is practical.The modified starches could be used for blending modification of PLA to reduce the cost.
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