Effect Of Low Content Polyhydroxyalkanoates(PHA) On Structure And Properties Of Polylactide(PLA) Fibers

Based on the disadvantages of poor thermal stability,brittleness and low crystallization rate of polylactide（PLA）,blending high content of polyhydroxyalkanoates（PHA≥30 wt%）with PLA provides an effective strategy to significantly improve heat resistance and toughness of PLA fibers.However,it has proven challenging to maintain good spinnability of the PLA/PHA blends with the high content of PHA,and the effect of PHA on the crystallization properties of PLA was not further discussed.In this study,a series of PLA/PHA blend fibers with low PHA content（≤8 wt%）was successfully fabricated,focusing on the effects of low content of PHA on the spinnability,crystallinity,heat resistance and toughness of PLA blend fibers.Poly（3-hydroxybutyrate）（PHB）and poly（3-hydroxybutyrate-co-4-hydroxybutyrate）（P34HB）,the most commonly used polyesters in PHA series,were selected to modify PLA fibers.Firstly,PLA/PHB blends and PLA/P34HB blends with blend ratio 99/1,98/2,96/4,92/8were prepared,the rheological properties,compatibility and crystallization properties of PLA/PHB blends and PLA/P34HB blends were investigated.Significantly,PLA/PHB and PLA/P34HB blend fibers were prepared by melt spinning and hot drawing process,and the spinnability,heat resistance,mechanical properties,crystallization and orientation properties of the blend fibers were studied.The main conclusions are as follows:（1）Both PLA/PHB blends and PLA/P34HB blends were non-Newtonian fluid.All the samples show characteristic shear-thinning behaviors,the adding PHB or P34HB improved the fluidity of the PLA blends and thus reduced the spinning temperature.DMA results show that the Tanδcurve of PLA/PHB and PLA/P34HB blends had only one peak,and with increasing the PHB or P34HB content,T_g of PLA decreased gradually from 72°C to 58°C and 64°C respectively,indicating that low content of PHB or P34HB had good compatibility with PLA,which was beneficial to the subsequent spinning of blends.The isothermal crystallization kinetics of PLA/PHB and PLA/P34HB blends show that the adding PHB or P34HB promoted the crystallization ability of PLA,increased the crystallization rate of PLA by nearly 8 times and 4 times respectively,reduced_1/2 nearly doubled,and accelerated the overall crystallization process of PLA.（2）The PLA/PHB blends showed excellent spinnability,and there was no obvious break and stick roller phenomenon in the melting-spinning process.Interestingly,the boiling water shrinkage of the PLA/PHB blend fibers decreased significantly to 5%with increasing the PHB content,showing that the incorporation of PHB markedly improved the heat resistance of the PLA fibers.The modulus of the PLA/PHB blend fibers changed little with increasing the PHB content,while the tenacity of blend fibers decreased with increasing the PHB content.The elongation at break of the blend fibers decreased with increasing the PHB content at low take-up speed.DSC,XRD and WAXD results showed that the incorporation of PHB significantly promoted the crystallization and orientation of PLA phase in the blend fibers.（3）The PLA/P34HB blends also showed good spinnability,and the boiling water shrinkage of the PLA/P34HB blend fibers decreases significantly to 9%with increasing the P34HB content,showing that the adding P34HB also improved the heat resistance of the PLA fibers.Interestingly,the modulus of the PLA/P34HB blend fibers is slightly lower than that of the neat PLA fibers,which may improve the hand feel and softness of the blend fibers.the elongation at break of the PLA/P34HB blend fibers remains constant with increasing the P34HB content.DSC,XRD and WAXD results show the incorporation of P34HB significantly promoted the crystallization and orientation of PLA phase in the blend fibers.These results provide a facile and effective method to produce industrial-scale PLA/P34HB blend fibers with enhanced heat resistance.