Preparation Of PHA/PLA Blend Fibers And Their Structure And Properties

In the past several decades,synthetic fibres derived from petroleum have been extensively used in multiple fields such as textiles,biomedicine,and agriculture.However,these petroleum-based synthetic fibres lead to a series of environmental problems owing to their non-biodegradability and non-renewable origins.In addition,the rapid depletion of petroleum resources has limited non-biodegradable synthetic fibre applications.Therefore,fully bioresource-based and biodegradable fibres,most of which are sustainable,have attracted considerable attention as promising candidates for the substitution of petroleum-based synthetic fibres.Therefore,in this paper,we select a biodegradable,biocompatible,and renewable new biomass material,Polyhydroxyalkanoates(PHA),for the preparation of bio-based synthetic fibers.Due to the shortcomings of PHA,such as poor thermal stability,low nucleation density,large spherulite size,and easy secondary crystallization at room temperature,the stable preparation of PHA fiber is greatly hindered.In this paper,PHA/PLA blend fibers were prepared by melt spinning using the fourth generation PHA material poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P3HB4HB)and polylactic acid(PLA).Firstly,the compatibility of PHA/PLA blends was studied and then the effects of spinning processes on the spinnability of PHA/PLA blends were explored,as a result,we obtained the substantial spinning processes which affected the spinnability of PHA/PLA blends.The influences of parameters of various spinning processes on the spinnability of PHA/PLA blends was analyzed,and the optimum spinning processes of PHA/PLA blends for steadily continuous spinning were determined.The effects of blending ratio,winding speed and drawing ratio on the structure and properties of PHA/PLA blend fibers were investigated.The major findings are summarized below:(1)Compatibility,crystallinity,and thermal stability of PHA/PLA blends:PHA/PLA blends were found to be incompatible systems;PHA/PLA blends with PHA content of 50 wt%and 45 wt%were dual continuous phase morphology,and the phase morphology of PHA/PLA blends gradually changed from the dual-continuous phase to the distinct sea-island phase when the PHA content is less than 45 wt%.PHA was very sensitive to temperature,and the window of process temperature was narrow.The addition of PLA increased the thermal stability of PHA and broadened the window of process temperature of PHA.It is particularly notorious that the neat PHA has low nucleation density and slow crystallization rate,while the neat PLA could completely crystallize in a short time.Therefore,the rapid crystallization of PLA phase in the spinning process of PHA/PLA blends imparted certain properties of as-spun fibers and improved the spinnability of PHA.There were significant gaps between adjacent spherulites of the PHA/PLA blends after storage for 24 h at room temperature,which was the principal reason for the high brittleness of PHA.While the sizes of spherulites in the PHA/PLA blends were much smaller than those of neat PHA,it is feasible to mix the PHA and PLA to improve the mechanical properties of the PHA fibers.(2)Evaluation of the spinnability of PHA/PLA blends:The blending ratio,spinning temperature,melt extrusion rate,winding speed,and drawing ratio were the major factors affecting the formation of PHA/PLA fibers during the experimental spinning and drawing of PHA/PLA as-spun fibers.It was found that the PHA/PLA blends could be melt-spun with the PHA content of less than 50 wt%,the spinning temperature of 165℃ the melt extrusion rate of 10～20 rpm,and the winding speed of 20～40 m/min.Further research found that the parameters of the spinning processes of PHA/PLA blends which could be continuously and steadily spun were the spinning temperature of 165℃,PHA content of not more than 40 wt%,and winding speed of 20-30 m/min.(3)Effects of the blending ratio,winding speed and drawing ratio on the structure and properties of PHA/PLA blend fibers:The results showed that the PHA/PLA blend fibers had poor strip uniformity,and the lower the PHA content,the smaller the fiber diameter.The addition of PLA improved the degrees of crystallinity of the blend fibers and reduced the sizes of the lamellar stacks of the blend fibers,so the addition of PLA would improve the mechanical properties of the blend fibers.When the PHA content is 35 wt%,the blend fibers had better flexibility.The stress and strain were up to 904 MPa and 81%,respectively.The higher the PHA content in the blend fibers,the higher the dry heat shrinkage.The winding speed and the drawing ratio were contradictory to the crystallization of the PHA phase and the PLA phase in the blend fibers for B40.In other words,with the increasing of the winding speed,the degrees of crystallinity of the PHA phase first increased and then decreased,whereas that of the PLA phase first decreased and then increased.Moreover,the degrees of crystallinity of the PHA phase gradually increased as the drawing ratio increased,while that of the PLA phase gradually reduced.At the same time,the increasing of the winding speed slightly hindred the increasing of the degrees of crystallinity of the PHA/PLA blend fibers,whereas the increasing of the drawing ratio had the definite effect on it.The increasing of both of winding speed and drawing ratio could promote the enhancement of the stress,strain and modulus of the blend fibers,and the mechanical properties of the blend fibers were optimized for the winding speed of 30 m/min and the drawing ratio of 2.0.