Spinning of photochromic polylactic acid/polyhydroxybutyrate blend fiber and its structure and properties
Objective The requirements for environmental protection are getting higher and higher,and the use of bio-based polymers to replace petroleum-based polymers is an inevitable development trend.It is hence of interest to develop bio-based photochromic synthetic fibers with good mechanical properties and color-changing effects.Method With polyactic acid(PLA)was as fiber matrix,polyhydroxybutyrate(PHB)as modified polymer material and phase-change materials(PCMs)as photosensitive indicator,a new bio-based photochromic synthetic fiber with good mechanical properties and chromic effect was prepared using melt spinning technology.The rheological properties of the photochromic PLA/PHB blend were analyzed.The effects of post-drafting process on the structure and properties of fibers were systematically studied.Results The apparent viscosity of photochromic PLA/PHB blends decreased with the increase of temperature and shear rate,and the decrease was more obvious with the increase of PHB content.The blend is an incompatible system and the PHB is thermally degraded during processing.The cross section and surface of the fibers were smooth,with no obvious structural defects,and the diameter was about 20 μm.When the drafting multiple was 4.0 times,with the increase of the drafting temperature,the breaking strength of the fiber basically remained unchanged,the elongation at break increased,the initial modulus decreased somewhat,and the thermal shrinkage of the fiber decreased.XRD results showed that the addition of PHB and PCMs did not produce new crystal types,and the crystallinity of the fiber decreases and the grain size of the(200&110)crystal plane of PLA showed a downward trend.With the increase of the drafting ratio,the breaking strength of the fiber was increased,the elongation at break decreased,and the initial modulus increased.When the drafting ratio was 4.2,the fracture strength of F15-150-4.2(the PHB mass fraction was 15%,the drafting temperature was 150℃,and the drafting multiple was 4.2 times)reached(3.79±0.40)cN/dtex,the elongation at break(25.51±1.72)%,and the initial modulus(20.19±2.51)cN/dtex,indicating the good mechanical properties.The thermal shrinkage rate of blended fiber showed an increasing trend.The crystallinity and grain size of the fibers was increasd,so the fracture strength and initial modulus increase with the increase of the drafting ratio.The fibers began to change color in the first second under the sunlight,from white to light green,and are responsive.After 50 times of ultraviolet illumination,the color difference value hardly changed,and the fiber returned to a color that was difficult to be distinguished by the naked eye in 10 min.Conclusion The photochromic PLA/PHB blend fibers were successfully prepared by melt spinning technology.The breaking strength of the fibers was(3.09-3.79)cN/dtex,the elongation at break was 21.78%-29.13%,and the initial modulus was(14.29-24.62)cN/dtex.The improvement of fiber properties is closely related to the post-drafting process.With the increase of drafting temperature,PHB forms a large amorphous region inside the fiber and entangles seriously with PLA macromolecular chains.The crystallinity and grain size of the fiber decrease,the thermal shrinkage rate decreases,the fracture strength remains unchanged,the initial modulus decreases,and the fiber flexibility improves.With the increase of the drafting ratio,the axial orientation of the macromolecular chain increases,the crystallinity and grain size increase,the fracture strength of the fiber increases,and the thermal shrinkage of the fiber increases.Photochromic PLA/PHB blend fiber can change color from white to light green in 1 s under the sunlight,and has a sensitive response.After 50 times of ultraviolet illumination,it can still maintain acceptable color difference,and has good light stability and good light recovery.It provides a scientific basis for developing functional bio-based synthetic fibers and expanding the application of PHB in textiles.
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