| Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV)copolyester,which is one of the PHAs materials, is a thermoplastic bio-polymer synthesized by microbial fermentation, presenting the advantages of good biodegradability, histocompatibility and antithrombogenicity. It has a wide range of applications in industry, agriculture, packaging, biomedicine and other fields. It is a rich source in nature and no need of complex polymerization equipment. Besides, it is an alternative to general resins. For all these reasons, it has attracted many domestic and foreign researchers a great deal of attention in recent years.However, PHBV suffers from its poor thermal stability, narrow melt processing window, and especially its embrittlement stored at room temperature, which has, to a large extent, limited its industrial processing and application. Our group has researched PHBV melt spinning for several years, and found that the melt spinning process is deeply influenced by the properties of raw material. The phenomenon of the spinning process and the fiber properties are widely divergent even if the same raw material and spinning parameters are applied. PHBV is regarded as a melt unstable material and degrades severely just above melting point. It is suggested that the melting temperature and residence time should be minimized to alleviate degradation, but the homogeneity of the melt cannot be insured. Besides, the melt solidifies very slowly after extruded, the fibers stick to each other where winded and cannot be unreeled. Moreover, the fibers quickly become brittle after several minutes storage, and cannot be drawn even at a high temperature. All the problems can be resolved by one-step formation method, but the equipments are complex, assisted by a coagulation bath. However, the method is difficult for industrial use, and the affect of the bath liquid on fiber postprocessing is still unestimated. In view of these questions mentioned above, dry spinning method is carried out to take the place of melt spinning to resolve the problems such as degradation, stickiness and embrittlement. And it is expected to explain and solve the problems in melt spinning by the research of the dry spinning process.In this research, the basic parameters of PHBV with different HV content are tested by 1HNMR, GPC and DSC. And it is found that chloroform may be the best solvent for PHBV dry spinning, we choose it as the solvents of PHBV juat as mentioned in many other literatures. The preparation of PHBV/chloroform spinning solution is investigated, and the stability of the four series 16%(w/w) solutions with different HV contens as 5%,10%,15% and 20% and the effect to spinning are discussed. Combining with spinning experiment, it is detected the solution with HV contents 20% fail to be preoared by dry spinning under current conditions. But other three solutions has good spinnability and theiras-spun fibers are successfully prepared by dry spinning by controlling the spinning parameters.PHBV is a brittle material commonly, but it is observed that as-spun fibers are tough and plasticized less than several hours after formation. Nevertheless, fibers from dry spinning become brittle in several hours, much slower than which from melt spinning. The mechanical properties, crystallization and orientation behaviors of PHBV as-spun fibers changing with time were synchronously tracked by means of fiber mechanical testing machine, wide-angle X-ray diffraction (WAXD), sound velocimeter and residues ratio of solvent in order to find out the relationship between the polymeric structure and mechanical properties. The fiber elongation at break can. achieve more than 600% when the storage time is shorter than 4 hours at room temperature, but it declined sharply to less than 10% when the storage is longer than 4 hours. However, in this experiment, it is found that the fiber can be drawn more than 5 times at 80℃as long as the storage time is less than 4 days. After 3 days, the fiber cannot be drawn at even a higher temperature. WAXD experiment shows that, during the evolution of the as-spun fiber, the crystallinity, crystal lattice and the average grain size do not change notably when shortly stored. And the crystallinity of PHBV fibers after 4days'storage increase more significantly than short storage. Therefore, crystallinity is not the most important factor leading to the fiber from toughness to brittlement. Fiber sound velocity is increasing monotonously and quickly in 7 hours after spinning, and later changing slightly. The principle according to sound velocity, is generally believed that the value of increased sound velocity is due to molecular chain orientation of fibers. But the fibers are not drawn and infrared dichroism showed those three series as-spun fibers are not oriented. So that sound velocimeter of PHBV in the study can not be applied to as-spun fiber, only to meet the basic principles of acoustics, the Young's modulus increased with the sound velocity. The results accord with the mechanical test. DSC showed melting peak fiber had no significant changes in melting peak and melting enthalpy. However, with increased storage time, the perfection of crystal is increasing. The residue amount of solvent seems to have no significant effect on the dry-spun PHBV fiber evolution.Two different methods of drawing and annealing process of PHBV fiber are preliminary studied. According to the previous study, we further the study by the PHBV as-spun fiber blending with high HV content. In the first method, the as-spun fiber stored less than 4 hours can be drawn well. Drawing experiment at different ratios under room temperature is taken, and finds that fiber drawn at 6 ratios has good strength and seldom breaks down when drawing. Fiber mechanical testing machine and DSC are used to measure the mechanical properties, the degree of crystallinity. Then the fibers are annealed at 60-100℃with different tension, and fibers with different strength and elongation at break are gained. The strength and elongation at break of fibers which are drawn 6 times and annealed with 0.36cN/dtex tension under 80℃, which can reach up to 1.98cN/dtex and 85%, respectively. On the other hand, we have develop the constrained amphous chains between a-form crystals which make the fibers have good elongationg at break. The as-spun fiber was directly quenched into liquid nitrogen bath for 48h which make the srystal nuclear grow in small size and the fiber with good tensile strength and are drawn 2-6 ratios under room temepreture. The fiber drawn with 6 ratio has good strength which are drawn 2 ratio again in higher temperature. After that, the fiber has better enlogation at break. Then the fiber is annealed at 100℃with different tension. The fiber annealed at 100℃with 0.18cN/dtex has the good mechanical properties. Its stensile strength and anlongation at break are 1.90cN/dtex and 110.9%, respectively. |
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