摘要
随着人类环保和石油危机意识的不断提高,大量使用的用即弃产品的环保性和可持续性逐渐引起人们的重视。聚丁二酸-共-对苯二甲酸丁二醇酯(PBST)作为脂肪族/芳香族共聚酯的一种,由于具有脂肪族聚酯良好的生物降解性能和芳香族聚酯优良的机械性能,已成为可降解材料研发的热点。目前,已有学者对此共聚酯的热力学性能及降解性能、成膜性能、纺丝工艺及纤维结构性能等做了大量的研究。但是,关于利用熔喷技术制备PBST非织材料的报道尚未出现。
在此背景下,本文研究了PBST的基本物理性能,为其熔喷成网提供技术支持;探索了熔喷成网工艺条件,成功研制出PBST熔喷非织材料,并分析了熔喷主要工艺参数对材料性能的影响;利用分形理论对纤网孔隙结构进行分析,讨论了纤网透气性与孔隙结构之间的关系,为PBST熔喷非织材料的工业化生产提供了理论依据和实践经验。
通过对PBST的热学、结晶和流变性能进行研究,为熔喷成网工艺参数的初步设置提供依据。结果表明,PBST有相对较高的熔点和良好的耐热性,热熔融温度达180℃,热裂解温度达380℃;PBST晶体结构为三斜晶系,结晶度为46.5%;PBST的表观粘度随剪切速率的增加而降低,是典型的切力变稀型非牛顿流体,熔体的粘流活化能随剪切速率的上升而降低,故其温度敏感性也随着剪切速率的上升而下降。
采用正交实验设计方案,以纤网中纤维直径为衡量指标,探索出制备PBST熔喷非织材料的最佳工艺参数为:模头温度275℃,空气压力0.25mpa,接收距离400mm,挤出速度4rpm。随着模头温度的升高,接收距离的增大,空气压力的加大,纤网中纤维直径均逐渐减小。随着螺杆挤出速度的加大,纤网中纤维直径逐渐增大。其中,螺杆挤出速度和空气压力是影响纤维直径的主要因素。此外,采用单一因素分析法,讨论了各工艺参数对纤网性能(包括纤网面密度、强力、透气性、厚度等)的影响。
采用分形理论并结合图像处理技术对PBST熔喷非织造纤网的孔隙结构进行了分析,并讨论了纤网透气性与孔隙结构之间的关系。结果表明,纤网孔隙结构具有明显的分形特征,而且孔隙分形维数随纤网定量的减小而减小。纤网的透气性也具有明显的分形特征,并与孔隙分形维数具有良好的一致性,透气分形维数也随纤网定量的减小而减小,因此研究纤网的孔隙分形维数具有实际意义。
Recently, with preservation of environment and oil crisis concerns taken into consideration, the environment protection and sustainability of many disposable products have attracted much more attention. Poly(butylene succinate-co-butylene terephthate) (PBST), as a new aliphaticearomatic copolyester, has particularly been found to be the most attractive biodegradable synthetic polymers because of its desirable biodegradability and good mechanical properties. So far, the thermodynamic and degradation properties of PBST copolymers, film-forming property, spinning process and properties of fibers have been reported by many researchers. However, PBST nonwovens manufactured by meltblowing have never been attempted.
In the above cases, the physical properties of PBST prepared for meltblowing were studied and PBST nonwoven with good properties was successfully yielded. The influences of process parameters on the properties of nonwovens were discussed in detail. Fractal geometry was used to evaluate the irregularity of pore size distribution. Furthermore, air permeability of PBST meltblowing nonwovens and its relationship with fractal dimension of pore size distribution were also investigated, which provided theoretical foundation and practical experience for its commercial process.
Studying on thermal, crystalline and rheological properties offered foundation for the initial setting of web froming's technological parameters. It was found that PBST copolyester had relative higher melting temperature and good thermal stability, whose melting peak temperatures at about 180℃and decomposion temperatures at about 380℃. The crystal structure of PBST was triclinic system and degree of crystallinity was 46.5 percent. The apparent viscosity of PBST decreased with the increase of shear rate and temperature. The shear-thinning results indicated the PBST melts belonged to non-Newtonian pseudoplastic fluid. The flow activation energy of PBST decreased with the increasing of shear rate, so the sensitivity to temperature decreased.
Orthogonality experimental design was employed, based on fiber diameter as measure index, to investigate the optimized process parameters. The result showed that die temperature was at 275℃, injection pressure was 0.25 mpa, the die to collector distance was 400mm and extruder rate was 4 rpm. The fiber diameter deceased with the increase of die temperature, the die to collector distance and injection pressure, but it rose with the increase of extruder rate. And extruder rate and injection pressure were the main factors effecting fiber diameter. Furthermore, the influences of the process parameters on the properties of fiberweb density, mechanical properties, filtration properties and thickness were also discussed in detail using single factor analysis method.
Fractal geometry combining with computer image analysis was used to evaluate the irregularity of pore size distribution of PBST meltblwing nonwoven. Furthermore, air permeability of PBST meltblowing nonwovens and its relationship with fractal dimension of pore size distribution were also discussed in detail. The results revealed that pore structures of PBST nonwovens could be regarded as a fractal and the fractal dimension of pore size distribution declines with the decrease of mass per unit area of samples. Air permeability of PBST nonwovens which could be also regarded as a fractal has good consistency with fractal dimension of pore size distribution, and fractal dimension of air permeability declines with the decrease of mass per unit area of samples too. Therefore, evaluating the pore structures using fractal geometry is of great guiding significance in practical production.
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