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Enhanced processability of poly-hydroxy-alkanoates by thermal stabilization and nucleation.

机译：通过热稳定化和成核作用增强了聚羟基链烷酸酯的可加工性。

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摘要

Poly-Hydroxyalkanoates, PHAs, are considered as one of the most promising family of bio-plastics technologies. PHAs are thermoplastic, semi-crystalline, aliphatic polyesters produced by bacteria and fully biodegradable.;Poly-Hydroxy-Butyrate, PHB, a common PHA, and its copolymers, is bio-plastic comparable in properties to Polypropylene, Polyethylene, and even Polystyrene. However, with no modification PHBs possess inherent weaknesses like: limited thermal stability, slow recrystallization and, poor toughness that limit its use in many applications were biodegradation and sustainability can be an advantage.;In this work, P3HB-co-4HB copolymer was studied with respect to its thermal stability, recrystallization from the melt, rheological and mechanical properties.;Two types of nano modifiers were characterized with the aim to overcome the above mentioned drawbacks. Nano structured Poly-Oligomeric-Silsesquioxane, POSS, and Hyperbranched Polymers, HBP, were introduced into PHB through melt mixing.;The first one, POSS, is an inorganic/organic hybrid nano-particle. Its unique core---shell structure, was found to impart good plasticization effect, leading to molecular weight retention under high shear. The Plasticizing effect was compared to a those achieved with Citrate Oil Plasticizer, CTP. It was concluded that the mechanism for molecular weight retention is based on physical interactions rather than chemical chain extension.;The second nano-modifiers, solid and liquid Hyperbranched polymers, HBP, were examined for the effects on PHB.;The solid HBP, was melt mixed into PHB copolymer, up to 5wt%. The most significant effect of the solid HBP was the increase in the recrystallization rate. In the presence of the Solid HBP, the half time recrystallization was more than 46 times shorter; Tc, increased by up to 22°C, and the degree of crystallinity increased from 30 to 42%.;The liquid HBP, comprised of fatty acid modified second pseudo generation, Hyperbranched polyester, was incorporated into PHB, up to 5wt%. It was concluded that plasticization effects and the resultant molecular weight retention were the decisive phenomenon, similar to the effect obtained with POSS. CTP, was found to dissolve the liquid HBP. Hence, it was used for plasticizing and as a dispersing agent for the HBP.;The Zero Shear Viscosity of the PHB/HBP compounds indicated a plasticization effects, and supported the conclusions drawn. Furthermore, when introduced together with CTP, the Zero Shear Viscosity increased above the level when only HBP was used. High viscosity was shown to conform to a higher level of molecular weight retention. The modification of PHB with HBP/CTP solution led to a molecular weight higher by 18%, compared to un-modified PHB.;Furthermore, with the introduction of CTP an increase in the rate of recrystallization by close to 200 times was obtained, accompanied with an increase of Tc, by 25°C and doubling of the degree of crystallinity. SEM images supported the hypothesized mechanism.;Finally, the presence of a low Tg, liquid HBP, improved the toughness and extensibility of the PHB. Experimental results indicated that the addition of CTP as co-modifier led to a synergistic effect increasing both the energy to break and elongation to break by more than 100%. Modulus retention was exhibited in the ternary PHB/HBP/CTP blends.;The results obtained in this work are of great importance for PHB's processability and it acceptance in the plastics industry. The significant drawbacks, related to processability and performance of PHB were addressed and consequently were remedied by the introduction of long-chain grafted POSS and HBP, polyesters.
机译：聚羟基链烷酸酯（PHA）被认为是最有前途的生物塑料技术家族之一。 PHA是由细菌产生并可以完全生物降解的热塑性半结晶脂肪族聚酯。;聚羟基丁酸酯，PHB，一种常见的PHA及其共聚物，具有生物塑料的性能，可与聚丙烯，聚乙烯甚至是聚苯乙烯相媲美。但是，未经修饰的PHB具有固有的弱点，例如：热稳定性有限，重结晶缓慢以及韧性差，这限制了其在许多应用中的用途是生物降解性，并且可持续性可能是一个优点。关于其热稳定性，从熔体中重结晶，流变和机械性能。表征了两种类型的纳米改性剂，目的是克服上述缺点。通过熔融混合将纳米结构的聚低聚倍半硅氧烷POSS和超支化聚合物HBP引入PHB。第一个POSS是无机/有机杂化纳米颗粒。发现其独特的核-壳结构具有良好的增塑效果，可在高剪切力下保持分子量。将增塑效果与柠檬酸油增塑剂CTP的增塑效果进行了比较。结论是，分子量保留的机理是基于物理相互作用而不是化学链的延伸。研究了第二种纳米改性剂，固体和液体超支化聚合物HBP对PHB的影响。熔融混入PHB共聚物中，最高可达5wt％。固体HBP的最显着影响是重结晶速率的增加。在固体HBP存在下，半衰期重结晶的时间缩短了46倍以上； Tc升高到22°C，结晶度从30％增至42％。液体HBP由脂肪酸改性的第二代假代Hyperbranched聚酯组成，已掺入PHB中，达到5wt％。结论是，增塑作用和所得的分子量保持率是决定性现象，类似于用POSS获得的效果。发现CTP溶解了液体HBP。因此，它被用作增塑剂和HBP的分散剂。PHB / HBP化合物的零剪切粘度表明了增塑作用，并支持得出的结论。此外，当与CTP一起引入时，零剪切粘度增加到仅使用HBP时的水平。已显示出高粘度符合较高的分子量保留水平。与未改性的PHB相比，使用HBP / CTP溶液对PHB进行改性使分子量提高了18％。此外，随着CTP的引入，重结晶速率提高了近200倍，同时随着Tc的增加，温度增加25°C，结晶度增加一倍。 SEM图像支持了这种推测的机理。最后，低Tg的液态HBP的存在提高了PHB的韧性和可扩展性。实验结果表明，加入CTP作为助改性剂会产生协同作用，使断裂能和断裂伸长率均增加100％以上。三元PHB / HBP / CTP共混物中表现出模量保持力。;这项工作中获得的结果对于PHB的可加工性及其在塑料工业中的接受度具有重要意义。解决了与PHB的可加工性和性能相关的重大缺陷，因此通过引入长链接枝POSS和HBP聚酯来弥补。

著录项

  • 作者

    Shaked, Yanir.;

  • 作者单位

    University of Massachusetts Lowell.;

  • 授予单位 University of Massachusetts Lowell.;
  • 学科 Plastics Technology.
  • 学位 Ph.D.
  • 年度 2008
  • 页码 178 p.
  • 总页数 178
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 整形外科学（修复外科学）;
  • 关键词

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