SusChEM: Studies of Molecular Orientation, Degradation and Thermoreversible Gelation in Environmentally Sustainable Polymers: Poly(hydroxybutyrates) and Their Copolymers

非技术摘要：塑料包装通常被丢弃在垃圾填埋场或焚烧，增加了世界许多地区普遍存在的空气污染。许多第三世界国家太穷，无法回收，几乎没有卫生垃圾填埋场和焚烧设施。目前用于包装的大多数聚合物都不是可生物降解的，在垃圾填埋场中持续存在数十年。如果包装材料以可再生来源的可生物降解聚合物为基础，这些问题就可以得到解决。然而，可生物降解的聚合物在强度和柔韧性方面往往会降低机械性能。这个研究小组正试图使用可生物降解和以生物合成方式生产的聚合物来解决这些问题。这项关于一类可持续聚合物--聚羟基丁酸酯(PHB)及其无规共聚物的化学和生物降解研究的跨学科研究，结合了化学合成、使用静电纺丝技术的新加工以及使用新的仪器组合对所得到的材料进行表征的方法。该小组将评估在PHB聚合物分子中随机加入第二组分的效果，以改善其机械性能，同时保持降解速度和降解产物的性质。最终目标是一种可持续的聚合物材料，价格低廉，可加工，在垃圾填埋场中迅速降解(30-45天)，同时为包装提供更好的强度和弹性性能。如果成功，这种开发优化的、可持续的和可生物降解的聚合物的方法可能会扩展到PHB系统之外，并对新的可持续材料的开发和生产产生重大影响。技术摘要：聚羟基丁酸酯(PHB)是一种可生物降解的脂肪族聚酯，可以通过化学过程或细菌发酵来生产。它可以通过生物方式生产，具有热塑性塑料的特性，并且是自然可生物降解的，这一事实使其成为世界各地许多工业和学术实验室的研究课题。然而，细菌产生的PHB导致聚合物脆性和缺乏弹性。为了改善这些性能，添加了3-羟基己酸酯(3HHx)作为共聚单体，这些新材料(称为PHB-HHx)的结晶含量显著减少，从而改善了机械性能和加工性。虽然这种方法肯定会带来重要的改进，但随之而来的是其他重要特性的变化，如生物降解性。如果这些可持续的热塑性聚合物的降解性能够得到优化，以便在垃圾填埋场中快速酶促降解(30-45天)，这将是对环境和社会的极其重要的贡献，对土地利用、土壤污染和材料处置的经济性产生影响。在这个项目中，研究人员将使用不同量的3HHX共聚单体(0mol%(纯PHB)、3.9mol%、5.8mol%、6.2mol%、7.6mol%、9.4mol%、11.9mol%和13mol%)来探索这一假设。此外，研究人员将探索结构、加工和链取向/结晶度之间的相关性，并测试改善电纺纳米纤维的链取向度可以增加弹性系数和韧性的假设，即使适当的共聚单体组成破坏了结晶度。他们还将探索替代的加工方法，以生产类似于电纺薄膜的纤维结构，而不会显著改变所需的性能。已发现的PHB和PHB-HHx的热可逆凝胶化，提供了一条在凝胶化之后进行冷冻干燥时形成非织造纤维状结构的途径。研究人员推测，这种加工方法可以显著提高产量，同时保持结构具有与电纺薄膜相同的性能范围。

NON-TECHNICAL ABSTRACT: Plastic packaging is usually disposed of in landfills or incinerated, adding to the air pollution which is endemic in many regions of the world. Many third world countries, too poor to recycle, have few sanitary landfills and few facilities for incineration. Most of the current polymers used for packaging are not biodegradable and persist in landfills for many decades. These problems could be addressed if packaging materials were based on biodegradable polymers from renewable sources. However, polymers that are biodegradable often suffer from reduced mechanical properties in terms of strength and flexibility. This research group is trying to address these issues using polymers that are biodegradable and biosynthetically produced. This interdisciplinary research on the study of chemical and biological degradation of a class of sustainable polymers, poly(hydroxybutyrates) (PHB) and their random copolymers, combines approaches involving chemical synthesis, novel processing using an electrospinning technique, as well as characterization of the resulting materials using new combinations of instrumentation. The group will assess the effects of randomly incorporating a second component into the PHB polymer molecules in order to improve their mechanical properties while maintaining the rate of degradation and the nature of the degradation products. The ultimate goal is a sustainable polymeric material that is inexpensive, processable, and degrades rapidly (30-45 days) in landfills, while providing improved properties of strength and flexibility for packaging. If successful, this approach to the development of optimized, sustainable, and biodegradable polymers may be extended beyond the PHB systems and have significant impact on development and production of new sustainable materials.TECHNICAL ABSTRACT:Poly(hydroxybutyrate) (PHB) is a biodegradable, aliphatic polyester that can be produced by chemical processes or bacterial fermentation. The facts that it can be produced biologically with the properties of a thermoplastic and is naturally biodegradable have made it a subject of research in many industrial and academic laboratories worldwide. However, bacterially produced PHB results in a polymer that is brittle and lacks flexibility. In order to modify these properties 3-hydroxyhexanoate (3HHx) has been added as a co-monomer and these new materials, referred to as PHB-HHx, exhibit a significantly reduced crystalline content, resulting in improved mechanical properties and processability. While this approach definitely leads to important improvements, there is always the question of concomitant changes in other important properties like biodegradability. If the degradability of these sustainable, thermoplastic polymers can be optimized so as to enzymatically degrade rapidly (30-45 days) in landfills, this would be an extremely important contribution to the environment and society with impacts on land use, soil contamination, and the economics of material disposal. It is this hypothesis that researchers will explore in this project using a wide range of copolymers with varying amounts of 3HHX comonomer (0 mol% (pure PHB), 3.9 mol%, 5.8 mol%, 6.2 mol%, 7.6 mol%, 9.4 mol%, 11.9 mol%, and 13 mol%).In addition, the researchers will explore the correlation between structure, processing, and chain orientation/crystallinity, and test the hypothesis that improved chain orientation in electrospun nanofibers can increase modulus and tenacity even while crystallinity is disrupted by appropriate comonomer compositions. They will also explore alternate processing approaches to produce a fibrous structure similar to an electrospun membrane without significantly changing desired properties. Thermoreversible gelation, which has been discovered for PHB and PHB-HHx, offers a route to a non-woven fiber-like structure when gelation is followed by lyophilization. The researchers hypothesize that this processing method may significantly improve throughput while maintaining structures with the same range of properties as electrospun membranes.