权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Multi-Scale Investigation of Metastable Phases in Sustainable Polymers

可持续聚合物亚稳相的多尺度研究

基本信息

批准号：
1809977
负责人：
John Rabolt
金额：
$ 28.5万
依托单位：
University of Delaware
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-07-01 至 2021-12-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1809977&HistoricalAwards=false
关键词：
Multi Scale Investigation Metastable Phases

项目摘要

NON-TECHNICAL SUMMARY:Plastic materials have played a major role in everyone's life for the last half century. However, the widespread use of plastics has led to intense problems with respect to disposal as many millions of tons of used plastics that occupy landfills, roadsides, as well as open and confined waters. In order to keep the beneficial aspects of plastic materials it is therefore critical to explore materials that are renewable, i.e. both sourced from nature and biodegradable. Polyhydroxybutyrates (PHBs) fill this need since they are synthesized by microbes and also biodegrade to form carbon dioxide and water on relevant timescales. However, the switch from petroleum-based plastics to materials like PHBs requires that the new biodegradable plastics possess similar mechanical and electrical properties compared to the petroleum-based plastics. Properties such as strength, stretch, and stiffness must be at least equivalent to current commodity plastics. It has been discovered in previous work that the ultimate mechanical properties of PHB can be changed by how the PHB is processed. Mechanical strength can be increased by stretching or compressing the material rapidly during the formation process, resulting in a plastic that is still biodegradable but has the desired properties. If the processing is fast enough, then new properties can be generated in PHB plastics, such as improved mechanical properties, as well as piezoelectricity (i.e., an electrical response to a mechanical stimulus, which is a desirable electronic property). This work focuses on the rapid processing of PHB plastic materials into fibers and films with higher strength, improved toughness, and a piezoelectric response. These new properties arise from a different arrangement of the PHB molecules in a crystalline lattice, obtained when spinning fibers or rapidly stretching films. The resultant material can be "locked" into this new arrangement, which yields improved properties. This project is directed towards finding the appropriate conditions that maximize this new polymer structure, and could thus enable the production of sustainable plastics with new possibilities for packaging, environmental sensors, and electronic applications. TECHNICAL SUMMARY:The processing of semi-crystalline polymers to produce films, fibers and molded articles involves manipulating the secondary and tertiary structure to produce the required macroscopic properties for the intended application. Since the bulk of the processing methods are slow relative to the chain and segmental motion, generally the thermodynamically stable crystalline structure is obtained. It has been shown that when poly(hydroxybutyrate) (PHB) is copolymerized with hydroxyhexanoate (Hx) comonomers, using microbes, a random copolymer, PHBHx, is formed that exhibits very different properties compared to PHB homopolymer. When these PHBHx copolymers are processed (e.g., electrospun from a polymer solution into nanofibers), a metastable beta crystalline form is produced in which the polymer backbones adopt a planar zig-zag conformation. This crystalline modification gives rise to a piezoelectric response and higher mechanical strength. The focus of this research will address the following question: Under what conditions (solvent and solvent evaporation kinetics, high pressure and temperature, tensile deformation) can metastable crystalline form(s) be produced and stabilized and how do these phases affect the mechanical properties and the piezoelectric response of PHBHx as a function of Hx concentration?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术综述：在过去的半个世纪里，塑料材料在每个人的生活中发挥了重要作用。然而，塑料的广泛使用导致了处理方面的严重问题，数百万吨旧塑料占据了垃圾填埋场、路边以及开放和受限水域。因此，为了保持塑料材料的有益方面，至关重要的是探索可再生材料，即既来自自然又可生物降解的材料。聚羟基丁酸酯(PHBs)满足了这一需求，因为它们是由微生物合成的，也可以在相关的时间尺度上生物降解形成二氧化碳和水。然而，从石油基塑料转向像PHBs这样的材料，要求新的生物降解塑料与石油基塑料具有类似的机械和电学性能。强度、拉伸和硬度等性能必须至少与目前的商品塑料相当。以前的工作已经发现，PHB的最终力学性能可以通过PHB的加工方式来改变。在成型过程中，可以通过快速拉伸或压缩材料来提高机械强度，从而产生仍可生物降解但具有所需性能的塑料。如果加工速度足够快，则PHB塑料可以产生新的性能，例如改善的机械性能以及压电性(即对机械刺激的电响应，这是一种理想的电子性能)。这项工作的重点是将PHB塑料材料快速加工成强度更高、韧性更好、具有压电响应的纤维和薄膜。这些新的性质源于PHB分子在晶格中的不同排列，这种排列是在纺丝或快速拉伸薄膜时获得的。合成的材料可以被“锁定”到这种新的排列中，从而产生更好的性能。该项目旨在寻找适当的条件，使这种新的聚合物结构最大化，从而使可持续塑料的生产具有新的包装、环境传感器和电子应用的可能性。技术概述：半结晶聚合物的加工生产薄膜、纤维和模制制品涉及操纵二级和三级结构，以产生预期应用所需的宏观性能。由于大多数加工方法相对于链条和链段运动速度较慢，因此通常可以获得热力学稳定的晶体结构。研究表明，当聚羟基丁酸酯(PHB)与羟基己酸酯(Hx)共聚时，在微生物的作用下，会形成一种随机共聚物PHBHx，其性能与PHB均聚物有很大的不同。当这些PHBHx共聚物被加工(例如，从聚合物溶液电纺丝成纳米纤维)时，产生亚稳定的β晶型，其中聚合物主链采用平面之字形构象。这种结晶修饰产生了压电响应和更高的机械强度。这项研究的重点将解决以下问题：在什么条件下(溶剂和溶剂挥发动力学、高压和温度、拉伸变形)可以产生和稳定亚稳态晶型(S)，以及这些相如何影响PHBHx的机械性能和作为HX浓度函数的压电响应？该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。