Unconfined Melt Electrospinning with Control of Conductivity: A Green Processing Approach to Fabricate Small Diameter Fibers from Thermoplastics

极小直径的纤维可以形成廉价、轻质、超多孔材料，这对于正在进行的无数不同应用的开发至关重要，包括能量存储、超高效空气/水过滤、药物递送、伤口愈合和人工组织工程。目前的方法使用溶剂来处理超小直径纤维，其机械强度不足以充当独立的过滤器，并且在制造和/或生物医学应用期间无意地浸出有害的残留溶剂。该奖项支持基础研究，以使可加工材料的数量显着增加，包括相对不溶性的热塑性塑料，以及更高质量（即，更小直径）纤维的制造。新的开放几何静电纺丝工艺产生了许多紧密堆积的平行纤维，从而大幅提高了生产率，使商业化制造成为可能。 该方法是“绿色”的（无溶剂且与可回收塑料相容），产生具有改善的机械性能的纳米至微米级纤维，并且允许操纵静电纺丝工艺以产生比通常使用传统加工路线可实现的更小的纤维直径。由这些纤维制成的基材可用于上述许多不同的技术领域，从而使美国经济和社会受益。该研究涉及材料科学、聚合物和纤维加工与制造、流体物理学和电气系统等多个学科，将扩大研究领域中代表性不足的群体的参与，并对工程教育产生积极影响。这项工作的目标是发展基本的理解，以实现强大的绿色制造方法来生产热塑性介观纤维。传统的针熔融电纺丝由于加工问题而困难（即，经常堵塞）。从熔融聚合物的无限制表面进行熔融静电纺丝是一种新的范例。这种变革性的方法消除了熔体静电纺丝和受限进料几何形状之间的根本不相容性，同时促进了商业可行性所需的制造速率的扩大。 待测试的科学假设是通过电场、聚合物温度和熔体电导率（通过添加剂或受控放电调节）控制流速将产生以前无法达到的小射流直径以形成纳米纤维。无限制的几何形状能够控制低流速和局部传导性，而这在有限制的方案中是不容易实现的。 电导率的明确作用以前在熔体静电纺丝中没有被探索。这项工作解决了熔体静电纺丝的导电性的机械效果，通过控制放电调整熔体导电性的能力，由于熔体导电性的变化，流动速率的改变，发生这种情况的力学，以及使用熔体的静电纺丝的基本限制。

Extremely small diameter fibers can be formed into inexpensive, lightweight, ultra-porous materials which are crucial to the ongoing development of myriad, diverse applications including energy storage, ultra-high efficiency air/water filtration, drug delivery, wound healing, and artificial tissue engineering. Current approaches use solvents to process ultra-small diameter fibers that have insufficient mechanical strength to act as stand-alone filters and unintentionally leach harmful residual solvent during fabrication and/or biomedical applications. This award supports fundamental research to enable a significant increase in the number of processable materials including relatively insoluble thermoplastics, as well as the fabrication of higher quality (i.e, smaller diameter) fibers. The new open geometry electrospinning process creates many closely-packed parallel fibers resulting in a substantial increase in the production rate enabling commercial manufacturing. This method is "green" (solvent-free and compatible with recyclable plastics), results in nano- to micro-scale fibers having improved mechanical properties, and allows manipulation of the electrospinning process to create smaller fiber diameters than can typically be achieved using traditional processing routes. Substrates made from these fibers can be used in the many different technology fields described above, consequently benefitting the U.S. economy and society. Involving several disciplines including materials science, polymer and fiber processing and manufacturing, fluid physics, and electrical systems, this research will broaden participation of underrepresented groups in research and positively impact engineering education.The objective of this work is to develop fundamental understanding to enable a robust, green fabrication methodology to produce thermoplastic meso-fibers. Traditional needle melt electrospinning is difficult due to processing issues (i.e., frequent clogging). Melt electrospinning from an unconfined surface of molten polymer is a new paradigm. This transformative approach removes the fundamental incompatibility between melt electrospinning and confined feed geometries while promoting scale-up to fabrication rates necessary for commercial viability. The scientific hypothesis to be tested is that control of the flow rate via the electric field, polymer temperature, and melt conductivity (tuned via additives or by controlled electrical discharge) will produce previously unattainable small jet diameters to form nanofibers. The unconfined geometry enables control of low flow rate and local conductivity not readily achievable in confined schemes. The explicit role of conductivity has not been previously explored in melt electrospinning. This work addresses the mechanistic effects of conductivity on melt electrospinning, the ability to tune melt conductivity via controlled discharge, alteration of flow rate due to changes in melt conductivity, the mechanics by which this occurs, and the fundamental limits to electrospinning using melts.