Multiscale Transport in Expanding Biopolymers During Extrusion: Modeling and Experimental Verification

食品、饲料、塑料和生物医药行业的大量产品都是通过挤压淀粉形成的，这涉及到在高温和高压下迫使淀粉通过一个狭窄的模具。出模后，淀粉由于压力突然下降而膨胀。膨胀引起淀粉的结构、力学和质地特性的变化。在膨胀过程中控制最终产品的特性是一项繁琐的任务，因为涉及到从微观到宏观尺度与周围生物聚合物基质相互作用的多尺度热量和流体（液体和蒸汽）传输过程。【智力优势】本研究将利用多孔介质的混合理论，开发一种三尺度预测建模工具。质量、动量和能量守恒的三尺度定律将被使用，热力学第二定律将被利用来建立多尺度流体和热输运方程，并与膨胀热力学相结合。所建立的方程将用于预测淀粉基质在膨胀过程中的液体和蒸汽输运以及热力学变化。固相将被建模为粘弹性，液相将被建模为粘性。玻璃化转变对淀粉的膨胀和最终产物的特性起着关键作用。数学模型将通过数值模拟来求解。所需的实验参数包括液体和蒸汽的渗透率、玻璃化转变行为、热扩散率和粘弹性。其中一些参数将从文献中获得，其余的将通过实验测量。将使用超皮热电偶记录出模具的淀粉的表面温度和热梯度。传热将通过建立一个三尺度广义拉普拉斯方程来计算。扩展的各个阶段将用数码摄像机记录下来。膨胀淀粉泡沫的结构和结构特性将使用孔隙度测量、扫描电子显微镜和力学测试来测量。计算机程序将通用化，以便在利用不同性质后也可用于其他生物聚合物。【更广泛影响】本项目将培养博士生2名、本科生1名。将努力从妇女和（或）少数群体中招收这些学生。实验练习将包含在pi教授的高级/研究生课程中，学生将在基本理解潜在方程的基础上玩开发的计算机程序，并将结果与实验观察结果进行比较。在参观德克萨斯理工大学和内布拉斯加大学期间，少数民族新生、高中生和对工程感兴趣的女性将根据这些大学的各种项目简化和重复实验练习。该项目将允许在德克萨斯理工大学为少数族裔学生设计的导师技术项目中加入一个新的组成部分。研究成果将通过会议报告和同行评审的出版物传播给科学界和生物聚合物行业。[潜在的变革性质]这项研究将为通过挤压高效生产食品、可生物降解塑料和许多其他医疗和生物技术应用产品作出重大贡献。它将帮助这些不同领域的研究人员和工程师利用从计算机预测工具中获得的知识开发新的淀粉基产品。由于淀粉膨胀过程的高效设计和操作，这将节省时间、精力、能源和原材料。

CBET-0756762TakharA large number of products in food, feed, plastics and biomedical industries are formed by extrusion of starch, which involves forcing it at a high temperature and pressure through a narrow die. Upon exiting the die, the starch expands due to sudden drop in pressure. The expansion causes changes in structural, mechanical and textural characteristics of starch. Controlling the final product characteristics during expansion is a tedious task because of the involvement of multiscale heat and fluid (liquid and vapor) transport processes interacting with the surrounding biopolymeric matrix from micro to macroscale. [Intellectual Merit] In the proposed research, a three-scale predictive modeling tool will be developed using the hybrid mixture theory of porous media. Three-scale laws of conservation of mass, momentum and energy will be used and the second law of thermodynamics will be exploited to develop multiscale fluid and heat transport equations coupled with thermomechanics of expansion. The developed equations will be used for predicting the liquid and vapor transport and thermomechanical changes in the starch matrix during expansion. The solid phase will be modeled as viscoelastic and the liquid phase will be modeled as viscous. The effect of glass transition, which plays a key role in expansion of starches and end-product characteristics, will be investigated. The mathematical model will be solved using numerical simulations. The required experimental parameters are expected to be the liquid and vapor permeabilities, glass transition behavior, thermal diffusivity and viscoelastic properties. Some of these parameters will be obtained from the literature and the remaining will be measured experimentally. Surface temperature and thermal gradients in the starch exiting the die will be recorded using hyperdermic thermocouples. Heat transfer will be accounted by developing a three-scale generalized Laplace equation. Various stages of expansion will be recorded with a digital camcorder. Structural and textural characteristics of expanded starch foam will be measured using porosity measurements, scanning electron microscopy and mechanical testing. The computer program will be made general so that it could also be used for other biopolymers after using different properties. [Broader Impact] The project will train two doctoral students and one undergraduate student. Efforts will be made to recruit these students from women and/or minority groups. A lab exercise will be included in senior/graduate level courses taught by PIs, in which the students will play with the developed computer program with basic understanding of the underlying equations and compare the results with the experimental observations. The lab exercise will be simplified and repeated for minority freshmen, high school students, and women interested in engineering during their visit to Texas Tech and University of Nebraska under various programs in place at these Universities. The project will allow including a new component to Texas Tech's Mentor Tech program designed for minority students. The research outcomes will be disseminated to the scientific community and biopolymer industry through conference presentations and peer-reviewed publications. [Potentially Transformative Nature] The study will contribute significantly for the efficient production of foods, biodegradable plastics and numerous other products for medical and biotechnological applications by extrusion. It will aid the researchers and engineers in these diverse fields to develop novel starch based products using knowledge gained from the computer based predictive tool. This will allow saving time, effort, energy and raw materials due to efficient design and operation of the starch expansion process.