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

CBET-0756762 TakharA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，这涉及到将淀粉在高温和压力下通过狭窄的模具进行挤压。当离开模具时，由于压力的突然下降，淀粉膨胀。膨化会引起淀粉的结构、机械和质构特性的变化。在膨胀过程中控制最终产品的特性是一项繁琐的任务，因为涉及从微观到宏观的多尺度的热和流体(液体和蒸汽)传输过程与周围的生物聚合物基质的相互作用。在拟议的研究中，将利用多孔介质的混合混合理论开发一个三尺度预测建模工具。将利用质量、动量和能量的三尺度守恒定律，利用热力学第二定律，建立与膨胀热力学相耦合的多尺度流体和热传输方程。所建立的方程将用于预测膨化过程中淀粉基质中的液体和蒸汽传输以及热机械变化。固相将被建模为粘弹性，而液态将被建模为粘性。玻璃化转变对淀粉的膨胀和最终产品的特性起着关键作用，我们将对此进行研究。数学模型将使用数值模拟来求解。所需的实验参数应为液体和蒸汽的渗透率、玻璃化转变行为、热扩散系数和粘弹性性质。其中一些参数将从文献中获得，其余参数将通过实验测量。出模的淀粉的表面温度和温度梯度将使用皮下热电偶进行记录。热传递将通过建立一个三尺度的广义拉普拉斯方程来计算。扩张的不同阶段将用数字摄像机记录下来。利用孔隙率测量、扫描电子显微镜和机械测试来测量膨化淀粉泡沫的结构和质构特征。计算机程序将被通用化，这样在使用不同性质后，它也可以用于其他生物聚合物。[更广泛的影响]该项目将培养两名博士生和一名本科生。将努力从妇女和/或少数群体中招收这些学生。在PIS教授的高级/研究生水平的课程中将包括一项实验练习，学生将在基本了解基本方程的情况下使用开发的计算机程序，并将结果与实验观察进行比较。根据德克萨斯理工大学和内布拉斯加大学现有的各种计划，少数民族新生、高中生和对工程感兴趣的女性在访问德克萨斯理工大学和内布拉斯加大学期间，实验室练习将得到简化和重复。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Mentor Tech计划中加入新的组成部分。研究成果将通过会议报告和同行评议的出版物向科学界和生物聚合物行业传播。[潜在的变革性]这项研究将对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产品做出重大贡献。它将帮助这些不同领域的研究人员和工程师利用从基于计算机的预测工具获得的知识来开发新型淀粉产品。由于淀粉膨化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.