Ubbink Job, Dupas-Langlet Marina
Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Ave., St. Paul, MN 55108, USA.
Nestlé Research Center, Vers-chez-les-Blanc, 1000 Lausanne, Switzerland.
Food Res Int. 2020 Dec;138(Pt B):109801. doi: 10.1016/j.foodres.2020.109801. Epub 2020 Oct 17.
Several modifications of the Williams-Landel-Ferry (WLF) equation that incorporate the water-content dependence of the viscosity are introduced and applied to the fitting the zero-shear viscosity of a systematic series of maltopolymer-maltose blends for water contents w between 4% and 70% (M. Dupas-Langlet et al., Carbohydrate Polymers 213 (2019) 147-158). These models include a previously published model that addresses the water-content dependence of the viscosity via a Gordon-Taylor-type modification of the C coefficient of the WLF equation. New models that are based on two simple assumptions are introduced: 1. The viscosity at the glass transition temperature T decreases exponentially with the water content and 2. The WLF coefficient C depends linearly on the water content. The modified WLF models allow to extract the so-called isoviscosity lines, that connect points of varying temperature and water content that are characterized by the same viscosity. Based on data obtained between T = -15 °C and 70 °C using shear rheology (w = 30-70% w/w) and dynamic mechanical thermal analysis (w = 4-9% w/w), we conclude that the models provide a good fit of the experimental data, and that additional data, specifically very close to the glass transition line, is needed, to assess the hypotheses underlying the various modified WLF models. It is established that the viscosity at T is dependent on the composition and decreases with the content of maltose and water. The modified WLF models are used to determine Angell's fragility parameter m and Roos' strength parameter S. m and S are observed to increase, respectively decrease with increasing water and maltose content, signifying an increasing temperature dependence of the viscosity close to T with decreasing diluent content. The application of the isoviscosity concept to unit operations in the food and pharmaceutical industry is discussed. Specifically, we show how to analyze atomization, agglomeration, sintering and compaction using the isoviscosity concept.
引入了Williams-Landel-Ferry（WLF）方程的几种修正形式，这些修正形式考虑了粘度对含水量的依赖性，并将其应用于拟合一系列麦芽聚合物-麦芽糖共混物在4%至70%（质量分数）含水量（w）下的零剪切粘度（M. Dupas-Langlet等人，《碳水化合物聚合物》213（2019）147 - 158）。这些模型包括一个先前发表的模型，该模型通过对WLF方程的C系数进行Gordon-Taylor型修正来处理粘度对含水量的依赖性。引入了基于两个简单假设的新模型：1. 玻璃化转变温度T下的粘度随含水量呈指数下降；2. WLF系数C与含水量呈线性关系。修正后的WLF模型能够提取所谓的等粘度线，这些等粘度线连接了不同温度和含水量但具有相同粘度的点。基于使用剪切流变学（w = 30 - 70% w/w）和动态机械热分析（w = 4 - 9% w/w）在T = -15°C至70°C之间获得的数据，我们得出结论，这些模型能很好地拟合实验数据，并且需要额外的数据，特别是非常接近玻璃化转变线的数据，以评估各种修正后的WLF模型所依据的假设。已确定T下的粘度取决于组成，并随麦芽糖和水的含量降低。修正后的WLF模型用于确定安吉尔脆性参数m和鲁斯强度参数S。观察到m和S分别随水和麦芽糖含量的增加而增加、降低，这表明随着稀释剂含量降低，接近T时粘度对温度的依赖性增加。讨论了等粘度概念在食品和制药行业单元操作中的应用。具体而言，我们展示了如何使用等粘度概念分析雾化、团聚、烧结和压实过程。
