Study on moisture resistance and moisture-proof package shelf life of polymer packaging materials Xiang Xianwei (College of Packaging and Printing Engineering, Zhuzhou Institute of Technology, Zhuzhou, Hunan 412008, China) Influenced by the food quality of packaged goods, the relationship between the moisture resistance of polymer packaging materials and their shelf life was analyzed. The prediction of shelf life was studied. During the manufacture, packaging, transportation, and storage of food, under the influence of various conditions such as internal gas, temperature, humidity, and surrounding environment, the quality of food must be properly maintained. The preservation of food should be considered from the food and packaging and the surrounding environment system before the shelf life of the food can be presumed. 1 Moisture content, moisture content, and quality-related foods of packaged foods Foods contain varying degrees of moisture and are necessary for the food to maintain its inherent properties. According to the different moisture content in food, food can be divided into several categories. ~8% of the equilibrium humidity is lower than the humidity in the ambient air and it is easy to absorb moisture from the air. After a dry food absorbs water, it will not only change and lose its inherent properties (such as fragrant and crunchy), but also easily lead to oxidation and decay reaction of food, and accelerate food spoilage. Therefore, such foods require strict moisture-proof packaging. (2) Moisture content is 6%~30%, its own water content is relatively close to the relative humidity of the environment, and has good storage, but under the condition of external humidity, the water content will also change, causing changes in quality. , must take moisture-proof packaging. For example, when the flour is stored at a suitable moisture content of 11% to 13%, if the moisture content exceeds 13%, the mold will rapidly colonize and cause moldy mildew. After the bakery products such as bread and cakes have been processed, their internal moisture content can be as high as 45%. During the cooling process and transportation sales, the moisture will gradually transfer to the outside surface and become hard, losing the inherent soft and fresh nature, unable to sell and edible. Fund Project: Natural Science Fund of Hunan Province in 2000 (ssy2066). Xiang Xianwei: Moisture resistance and moisture-proof packaging of polymer packaging materials Shelf life Relative humidity of research RH/% Moisture absorption isotherm of foods Shelf life t of the packaged food under the condition of 9t, relative humidity he(%) The number of days can use formula a) to obtain M as the initial moisture of the food in the package (%); Mc is the allowable limit of the packaged food moisture (%); A is the outer surface area of ​​the package (m2)hi is the relative humidity of the storage environment; H2 is the average relative humidity in the packaging; Pe is the saturated water vapor pressure when the package storage environment temperature is e*C; R is the moisture permeability of the JIS when the packaging container is at a temperature of 40°C and a humidity of 90% (/ (m2.24h)); (P4)/Pe) is the ratio of the moisture permeability coefficient of the packaging container when the temperature is 40*C and 0*C respectively, ie the temperature dependence coefficient. If the value of shelf life T is given in formula (3), the moisture permeability of the packaging container can be calculated and the moisture permeability of the packaging material can be calculated, thereby guiding the design of the moisture-proof packaging and the selection of the moisture-proof packaging material. When applying formula (3), when determining the value of h2, generally take (h + h (,)/2, but this value is only a rough value, it is best to use from M to M (, changing the water integral average. In addition, It is necessary to first determine the value of (P40/Pe), that is, the temperature dependence coefficient of the moisture permeability coefficient P of the packaging container. The individual materials can refer to the ready-made values ​​specified in the industry standard specification manual. For composite materials, data must be obtained in advance. 3.2 using absorption rate relationship seeking packaged food shelf life of two packaging materials and moisture permeability measured moisture resistant container (moisture barrier property) of the packaging material measured JE 96, ISO (measured international industrial standard 1037 * 87 method can be adopted, and for The material with high moisture resistance can be measured using the LYSSY method (test method using a temperature sensor, type L-80) and the model control method (Modem control method, that is, testing the moisture resistance of an actual packaging container using an IR detector. test methods commonly used method .JIS * D895 predetermined weight as follows: filled with anhydrous calcium chloride or absorption of moisture in the product packaging container, RH at a temperature of (40 * 1) * C (90 * 2)% of Under conditions, the weight of the container increased by moisture permeability was weighed at appropriate intervals to obtain the moisture permeability of the container.This method is effective because it can obtain a practical approximation and the operation is simple and useful for estimating the shelf life of the product. 3 Prediction of shelf life of moisture-proof packaging foods Experiments conducted to predict the shelf life of packaged foods are related to the development and improvement of packaging products and the design of container packaging. Therefore, the test is usually conducted under the harsh storage conditions of the simulated circulation process, and the preservation life of the food is predicted based on the data of product quality changes. The shelf-life test for moisture-proof food packaging is to determine the time during which the product's internal moisture is maintained in the moisture-absorbing or drying-allowed value of the product, and it is used as the characteristic value of the food for the actual moisture-proof performance of the package and the food. Shelf life forecast and evaluation. From the perspective of the moisture-proof effect of the packaging itself, under certain conditions, through a packaging container with a moisture permeability of q (g/(m2° 24h)), the moisture content of the inner food of W() is from M()(%) (filled). The time T required when the product moisture is changed to Mc (%) (permissible limit moisture) can be expressed by the following formula: The moisture permeability value required for the moisture-proof packaging material can be obtained from the formula (2). 3.1 Predicting moisture permeability from packaged foods The hygroscopicity isotherms of packaged foods reflect the hygroscopic properties of foods as shown. The initial food moisture at the time of packaging was M () (%) The relative humidity inside the package was h0 (%), and the allowable limit moisture value was Mc (%). The relative humidity indicating equilibrium is hc (%). iePub Mc structure Harbin University of Commerce (Natural Science Edition) for moisture-proof packaging containing moisture containing M food ((=0), after the time T contained water divided into M (set the gas temperature in the preservation, relative humidity is fixed After a certain period of time, the moisture content of the packaged food becomes Me, and finally the gas is in equilibrium with the surrounding gas. The moisture absorption or drying rate is proportional to the water vapor pressure of the gas and packaged food. Equation (4) can be used to denote he is the relative humidity of the gas; h is the relative humidity of the packaged food containing moisture M; if the water content is changed very much Small, M can be regarded as a function of h, then the moisture absorption speed of food and packaging system can be expressed by formula (5) dM/dt=proportional constant K can be regarded as the characteristic value of packaged food related to drying or moisture absorption speed, ( Me-Mo means that the saturated moisture absorption of the packaged food means that the product absorbs moisture. If the allowable moisture limit of the packaged food is M (., the shelf life of the packaged food (the moisture-proof storage-possible days) T can be calculated by obtaining the value of T=1Kng from Expression (9), since the straight line passes the origin of the coordinates, it has The advantages of difference can be avoided. Bath Hardware Set,Brass Bath Hardware Set,Gold Bathroom Accessory Set,Luxury Bath Hardware Sets Kaiping Jenor Sanitary Ware Co., Ltd , https://www.jenorsanitary.com