In today’s world, the problem of “white pollution” is becoming more and more serious, and many countries have paid special attention to this problem, and it has become one of the most important tasks to reduce polymer waste and to protect the environment. Due to the degradability, safety, economy and practicality of biodegradable packaging film materials, biodegradable packaging film materials have become a major trend in the packaging industry to replace traditional packaging film materials, provided that the packaging performance requirements are met. This paper reviews the degradation mechanisms and performance characteristics of biodegradable packaging film materials, such as photodegradation, hydrodegradation, thermo-oxidative degradation and biodegradation, focuses on the research progress of the modification of biodegradable packaging film materials, and summarizes some challenges and bottlenecks of current biodegradable packaging film materials.
The polylactic acid (PLA) resin Ingeo 4032D was selected as the research object, with a focus on PLA modification by using polymers such as linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE) and ethylene–propylene-diene monomer grafted with glycidyl methacrylate (EPDM-g-GMA), by using fillers such as nano calcium carbonate and zeolite. In order to characterize the deposition effect of Al2O3 on the film surface by plasma-assisted atomic layer deposition, Bio-oriented PLA (BOPLA) with more uniform thickness than blown film was purchased for study. The mechanical properties, friction coefficient, surface contact angle and water vapour transmission rate of the modified PLA film were compared and discussed. The aim was to find out the most influencing factors of film’s water vapour resistance.
To understand the physical condition and change rule of undergraduate students of different nationalities in Guangxi in their four-year life, and to provide basis for Han and minority students to formulate measures to enhance their physical condition and prevent physical decline. By using the methods of literature review and mathematical statistics, the monitoring data of 3314 students of Grade 2015 from Guangxi University of Science and Technology with complete 4-year physical fitness test results were analyzed. 14.45% of the freshmen had normal BMI and the seniors did not meet the standard. 21.03% of the freshmen and seniors did not meet the BMI standard. 10.29% of freshmen whose BMI is not up to standard and seniors are normal; 54.22% of the freshmen and seniors had normal BMI. The differences in height, weight and vital capacity between Han students and minority students are statistically significant. On the whole, the physique of Han students is better than that of minority students. The physical changes of Han students and minority students in 4 years have their own characteristics. It is an effective way to promote the physical health of college students of different nationalities to continuously study and improve the methods and means of physical health monitoring, strengthen the exchange and mutual learning of national cultures, and advocate a healthy campus cultural atmosphere.
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