Degradation mechanisms and characterization of biodegradable polymer materials
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Any material that does not cause damage to the Earth’s ecological environment can be referred to as a recyclable material. There are many types of recyclable materials, and the ones that are currently receiving the most attention for development are biodegradable polymer materials. The biodegradation of polymer materials refers to the process by which polymers are degraded and assimilated under the action of organisms (mainly fungi, bacteria, etc.). The degradation mechanism of polymers is highly complex. It is generally believed that biodegradation is not based on a single mechanism, but rather on complex biophysical and biochemical processes, along with other physicochemical reactions such as hydrolysis and oxidation. Biological and physical processes reinforce each other, resulting in a synergistic effect. When polyurethane materials modified with natural polymers undergo biodegradation, it generally occurs in two stages: (1) the degradation of the natural polymers, which results in the formation of numerous micro-pores on the surface of the polyurethane. As the pores gradually enlarge, the urethane bonds are first broken down by microorganisms; (2) as micropores are formed, it becomes easier for microorganisms to invade the internal natural polymers, leading to the formation of more micropores within them, and this process accelerates until the polyurethane is completely degraded. The commonly used methods for characterizing biodegradability currently include: residue and relative molecular mass determination, structural change analysis, detection of decomposition products, mechanical strength testing, visual inspection, and mold testing. Various analytical and characterization methods related to biodegradability still have some shortcomings; therefore, in the course of research, it is often necessary to employ a combination of multiple methods depending on the specific circumstances.
Polymer materials possess excellent properties that other materials do not have, and they are widely used in various fields such as cutting-edge technology, national defense, and the national economy. They are essential and irreplaceable materials in modern science and technology as well as in daily life, and their production and consumption continue to show strong momentum. The 21st century is a new era of rapid development and extensive utilization of polymer materials. However, most polymer materials do not degrade quickly in the natural environment, and the increasing amount of waste polymer materials has become a major source of urban waste. The resulting white pollution has severely affected the human living environment, and this has turned into a global issue. Therefore, it is very meaningful to research and develop biodegradable polymer materials. Polymer degradation refers to the reaction in which the macromolecular chains that make up polymers break. The degradation process of polymers under environmental conditions such as oxygen, water, radiation, heat, light, chemical reagents, pollutants, mechanical forces, and organisms (especially microorganisms) is known as environmental degradation. Mechanistically, degradation factors can be classified into biological, photolytic, and chemical degradation; among these, photolytic and biological degradation hold the greatest potential for practical application. According to their degradation mechanisms, degradable polymer materials can be roughly divided into three categories: photodegradable polymer materials, biodegradable polymer materials, and photo-biodegradable polymer materials. The current key areas of research are polymer materials with photo-biodegradable properties, as well as fully biodegradable polymers with complete degradation capabilities; these represent the direction for future industrial development.