Research on biodegradable plastics?
The answerer mentioned earlier that the stability and degradability of plastics are opposites, which is true to a certain extent, but this does not mean that it is not related to technology or the technical level is enough.
We have different needs for the polymer materials used in different occasions. There are indeed some plastics that we need to have high strength, high modulus and high toughness, but biodegradability is another very valuable demand, such as disposable cups for lunch boxes, Do you need how hard it can break walnuts? As long as it can be used normally once, we hope it will degrade quickly after use to avoid pollution. According to statistics, about 40% of all plastic products are single-use, which shows that biodegradation is not a small demand, but a very large demand.
In addition, I saw an answerer who said that degradable plastics can even decompose microorganisms, and the performance must be very poor, which is precisely caused by the current lack of technology and cognition. It is often the role of microorganisms or enzymes that play a role in the biodegradation process. They act on some fragile chemical bonds of the polymer molecular chain to break it, and eventually form small molecules.
But this does not mean that the performance of biodegradable materials must be poor. Even the plastics that are approved to degrade quickly, the degradation process is often slow, and it generally takes several months under composting conditions, just with non-degradable plastics. It is very fast compared to millions of years, and the use environment of the material may be free of such microorganisms or enzymes, and the temperature and humidity of the composting condition are far from reached, so it will not occur significantly during normal use. Degradation, all aspects of performance can be guaranteed.
But after all, the contradiction between degradability and mechanical properties does exist. Of the chemical bonds of all polymers, the most easily broken is the ester bond, and the aromatic structure in the molecular chain tends to increase the steric resistance of the ester bond, making the ester bond more stable and not easy to break, such as PET is very difficult to degrade . This is why the currently accepted degradable plastics are basically some aliphatic polyesters, such as polylactic acid (PLA), polycaprolactone (PCL), polyhydroxy fatty acid (PHAs), even if they contain degradable aromatic structures The material PBAT no longer degrades when the content of terephthalic acid containing benzene rings exceeds 50%. Therefore, these many degradable plastics have a common problem, that is, the lack of a rigid structure of aromatic rings directly leads to their mechanical properties. As long as the carbon chain is shorter, it is very brittle, and the carbon chain is longer, and it is soft and collapsed, and it has no strength.
Because of this, this leads to the most important direction in the current research on degradable plastics, the modification of degradable plastics.
For the simplest example, polylactic acid (PLA) is currently the largest biodegradable plastic, but the pure polylactic acid melt has very low strength, difficult processing, and fast crystallization speed, and the product is very brittle, limiting its application , Then the modification of polylactic acid is a subject with a very long history. Those who are interested can take a look at the related research of Academician Chen Xuesi of Changchun Yinghua Institute of Chinese Academy of Sciences.
Based on my superficial understanding, the field of biodegradable plastics is still very immature and there is a lot of work to be done. For example, to achieve degradation under some harsh conditions (such as seawater degradation, low temperature degradation in frozen soil), another example is the modification of some degradable plastics, enhanced toughness and improved processing performance, and so on, such as upstream lactide, The preparation process of monomers such as furandicarboxylic acid, the polymerization process of polymers, etc. (the production capacity of polylactic acid has not been enough recently, and the supply is in short supply), and even the relevant laws and regulations on degradable plastics are currently very imperfect.
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