At present, plastic pollution has become another important threat to climate change on Earth, because it is rapidly and irreversibly polluting every natural system and endangering more and more creatures.
For a long time, people have been focusing on plastic pollution in the soil environment on land, and little attention has been paid to the plastic pollution problem in the ocean, another component of the Earth. In fact, marine plastic waste pollution and their impact on marine ecosystems The harm has been far beyond our imagination.
How serious is the pollution of marine plastic waste?
Global annual plastic waste more than 30 million tons, of which more than 20 million tons of plastic waste is directly discarded or from the land through the river, the wind eventually into the ocean.
Figure 1 Marine 'Plastic Waste Island' (Images from the Internet)
Currently, almost all types of plastics are found in the oceans, of which over 80% are nylon (PA), polypropylene (PP), polyethylene (PE), polyvinyl chloridepvc ) And other non-degradable resinous materials that are exposed to light, weathering, eddy currents, and biota in seawater to eventually form 'plastic debris' that are less than 5 mm in diameter. After decades or even hundreds Years of accumulation of large quantities of plastic particles, ranging from the equator to the poles, from the shallow to the deep sea, all over the ocean, the high density and widespread distribution of plastic particulates has put an end to millions of seabirds, fish and other marine life, Toxins are gradually being brought to humankind's table through the food chain, and in Europe a seafood diner may eat up to 11,000 plastic particles a year through seafood.
Unlike the white pollution control on land, it is almost impossible to collect and dispose of these fine plastic particles by the traditional salvage method because of the environmental limitation of marine special waters, so the treatment of marine plastic pollution is becoming increasingly urgent and difficult.
Development and use of plastic products that can be degraded in the marine environment to replace PP, PA, PS and other difficult to degrade plastic products, is currently recognized to solve this problem the most fundamental and the only effective way.
Where is the research and development of seawater degradation material difficult?
At present, the international Shanghai water degradation materials related research has just started, many people blindly hope that biodegradable materials to solve the problem of plastic pollution in the ocean.
National Institute of Physical and Chemical Technology, Chinese Academy of Sciences National Engineering Research Center has long been engaged in the development of degradable plastics, industrialization and application of research, in view of the current increasingly serious problem of marine plastic pollution in the country launched the first marine degradation materials.
Ji Junhui, the director of the engineering center, said that at present, the awareness of environmental protection at home and abroad has been gradually enhanced and the ban on plastic injection has been gradually popularized around the world. PLA, PBDE and PBAT ), Polycaprolactone (PCL), and polyhydroxyalkanoates (PHAs). They have good biodegradability in soil and compost, and have replaced many non-degradable common plastics in many fields, To some extent, alleviate the white pollution on land.
Figure 2 Institute of Physics and Chemistry All biodegradable plastic products
However, the degradation of polyester composites is mainly due to the enzymatic hydrolysis reaction of the polymer under the action of microorganism-secreting enzymes, and the species, quantity, temperature, etc. of the environment need to meet certain requirements for rapid degradation.
Compared with the terrestrial environment, the marine environment is characterized by rich water, salt, high pressure, low temperature, mobile and dilute nutrition. In addition to the density of marine microorganisms in the offshore area slightly larger, the density of marine microorganisms in the ocean is smaller, the average is generally Few to dozens of milliliters per milliliter are almost negligible compared to the count of hundreds of millions of liters of microorganisms per liter of soil in the composting process.Different degradation conditions and degradation conditions make aliphatic polyester materials in seawater Degradation performance and composting process are significantly different.
Obviously, the existing biodegradable materials and their research results can not be directly applied to the development of seawater degradation materials.For PLA (polylactic acid) as an example, under the composting conditions, 50 times the weight of PLA samples is about 70% ℃ water for 1 year did not observe significant weight loss, GPC test showed no significant changes in molecular weight.
Dr. Wang Gexia, who is responsible for the development of seawater degradation materials at the engineering center, also said that through the degradation experiments of typical biodegradable materials in different simulated water environments, we have a preliminary understanding of the two mechanisms of seawater degradation and composting processes. Typical biodegradable polyester materials have a preliminary grasp of the degradation cycle in seawater and fresh water.
The results show that the current degradation of biodegradable polyester materials in seawater and composting have great differences in seawater is difficult to have biodegradable conditions, most of the polyester material degradation cycle in seawater is very slow, or even difficult to degrade .The enzymatic hydrolysis reaction of polyester material under the process of enzyme secreted by microorganisms in composting process, while the degradation of seawater is more likely to be caused by non-enzymatic hydrolysis reaction in high salt complex water environment.The degradation process of seawater is affected by the structure of segment, Crystallization properties, as well as water salinity, temperature has a huge impact.
In general, it has been clearly recognized that the current use of refractory plastic products for the marine ecological environment caused by the great damage, and is actively engaged in research of seawater degradation materials to improve this situation.
But as in the implementation of the 'ban on the use of land on the use of complete biodegradable plastic products instead of generic plastics progress is slow, the development of the use of seawater degradation of plastic products to control marine plastic pollution has just begun, a single polyester biodegradable materials and Can not be directly applied to the sea to effectively solve the problem of marine plastic pollution.
Seawater degradation materials research needs to be based on the existing biodegradable materials to build a new material system, can be said to be long way to go.