It is understood that China's annual packaging waste of about 200 million tons, of which nearly 5% of petroleum plastic products waste. Petroleum plastic products are mainly composed of polyethylene or polystyrene, if the direct burning of these garbage, in the combustion process will produce carcinogenic substances on the human body. If landfill, they will not be degraded after a hundred years, it will pollute the marine environment, resulting in compaction of cultivated land, serious damage to ecological balance, a recent use of biotechnology to create new materials - the advent of plant plastics, broke the situation.
The so-called plant plastic is made of corn or sugar cane and other polylactic acid plastic, and now the use of plant plastic practical products have been used for agricultural film and fast food boxes and so on. In addition, some electrical products and clothing, also began to use the plant plastic, plant plastic has long been regarded as environmentally friendly and "biodegradable plastic" one. The biodegradable plastic refers to a plastic that can be decomposed into water and carbon dioxide by the action of microorganisms in nature.
However, compared with the past from the oil or natural gas plastic, plastic plant there is high manufacturing costs, and more than 60 ℃ and other shortcomings easily deformed, there is no wide range of applications. However, the scientists predicted that in five years is expected to be fully replaced by the plastics plant petrochemical plastics.
So, corn, sugar cane and other plants is how to create plastic it? First, from corn, sugar cane and other plants extract the starch; Then, the enzyme decomposition of starch into maltose or glucose; then, the maltose or glucose supply microbial consumption And fermenting to produce lactic acid; and finally, polymerizing lactic acid to produce polylactic acid. The polylactic acid material thus produced is very hard and has a high degree of transparency. However, the polylactic acid single crystal is close to the glass property at room temperature, and will be broken down by a slight impact. In addition, since the melting point of the polylactic acid is only 170 ° C, it is necessary to improve the heat resistance and the strength thereof as a commercial product if it is intended to be used as a plastic material.
Polylactic acid is a helical structure of the polymer, if allowed to crystallize, although it can increase the heat resistance or strength, but will lose transparency. On the other hand, if the transparency is maintained, it can be used only at 60 ° C or lower. In addition, there is a problem that the crystallization rate is slow.
Polylactic acid plastic is the most prominent feature in the nature of decomposition. When water is added to the polylactic acid plastic, it becomes an easily decomposable ester. The polylactic acid plastic into the compost, the first through the decomposition of water and enzymes into lactic acid; and then known as the aerobic microbial food and substitutes, and ultimately be broken down into water and carbon dioxide. While carbon dioxide and water are originally plant from the absorption of nature, so, on the whole, it did not increase the burden on the environment.
First of all, these plastics from plants, as a source of material it is better than petrochemical plastics. Second, the plant can be obtained by planting, so polylactic acid plastic can be said to be renewable resources or sustainable use of materials. In addition, the use of polylactic acid produced mainly from grain, whether incinerated or decomposed in nature, will not increase the burden on the environment. Now the world's production of petrochemicals, the annual output of 150 million tons of plastic. If the use of polylactic acid plastic, which reduces the consumption of oil or natural gas, which is facing the depletion of the status of fossil fuels is undoubtedly one of the greatest gospel.
In addition, the burning of waste petrochemical plastics, equivalent to buried underground fossil fuels in the release of carbon dioxide into the atmosphere, which undoubtedly deepen the growing problem of global warming, if the use of carbon dioxide absorption plants to produce polylactic acid plastic, can be So that the atmosphere of carbon dioxide to be a better cycle.
In addition to the extensive application of daily necessities, polylactic acid plant plastic in the application of medical advantage is particularly prominent, is currently the most successful application of the field, the first is the production of medical nail, bone fracture and other orthopedic diseases previously used stainless steel bone Nail, the patient must undergo two operations to cure, that is, the first operation with nails to fracture reduction fixed, to be a long bone, and then moving the second operation, the nail out. The use of polylactic acid plant plastic surgery only once implantation of bone nails, recovered at the same time, bone nails are also degraded in the human body. Because the degradation of carbon dioxide and water, it will not have adverse consequences on the human body, although, at present polylactic acid plant plastic nail the price of stainless steel nails than 50% higher, but most patients in order to avoid the pain of two operations, Or choose polylactic acid plant plastic nail.
On the other hand, polylactic acid plant plastic made of artificial organs skeleton research is also ongoing. For example, some experts are in the PLA lactic acid plant liver tissue on the whole surface of the liver cells, the manufacture of artificial liver, made in this way artificial liver moved to the body, as the skeletal part of the polylactic acid plant plastic will soon be decomposed in vivo absorption, and finally left the same shape with the skeleton of the liver, which is an effective use of plastic biodegradable nature of polylactic acid model.
To make polylactic acid plant plastic universal, there are some problems must be solved, especially the high cost of manufacturing the most troublesome business headache. But with the continuous improvement of people's awareness of environmental protection, polylactic acid plastic will be welcomed by the public, to this end, polylactic acid plant plastics certainly have prospects for development.
If that is the case, how to supply grain as a raw material of polylactic acid in the future is a problem. Now its main raw material is corn. Scientists suggested that the number of starch resources should be the dominant "rice" to start manufacturing polylactic acid plant plastic. Scientists concerned about the production of polylactic acid rice plant plastic Another reason is that polylactic acid spiral structure of the rotating direction is different, can be divided into L polylactic acid and D polylactic acid. Polylactic acid is now manufactured almost L polylactic acid. At present, scientists have successfully produced from the rice D-lactic acid, and found on the PLGA plant plastic meaningful properties, first of L polylactic acid and D polylactic acid blending, the melting point increased to about 110 ℃, greatly improved Heat resistance problem, and secondly, the method of changing the mixture can produce various kinds of polylactic acid plant plastics having different properties.
Compared with petroleum plastic. Polylactic acid plant plastics and other biodegradable plastics, can be said that almost no popularization, but with the further improvement of environmental awareness, universal is only a matter of time.