1、 Question raising
It is an environmental protection measure under implementation in many cities in China to cover the loess exposed sports ground of schools with plastic runways. Before 2002, the playgrounds of nearly 1000 primary and secondary schools in Beijing's colleges and universities and eight urban districts were basically soil fields, cement fields, and asphalt fields (cinder runways). Due to the heavy sandstorms in spring and autumn in Beijing, the soil field is very easy to cause dust. In summer, when it rains, the ground is covered with mud. Although the cement field and asphalt field have hardened the ground of the playground, they do not meet the sports safety standards and are not conducive to the growth and protection of young people's bones and joints. In particular, students are prone to sprain and fall accidents during physical education classes or after-school activities. Therefore, according to the suggestions put forward by the environmental protection department, Beijing plans to pave artificial lawns and plastic runways on as many school playgrounds as possible before the 2008 Beijing Olympic Games, and cover all sports grounds exposed in loess with this material, so as to solve the problem of raising dust and implement the environmental protection project of "loess is not exposed in the open air" in Beijing.
However, at the Second China School Sports Science Conference held in 2003, Bai Wenfei, a lecturer in the Basic Education Research Office of the Beijing Academy of Education Sciences, declared in a paper submitted by himself: "The plastic sports ground contains TDI, a toxic substance, and the practice of laying plastic runways on the school sports ground should be ended as soon as possible" (in fact, Bai Wenfei is neither a chemical expert nor a sports expert). At that time, it was widely hyped in various domestic media, with different opinions. Some CPPCC members called for the "release of the comprehensive test results of the plastic playground as soon as possible". Fan Boyuan, Vice Mayor of Beijing, also gave a special instruction to this end: "The Municipal Education Commission is requested to organize experts to demonstrate the plastic track quickly. Experts should be authoritative and have measured data.".
2、 Organize inspection and investigation
Since the end of 2003, the Municipal Education Commission, the Municipal Development and Reform Commission, the Municipal Sports Bureau, the Municipal Environmental Protection Bureau, the Municipal Labor Bureau, the Municipal Science and Technology Commission and other relevant government departments have organized experts in sports, education, environmental protection, materials, chemistry and analytical testing to analyze and demonstrate. In view of the fact that there is no special testing standard for the chemical toxicity of plastic runways at home and abroad, a special project has been established to organize relevant testing and research work, Having overcome all kinds of difficulties, with reference to the relevant chemical and environmental protection testing standards in all aspects, Beijing Physical and Chemical Analysis and Testing Center, which has the qualification of a national laboratory certification authority, began to conduct a detailed test analysis and demonstration on the raw materials, laying process and products after use of polyurethane plastic runways currently used in China in January 2004. Focused on the testing of multiple indicators for the finished products and raw materials produced by more than a dozen plastic runway manufacturers, and strictly tested whether some paved polyurethane plastic sites contain residual TDI after delivery, the smell of some plastic sites during construction and use, and whether the plastic runway contains other harmful substances. At the same time, experts from infrastructure projects, stadiums and gymnasiums, labor protection and physical education teachers (users of the playground) in schools and colleges were also organized to conduct research, and finally came to the conclusion that "plastic runways are basically harmless".
3、 Development History of Plastic Runway
The United States first laid a 200 meter polyurethane track for horse racing in 1961, and began to lay a sports track and field track in 1963. The 19th Olympic Games held in Mexico in 1968 officially adopted polyurethane plastic track. Because of its good elasticity, high strength, wear resistance and skid resistance, bright colors, and good track and field performance, the International Olympic Committee and various sports professional committees have officially designated the plastic track as a necessary facility for international sports competitions. In September 1979, China first used polyurethane plastic track in Beijing Workers' Stadium. By 1998, there were more than 30 manufacturers of raw materials for plastic runways nationwide, with a raw material output of 5000 tons. In recent years, the development speed of plastic runway is amazing, with an annual growth rate of more than 30%. In 2002, the world's output was 1.3 million tons. In 2002, China's output was less than 40000 tons, but the consumption was about 220000 tons, most of which were imported. It is estimated that the output of raw materials in China will reach 100000 tons by 2008.
The laying of plastic track or artificial lawn playground has produced the following effects: the slightly elastic rubber surface and turf enable students or athletes to maximize their physical strength and improve sports performance; At the same time, the collision, fall and other injury accidents that are easy to occur in the intense exercise are eliminated; It has more positive significance for reducing inhalable particles and improving the sports environment; The great changes of the school track and field field have greatly beautified and purified the campus environment, and become a beautiful scenery on each school campus.
4、 Production of plastic runway and its main components
At present, the international sports ground pavement materials can be divided into natural polymer materials and synthetic polymer materials. Natural polymer materials are natural rubber, synthetic polymer materials are mainly polyurethane materials, polyethylene and polypropylene materials, and polyethylene and polypropylene materials are mainly used for artificial turf. The paving of natural rubber runway and artificial lawn is prefabricated into coiled materials in the factory, and then pasted on the asphalt or cement ground with polyurethane adhesive. What we are demonstrating this time is mainly related to the polyurethane plastic track of synthetic polymer materials. The polyurethane plastic runway is a two-component liquid that is pre synthesized in the production workshop, mixed on the site, and then paved on the asphalt or cement ground like cement.
The main component of the plastic runway is polyurethane elastomer. Its basic raw materials can be divided into non-toxic raw materials such as polyether polyols, catalysts and polyisocyanates (mainly TDI). At present, the process is generally two-component process. That is, the prepolymer containing isocyanate end group (component A) and component B mixed with polyether polyol, inorganic filler, pigment, plasticizer, antioxidant and ultraviolet absorber are prepared by the reaction of excess polyisocyanate and polyether polyol in the raw material plant. The construction team will mix the large barrels of A and B components purchased from the raw material manufacturer in the on-site mixing equipment at the construction site, and then add a catalyst. The paved runway will be mechanically or manually paved. The surface of the paved runway will be solidified within a few hours, and will be completely solidified within 3 to 7 days. Generally, it will be delivered for use after 10 days.
Polyether polyols, inorganic fillers, pigments, plasticizers, antioxidants and UV absorbers in the above component B are safety raw materials widely used in various plastics, most of which can also be used as packaging materials in the food industry.
5、 Toxic substances of catalyst in plastic runway laying
Catalyst shall be added when mixing raw materials of components A and B on site in the laying of plastic runway project. The main role of the catalyst is to promote the full reaction of TDI prepolymer A and B components, so that the two components of polyurethane can achieve their strength, elasticity and hardness within the specified time. At present, the catalysts used in polyurethane elastomer can be divided into toxic catalysts and non-toxic catalysts.
As far as polyurethane elastomer itself is concerned, it has little toxicity and is a kind of good biological digestibility. It is recorded that the first artificial heart valve was made of polyurethane elastomer. At the same time, polyurethane foam is widely used in automobile manufacturing, home decoration, furniture manufacturing and household appliance insulation industries. That is to say, if reasonable raw materials, reasonable formula and reasonable process are used, polyurethane plastics cannot be toxic.
In addition to the toxicity test of the plastic runway, we also tested and analyzed the relevant catalysts, and tested and analyzed the catalyst materials of the relevant manufacturers and construction units and the paved plastic samples, including benzene homologues, halohydrocarbons, total volatile organic compounds (TVOC), TDI, heavy metals, etc. The purpose is to find toxic and harmful substances in plastic runway materials and related products.
TVOC refers to organic substances with saturated vapor pressure exceeding 70.91 Pa or boiling point<260 ℃ at room temperature. It is the most common pollutant discharged by petroleum, chemical and pharmaceutical, printing, building materials, spraying and other industries. The main components of TVOC are as many as 900 kinds of aromatic hydrocarbons, halogenated hydrocarbons, oxyhydrocarbons, aliphatic hydrocarbons, nitrogen hydrocarbons, etc. Indoor TVOC concentration is affected by seasonal changes, ventilation conditions, decoration degree, human activities, etc. The indoor TVOC concentration is high in winter, but lowest in summer.
From the polyurethane plastic materials (unpaved liquid) produced by some large enterprises we tested, most of the enterprises' products do not contain benzene analogues. However, some solid plastic products laid by some construction enterprises were detected to contain harmful gases such as benzene and toluene. According to the analysis and understanding of experts, some small non professional construction teams in China do not have production bases or even construction qualifications. In order to reduce costs and facilitate construction, some diluents are added to the construction in violation of regulations, so that the smell of the construction site is pungent, so that the site after paving still has an unpleasant smell for a long time. It is said that even more serious, some small manufacturers, in order to reduce costs, have added coal tar to the plastics, which is strictly prohibited by the state, seriously affecting the chemical safety and mechanical properties of the products, and even causing the tofu dregs project.
In the test of this catalyst and adhesive, we focused on five heavy metal elements (lead, mercury, arsenic, chromium, cadmium) that are harmful to human health. From the test results, the plastic runway is prone to high lead content, and the artificial lawn is prone to high chromium content. Through investigation, it is found that these problems are mainly caused by the limited technical level of some domestic manufacturers, backward formula and process, and even the use of toxic heavy metal catalysts containing organic mercury and organic lead. At the same time, because of the fierce market competition, some non-standard construction units use fake catalysts and adhesives to earn profits. That is, they use unqualified materials, formulas and processes, which may be toxic.
According to Chen Jianding, director of the synthetic surface testing laboratory of the China Track and Field Association and professor of the School of Materials Science and Engineering of East China University of Science and Technology, if the plastic runway volatilizes odor, theoretically, it may be related to insufficient chemical reaction in the processing of plastic runway materials, or toluene added in the laying of plastic runway to facilitate construction and enhance viscosity. However, according to her research practice over the years, especially the detection experiment of the synthetic surface of the field association site, there is no toxic gas released from the plastic runway.
Ma Zhenzhu, the director of the Testing Institute of China Academy of Building Materials Science, the director of the National Building Materials Testing Center, and the director of the National Construction Industry Radioactive Supervision, Inspection and Testing Center, pointed out that the main environmental protection projects that people are most concerned about, such as formaldehyde and benzene, have not been detected, but the products of individual enterprises have experienced high values of heavy metals such as lead.
6、 Relevant practice investigation results
During the inspection, we also held various symposiums and research activities attended by leaders of education and sports management departments, sports teachers of sports venues and schools (i.e. users of the playground), and experts in environmental protection and labor protection. According to the deputy manager of the Beijing Workers' Stadium, the first plastic track in China, the plastic track of the Workers' Stadium has been laid for 25 years since 1979, and has been in normal use. None of the field workers who have worked on the ground all the year round and stayed longer than the athletes on the plastic track have suffered from respiratory diseases or other diseases caused by it. The same is true of Beijing Xiannongtan Stadium, which has been paved with plastic runways for nearly 20 years. Sports workers from Tsinghua University, Capital Institute of Physical Education, Beijing No.4 Middle School and other schools that have used plastic runways for many years have fully affirmed the role of plastic runways in the development of school sports and prudently recognized the use safety.
Zhou Baorui, the former director of the Standardization Office of the General Administration of Sport of China, who has experienced the whole process of the rise and development of plastic runways in China, said: "After nearly 30 years of inspection, the production and construction process of plastic runways in China is reasonable. In 1995, the samples of plastic runways produced in China were sent to the IAAF testing agency for testing, which fully met international standards, and some indicators were even far higher than international standards. In recent years, there has been no poisoning caused by the use of plastic runways in schools and universities with the largest use area."
