Environmental protection performance and solutions

2022-09-19
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Environmental protection performance and solutions of polyurethane raw materials

polyurethane (PU) is an important synthetic material with a wide range of properties, a wide range of products and a wide range of uses. The environmental protection issues involved are also multifaceted. Now choose its main points to make a brief introduction

I. isocyanate

isocyanate is the basic raw material of PU. There are many kinds, but the most commonly used are TDI and MDI. They are serious hazards to human body, mainly the emission in the working environment and the emission of residues in products, which are inhaled into the body or in contact with skin and mucous membranes. As isocyanate is not replaceable in PU production, only appropriate safety and environmental protection measures can be taken, mainly:

1. formulate strict environmental protection standards and take effective measures (for example, minimize open operation links, prevent leakage, effective ventilation, detection and warning of isocyanate content in the on-site environment, occupational protection measures for operators, etc.), The dispersion of isocyanate in the working environment comes from Craig nikrant, head of PolyOne's special engineering materials department, Said: "Through cooperation and innovation with local customers in various countries in India, the development volume is limited to a relatively low level.

2. Adopt reasonable formulas and processes, including necessary post-treatment, to control the residual amount of isocyanate in products at a very low level.

3. In recent years, people have paid more and more attention to the formula and process technology of replacing TDI with MDI, and made great progress. The application scope of MDI has been expanding, and even expanded There are also many successful application examples in the unified field of TDI soft bubble. In addition to process and performance factors, environmental protection is a strong driving force. As we all know, MDI is much less volatile than TDI, which is relatively conducive to environmental protection

the industry has accumulated a lot of knowledge and experience about isocyanate safety and environmental protection, and the corresponding specifications and countermeasures are relatively perfect. Large isocyanate manufacturers pay more and more attention to care. All these have created favorable conditions for the safe use of isocyanates. After the isocyanate is emitted, it will react with the water in the atmosphere and be destroyed to produce amine and carbon dioxide. The environmental protection problem of isocyanate is mainly for local environment

at present, in the domestic polyurethane industry, insufficient attention is paid to the safety and environmental protection of isocyanates to varying degrees. Insufficient investment, ineffective measures, and failure to strictly implement the relevant safety and environmental protection specifications are worrying problems

II. Precautions for the use of tensile testing machine

cfcs (F11, F12, etc.) destroy the atmospheric ozone layer and seriously threaten the safety of earth organisms. An international consensus has been reached on the issue of phasing out CFCs and replacing them with environmentally friendly substances, and relevant international conventions have been signed. As effective measures were taken in time, the situation has taken a good turn. However, long-term unremitting efforts are needed to completely restore the destroyed ozone layer, and the environmental protection task in this regard is a long way to go

polyurethane industry is a large user of CFCs (as foaming agent). F11, which was rejected by environmental protection, has many advantages in other aspects that are difficult for substitutes to achieve. Therefore, the replacement of CFCs is very difficult. In the past ten years, the polyurethane industry has made arduous and great efforts to replace CFCs and paid a high price. Because it involves important factors such as formula, process, product performance and cost, it is like breaking bones and muscles for the polyurethane industry. Nevertheless, this imperative work has achieved great success. A number of substitutes have been launched, and the alternative routes of various products have been basically determined. The general situation is as follows:

1 Soft polyurethane foam

soft foam mainly uses water as chemical foaming agent, and F11 is traditionally used as physical foaming agent. At present, dichloromethane is the main substitute. However, dichloromethane still has a certain ozone destroying potential (ODP ≠ 0), which is only smaller than that of F11. In recent years, the technology of using carbon dioxide as physical foaming agent has become increasingly perfect, and has been successively put into industrial application. ODP of carbon dioxide = 0, which is the final substitute. When considering alternatives, we must also take into account the important factor of GWP (the potential to make the earth warm), that is, the amount of greenhouse gases produced directly and indirectly, mainly carbon dioxide, which is a general ledger. Of course, the relatively small alternative of GWP should be preferred. Taking carbon dioxide as a physical foaming agent fully conforms to this principle. The carbon dioxide used here is only a by-product of other industrial processes and belongs to reuse

in recent years, new soft cannon production processes such as variable pressure foaming and forced cooling foaming have also been developed, which are also part of the environmental protection plan

2 DuPont high performance materials will increase zytelreg; And delrinreg; The CFCs replacement of rigid polyurethane foam is carried out step by step. First, HCFC-141b (much smaller than the ODP of F11) is used as the transitional foaming agent. Developed countries stopped using it in 2003, and China is still using it. The international convention allows the replacement progress of developing countries to be slightly slower

hydrocarbon foaming agents (cyclopentane, etc.) are cheap and easy to obtain, but the thermal conductivity of the products is high and flammable. Reliable safety measures must be taken, which increases the trouble of application. At present, this route is widely used in the European Union and Japan, as well as in China. At the beginning, it started almost at the same time as HCFC-141b route. The ODP of cyclopentane is zero, and the GWP is far smaller than HCFC-141b, which is considered to be a more environmentally friendly alternative. The United States has strict control over the emission of volatile organic compounds (VOCs), cyclopentane and other VOCs, so it has always been cautious about this route

hydrofluorocarbons (HFC) are ideal final substitutes (odp=0, GWP is very small), but only a few of them can fully meet the requirements. Its prediction, synthesis, screening, toxicity test, pilot test, industrialization and a series of work are very complicated and time-consuming. Fortunately, the long-awaited HFC substitutes in the industry are finally on the market. It is worth noting that HFC-245fa and hfc-365mfc are the main substitutes. In specific applications, they also include the mixing of various HFC substances (such as HFC-227ea, etc.) to achieve the best results

(to be continued)

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