Environmental Performance and Solutions of Polyurethane Raw Materials

Polyurethane (PU) is an important synthetic material with a wide range of properties, a wide variety of products and a wide range of uses. The environmental protection issues it involves are also manifold. We will now choose its main points and make a brief statement.

An isocyanate

Isocyanate is a basic raw material of PU, and it is a variety of species, but the most commonly used are TDI and MDI. They are seriously harmful to the human body, mainly in the distribution of the operating environment and the distribution of residues in the product, being inhaled into the body or touching the skin, Mucosal damage. As isocyanates are not yet replaceable in PU production, only appropriate safety and environmental protection measures can be taken, mainly:

1. Formulate strict environmental protection standards and adopt effective measures (eg, minimize open operation, prevent leakage, effective ventilation, detection and warning of isocyanate content in the on-site environment, occupational protection measures of operators, etc.) to make isocyanate in the working environment The amount of emissions is limited to a relatively low level.

2. Reasonable formulations and processes, including the necessary post-treatment, are used to keep the isocyanate residues in the product low.

3. In recent years, the formula and technology for replacing MDI with TDI have attracted increasing attention and great progress has been made. The application scope of MDI continues to expand, and there are many successful application examples even in the soft foam of TDI. In addition to process and performance factors, environmental protection is a powerful driving force. As we all know, MDI is much less volatile than TDI, and it is relatively environmentally friendly.

The industry has accumulated a great deal of knowledge and experience concerning the safety and environmental protection of isocyanates, and the corresponding regulations and countermeasures are also relatively complete. Large-scale isocyanate manufacturers pay increasing attention to responsible care. All this creates favorable conditions for the safe use of isocyanates. After the isocyanate is emitted, it reacts with the water in the atmosphere and is destroyed to produce amine and carbon dioxide. The environmental problems of isocyanates are mainly for the local environment.

At present, in the polyurethane industry in China, there are different degrees of attention to the safety and environmental protection of isocyanate, insufficient investment, inadequate measures, and failure to strictly implement relevant safety and environmental protection regulations. This is a worrying issue.

two. Alternatives to chlorofluorocarbons (CFCs)

Destruction of the atmospheric ozone layer by CFCs (F11, F12, etc.) poses a serious threat to the safety of Earth's living things. For the phase-out of CFCs and the substitution of environmentally friendly substances for this issue, an international consensus has been reached and related international conventions have been signed. Due to the timely adoption of effective measures, there has been a good turn of events. However, to fully recover the depleted ozone layer, it must go through long-term and unremitting efforts. The environmental protection task in this area can be described as a long way to go.

The polyurethane industry is a large user of CFCs (as a blowing agent). The F11 that was rejected by environmental protection by one vote has many advantages in other aspects that the alternatives are difficult to achieve. Therefore, the replacement of CFCs is very difficult. In the past ten years, the polyurethane industry has made arduous and enormous efforts for the substitution of CFCs, and has paid a high price because it involves important factors such as formula, process, product performance and cost, and it is similar to the polyurethane industry. Bent bones. In spite of this, great success has been achieved in this imperative work. A number of alternatives have been introduced, and alternative routes for various products have also been basically established. The general situation is as follows:

1. Flexible polyurethane foam

The soft foam mainly uses water as a chemical foaming agent, and traditionally uses F11 as a physical foaming agent. The alternatives are currently based on methylene chloride. However, methylene chloride still has some ozone depletion potential (ODP ≠ 0), but it is only slightly smaller than F11's ODP. In recent years, the technology of using carbon dioxide as a physical foaming agent has become increasingly sophisticated and has been gradually put into industrial applications. The ODP of CO2 = 0 and it is the final replacement. When considering alternatives, we must also take into account the important factor of GWP (the potential for warming the planet), that is, the amount of greenhouse gases directly and indirectly, mainly carbon dioxide, which is a general ledger. Of course, relatively small alternatives to GWP should be preferred. The use of carbon dioxide as a physical blowing agent is in full compliance with this principle. The carbon dioxide used here is only a by-product of other industrial processes and belongs to reuse.

In recent years, a new process for the production of soft guns, such as variable pressure foaming and forced cooling foaming, has also been developed. It is also part of the environmental protection program.

2. Rigid polyurethane foam

The replacement of rigid foam CFCs is a step-by-step process. First, HCFC-141b (a much smaller ODP than F11) is used as a transitional foaming agent. Developed countries have stopped using it in 2003 and China is still in use. International conventions allow it. The progress of alternatives in developing countries can be slightly slower.

Hydrocarbon blowing agents (cyclopentane, etc.) are cheap and easy to obtain, but they have high thermal conductivity and are flammable. They must have reliable safety measures and increase the application trouble. This route is currently applied more in the European Union and Japan, and China also has applications. Originally starting at almost the same time as the HCFC-141b route, cyclopentane had an ODP of zero and GWP is much smaller than HCFC-141b, and is considered to be a more environmentally friendly alternative. The United States has strict control over the distribution of volatile organic compounds (VOCs). Cyclopentane is a VOC, so it has been cautious about this route.

Hydrofluorocarbons (HFCs) are the ideal final replacement (ODP = 0, GWP is small), but only a few of them can truly meet the requirements. Its pre-judgment, synthesis, screening, toxicity test, pilot test, industrialization and a series of work are very complicated and time consuming. Fortunately, the long-awaited HFC-type substitutes in the industry are finally on the market, mainly HFC-245fa, HFC-365mfc, and in specific applications also include the mixture of various HFC-type substances (such as HFC-227ea, etc.) Match to achieve the best results.

(to be continued)