It is therefore very important to always choose the proper materials and to observe the mixing ratio specified by the manufacturer. Otherwise, unintended reactions may occur, or the product may not harden at all. Epoxy system may also have added accelerators (catalysts) to aid the hardening process. These are often amines or phenols. Dissolving Agents Dissolving agents are added to make the resin, or the composite of resin and hardener, adequately liquid for practical handling. Like in standard dissolving agents, which evaporate during the curing process, hydrocarbons, alcohols, esters etc. are used. Reactive dissolving agents, which are used in the curing process itself and thereby remains (chemically combined) in the finished product, particularly uses low molecular epoxy composites. A number of these reactive dissolving agents evaporate easily and are associated with high health risks. The lowest molecular resins, and therefore the most liquid ones, can be utilized without any form of dissolving agents or may be dispersed in water. Other Additives Other than hardeners and dissolving agents, epoxy systems may contain pigments, fillers and other additives.
Products Containing Isocyanates Isocyanates is a generic term for chemical substances with one or more functional isocyanate groups (NCO) in their molecular structure. The resin is a polyol, which chemically is an alcohol. Polyols have a high viscosity and are therefore not very hazardous to the health. Pure polyols are not hazardous to the health. Isocyanates are aggressive chemicals, which can react with water, alcohols, amines, etc.
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Isocyanates pose the greatest health risk associated with the manufacturing of polyurethane products. Isocyanates in the form of fumes, mists (aerosols), or (unreacted) drops of PUR spray mixtures, are harmful when inhaled. Even very small quantities irritate the nose, throat, or lungs. The hardener is a diisocyanate or a related substance. Diisocyanates have two functional isocyanate groups and are used as a starting point for the formation of polyurethanes (often called monomeric isocyanates). Common diisocyanates (hardeners): • MDI – Methylene diphenyl diisocyanate (harmful to health) • TDI – Toluene diisocyanate (very toxic) • HDI – Hexamethylene diisocyanate (toxic) • IPDI – Isophorone diisocyanate (toxic) One reason that TDI is classified as very toxic is the fact that when heated (to approx. +150 °C) it will release isocyanates. This is called secondary exposure. TDI (2,4- and 2,8- toluene diisocyanate) is listed on the Danish Working Environment Authority’s list of substances that are considered carcinogenic.
Polyurethane – PUR Many polyurethane products (PUR) are now available for filling, grouting and bonding. These are the so-called prepolymeric polyurethanes, in which polyol and isocyanate are combined in a container. The chemical reaction only starts when the substances come out of the container and come into contact with the humidity of the air. Here it is important to ensure the necessary ventilation and protect the respiratory system. Polyurethane is formed when an isocyanate reacts with an artificial resin Polyurethanes may appear as: • Solid thermoplastics • Foamed plastics, that may be rigid, half-rigid, or flexible • Thermoplastic elastomers
Product Knowledge
25-09-2019 11:31:05