Attività

There are various kinds of modified MDI, and several MDI manufacturers giants have also been stepping up the research and development of modified MDI, which has enriched modified MDI types. And the products that have been produced and used in a large scale.

The two major components of polyurethane formulations are a polyol component and an isocyanate component. Polyols for Polyurethanes and polyester polyols have been used as the polyol component in polyurethane formulations for many decades. They remain the most commonly used polyols. Vast numbers of polyether polyols and polyester polyols, optimized to provide different combinations of behavior during fabrication processes and performance characteristics of fabricated articles, are available from many different manufacturers.

More recently, polycarbonate polyols have been gaining increasing interest and use in polyurethane formulations, either by themselves or more often in mixtures with selected polyether polyols or polyester polyols, because of their many attractive attributes. These attributes include performance benefits resulting from the high-density polycarbonate backbone. Furthermore, polycarbonate polyols are based on carbon dioxide (CO2), and sequester CO2 directly in their backbones, enhancing the sustainability of polyurethanes.

The images shown in this post are reproduced from product literature by Novomer which is a leading supplier of polycarbonate polyols.

The following reaction scheme shows how CO2 is sequestered in the backbone of a polycarbonate polyol by reaction with an epoxide during synthesis. Many different “R” groups can be used, to provide a broad range of polycarbonate polyol molecular structures.

The functionality of a polycarbonate polyol can also be chosen as desired, by using any one of many different possible starting molecules. For example, the choices of the following three starting molecules produce, from left to right, a diol, a triol, and a tetrol.

Rigid polyisocyanurate panel foams with better blowing efficiency (and hence smaller density when using the same concentration of the blowing agent pentane) and smaller cell sizes were obtained, while keeping the formulation viscosity manageable, by mixing 25% to 70% by weight of a polycarbonate polyol with a polyester polyol.

It can speed the expansion, speed the gelling, cool the reaction (so you have less of a fire hazard on your hands), etc. There are also curing agents, which include chain-extenders and cross-linking agents. Chain-extenders, like their name suggests, extend polymer chains, which increases material flexibility. Cross-linking agents promote and strengthen cross-linkages, increasing structural integrity for more rigid foams.

Remember that CO2 gas from the reaction with water acts as a blowing agent? Well, other blowing agents may also be used or added. The main inconvenience of water blowing in the high temperature of the reaction, making PU foaming a fire hazard. Physical blowing agents (additives that physically encourage the expansion of cells instead of that initial CO2, which is chemically blown) reduce that fire hazard.

A similar class of additives is fillers. They come as particles or fibers.