Rubbers : manufacturing and properties

The term "rubber" is quite generic, encompassing a large number of families, properties and dedicated applications. It is characterized by two particular elements: the role of formulation in matching properties to the intended function, and vulcanization. Some forming techniques are similar to those used for other polymers (molding, injection, extrusion, etc.), although there are some specificities, such as the confection process for tires, or the dipping process for latex gloves.

From an economic point of view, there are two main areas: tires and industrial rubber. The latter covers, in descending order of importance: automotive, non-automotive transport, industrial equipment, medical, construction, semi-finished products, adhesive tapes and leisure.

The rubber industry differs radically from that of thermoplastics in two particular respects. Firstly, rubber manufacturers prepare their own "mixes" using specific tools (internal mixers and cylinder mixers). They therefore have their own proprietary formulas and their own mixing parameters, developed and constituting their know-how. These formulations contain the base elastomer (the rubber marketed by major groups – Lanxess, Zeon, Du Pont, Exxon...), fillers (most often carbon black or silica), vulcanizing agents, oils and various processing and protective additives. The second point that characterizes the rubber industry is the need to vulcanize the material to give it the properties that are essential for its use, which calls for a variety of techniques: hot molding, hot-air tunnel, microwave, salt bath, etc. Conversely, the thermoplastics manufacturer generally buys the raw material directly on the market in granulated form, which then feeds its processing machines without any prior transformation.

The rubber industry's main challenge is therefore to find the least expensive formulas and processing techniques possible, so as to obtain products that best meet the required functions. The cost issue is particularly important in a context of rising raw material prices linked to oil prices and growing demand from BRIC countries. This is a difficult challenge, given the demands of users, who are also calling for cost reductions. Environmental constraints represent a second challenge, particularly in the case of certain vulcanization gas pedals considered hazardous to the health of both operators and users. These substances are covered by the REACH regulation (EC no. 1907/2006) and are gradually being replaced by compounds of no concern.

In this context, this article presents the basic knowledge and concepts needed to understand the techniques involved in rubber, and the wide variety of manufacturing methods, properties and prices. This is a general overview, as more...