EoW March 2009

technical article

2 PVC compounds: a contribution to sustainability

Resin manufacturing and the nature of stabilisers have undergone a tremendous change during the past decade as a result of regulatory limitations of hazardous substances, as well as efforts to make the material recyclable and complying with sustainability requirements. PVC stabilisers have long been under scru- tiny and there is much concern regarding heavy metal-containing products. As a result, many restrictions are being imposed, either by the industry itself, by governmental regulations or by PVC users. An example of this versatility is the replacement of lead stabilisers with other heavy metal-free systems as Ba-Zn, Ca-Zn and Al/Mg/Ca/Zn stabilisers. development of FREC (Flame Retardant Eco Compounds) The B & B Compounds project was targeted at developing a new range of PVC flame retardant eco-compounds. There are a number of technological options available to replace heavy metal stabilisers and Sb 2 O 3 . 3.1 The function of stabilisers in PVC When PVC is processed at high temperatures, it is degraded by de- hydrochlorination, chain scission, and crosslinking of macromolecules. Free hydrogen chloride (HCl) evolves and discolouration of the resin occurs along with important changes in physical and chemical properties. The evolution of HCl takes place by elimination from the polymer backbone; discolouration results from the formation of conjugated polyene sequences of 5 to 30 double bonds (primary reactions). Subsequent reactions of highly reactive conjugated polyenes crosslink or cleave the polymer chain, and form benzene and condensed and/or alkalised benzenes in trace amounts depending on tempera- ture and available oxygen (secondary reactions). Degradation must be controlled by the addition of stabilisers. The heat stabiliser must prevent the de-hydrochlorination reaction that is the primary process in degradation. 3 Targets for

The most common small-scale test method for measuring smoke from burning products is the traditional NBS smoke chamber in the vertical mode, according ASTM E662. Because of the great number of possible parameters that influence burning and smoke propagation, a real fire scenario cannot be simulated in the NBS chamber. However, it is possible to assess smoke generation of various formulations under identical boundary conditions. The ASTM standard requires measurements in both the non-flaming mode (where the sample, mounted in a vertical position, is subjected only to a heat radiant source) and the flaming mode (with flaming to the bottom of the sample). The resulting smoke reduces the intensity of a light beam that vertically crosses the chamber. Toxicity : Finally, fire hazard also is associated, at least to some extent, with the toxicity of the smoke itself. The main reason for this is that the most important toxic product in any fire is carbon monoxide (CO), which is produced by all organic materials when they burn. During combustion PVC, compared with other materials, gives offmore hydrochloric acid and little carbon monoxide. Both of these gases are toxic, but with one substantial difference. The hydrochloric acid is immediately perceptible and irritating, with an acrid odour that stimulates people to leave the affected area. Moreover, it will deposit itself on the walls, disappearing quickly from the gaseous mass. Carbon monoxide, instead, is odourless and flavourless, building up a concen- tration enough to cause unconsciousness before evacuation from the area has occurred. It is the carbon monoxide, and the heat and the smoke that develops with the combustion of all the organic materials that is mainly responsible for deaths during fires: it is called “the silent killer”. So far as the risk of formation of dioxins is concerned (normally correlated to the uncontrolled combustion of materials containing chlorine), it appears from studies that the amounts emitted during an accidental fire are very small. There is no noticeable increase (the levels are lower than 0.1%) of the general level of dioxins present in the atmosphere. There are therefore no increased risks to people or the atmosphere in the case of a fire that involves large amounts of PVC.

The trend of the last years is to eliminate risks to the environment and to human health. The RoHS (directive 2002/95 EC) stands for ‘the restriction of the use of certain hazardous substances in electrical and electronic equipment.’ This directive bans the placing on the EU market of new electrical and electronic equipment containing more than agreed levels of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants. This is only one of the steps in order to arrive at the production of materials that respect the environment. On 1 st June 2007, Regulation EC 1907/2006 REACH (Registration Evaluation and Authorisation of Chemicals) came into force, for an elevated level of protection of human health and the atmosphere. It included the promotion of different methods for the evaluation of the dangers that the substances involve, let alone the free circulation of substances in EU market, strengthening at the same time the competitiveness and the innovation. The Reach priorities are: registration of about 30,000 substances, • commercialised before 1981 and produced or imported in amounts of 1 ton a year; defining principle OSOR ‘one substance, one registration’ and to invert the burden of proof to make the people who place chemicals on the market (manufacturers and importers) responsible for understanding and managing the risks associated with their use authorisation and substitution of the • dangerous substances, assuring that the risks are adequately controlled and that these substances are replaced by suitable substances or alternative technologies compliance by manufacturers, impor- • ters and users restrictions in specific applications • to provide a high level of protection • of human health and the environment from the use of chemicals availability of relevant data (no data – • no market) Due to its versatility in applications and its cost competitiveness, PVC has remained a material of choice for the construction industry as well as for medical parts and equipment since its large-scale introduction in the early 1950s.

HCI

PVC

HCI

Chain reaction (zip mechanism)

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EuroWire – March 2009