Traction polyethylene

In the second half of the 1960s, at the same time but independently, three basically different plastic separators were developed. One was the polyethylene separator [16] already referred to in starter batteries, used only rarely in stationary batteries, but successful in traction batteries. The others were the microporous phenolic resin separator (DARAK) [18] and a microporous PVC separator [19], both of which became accepted as the standard separation for stationary batteries. They distinguish themselves by high porosity (about 70 percent) and thus very low electrical resistance and very low acid displacement, both important criteria for stationary batteries. 

A detailed description of the production process and the properties of polyethylene separators can be found in Sec. 9.2.2.1, so only the modifications, which are important for traction battery separators are covered here. 

Polyethylene separators offer the best balanced property spectrum excellent mechanical and chemical stability as well as good values for acid availability and electrical resistance have established their breakthrough to be the leading traction battery separator. Rubber separators, phenolic resin-resorcinol separators, and mi-croporous PVC separators are more difficult to handle than polyethylene separators their lack of flexibility does not allow folding into sleeves or use in a meandering assembly in addition they are more expensive. 

FJfects of Constraint on the Traction-Separation Behaviour of Polyethylene 147... 

There are no data available on the effect of WPC density on the slip coefficient. However, it is known that polyethylene of lower density has a better traction than that of a higher density. In other words, HDPE is characterized by a low coefficients of friction, and the higher the density (specific gravity), the lower the static (and dynamic) coefficient of friction. For polyethylene density of 0.915 g/cm, coefficient of friction equals to 0.50 for 0.932 g/cm, it is equal to 0.30, and for 0.965 g/cm, it is equal to 0.10 [3]. 

The microporosity is also important for this apphcation, in order not to allow shorts through the backweb during battery hfe. Bottom shorts are avoided by a mud room of sufficient dimensions, and side shorts by plastic edge protectors on the frames of the negative electrode. Some manufacturers have switched to using sleeves of polyethylene separator material, rendering an edge protection superfluous. The use of three-side-sealed separator pocket in traction batteries should be avoided, because experience has shown this can lead to increased acid stratification, subsequent sulfation, and thus capacity loss. 

A lot of work has also been carried out in Brazil when it comes to using this technique for the devulcanisation of EPDM [99]. Waste EPDM from the automotive sector was exposed to microwave radiation for between 2 and 5 min and the DR produced characterised by a DSC and TGA. The degree of devulcanisation was assessed using gel content measurements. Workers from the same Brazilian university [100] have also devulcanised EPDM rubber by microwaves and then blended it with low-density polyethylene (LDPE) in the presence of a peroxide to improve the interfacial interaction between the two phases. The presence of the devulcanised EPDM in the LDPE matrix resulted in a reduction in the deformation and traction strength, but a significant increase in the elastic modulus values and impact strength. DSC data obtained on the mixture showed that the... 

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