PVC separation

PVC and their low-cost industrial production process, sintered PVC separators have been used since around 1950 and some are still employed today. 

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. 

Polyethylene separators Phenol- formald.- resorcinol separators PVC separators Rubber separators Micro fiber glass mat separators Total... 

Electric road vehicles have been reduced to insignificance, as mentioned already by, vehicles with combustion engines. Another electric vehicle — the electrically driven submarine — presented a continuous challenge to lead-acid battery separator development since the 1930s and 1940s. The wood veneers originally used in electric vehicles proved too difficult to handle, especially if tall cells had to be manufactured. Therefore much intense effort took place to develop the first plastic separators. In this respect the microporous hard rubber separator, still available today in a more advanced version, and a micro-porous PVC separator (Porvic I) merit special mention 28]. For the latter a molten blend of PVC, plasticizer and starch was rolled into a flat product. In a lengthy pro-... 

The production process is comparatively simple, even though — of course — the respective know-how is also decisive. The equipment for the production of sintered PVC separators is suitable in size and production capacity to be operated on its own by individual, medium-sized, starter battery plants, in contrast to the far larger units required for the production of polyethylene pocket material. 

Typical pore size distributions result in mean pore diameters of around 15 //m. Even long and intensive efforts did not succeed in decreasing this value decisively in order to enable production of micropo-rous pocketing material resistant to penetration [65, 66], In practice PVC separators prove themselves in starter batteries in climatically warmer areas, where the battery life is however noticeably reduced because of increased corrosion rates at elevated temperature and vibration due to the road condition. The failure modes are similar for all leaf separator versions shedding of positive active mass fills the mud room at the bottom of the container and leads to bottom shorts there, unless — which is the normal case — the grids of the positive electrodes are totally corroded beforehand. 

In many countries starter batteries are almost 100 percent recycled PVC separators can cause some problems here [67]. A prior separation of PVC from other battery components, which is quite tedious, would be desirable, because a PVC content decreases the recycling purity of the container polypropylene and makes further processing of this plastic more difficult. Also, any chlorine compounds liberated can form environmentally hazardous products with other substances the usual remedy is to install costly filter stations, with the residues representing possibly toxic wastes requiring special disposal methods. 

Sintered PVC separators are frequently produced only for captive consumption beyond that there are specialized producers for these separators [64,68,69] and for equipment for their production [64]. The data compiled in Table 6 comprise only premium products of independent producers. 

A thorough study (cf. Ref. [40]) of failure modes in practice has shown that with this form of separation also the cause of failure has not been the separator the usual failure modes for leaf-type separators, as they have been described for sintered PVC separators, apply here as well. 

Polyethylene separators Rubber separators Phenol formaldehyde-resorcinol separators Microporous PVC separators... 

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. 

Much of the above also holds true for the application of microporous PVC separators (see Sec. 9.2.3.1) in open stationary batteries. Very high porosity and thus low acid displacement and electrical resistance are also offered by this system. The relevant properties are compiled in Table 12. 

Since the early days of using PVC separators in stationary batteries, there has been a discussion about the generation of harmful substances caused by elevated temperatures or other catalytic influences, a release of chloride ions could occur which, oxidized to perchlorate ions, form soluble lead salts resulting in enhanced positive grid corrosion. Since this effect proceeds by self-acceleration, the surrounding conditions such as temperature and the proneness of alloys to corrosion as well as the quality of the PVC have to be taken carefully into account. 

Sintered PVC separators for open stationary batteries are produced in the same way as the corresponding starter battery version (Sec. 9.2.2.2). Their brittleness and thus difficult processability are disadvantages, as is their relatively low porosity the concerns about release of chloride ions and subsequent increased corrosion are to be considered here as well. On the other hand,... 

Polyethylene separators Phenol-Formal dehyde-resorcinol Separators Microporous PVC separators Sintered PVC separators Rubber separators... 

Among the separator varieties described, the phenol-formaldehyde-resorcinol separator (DARAK 2000) [60] as well as the microporous PVC separator [86] have proven effective for this construction. For applications without deep discharges, concessions may be made with the respect to porosity and pore sizes of the separator therefore polyethylene separators or a spe-... 

In the plastics recovery section, the polypropylene is separated from other plastics and products such as PVC separators, ebonite cases, labels, rope handles, etc., via a series of classifiers and hydro-cyclones. The polypropylene pieces or chips are cleaned, washed, and separated from any remaining paste and dust. Once the material has been shredded to smaller fragments, the plastic is a valuable by-product of battery recycling. Plastic cleaning and processing methods are so effective that heavy metal contamination in the final polypropylene product is very low. The final product can be used in household goods such as washing machines, vacuum cleaners, and dishwasher parts, or in products for the automotive industry [5]. 

The presence of chlorides from the PVC separators in the battery posed significant problems with the larger, integrated lead smelters who recovered other metals such as silver, copper, and zinc. Chlorides have serious implications for the recovery of these other elements. They reduce the life of the refractory lining of the furnace and affect the sinter quality. These difficulties have largely abated with the shift to polyethylene separators. 

Polyethylene separators Phenol-formald.-resorcinol separators PVC. separators Rubber separators Microfiber glass mat. separators Total... 

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