Resin‐Bonded Cellulose Separators: An Overview with Prognoses

Abstract

Resin-bonded cellulose separators are very widely used in the starting, lighting, and ignition battery industry. Since their appearance and maturity, they have undergone systematic improvements, but their basic shortcomings have remained. Separator development is reviewed here, and the pertinent structure and chemistry of the cellulose substrate is discussed. The current literature, which indicates that improvements in substrate character and acid resistance can be made, isalso reviewed.In 1917, almost the beginning of the modern starting, lighting, and ignition battery industry, Brooks pointed out the lead-accumulator was unexcelled in portable service applications (1). Separators at that time were wood veneer and were superior to anything in use despite the stringent requirements of their manufacture. At that time, only treated wood possessed good wicking action and reasonable conductivity and held active material in place against vibration and the eroding action of hydrogen generated on overcharge. Other materials had been tried, but until the microporous hard rubber separator appeared, wood veneers and combinations of wood and other materials dominated separator practice. Eyanson developed an unglazed porcelain membrane with incorporated lead spacers (2), but this product undoubtedly gave a cell of high internal resistance. Sperry developed a perforated, corrugated, hard rubber sheet that was really a simple, open spacer (3). ~he earliest hard rubber separators, used as adjuncts to wood, were approximately 30% porous. Batteries in which they were used were poor for cranking purposes (4).Hardy and Hungerbuhler (5) experimented with artificial stone for making separator membranes. They compressed and then baked silicates, feldspars, bone, and lime to form refractory porous sheets. Rodman (6, 7) experimented with techniques to make porous glass separators, developing membranes of sand or fine glass powder flitted together.In 1910, Flanders described an untreated wood veneer separator using a well-defined rib structure (8), and after this a number of wood/hard rubber combinations were developed. Carpenter (9) coa'~ed thin wood sheets with' vulcanized rubber, and Chamberlain described a process to produce wood veneers machined so that the ribs were integral to the separator structure (10). Gould's patent, describing the use of hard rubber and wood laminated together, appeared in 1916 (11).Many battery researchers applied themselves to the separator problem between Brooks's time and the period during which the resin-bonded paper separator appeared, then matured. One of the more interesting * Electrochemical Society Active Member, 1 Present address: Institute of Gas Technology, Chicago, Illinois 60616.inventions was Bliss's (12) ingenious attempt to make a porous phenol-formaldehyde sheet. He mixed asbestos and zinc with resin, polymerized it, and removed the zinc with acid. A number of other inventions included a separator of chopped bird feathers and sodium sulfite (13), bitumen-impregnated felts (14), roofing fel...