Fleeces

Triacetate offers better ease-of-care properties than secondary acetate ia many apparel appHcations. Of particular importance are surface-finished fabrics, eg, fleece, velour, and suede for robes and dresses. These fabrics offer superb aesthetic quaHties at reasonable cost. Triacetate is also deskable for print fabrics, where it produces bright, sharp colors. The recent discontinuance of triacetate fiber Hi the United States has led to the use of acetate with fibers such as polyester (47—50). 

Fully Adhered. The substrate, ie, insulation, cover board, etc, that the single-ply membrane is to be attached to is either fuUy adhered or mechanically fastened to the deck. However, there are also appHcations where the membrane is adhered directly to the deck. The membrane is then adhered to the substrate. The typical method for adhering the membrane to the substrate is by applying a contact adhesive to the membrane and substrate, rolling the membrane into place, and brooming once the adhesive is ready. There are one-sided appHcations where the membrane is roUed directly into the adhesive that has been appHed to the substrate only. The membrane used in this appHcation method may be fleece-backed. FuUy adhered systems can be installed on any slope. The fuUy adhered appHcation offers a smooth surface that is easy to maintain and inspect, as weU as exceUent wind resistance on account of positive attachment. 

The flexible single-ply membranes are manufactured in three forms reinforced, nonreinforced, and fleece-back sheet. 

Fleece-Back Sheet. A fleece-back sheet is a nonreinforced polymeric membrane that has had a nonwoven mat made of polyester, weighing 101.7—203.4 g/m, laminated to the back of the sheet. The prime use of the fleece-back sheet is in the fully adhered roofing systems. The fleece provides the chemical separator, which eliminates the need for an adhesive that is compatible with the specific membrane or a compatible substrate. 

The greater portion of PVC is installed in the mechanically fastened roofing system a lesser portion is installed in fully adhered appHcations. Although PVC was once heavily used in ballasted roofing systems, there are only a small number installed in the 1990s. Fleece-back membrane is popular in the PVC constmction for both fully adhered appHcations as well as in appHcations where a separator sheet is needed. PVCs ate resistant to vafious weather conditions, bactefial growth, and industfial chemicals. These membranes ate chemically incompatible with bituminous materials. PVCs ate offered in a variety of colors. The physical characteristics of a PVC membrane have been described (15). 

Car roofs (composites made of the natural fiber fleece (flax) with epoxy resins or PUR composites)... 

Other than the processes mentioned here, natural fibers are used as construction units, by applying hybrid nonwovens, i.e., natural fiber staple fiber fleece [6I]. 

For the separation of such batteries, gel construction and microfiber glass fleece separators again compete because of the deep discharge cycles, the gel construction with its lower tendency to acid stratification and to penetration shorts has advantages for the required power peaks, microfiber glass fleece construction would be the preferred solution. The work on reduction of premature capacity loss with lead-calcium alloys has shown that considerable pressure (e.g., 1 bar) on the positive electrode is able to achieve a significantly better cycle life [31-36], Pressure on the electrodes produces counter pressure on the separators, which is not unproblematic for both separation systems. New separator developments have been presented with... 

The development of the starter battery in Japan has taken an independent course (see Sec. 9.2.1.2), visibly expressed by the separator s thick glass mat and its lack of spacing ribs (cf. Fig. 19). The cellulosic backweb impregnated with phenolic resin, generally in use until around 1980 and largely identical to the separator of the same type already mentioned has been completely replaced by thin ( 0.3 mm) fleece materials made of organic fibers. 

Since the glass mat supplies sufficient stiffness, high backweb thickness was no longer needed These fleeces are made of organic fibers (polyester and polypropylene, as well as so-called synthetic pulp , i.e., fibrillated polypropylene) on paper machines. 

Microfiber glass fleece mats are typically produced from a blend of 20 - 30 percent glass microfibers <1 //m in diameter, with the balance of the glass fibers thicker (3 - 10 //m) and longer (cf. Fig. 1), on a specialized paper machine (Fou-drinier), since this is the only way of achieving the desired tensile strength without binder. The material is supplied in roll form, even though it is normally not processed into pockets, which are not required due to the absence of free electrolyte. The classification here as a leaf separator should be seen in this sense. 

Because of the increased shedding with these alloys, pure leaf separation is hardly suitable. Separations with supporting glass mats or fleeces as well as microfiber glass mats provide technical advantages, but are expensive and can be justified only in special cases. Also under these conditions of use the microporous polyethylene pocket offers the preferred solution [40]. Lower electrical properties at higher temperatures, especially decreased cold crank duration, are battery-related the choice of suitable alloys and expanders gains increased importance. 

These generally defined requirements are met quite comprehensively by microfiber glass fleeces. These are blends of C-glass fibers of various diameter, which are processed in the usual way on a Foudrinier paper machine into a voluminous glass mat. The blending ratio gains special importance since cost aspects have to be balanced against technical properties. The... 

Table 13 compares the specification data of microfiber glass fleeces from various manufacturers. 

AMER-SIL s. a. [861 has recently introduced a micrufiber glass fleece separator ( AMER-GLASS ). 

Mechanical strength becomes an important criterion, because wound cells (spiral-type construction), in which a layer of separator material is spirally wound between each two electrodes, are manufactured automatically at very high speed. Melt-blown polypropylene fleeces, with their excellent tensile properties, offer an interesting option. Frequently two layers of the same or different materials are used, to gain increased protection against shorts for button cells the use of three layers, even, is not unusual. Nevertheless the total thickness of the separation does not exceed 0.2 - 0.3 mm. For higher-temperature applications (up to about 60 °C) polypropylene fleeces are preferred since they offer a better chemical stability, though at lower electrolyte absorption [ 114"]. 

Thus in this system, in addition to the usual requirements, the separator has the task of delaying penetration for as long as possible. A membrane would be regarded as perfect which lets hydroxyl ions pass, but not the larger zincate ions. This requirements is best met by regenerated cellulose ( cellophane ) [10,11], which in swollen condition shows such ion-selective properties but at the same time is also chemically very sensitive and allows only a limited number of cycles the protective effects of additional fleeces of polyamide or polypropylene have already been taken into account. 

Advanced development of ion-selective films has been attempted by radiation grafting of methacrylic acid on polyethylene films, and combination of this with cellophane are also being tested. Polyamide fleece impregnated with regenerated cellulose, is another option for zinc-silver oxide batteries. 

Occasionally the zinc electrode is wrapped in a polypropylene fleece filled with inorganic substances, such as potassium titanate, in order to reduce the solubility of zinc since the problem of dendrite growth is aggravated even by the metallization of the cellophane separator due to the aforesaid silver reduction and its promoting the generation of shorts. 

Of all possible manufacturing proceses for macroporous separators to be employed in alkaline batteries, the wet-fleece process using paper machines is the predominant one [130] it permits a very uniform ( cloud-free ) production of such material and the use of different types of fibers as well as of short and very thin fibers, thus achieving a uniform structure of small pores (Table 15). 

Whereas PVA fleeces are used only in primary cells polyamide fleeces compete with polyolefin, preferably polypropylene fleeces. The latter are more stable at higher temperatures and do not contribute to electrolyte carbonation, but they wet only after a pretreatment either by fluorination [131] or by coating and crosslinking with hydrophilic substances (e.g., polyacrylic acid [132]) on the surface of the fiber. 

Only very recently the production of melt-blown polypropylene fleeces with considerably thinner fiber diameter became possible [100], thus making it possible — a low-cost hydrophilization provided — to achieve attractive properties with regard to small pore size and excellent tensile performance for use in highly automated assembly processes. 

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