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T. J. GILLICK,Jr. American Felt
Co., Glenville,
Conn.
Natural and Synthetic Fiber Felts F E L T is defined as fabric made of matted fibers of wool, or wool and fur or hair, fulled or wrought into a compact material by rolling or pressure, with lees or sizing, without spinning or weaving. I n all cases, felt materials result from interfiber friction or entangling without other nonfibrous additives. Three main classes of natural fiber felts are in use today-fur, hair, and wool. Fur felt usage is confined mostly to the hat industry. Cattle and goat hair felts are specialty products of the wool felt industry, and are consumed almost entirely in industrial polishing applications (7, 76). The nonwoven wool felt industry in the United States consists of about 10 manufacturers with a total annual fiber consumption of 30 million pounds. The ability of wool to felt is an outstanding characteristic. This phenomenon holds true for wool fiber fineness from 20 to 40 microns in diameter. Fur fibers from 10 to 15 microns in diameter do not felt well. Hairs ranging from 40 to 60 microns in diameter are also not outstanding as felting fibers. When a wool fiber is examined microscopically, the surface shows a scaliness. Speakman and Stott (24) reported a device for measuring the coefi.cients of friction of wool fibers when rubbed from tip to root and root to tip, respectively, and also established that for any wool fiber the coefficients of friction were different in each direction. These differences are now measured quantitatively and are referred to as the Differential Friction Effect (D.F.E.). A definite relationship was established between D.F.E. and felting ability when the D.F.E. was measured in a 5% soda ash solution showing that maximum felting efficiency occurred with wools having the highest D.F.E. (6). Chemical antishrink treatments also reduce the D.F.E. ( 7 ) . For felting to be possible, a fiber must possess a surface scale structure, must be easily stretched and deformed, and must possess the power of recovery from deformation (5). Moncrieff (27) points out these chemical and physical aspects of wool feltingpossession by the fiber of a scale structure; agitation; and moisture. These conditions also contribute to felting: Ease of extension and deformation (bending) Power of recovery from extension and deformation Curl and crimp in the fiber
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Fiber length Fiber fineness Warmth Acid or alkaline state of milling liquor One of the very important factors which contributes to felting is a necessary tendency of fibers to curl and become entangled under felting conditions. Curliness is due to difference in the elastic properties between the scales and cortex which are removed by chemical attack (73). Other work on the ortho- and para-cortex structure of keratin fibers (9, 74) supports these data.
Pertinent References in the Felts Field Subject Felts a s one of oldest fiber structures Felt for body comfort Theoretical chemical and physical aspects of mechanics of felting Relationship between D.F.E. and felting ability Wool properties for felting Ortho- and para-cortex structure of keratin fibers Standards and specifications of wool felt Chemical reactivity of wool in antishrink processes First shelter fabric Elastic and swelling behavior of wool fiber Felt wheel a s finishing tools Felts-sheet, wool, pressed Synthetic fiber and wool felts Four types of synthetic fiber felt Crimping of wool fibers Felt from man-made fibers Mechanical uses and properties of wool felt Theory of felting Felting of animal fibers Treated felts Nonwoven filter media
Fur Felt The hat industry is most outstanding in fur felt making. Rabbit, hare, and beaver furs are the typical fibers used. Fur felt hat making processes include: CARROTTING. After trimming and cleaning, the pelts are brushed with a solution of nitric acid and peroxide and then dried. Uncarrotted fur does not felt well. Carrotting makes the coarse tips of the fiber more flexible and deformable than the finer roots (ZO), enabling the tips to follow the roots through entanglements which obstruct movement and felting of uncarrotted fibers. CUTTING.Sharp rotary knives cut the
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
skin from the fur so that whole fur can be bagged, or so that select portions may be removed and segregated before bagging. BLOWIXG A N D BLEXDING.In standard practice, blends of several types of fur, not all of which need to be carrotted, are used, depending on weight, price, hand, and other factors desired in the end product. The furs are subjected to air blowing which separates thc lighter, finer fibers into the collector, and allows the coarser heavier grade fibers to drop out and to be discarded. FORMING. The required amount of blown and blended fur for each hat is weighed out separately and is about 2.5 to 4 ounces. The weighed portion is then fed onto the forming machine by a traveling apron which slowly drops the fur into the air near the top of a perforated cone about 3 feet in height and 30 inches in diameter at the base. The cone, revolving at high speed with suction employed at its base, is covered with a wet burlap so that the fur is collected over its entire surface. When all the fur is deposited another wet burlap is placed over the fur-covered cone, a perforated cover put over it, and the entire unit is placed in warm water. When removed, the fur is a thin fragile cone. STARTING.This preliminary gentle felting process gives the cones sufficient strength for further processing. FELTING. This operation generally called “sizing” in the hat trade reduces the cones by felting to specified size. The cones are subjected to mechanical forces in two planes while traveling on rubber aprons between rollers in water at about 150’ F. Water is generally adjusted to pH 5.5 to 6.5. After felting the cone is about 10 inches high and a foot in diameter at the base. DYEING. This operation is done usually in either open tubs or revolving cagetype equipment. Hats are handled by the dozen and a typical dye lot would be 25 or 50 dozen. Dyeing is done either after felting or a t a point midway in the felting cycle. In a few cases the cones are felted in a dye liquor so that felting and dyeing is accomplished in one operation. DRYING.After felting to size and dyeing, the cones are dried. STIFFENING. The dried cones are wetted with a borated shellac solution to a point midway between base and tip and then redried. Residual acid from felting and dyeing neutralize the mild alkali
NONWOVEN FABRICS
Crosser carding. The crosser web is being delivered from the slatted apron across the straight web which is approaching the endless apron from the lower left
and "sets" the shellac so that in subsequent finishing the brim and side wall below the band line can be shaped and stiffened. TIPPING AND BRIMMING. The dried cones after shellac impregnation and drying are soaked in hot water and are then subjected to manual or mechanical molding operations to form a rough hat body having a distinct crown and brim. Before removal from themold the hot shaped felt body is quenched with cold water to set the shape. FINISHING.These dry and wet operations are many and varied and convert the rough hat into attractive head apparel.
Hair Felt Nonwoven hair felt is a specialty item produced by the nonwoven wool felt industry as sheets, either square, rectangular, round, or oval. PICKING AND BLENDING. Cattle and/or goat hairs are prqcessed in conventional metal tooth, high speed opening and blending pickers. Debris is removed and the opened fibers are stored. CARDING.This is done on 48- or 60inch woolen cards. The fibers are aligned generally parallel to the direction of delivery, in the form of a web. The web is delivered to an apron moving slowly at right angles to the direction of the web delivery. Based on card feed and apron speed, batts of predetermined length, width, and weight are periodically rolled up and removed. LAY-UP. The carded batts are opened and cut into squares or circles to pattern. Individual squares and circles are piled
This felt is being placed on tenter frame for drying
up to a unit weight at right angles to fiber direction. HARDENING. The individual squares or sheets are placed upon a perforated table containing a steam box, and covered with burlap. Steam is blown through until proper temperature and moisture conditions are reached, then a heavy platen is lowered onio the hot moist batt. The platen is driven with a reciprocating short stroke in a plane parallel to the table top. Heat, moisture, and mechanical action produce initial felting. The thickness of the batt is reduced from 4 to 6 inches to 1 inch or less. FULLING. The hardened sheets are steeped in sulfuric acid solutions at Z0 to 6' Twaddle, drained, and then fulled in fulling mills of the pusher or kicker type. Several sheets are required for a mill load. Each sheet is fulled to a predetermined area and thickness dimension; area shrinking may be as much as 50%. Thickness may increase to 2 or 3 inches. WASHING AND DRYING. Excess fulling acid is removed by centrifugal extractors fitted with spray nozzles. After water spraying and rinsing, the sheets are finally extracted and dried in forced hot air ovens. FINISHING.Each sheet is inspected for weight, thickness, and then trimmed or framed to dimension. When desired, thickness may be set by heat and pressure in platen presses.
Wool Felt Felt, wool and part wool, is built by interlocking of fibers by a combination of mechanical work, chemical action, moisture, and heat, without spinning,
weaving, or knitting. Felt may consist of wool, reprocessed wool, and re-used wool, with or without admixture with animal, vegetable, and synthetic fibers. Two main classes of wool felts are roll and sheet. Sheet felts are produced in a manner similar to that for hair felt and are generally 36 inches square. Commercially available thicknesses range from l / 4 to 3 inches, with a weight from 3 to 8 pounds per square yard for 1/4 inch thickness and up to 66 pounds per square yard for the 3 inch thickness. Sheet felts can be made as thin as '/I6 inch in certain densities. Roll felts, the predominant product of the industry, are made in lengths from 10 to 60 yards and in widths from 54 to 80 inches. Weights may range from 3 ounces per square yard to 18 pounds per square yard, in a thickness range from '/as to 11/4 inches. Seven major manufacturing operations in the production of roll felt are: PICKING AND BLENDING.The various types of fibers selected are floor laid and then fed to textile mixing pickers where the fibers are opened, blended, and burrs and other foreign nonfibrous objects removed. CARDING. Woolen cards are used. A typical carding unit consists of four 60inch breaker cards each feeding roving to a 100-inch finishinq card. Two finishing cards are placed in a straight direction to feed onto an endless apron, while the other two finishing cards are placed a t right angles to the other pair. This crosscard setup produces dimensional stability in the felt. At intervals. carded fibrous batts are rolled up and removed from the endless apron. VOL. 51, NO. 8
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HARDENING.This is a condensing, steaming, heating, and vibrating operation. In roll felts, several rolled batts are unrolled on a long table to produce one felt The batts are passed over a steam table, then under the hardening platen, and rolled. After drying, this product may be sold without further felting, being known in the trade as a soft pad or hardened only felt. FULLING.The moist and cooled hardened batts are passed through the fulling liquor. Depending upon end-use requirements, this fulling liquor may be hot water, sulfuric acid solutions from 1' to 6' Twaddle, soap solutions, or syndet solutions. Roll felt fulling mills are generally of the two or four hammer pusher type and mill loads may range from 50 to 500 pounds. WET FINISHING AND DYEING. This operation is usually done in conventional dolly washer or reel-type textile wet processing equipment. Scouring, neutralizing, bleaching, dyeing, and after treatment methods closely parallel those of the woolen and worsted cloth trades. Dyeing is usually done only on those goods for apparel and decorative uses. Most roll felt is sold in the natural undyed state. DRYING. The light weight roll felts are dried on a continuous basis in endless pin-clip forced-convection hot air dryers. The denser or thicker grades are usually dried on tentering racks or frames in heated rooms or ovens in a batch process operation. FINISHING.These felts are finished by shearing, microgrinding. napping, and pressing, or combination of these. The finished thickness is set by either roller or platen pressing, and this product is sometimes referred to as pressed felt. Properties a n d Modifications. The wide range of fiber blends, types, weights, and thicknesses of wool felts produced testifies to the versatility of these nonwoven materials. Major properties include the esthetic and warmth factors (which contribute to apparel and decorative usage) and such mechanical factors as wear resistance, oil absorption, capillary flow, thermal conductivity, coefficients of friction, porosity, compressional resistance, resistance to aging, energy absorption, and others. In recent years, owing to increased demands for ever widening applications, it has been found desirable to modify the properties of felt by combining, impregnating, or surfacing with other materials ( 7 7 , 22). Natural and synthetic elastomers and polymeric resins are generally used for impregnating, while sheet and film materials such as rubber or polyethylene are used for combining. In many cases, solvent activated or pressure sensitive adhesive coatings are also used to widen its end use. Because of its many mechanical properties, wool felt is applied indus-
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These modified wool felt seals sheet materials
are made by combining
trially for filtration: sound absorption, thermal insulation, shock absorbing, cushioning, padding, packaging, surfacing, spacing, and friction (78). Standards a n d Specifications. The development of the ~ l o ofelt l industry has led manufacturers and consumers to recognize the need for standards and specifications to govern seleciion, acceptance, and use of the many individual types and grades of wool felt. Standard methods for testing felt have also been developed (3, 23, 26). Synthetic Fiber Felts
Rapidly accelerating demands from design engineers for engineering materials
INDUSTRIAL AND ENGINEERING CHEMISTRY
with
elastomeric
for new uses have been met by the felt industry with modified or improved performance ~ r o o lfelts and with the deveicyment of synthetic fiber felts. The ckmical and thermal properties and limitations of the wool fiber are well knoivn. No additive can change the inherent fiber property limitations. Synthetic fiber felts are used today for felt applications beyond the range of utility of wool felt. Because chemical fibers do not felt naturally, methods have been developed to obtain feltlike structures (12). The basis of this method is the old textile technique of needle felting; it is called mechanical interlocking, There are four types of synthetic fiber
The manufacturing processes used for synthetic fiber felts are similar to those for producing other felts. 1. Picking and Blending 2.
3.
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Mechanical Interlocking
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4. Finishing
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Carding
3.
Mechanical Interlocking
4.
Felting
3.
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4. Mechanical Interlocking
5.
5.
r Finishing
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Combining
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5.
Washing
7.
Finishing
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Finishing
N O N W O V E N FABRICS felt constructions in current use (72)mechanically interlocked fibers alone and in combination with woven fabrics; mechanically interlocked fibers plus chemical felting; and any one of these three containing fibers that can be made cohesive or adhesive. The use of the first of these types parallels that of the low density wool pad felts. The second type is used in applications beyond the range of the high density thin gage mechanical roll felts, whereas the third type is most generally suited for potentially extending felt applications. The four class is experimental at this time, but will undoubtedly enable modified versions of the other types to be produced for special uses. The manufacturing procedure for the mechanically interlocked and chemically felted class are briefly outlined. In order for this structure to be achieved, a synthetic fiber which not only can be mechanically interlocked, but also under certain combinations of heat, moisture, and chemical action can be made to reorient or shrink along its lengthwise axis must be available. Shrinkage along the individual fiber length must be about 5070 to obtain the felting power that is necessary for this class of felt to result. With fibers of this type it is possible to produce synthetic fiber felts with percentages of nonshrinkable synthetic fibers in the blend. These new materials are not replacements for wool felt. Rather, they are finding greatest applications in industrial process equipment where wool felt
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has not been utilized. For example, in the mining of taconite, polyester fiber felts used on reverse air jet dust collectors have overcome one of the major process stumbling-blocks in using this ore. Other developmental types of industrial applications are currently under way. These new synthetic fiber fabrics in lighter weights and in colors have aroused interest in the fields of apparel and decoration. Natural protein fibers form basic building blocks for nonwoven felt materials over a wide range of types, grades, weights, and thicknesses. The materials are proved, established, and standardized. New synthetic fiber felts are being developed to extend felt applications and use beyond the limitations of natural fiber felts. References
(1) Alexander, P., Am. Dyestuff Rep&. 39, 420 (1950). (2) Alexander, P., Hudson, R. F., “Wool, Its Chemistry and Physics,” chap. 11, Reinhold, New York, 1954. (3) Am. SOC.Testing Materials, Philadelphia, Pa., ASTM Standards on Textile Materials, 1957. (4) Boeddinghaus, H., Think Mag., pp. 7-8 IBM publication (July 1952). (5) Bogaty, H., Sookne, A., Harris, M., Textile Research J . 21, 822 (1951). (6) Bohm, L., J . SOC.Dyers Colourists 61, 278-83 (1945). (7) Colwell, W., Products Fznishing (Felt Association reprint) 5 (January 1952). (8) Ditzell, Deut. Wollen-Gewerbe 23, No. 1 (1891). (9) Dusenbury, J. H., Menkart, J., Proc.
Intern. Wool Textile Research Conf., Australia, 1955. (10) Felt Association Inc., The, New York, N. Y . , “Felt-Wool,” 1952. (11) Gillick, T. J., Elec. Mfg.61, 126-31 (1958). (12) Gillick, T. J., Magnant, F. J., Prod. Eng. 28, 478-82 (July 1957). (13) Harris, M., Am. Dyestuff Reptr. 37, 72 (1945). (14) Horio, M., Kodo, T., Textile Research J . 23, 373 (1953). (15) Kaswell, E. R., “Fibers, Yarns, and Fabrics,” chap. 18, Reinhold, New York, 1953. (16) Kent, R. T., Iron Age 135, 124-8 11095\ \----,.
(17) Lauderbach, H., Textile Research J . 25, No. 2 (February 1955). (18) Lehmberg, W. H., Mech. Eng. 67,93-9 (February 1945). (19) Martin, A. J. P.. J . SOG. Dvers Colourists 60, 325 (1944). ’ (20) Menkart, J., Speakman, J. B., Nature 159, 640 (1947). (21) Moncrieff, R. W., “Wool Shrinkage and Its Prevention,” p. 147, Chemical Publ. Co., New York, 1954. (22) Rile M. W., Materials @ Methods 43, 89-93 &ecember 1956). (23) SAE Handbook, SOC. Automotive Inc., New York, p. 387, 1957. (2%; eakman, J. B., Stott, E., J . Textzle Research Inst. 22, T339 (1931). (25) U. S. Dept. of Commerce, Washington 25, D. C., Commercial Standard 18552, 1952. (26) U.S. Govt. Printing Office, Washington 25, D. C., Federal Specification C-F206a, 1954. (27) Wakelin, J. H., Textile Research Institute, Princeton, N. J., Ann. Rept. 1953-54, p. 41. (28) Williams, M. C., Natl. Geograjhic M a g . 61, No. 3, “First Over the Roof of the World.” (29) Wrotnowski, A. C., Chcm. Eng. Progr. 53, NO,7, 313-19 (1957).
NEIL H. SHERWOOD Products Application Laboratory, B. F. Goodrich Chemical Co., Avon Lake, Ohio
Binders for Nonwoven Fabrics the past I O years, progress in technology of nonwoven fdbrics has been much slower than for the nonwoven fabrics industry because there has been a ready market for products which can be made rather simply on comparatively inexpensive equipment. A nonwoven fabric is a textilelike product in which the fibers are held together by a bonding material. A nonwoven fabric has two parts-fiber and binder. Hence, the choice of the binder is equally as important as the choice of the fiber. Each construction must be judged separately on the basis of its end use. For certain uses many DURING
binders may be used with many different fibers and web construction. The vario-us binders are summarized with some of their defects and benefits. I
Binder Systems
No attempt is made to list all of the binders used for nonwoven fabrics. Binders may be separated, by their physical state a t the time of application, into the two broad classifications of dry or wet binders. 1. The dry systems are made up of thermoplastic fibers or powders,
2. Wet systems include solutions, of both aqueous and solvent types, as well as polymer dispersions or emulsions. Dry Binders. Attempts have been made to use thermoplastic polymers in powder form for binding nonwoven fabrics. Although some have been prepared commercially, the practice is very limited. The thermoplastic powders are satisfactory for binding, but the problems of distributing the powder into the web and keeping it where it can bind the fibers efficiently make this process unattractive a t the present time. O n the other hand, the use of thermoplastic fibers is practicable and is in VOL. 51, NO. 8
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