1. CHEMICAL BONDING Chemical bonding mainly refers to the application of a liquid based bonding agent to the web. -edana 2. WHY NEED CHEMICAL BINDER? To improved characteristics such as strength, softness, adhesion, firmness, durability, stiffness, fire retardence , hydrophilicity, hydrophobicity, anti-microbial properties, organic compatibility, reduced surface tension, improved dimensional stability and solvent, wash and acid resistance. The required properties can be varied depending on the end-uses. 3. PROPERTIES OF REQUIRED BINDER Strength of nonwoven fabric related to the strength of applied binder Binder to-fibers bond When a soft hand nonwoven fabric desired Strength Adhesion to fibers Flexibility/ handle 4. PROPERTIES OF REQUIRED BINDER To avoid permanent deformation of fabric Some need durability in cleaning process- according to end uses Binder should be stable and not degraded in the fabric during storage and use Elastic recovery Resistance to washing Resistance to aging 5. PROPERTIES OF REQUIRED BINDER Diverse ranges of colors are required, and the colorfastness and yellowing problems should be considered Minimizing the cost is an ongoing requirement Such as Flame resistance, resistance to chemicals, air, oxygen, light, heat, etc. Colour retention Economi- cal Special require- ment 6. HOW BINDERS WORK? Binder application to nonwoven web Removal moisture or solvent Formation of strong bond (binder and web) 7. Film Formation Schematic of film formation (source: http://www.engr.utk.edu/mse/pages/Textiles/Chemical%20Bonding.htm 8. CLASSIFICATIONS OF BINDERS CHEMICAL STRUCTURE FUNCTIONALITY CURING REACTION 1 2 3 9. CLASSIFICATIONS OF BINDERS There are three main kinds of binders: butadiene copolymers, acrylates, and vinyl copolymers. The chemical compositions influence Tg, hardness and softness, hydrophobicity and hydrophilicity, elasticity, aging, and dry tensile strength of binders. The higher the Tg, the higher will be the dry tensile strength of binders. CHEMICAL STRUCTURE 1 10. CLASSIFICATIONS OF BINDERS attached to polymer chains, which influences wet and solvent properties. To modify binder properties, copolymerization with a small amount of monomers with special functionality is performed. The main functionalities in binders are carboxyl and amide side chains. FUNCTIONALITY 2 11. CLASSIFICATIONS OF BINDERS FUNCTIONALITY 2 Carboxyl related to binders containing acrylic acid or methacrylic acid by copolymerization. The binders are crosslinkable since the functional group, carboxylic acid, provides sites for crosslinking reactions. Amide is related to binders containing acrylamide by copolymerization. The amide functionality provides crosslinking sites, and even the binders are self-crosslinkable. 12. CLASSIFICATIONS OF BINDERS CURING REACTION 3 refers to crosslinkability of binders, which is related to reaction with curing resins, crosslinking agents. The most common curing resin is melamine formaldehyde condensate resin involving reaction of n-methylol groups. 13. TYPES OF BINDERS offer the greatest durability, color stability, and dry/wet performance. Acrylic binders have the widest range of fabric hand properties. They can be formulated to vary from very soft (Tg = - 40C) to extremely hard (Tg = 105C). ACRYLIC tough, hydrophobic binders. The resulting textile hand ranges from soft-to-firm (Tg varies from 20C to +105C ).These binders can be used in applications where there is a need for some wet strength without crosslinking. STYRENATED ACRYLICS 14. TYPES OF BINDERS The vinyl acetate binders are firm (Tg = +30C to +40C); however, they are relatively low cost and find extensive use. They offer good dry strength and toughness, but are somewhat hydrophilic and have a tendency to yellow when subjected to heat. VINYL ACETATE (VAC) These binders are more hydrophobic than the straight VAC binders. They provide excellent toughness, flexibility, and better color stability. They are the compromise between VAC and acrylic, and can compete on a cost/performance basis. The hand range is limited to intermediate softness (Tg = - 10C) to a firm hand (Tg = +30C). VINYL ACRYLICS 15. TYPES OF BINDERS These latex binders have a (Tg range of 20C to +115C, which is equivalent to soft ranging to an intermediate textile hand. They exhibit high wet strength, coupled with excellent absorbency. In general, they are less costly than acrylics. They do have a tendency to have more of an odor compared to other binders. They are used primarily in wipes, air-laid pulp fabrics and similar applications. ETHYLENE VINYL ACETATE (EVA) These binders have an excellent combination of flexibility and toughness. When cross-linked, this class of binder is very hydrophobic and durable. They are affected somewhat by heat and light because of their tendency to oxidize. STYRENE- BUTADIENE 16. TYPES OF BINDERS The homopolymer of polyvinyl chloride is a very hard, rigid polymer (Tg = +80C). This polymer must be plasticized to provide flexibility and film-forming properties. As it is a thermoplastic, it performs well in heat and dielectric sealing applications. POLYVINYL CHLORIDE (PVC) have a slightly broader hand range (Tg = 0C to +30C). presence of the chlorine again conveys some flame retardancy. These binders exhibit good acid resistance, fair water resistance, and excellent adhesion to synthetic fibers. There is some tendency to yellow upon aging. ETHYLENE/VINYL CHLORIDE 17. FORMULATION Is an art since many ingredients are involved and many different possibilities exist for different end-uses. Surfactants External cross-linkers Defoamers Repellent agents Salts Thickeners Catalysts Acids and bases Dyes and pigments Fillers Optical brighteners Sewing aids 18. FORMULATION Surfactants : offer improvement in binder adhesion, stability, and ability to be converted into a foam External cross-linkers: provide cross-links with binder polymer to provide improved performance Defoamers: utilized to minimize foam in processing Repellent agents : convey water or oil repellency Salts: added to impart low flame response properties and to convey antistatic properties Thickeners: added to control the rheology of the binder liquid Catalysts: added to facilitate curing and to promote cross-linking Acids and bases: added to control pH of the latex Dyes and pigments: provide color to the binder and fabric 19. ORDER OF FORMULATION Most ingredients Latex binder Thickener Catalyst Some water, dye etc 20. CHEMICAL BONDING PROCESS Saturation Foam Spray Print Powder 21. CHEMICAL BONDING PROCESS Saturation Saturation chemical bonding involves complete immersion of the nonwoven web in a bath containing binder. Excess binder is removed by vacuum or roll pressure. 22. CHEMICAL BONDING PROCESS Saturation For fabric applications which require strength, stiffness, and maximum fiber encapsulation, such as carrier fabrics. Three variations of saturation bonding exist: screen, dip/squeeze, and size-press. Screen saturation is used for medium-weight nonwovens, such as interlinings. Dip/squeeze saturation is used for web structures with strength sufficient to withstand immersion without support, such as spunbonds. Size-press saturation is used in high speed processes, such as wet-laid nonwovens. 23. CHEMICAL BONDING PROCESS Saturation The amount of binder taken up by the nonwoven depends on the basis weight of the nonwoven, length of time spent in the bath, wettability of the fibres and nip pressure. Drying and curing may be carried out on steam- heated drying cans or in thru-air ovens or perforated- drum dryers. 24. CHEMICAL BONDING PROCESS Foam Foam bonding is a means to apply binder at low water and high binder-solids concentration levels. require less energy in drying, since less water is used. 25. CHEMICAL BONDING PROCESS Foam 26. CHEMICAL BONDING PROCESS Spray binders are sprayed onto moving webs. used for fabric applications that which require the maintenance of highloft or bulk, such as fiberfill and air-laid pulp wipes. 27. CHEMICAL BONDING PROCESS Print applies binder only in predetermined areas. It is used for fabric applications that require a part of the area of the fabric to be binder-free, such as wipes and coverstocks. 28. CHEMICAL BONDING PROCESS Powder Adhesive powder of thermoplastic polymers is applied onto webs by heat and pressure. Polyesters and polyolefins with low Tg's and molecular weight can be used as powder binders. 29. METHODS OF DRYING 30. APPLICATIONS Wipes and towels Medical nonwovens Roofing products Apparel interlinings Filter media Coating substrates Automotive trim Carrier fabrics Bedding products (high loft) Furniture applications (high loft) Apparel Pillows (high loft)