Starch adhesive, or glues were first used in large scale industrial application approximately in the 1910s. The chief kinds on the marked today are made from cornstarch, tapioca flour, wheat flour, and potato starch. Starch adhesive may be applied cold chief advantages over animal glues, although most of them have the disadvantage of less strength and lower water resistance than animal glues. Starch adhesives are less costly than synthetic resin adhesives. Native starch is widely employed as an adhesive for veneer, plywood and corrugated cartons and laminated boards where water resistance is not important. Incorporated with 5 to 15% resins, such as urea formaldehyde, it is used for cartons where water resistance is important. Through enzyme conversions it is a base for many liquid adhesives. Native starch is the raw material for hydration to dextrin and British gums; these are modified glues for glass, metal, and wood, cartoons, laminated broads, and padding glues. Tapioca dextrin is the adhesive used for postage stamps.
Native starches are prepared from grains or roots. Dextrin is made by heating a dry starch with dilute acid, causing partial hydration. British gums result from heating native starch with small amount of catalysts; they are gummier and more adhesive that dextrin. In the manufacture of starch adhesives, dextrin, British gums, or starch are rarely used alone. Many chemicals may be admixed as indicated. Borax increases viscosity, gum-mines, rate of tack, and speed of production.
Starch adhesive mostly used for paper glue, this starch adhesive price vary some of them are expensive depend on the anti-spoil substance and concentration of these chemical they use, some of cheap product very easy to spoil because they use low concentration of this substance.
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Wednesday, February 3, 2010
Starch Adhesives
Tuesday, January 26, 2010
Thermoplastic Resin Adhesives
A thermoplastic resin is one which melts or softens on heating and rehardens o cooling without (within certain temperature limits) undergoing any chemical change. At temperature above the melting point an irreversible chemical change such as depolymerisation or oxidative degradation may take place.
Thursday, January 21, 2010
Miscellaneous Thermosetting Adhesives
Thermosetting adhesive are adhesive that can’t be reuse after the limitation condition of these adhesive is over. The limitation of thermosetting adhesive is called as curing, curing condition is affected by chemicals, temperature and time, so even the adhesive is on cold condition below curing temperature but keep too long then adhesive also has cured. If the adhesive has cured then this adhesive can’t use anymore.
Many kind of thermosetting adhesive are describe here:
Silicone Adhesives:
Certain silicone adhesives are thermosetting. They are used mainly for bonding silicone rubber, an application in which crosslinking must be infrequent if the adhesives is to have a rubbery nature after curing.
The silicones is usually dimethyl polysiloxane, which is normally cured by heating with a silicic acid ester and catalyst. Certain form of the adhesive are capable of being cured at room temperature, and of giving good resistance to heat.
Although the bond strength of organo-silicon resins is normally not high, it can be improved by incorporating an epoxide, polyester or phenolic resin, additions which might be expected to reduce hot strength and thermal stability.
Furane Adhesives
These adhesives contain the chemical group known as a furane ring. They include the condensation polymers of furfraldehyde (“furfural”), and furfuryl alcohol. These furane compounds polymerise on addition of an acid, passing through a liquid resinous state, and have adhesive properties. Furfuryl alcohol imparts special properties to urea, phenolic and epoxy resins. Furane resin adhesive are claimed to effectively bond thermoplastic materials and rubbers, also phenolic laminates, with which it is said that adhesion to smooth surface is better than to sanded surfaces.
Thermosetting soluble Nylons
Adhesives utilizing alcohol soluble nylons for example methoxy nylon, can be rendered substantially infusible and insoluble especially by heating in the presence of an acid catalyst, and are claimed to give high adhesion to wood even alter immersion of the joints in boiling water.
Thermosetting Acrylic resins
Considerable interest has been aroused in the various ways of crosslinking acrylic monomers and polymers, e.g. by methylol or epoxide groups. The interest has been largely in coating applications with emphasis on high adhesion but it is felt that interest will develop in the use of these polymers as adhesives.
A number of papers on thermosetting acrylic resins were read at the 138th Meeting of the American Chemical Society, and work on them has also been reported from Japan.
Organic/Inorganic Adhesives
Although the intention is to embrace in this article only those adhesive that are organic and synthetic, since important development are taking place with inorganic adhesives, a reference to organic/inorganic adhesive system seems justified. Under development and of potential interest is the condensation polymer of cyclic phosphonitrile chloride and a polyhydric aromatic, compound, which when blended and polyhydric aromatic compound, which when blended with synthetic elastomers has possibilities as an aircraft structural adhesive for operation at 200 o – 315 oC. More particularly, cyclic phosphonitrilic chlorides, principally the trimer and tetramer, are condensed with hydroquinone or resorcinol, and adhesives produced either by blending with a polar rubber such as polycrylonitrile rubber, or by reacting with polyepoxides, polyisocyanates or polyester.
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