Adhesive softener

Simple Solvent Wipe Test. The simplest test method to determine the extent of cure is to rub a cotton swab that has been soaked in a suitable solvent (e.g., methyl ethyl ketone) against the surface of the cured adhesive. If the adhesive softens, it is very far from a fully cured condition, and the degree of softness is a very gross indication of the degree of cure. 

Figure 2.6 The effect of temperature on the stress/strain distribution within a lap joint. As the temperature rises and the adhesive softens and the initial load pattern changes. Greater distortion at the edge of the joint distributes load by transferring it to the central areas. As more of the inner area becomes stressed with continued temperature rise, the adhesive ultimately begins to creep. The rate increases as conditions become more extreme. Failure is imminent in curve b. (See also Figure 2.7.)...

In the past a glycerinated gelatin base was often used for pessaries. Glycerinated gelatin pessaries provide at body temperature a good adhesive, softened mass and they are tolerated weU. Because of many disadvantages however (see Sect. 11.4.3), this base is not used anymore in Dutch pharmacies. 

Softening Temp or Soft. Temp. Thermoplastic Hot-Melts Temperature, or range, when the adhesive softens, in C... 

Thermoplastic adhesives soften and melt when heated (provided that they do not decompose). In other words, they do not cross-link during cure. These adhesives are single-component and harden upon cooling by evaporation of a solvent or water vehicle. They have poor creep resistance, fair peel strength, and are used mostly in unstressed joints and designs with caps, overlaps, and stiffeners. The most common application is to bond nonmetallic materials such as wood, leather, cork, and paper.In general, thermoplastic adhesives are not used for structural applications or at temperatures above 66°C (150°F). Thermoplastic adhesives includeit t ... 

Adhesives can also stress crack or craze certain plastics and this can also indnce premature failure of the substrate. This generally happens whilst the adhesive is uncured and the plastic part is pre-stressed due to abrupt changes of section. The liquid adhesive softens and weakens the plastic leading to the formation of cracks and the liqnid adhesive then penetrates these cracks causing fnrther damage. With fast-curing adhesives, this is less likely to occur as once the adhesive has cured it is essentially a thermoset plastic (or thermoplastic) itself and is therefore inert. Amorphons thermoplastics are more prone to stress cracking than others and so it is important therefore to ensure that the adhesive is compatible with the substrate. 

Polymers are characteri2ed as thermosetting and thermoplastic with respect to the methods by which they are joined. Thermosetting polymers are permanently hard and do not soften upon the apphcation of heat they are joined by mechanical fasteners and adhesives. Several methods have been devised to join thermoplastic polymers, as weU as thermoplastic composite materials, which soften upon heating. 

Flaking paint is treated by infusion of an adhesive in the areas where needed, followed by resetting the flakes on the substrate the softening of the paint needed to bend it back is effected through solvent action or heat. Losses can only be filled and inpainted. Inpainting may also be necessary when cracks become so wide as to seriously affect the visual appearance of the painting. 

G-5—G-9 Aromatic Modified Aliphatic Petroleum Resins. Compatibihty with base polymers is an essential aspect of hydrocarbon resins in whatever appHcation they are used. As an example, piperylene—2-methyl-2-butene based resins are substantially inadequate in enhancing the tack of 1,3-butadiene—styrene based random and block copolymers in pressure sensitive adhesive appHcations. The copolymerization of a-methylstyrene with piperylenes effectively enhances the tack properties of styrene—butadiene copolymers and styrene—isoprene copolymers in adhesive appHcations (40,41). Introduction of aromaticity into hydrocarbon resins serves to increase the solubiHty parameter of resins, resulting in improved compatibiHty with base polymers. However, the nature of the aromatic monomer also serves as a handle for molecular weight and softening point control. 

Although most aromatic modified C-5 resins are typically higher softening point resins, certain appHcations, such as adhesives, require lower softening points. Copolymerization of a C-8—C-10 vinyl aromatic fraction with piperylenes in the presence of a C-4—C-8 mono-olefin chain-transfer stream yields resins with softening points ranging from 0—40°C (44). A particular advantage of these Hquid resins is the fact that they eliminate the need for plasticizers or oils in some pressure sensitive adhesive appHcations. 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

Pontia.na.k. This resin is a copal and is similar to the alcohol-soluble Manilas. It is partially fossilized, so it melts at a higher temperature. Softening points range from 99—135°C, and acid numbers from about 112—120. Pontianak [9000-14-0] is used in specialty coatings and adhesives. 

Mastic. Most commercial mastic [61789-92-2] is collected on the Greek island of Chios, near the Turkish coast. It is a soft resin with a softening point of 55°C. It has an acid number of 50—70 and a saponification number of 62—90. It is soluble in alcohols and aryl hydrocarbons. Mastic is used in wood coatings, lacquers, adhesives, and printing inks. 

---