Adhesives, natural base polymers

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. 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

Natural rubber adhesives were traditionally used as contact adhesives. However, synthetic polymers are more generally used today. Polychloroprene adhesives are the most common contact adhesives based on synthetic rubber, although recently some have been displaced by polyurethane and acrylic polymers [2]. 

Recently, Caster et al. described the surface modification of multifilament fibers such as nylon or Kevlar [70]. Coating techniques using preformed ROMP-based polymers and process contact metathesis polymerization (CMP), initially described by Grubbs et al. [71], were both used. The latter involves a procedure where the initiator is physisorbed onto the surface of a substrate and fed with a ROMP-active monomer that finally encapsulates the substrate. These modified fibers showed improved adhesion to natural rubber elastomers. 

Epoxy resins are not ideal adhesives in their natural form so they are mixed with materials to improve and enhance their properties and, thereby, make them more useful in a variety of applications. This process is called compounding or formulating. Compounding is the combining of a base epoxy resin with curing agents, modifiers, additives, reinforcement, fillers, and other polymers to make the base polymer perform better, cost less, and process more easily. 

The development of useful adhesive compositions based on the interaction of isocyanate resins with natural polymers such as lignin, proteins, and carbohydrates. 

Plastic products are based on polymers, materials which are omnipresent in nature (cellulose, proteins) or in synthetic form (textiles, adhesives). In contrast to metals and other construction materials, polymers are organic materials with properties that depend strongly upon the environment in which they exist. A prerequisite to fully understand the life cycle of a plastic product is to examine the structure and nature of polymers. 

Water-based Polymer Isocyanate (JIS name [7]) or Emulsion Polymer Isocyanate (EPI) adhesives were developed in Japan by Kuraray Co., Ltd, Koyo Sango Co., Ltd and Asahi Plywood Co., Ltd in the early 1970 s [8]. The driving forces were to establish new markets for poly(vinyl alcohol) (PVA) and to develop alternatives to formaldehyde-based wood adhesives. The technology was patented [9], and thereafter licensed to different companies worldwide [8]. The licenses led to introduction of EPI adhesives into Europe, North America and Oceania. Since the EPI adhesives are of Japanese origin, their popularity is naturally concentrated in the Asian markets. Non-Asian consumption is growing, but the market for this adhesive type is still limited. 

Lithium ion cells serve the smaU-sealed rechargeable battery market and compete mainly with the Ni-Cd and Ni-MH cells for the various applications. The Li-Ion cells are available in cylindrical and prismatic format as well as flat plate constructions. The cylindrical and prismatic constructions use a spiral-wrap cell core where the ceU case maintains pressure to hold and maintain compression on the anode, separator, and cathode. The lighter-weight polymer constructions utilize the adhesive nature of a polymer/laminate-based electrolyte to bond the anode to the cathode. 

Fujita M., Kajiyama M., Takemura A., Ono H., Mizumachi H., Hayashi S., Effects of miscibihty on probe tack of natural-rubber-based pressure-sensitive adhesives, J. Appl. Polym. ScL, 70(4), 1998, 771-776. 

It has also been found that moisture absorbance of the natural fibre-polymer composite can be prevented if the fibre-matrix adhesion is optimized [15, 24]. Indeed, whereas composites based on standard PP and cellulosic fibres displayed high water content at the interphase, due to the presence of microcavities, the encapsulation of the fibres with MAPP decreased the water sensitivity of the composites in terms of both the water uptake and its diffusion coefficient [25], as shown in Fig. 19.9. 

These materials are based on synthetic or naturally occurring polymers. They have superior toughness and elongation. Elastomeric adhesives may... 

The design is based on the maximum shear stress which occurs at the end of the joint. However, the shear stress decreases rapidly within a short distance from the Joint end. It should also be noted that this peak stress occurs immediately after a load is applied, but owing to the viscoelastic nature of polymer adhesives, this peak flattens in the course of time. This behaviour is shown in Figure 5.32, based on the work of Groth (reference 5.36). This viscous behaviour further increases the margin of safety in the design approach. 

Another important aspect is the moisture content of natural fibres. These fibres are hydrophilic and absorb water. The moisture content can be as high as 20%, but in most cases it will be in the range of 5-10%. Lack of good interfacial adhesion with the polymer phase, due to the inherently poor compatibility and the ability of the hydrophilic cellulose fibres to disperse with the hydrophobic resins, makes the use of cellulose-based fibre-reinforced composites less attractive. During processing, the presence of water can create voids in the matrix and also lead to a poor adhesion of the fibres with the hydrophobic resin. The hydrophilic nature of natural fibres can be a problem in the finished composites as well. 

Natural rubber (NR) is the base polymer for many Rubber-based adhesives. This article is designed to supplement with specific information the more general treatment given in Rubber-based adhesives compounding and Rubber-based adhesives typical characteristics. 

Manufacture and compounding The majority of organic solvent-based adhesives are based on rubbery polymers, the main ones being natural rubber, polychloroprene, butadiene-acrylonitrile, styrene-butadiene and polyisobutylene. Traditionally, the rubber was placed in a heavy-duty mixer and solvent was added slowly till a smooth solution was formed. In some cases, the rubber was milled beforehand to reduce viscosity and produce smoother solutions. Nowadays, it is possible to obtain some grades of material that only require stirring in a comparatively simple chums. 

Base polymers are classified as being either thermoplastic or thermosetting. Thermoplastic polymers are polymers that melt when heated and then resolidify when cooled. Thermoset polymers are those that do not melt when heated, but at sufficiently high temperatures they exhibit creep under load and even decompose. Polymers gain their thermosetting nature by a process called cross-linking, where the adhesive molecules chemically react with one another to form a three-dimensional network. The... 

---