Bonding EPDM

Standard cyanoacrylates do not bond particularly well to EPDM but certain grades of ethyl-based cyanoacrylates have been specially developed for bonding to EPDM. One such grade is Loctite 406, an ethyl cyanoacrylate and this is used to attach an EPDM rubber edge strip to an EPDM conveyor belt to prevent potash from falling off the production line. 

The same product is used for mitre bonding of EPDM rubber seals for automotive doors and windows. The cyanoacrylate produces high strength invisible bonds in seconds. 

For fixing an EPDM rubber seal to a polyvinyl chloride (PVC) beer pump mechanism the cyanoacrylate must not only produce a reliable bond but also be approved for use with potable water. The cyanoacrylate, once fully cured, is essentially an inert plastic and many grades are approved for potable water as well as for medical applications (see Section 10.11.4). 

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Bonding EPDM membrane with a cold adhesive is appropriate when structures are too light or roofs are steep with curves or sharp corners. Before application of the adhesive, the surface should be made smooth, clean, free from dust, oil, grease or other contaminates which may affect the adherence. This method is economical to cover all types of complex structures even on vertical walls. The sheets can be adhered to smooth surfaces of cement concrete, wood and metallic surfaces made of steel, aluminium, etc. An adhesive bonding system is also suitable for use on rigid insulation and old concrete roofing. 

An adhesive consisting of an epoxy resin, a medium high acrylonitrile rubber, and Pb, Cu, Ni, Pd or Co compound fillers was used to bond EPDM vulcanizates. Peel strengths of 22.5 kg/20 mm after a 1 hour at 100 C cure were obtained. Another adhesive composition involving a blend of carboxylated nitrile rubber, epoxy resin and a reactive metal filler has been described for bonding EPDM vulcanizates or EPDM rubber-nitrile or butyl rubber blends. 

The use of TAG as a curing agent continues to grow for polyolefins and olefin copolymer plastics and mbbers. Examples include polyethylene (109), chlorosulfonated polyethylene (110), polypropylene (111), ethylene—vinyl acetate (112), ethylene—propylene copolymer (113), acrylonitrile copolymers (114), and methylstyrene polymers (115). In ethylene—propylene copolymer mbber compositions. TAG has been used for injection molding of fenders (116). Unsaturated elastomers, such as EPDM, cross link with TAG by hydrogen abstraction and addition to double bonds in the presence of peroxyketal catalysts (117) (see Elastol rs, synthetic). 

Ozonc-rcsjstant elastomers which have no unsaturation are an exceUent choice when their physical properties suit the appHcation, for example, polyacrylates, polysulfides, siHcones, polyesters, and chlorosulfonated polyethylene (38). Such polymers are also used where high ozone concentrations are encountered. Elastomers with pendant, but not backbone, unsaturation are likewise ozone-resistant. Elastomers of this type are the ethylene—propylene—diene (EPDM) mbbers, which possess a weathering resistance that is not dependent on environmentally sensitive stabilizers. Other elastomers, such as butyl mbber (HR) with low double-bond content, are fairly resistant to ozone. As unsaturation increases, ozone resistance decreases. Chloroprene mbber (CR) is also quite ozone-resistant. 

Elastomers. Ethylene—propylene terpolymer (diene monomer) elastomers (EPDM) use a variety of third monomers during polymerization (see Elastomers, ethyiene-propylene-diene rubber). Ethyhdenenorbomene (ENB) is the most important of these monomers and requires dicyclopentadiene as a precursor. ENB is synthesized in a two step preparation, ie, a Diels-Alder reaction of CPD (via cracking of DCPD) with butadiene to yield 5-vinylbicyclo[2.2.1]-hept-2-ene [3048-64-4] (7) where the external double bond is then isomerized catalyticaHy toward the ring yielding 5-ethyhdenebicyclo[2.2.1]-hept-2-ene [16219-75-3] (ENB) (8) (60). 

In the EPDM polymerization, the double bond of the bicycloheptene ring system of ENB is involved. The amount of third monomers used in any polymerization varies, but it is usually present at less than 10 wt% of the finished polymer. 

Substituted and unsubstituted bi- or multi-cyclic mono-, di- or multi-olefins, i.e. containing condensed rings at least one of which contains a double bond. Norbomene is homopolymerised commercially whilst, as previously mentioned, ethylidenenorbomene and dicyclopentadiene are used as the cure site monomer in EPDM rubbers. 

Whilst the ASA materials are of European origin, the AES polymers have been developed in Japan and the US. The rubber used is an ethylene-propylene terpolymer rubber of the EPDM type (see Chapter 11) which has a small amount of a diene monomer in the polymerisation recipe. The residual double bonds that exist in the polymer are important in enabling grafting with styrene and acrylonitrile. The blends are claimed to exhibit very good weathering resistance but to be otherwise similar to ABS. 

Zinc salt of maleated EPDM rubber in the presence of stearic acid and zinc stearate behaves as a thermoplastic elastomer, which can be reinforced by the incorporation of precipitated silica filler. It is believed that besides the dispersive type of forces operative in the interaction between the backbone chains and the filler particles, the ionic domains in the polymer interact strongly with the polar sites on the filler surface through formation of hydrogen bonded structures. 

FIGURE 11.7 Inter-mbber bonding scheme for blending ethylene-propylene-diene monomer (EPDM) with nitrile mbber with a cross-linking agent. (From Naskar, M., Debnath, S.C., and Basu, D.K., Rubber Chem. TechnoL, 75, 309, 2002.)... 

Adhesion of melamine fiber to rubber matrices Rajeev et al. found that the dry bonding system consisting of resorcinol, hexamethylene tetramine and hydrated silica effectively reinforces EPDM [64], maleated EPDM [118], and nitrile mbber matrices [119]. They observed increase in tensile... 

Mechanical Properties and Cure Rate Index of the Mixes—Role of Dry Bonding System on the Reinforcement of Ethylene-Propylene-Diene Monomer (EPDM) Rubber with Melamine Fiber ... 

The polarity of the matrix helps to improve the adhesion between melamine fiber and rubber because of the polar-polar interaction between the fiber and the matrix [118]. The presence of fiber in the absence of bonding system showed only marginal improvement in tensile strength (from 1.5 to 1.6 MPa) in the case of EPDM rubber-melamine hber composites. However, maleated EPDM rubber-melamine hber composites showed more than 50% improvement in tensile strength in the absence of the bonding system [118]. This is because of the presence of maleic anhydride groups, which imparts polarity to the mbber. 

FIGURE 12.7 Monsanto rheometric curves of ethylene-propylene-diene monomer (EPDM) rubber-melamine fiber composites [64]. A, gum compound B, compound containing 30 phr melamine fiber but no dry bonding system and C, compound containing both dry bonding system and 30 phr melamine fiber. (From Rajeev, R.S., Bhowmick, A.K., De, S.K., Kao, G.J.P., and Bandyopadhyay, S., Polym. Compos., 23, 574, 2002. With permission.)... 

FIGURE 12.10 Tapping mode atomic force microscopy (AFM) images of the section analyzes of ethylene-propylene-diene monomer (EPDM) rubber-melamine fiber composites. A, composite containing no dry bonding system B, composite containing resorcinol, hexamine, and silica in the concentrations 5, 3, and 15 phr, respectively. 

The reaction of ozone with olefinic compounds is very rapid. Substiments on the double bond, which donate electrons, increase the rate of reaction, while electron-withdrawing substituents slow the reaction down. Thus, the rate of reaction with ozone decreases as follows polyisoprene > polybutadiene > polychloroprene [48]. The effect of substiments on the double bond is clearly demonstrated in Tables 15.2 and 15.3. Rubbers that contain only pendant double bonds such as EPDM do not cleave since the double bond is not in the polymer backbone. 

When an EPDM elastomer was examined, its tack was so low that no permanent cured mbber-to-rubber bond formed and the peel sample separated cleanly during test, at very low separation forces. No GD stage was necessary. 

EPDM backbone, together with the carbonyl and ether groups generated on the rubber itself causes the carbonyl and ether absorptions to increase. The absorption at 1630 cm of the fraw -vinylene bonds of TMPTA is mainly due to the grafting of TMPTA onto EPDM and partly due to the formation of vinylidene bonds at the chain ends on irradiation. The absorptions at 1460 and 1379 cm due to >CH2 scissoring vibration and —CH3 stretching vibration, respectively, result from the rubber and the grafted TMPTA. 

For the EPDM/NR joint, the modification of the EPDM rubber increases its cure compatibility with NR. This, thus, increases with radiation dose up to 50 kGy beyond which a drop in the absorbance values due to predominant chain scission of the rubber also lowers the bond strength. Besides, interdiffusion of the mbber molecules across the interface also contributes to the formation of the bond. 

Abraham et al. were the first ones to propose saturating commercially available microporous polyolefin separators (e.g., Celgard) with a solution of lithium salt in a photopolymerizable monomer and a nonvolatile electrolyte solvent. The resulting batteries exhibited a low discharge rate capability due to the significant occlusion of the pores with the polymer binder and the low ionic conductivity of this plasticized electrolyte system. Dasgupta and Ja-cobs patented several variants of the process for the fabrication of bonded-electrode lithium-ion batteries, in which a microporous separator and electrode were coated with a liquid electrolyte solution, such as ethylene—propylenediene (EPDM) copolymer, and then bonded under elevated temperature and pressure conditions. This method required that the whole cell assembling process be carried out under scrupulously anhydrous conditions, which made it very difficult and expensive. 

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