Solvent cementing

The information given in this brief chapter covers plastic foams, both thermoplastic and thermosetting, and elastomeric foams, although very little discussion is given in the latter subject. 

Most thermoplastic foams can be solvent cemented. However, some solvent cements will collapse thermoplastic foams. The best way to determine if such a problem exists is to try it. In cases where the foam collapses due to softening of the foam cell walls it is desirable to use water-based adhesives based on SBR or polyvinyl acetate, or 100%-solids adhesives. In general, the relatively amorphous thermoplastics, such as the cellulosics, polycarbonate, and polystyrene are easier to solvent cement than the crystalline materials, but there are exceptions. 

When two dissimilar plastic foams are to be joined, which is rarely done, adhesive bonding is generally preferable because of solvent and polymer incompatibility problems. Solvents used to cement plastics should be chosen with approximately the same solubility parameter (5) as the plastic to be bonded. The solubility parameter is the square root of the cohesive energy density (CED) of the liquid solvent or polymer. CEDs of organic chemicals are primarily derived from the heat of vaporization and molecular volume of the molecules, and are expressed as calories per cubic centimeter (cal/cm ). Literature sources provide data on 6 s of a number of plastics and resins (2) (3) (4). 

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Joining NonmetaUic Pipe Thermoplastic piping may be joined by a qiiahfied hot-gas welding procedure, a qnalined solvent-cement procedure, or by a qualified heat-fusion procedure. The general welding and heat-fiision procedures are described in ASTM D-2657 and solvent-cement procedures in ASTM D-2855. Two other techniques, for flared joints and elastomeric-sealed joints, are described in ASTM D-3140 and D-3139, respectively. 

E.I. Du Pont de Nemours, Colloidal stable solvent cement compositions comprising chloro-prene polymers, phenolic resins and polyisocyanate, U.S. Patent 3,318,834, 9 May, 1967. 

Beck MH, King CM Allergic contact dermatitis to epichlorohydrin in a solvent cement. Contaa Derm 9 315, 1983... 

Polyvinyl Chloride Polyvinyl chloride (PVC) pipe and tnbing are available with socket fittings for solvent-cementecf joints in sizes 24 in and smaller. PVC with gasketed bell and spigot joints is available in sizes 4 through 48 in. Chlorinated polyvinyl chloride (CPVC) pipe and tubing are available with socket fittings for solvent-cemented joints in sizes 4 in and smaller. PVC and CPVC are snitable... 

Solvent-cemented joints (Fig. 10-150) are standard, but screwed joints are sometimes used with Schedule 80 pipe. Cemented joints must not be disturbed for 5 min and achieve full strength in 1 day. A wide variety of valve types are available in PVC and CPVC. 

Joining Nonmetallic Pipe All joints should be made in accordance with procedures complying with the manufacturer s recommendations and code requirements. General welding and heat fusion procedures are described in ASTM D-2657. ASTM D2855 describes general solvent-cementing procedures. 

The method of fabrication for plastic items is influenced by whether or not one is dealing with a thermoplastic or a thermosetting plastic. In general, the first group may be heat-sealed, heat-molded, and solvent-cemented, but these possibilities are not available for the thermosetting resins. Both groups generally can be machined. 

As mentioned earlier, many thermoplastic materials dissolve or become tacky in the presence of a solvent, and this provides the basis of solvent cementing. The edges to be joined should be well mated one of the edges is then soaked for about 5 min in the solvent. The part is removed from the solvent, and excess liquid is allowed to drip off. While still damp, the part and its mate are lightly... 

Acrylonitrile-Butadiene-Styrene (ABS). ABS plastics are derived from acrylonitrile, butadiene, and styrene. ABS materials have a good balance of physical properties. There are many ABS modifications and many blends of ABS with other thermoplastics that can affect adhesion properties. ABS resin can be bonded to itself and to other materials with adhesives, by solvent cementing, or by thermal welding. 

Cellulosics are normally solvent-cemented unless they are to be joined to another substrate. In these cases, conventional adhesive bonding is employed. Polyurethane, epoxy, and cyanoacrylate adhesives are commonly used to bond cellulosics. Surface treatment generally consists of solvent cleaning and abrasion. Cellulosics can be stress-cracked by uncured cyanoacrylate adhesives and some components of acrylic adhesives. A recommended surface cleaner is isopropyl alcohol. 

Chlorinated Polyether. This thermoplastic resists most solvents and is attacked only by nitric acid and fuming sulfuric acids. Thus, it is not capable of being solvent-cemented. Chlorinated polyether parts can be bonded with epoxy, polyurethane, and polysulfide-epoxy adhesives after treatment with a hot chromic acid solution. Tensile shear strength of 1270 psi has been achieved with an epoxy-polysulfide adhesive. 

Because of their high thermal stability and excellent resistance to solvent, fluorocarbons cannot be joined by solvent cementing, and they are very difficult to join by thermal welding methods. Because of their inertness and low surface energy, they also tend to be difficult materials to join by adhesive bonding. Surface treatment is necessary for any practical bond strength to the fluorocarbon parts. 

Because of their excellent chemical resistance, polyolefins are impossible to join by solvent cementing. Because of their very low surface energy, polyolefins can only be adhesively bonded after surface treatment processes. The most common way of joining polyolefins is by thermal welding techniques. 

Polyethylene terephthalate cannot be solvent-cemented or heat-welded. Adhesives are the prime way of joining PET to itself and to other substrates. Only solvent cleaning of PET surfaces is recommended as a surface treatment. The linear film of polyethylene terephthalate (Mylar) provides a surface that can be pretreated by alkaline etching or plasma for maximum adhesion, but often a special treatment such as this is not necessary. An adhesive for linear polyester has been developed from a partially amidized acid from a secondary amine, reacted at less than stoichiometric with a DGEB A epoxy resin, and cured with a dihydrazide.72... 

Polystyrene is ordinarily bonded to itself by solvent cementing, although conventional adhesive bonding, thermal welding, and electromagnetic bonding have been used. When polystyrene is bonded to other surfaces, conventional adhesive bonding is usually employed. 

Adhesives recommended for polyphenylene sulfide include epoxies, and urethanes. Joint strengths in excess of 1000 psi have been reported for abraded and solvent-cleaned surfaces. Somewhat better adhesion has been reported for machined surfaces. The high heat and chemical resistance of polyphenylene sulfide plastics makes them inappropriate for either solvent cementing or heat welding. 

Abolins, V., and Eckert, J., Adhesive Bonding and Solvent Cementing of Polyphenylene Oxide, ... 

Literature continues to be rather extensive on this subject since the 1930s. A summarization is provided in this section. Products fabricated include sheets, films, rods and tubes, and embedment. Acrylic castings usually consist of polymethyl methacrylate (PMMA) or copolymers of this ester as the major component with small amounts of other monomers to modify the properties (Chapter 2). Adding acrylates or higher methacrylates lowers the heat deflection temperature and hardness and improves thermoformability and solvent cementing capability, with some loss in resistance to weathering. Dimethacrylates or other crosslinking monomers increase the resistance to solvents and moisture. 

Different joining techniques are used to fabricate PVC into the finished article. All welding techniques involve the application or generation of heat to soften the material whilst pressure is applied simultaneously. Solvent cement jointing relies on softening/swelling of the material. 

PP, PVDF, and PE are not jointed using solvent cements, but the weld regions contain relatively high levels of intrinsic stress caused by the thermal fusion process. Chemical stress cracking could occur at these welds if exposed to certain chemicals. When performing material compatibility tests for any... 

Acetal Homopolymer (DELRIN ) In general, solvent cements are relatively ineffective with DELRIN , a highly crystalline polymer. Methylene chloride, methylene chloride mixed with ethylene chloride, and DELRIN in methylene chloride have been used, however (6). 

Acetal Copolymer (CELCON ) As with DELRIN , this is a highly crystalline polymer with excellent solvent resistance. It is somewhat more amenable to solvent cementing than the homopolymer, however. The solvent cement recommended by the manufacturer, Hoechst Celanese, is hexafluoroacetone sesquihydrate, available from Allied Signal, Inc. This solvent is a severe eye and skin irritant, however, and should be handled with care (7). 

Polycarbonate Solvent cementing is the most common method of bonding polycarbonate. Bonding can be carried out with specific solvents, mixtures of solvents, and mixtures of polycarbonate and solvents. Methylene chloride, when used by itself, has an extremely fast evaporation rate and is recommended for fast assembly of polycarbonate parts. A solution of 1-5% polycarbonate resin in methylene chloride has a decreased evaporation rate. Parts bonded with methylene chloride are usable at elevated temperatures after approximately 48 hours, depending on the bonding area. Ethylene dichloride is also used (5). 

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