Plastics Bonding

Plastics are usually more difficult to bond with adhesives than are metal substrates. Plastic surfaces can be unstable and thermodynamically incompatible with the adhesive. The actual bonding surface may be far different from the expected substrate surface. The plastic part can possess physical properties that will cause excessive stress in the joint. The operating environment can change the adhesive-plastic interface, the base plastic, the adhesive, or all three. 

However, even with these potential difficulties, adhesive bonding can be an easy and reliable method of fastening one type of plastic to itself, to another plastic, or to a nonplastic substrate. Pocius et al. provides an excellent treatise on the use of adhesives in joining plastics.51 

The physical and chemical properties of both the solidified adhesive and the plastic substrate affect the quality of the bonded joint. Major elements of concern are the thermal expansion coefficient, modulus, and glass transition temperature of the substrate relative to the adhesive. Special consideration is also required of polymeric surfaces that can change during normal aging or on exposure to operating environments. 

Significant differences in the thermal expansion coefficient between the substrate and the adhesive can cause severe stress at the interface. This is common when plastics are bonded to metals because of the difference in thermal expansion coefficients between the substrates. Residual stresses are compounded by thermal cycling and low-temperature service. Selection of a resihent adhesive or adjustments in the adhesive s thermal expansion coefficient via fillers or additives can reduce such stress. 

FIGURE 16.3 Typical bond durability data for Ti-6 Al-4 V adherends bonded with an epoxy adhesive and aged at 60°C and 100 percent RH. (a) Crack propagation versus time for the wedge crack propagation test. (b) Applied stress versus time to failure for the lap shear geometry. PF—phosphate fluoride MPF—modified phosphate fluoride DP—PasaJell 109 dry hone LP—PasaJell 107 liquid hone CAA-5—-5% solution CAA-10—10% solution TU—Turco 5578 etch DA—Dapcotreat.50 

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Both RDX and HMX are substantially desensitized by mixing with TNT to form cyclotols (RDX) and octols (HMX) or by coating with waxes, synthetic polymers, and elastomeric biaders. Most of the RDX made ia the United States is converted to Composition B (60% RDX, 40% TNT, 1 part wax added). Composition A5 (RDX 98.5/stearic acid 1.5) and composition C4 (RDX91/nonexplosive plasticizer) account for the next largest uses. HMX is used as a propellant and ia maximum-performance plastic bonded explosives such as PBX 9401 and PBX N5 and the octols (147—150). 

E. James, Development of Plastic Bonded Explosives, UCRL 12439-T, University of California Press, 1965. 

J. R. Wanninger and E. Kleinschmidt, "Pressed Plastic Bonded Charges," in Proceedings of Joint International Symposia on Compatibility of Plastics and Other Materials with Explosives, Propellants and Pyrotechnics, ADPA, New Orleans, La., Apr. 1985. 

For plastic-bonded materials, no clear-cut expression for the coercivity is known. It may be expected that it is rather similar, but with a smaller influence of B. For loosely packed powders, the B influence has become zero and should be multiphed by 0.48 to account for the isotropy (71). In all cases high coercivity is obtained by using small grains with limited plate-like shape, ie, the value of Nis not too high. 

Brazing filler metal is carried on a plastic-bonded tape. ... 

Cell Construction. Nickel—2iac batteries are housed ia molded plastic cell jars of styrene, SAN, or ABS material for maximum weight savings. Nickel electrodes can be of the siatered or pocket type, however, these types are not cost effective and several different types of plastic-bonded nickel electrodes (78—80) have been developed. 

ABS plastic, a polymer consisting of polybutadiene spheroids is dispersed in a continuous phase of poly(styrene—acrylonitrile). The chromic acid attacks the polybutadiene at a much higher rate than the continuous phase. This gives an excellent microroughened surface with superior metal-to-plastic bond strength. A typical recommended formulation consists of 20 vol % sulfuric acid, 420 g/L chromic acid, and 0.1—1.0% of a fluorocarbon wetting agent. The plastic is treated with this formulation for 6—10 min at 60—65°C. 

The excellent adhesion, high cohesion, low shrinkage on cure, absence of volatile solvents and low creep of the resins have led to important applications as adhesives, particularly for metal-to-metal and metal-to-plastics bonding. As with... 

Pocket and tubular electrodes have been described in detail by Falk and Salkind [1]. McBreen has reviewed work on both sintered plate and plastic-bonded electrode technology [9], More recent work is on the use of nickel foams and nickel mats. 

S.E. Smith, Effect of Moisture on the Gelation of Castable Plastic Bonded Explosives ,... 

Crosslinking poly (2,2-dinitropropyl acrylate) in plastic-bonded explosives , US At Energy Comm, UCRL-50434 (1968) CA 70, 39419 (1969)... 

Paraplex Resin-Bonded Explosive. Usually consists of Paraplex P-43/RDX/Al/Styrene monomer/ Lupersol DDM (as a polymerization catalyst) in the following percentages, viz 6.0/65.0/ 20.0/9.0/0.5. Density 1.65g/cc. The material is mixed and polymerized using the usual procedure for polyester resins and Plastic Bonded Expls (see in this Vol)... 

PBX. An acronym for Plastic Bonded Explosive. A term applied to a variety of expl mixts which are characterized by high mechanical strength (above 10,000psi compressive strength), good expl properties (usually > 780Qm/sec deton vel),... 

Plastic-Bonded RDX, Its Preparation By the Slurry Method , Holston Defense Corp, Term, Control No 20-T-16 Series A (PAC 1081) (1953) 8) A.J. Pascazio, The Suitability of a Bare PBX Booster Pellet In The 2.75-Inch HEAT Ml Rocket Head , PATR 2271 (1955) 9) H.W. 

Skaar et al, Development of Plastic-Fiberglas Cased Plastic-Bonded-Explosive Warhead For the 2.0-inch Gimlet Rocket , NOTS 1114, NAVORD 3491 (1955) 12) W. Gordon, Vacuum... 

Plastic-Bonded Explosives At China Lake, California — 14 February 1956 , NOTS 1512, NAVORD 5287, (1956) 15) B.F. Armendt,... 

Qualitative Test of Dynamic Strength of Various Plastic-Bonded And Fiber-Reinforced Explosives , BRL, APG, MR 977 (1956) 16) K.G. 

K.S. Skaar et al, Plastic-Bonded Explosive (PBXN-1) And Its Use In A Fiberglas-Plastic Warhead , NOTS 1341, NAVORD 5007 (1957)... 

Falterman et al, Investigation of Nylon-HMX Plastic-Bonded Explosive , NOTS 1790, NAVORD 5586 (1957) 24) E.M. Fisher et al,... 

Warhead Configuration , PATM 1459 (1964) 40) D.K. Armstrong, A Feasibility Study of The Use of Plastic-Bonded Explosives (PBXN-102) In Mk 80 Series Low-Drag Bombs , NOTS TP 3831, NAVWEPS 8755 (1965) 41) S.B. 

Wright, Granular Explosive Molding Powder , USP 3173817 (1965) CA 62, 12968 (1965) 42) E. James, Development of Plastic Bonded Explosives , Univ of Calif, Rept No UCRL-12439-T (1965) 43) B.A. Stott, Castable... 

Wright, Granulated Crystalline Plastic-Bonded Explosives , USP 3296041 (1967) CA 66, 87227 (1967) 44b) J. Sato, Mechanical... 

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