Rubber toughened

R. Siebert, "Rubber-Modified Thermoset Resins," in C. K. Riew and J. K. GiUham, eds., ACS Advances in Chemistry Series 208, American Chemical Society, Washington, D.C., 1983, p. 179 W. D. Bascom and D. L. Hunston, "Rubber Toughened Plastic," Adv. Chem. Ser. No. 222, American Chemical Society, Washington, D.C., 1989. 

The aim of this chapter is to describe the micro-mechanical processes that occur close to an interface during adhesive or cohesive failure of polymers. Emphasis will be placed on both the nature of the processes that occur and the micromechanical models that have been proposed to describe these processes. The main concern will be processes that occur at size scales ranging from nanometres (molecular dimensions) to a few micrometres. Failure is most commonly controlled by mechanical process that occur within this size range as it is these small scale processes that apply stress on the chain and cause the chain scission or pull-out that is often the basic process of fracture. The situation for elastomeric adhesives on substrates such as skin, glassy polymers or steel is different and will not be considered here but is described in a chapter on tack . Multiphase materials, such as rubber-toughened or semi-crystalline polymers, will not be considered much here as they show a whole range of different micro-mechanical processes initiated by the modulus mismatch between the phases. 

Fig. 2. Morphology model of a core-shell, rubber-toughened epoxy adhesive.

The addition of Vamac B-124 to ethyl cyanoacrylate has a more pronounced effect on peel strength, both at ambient temperature and after thermal exposure. After 24 h at ambient temperature, the peel strength of the rubber-toughened formulation is almost 40% greater than the control formulation A without rubber. After heating the test specimens for 2 h at 121°C, the peel strength of formulation A, is almost non-existent, while that of C has increased significantly, as seen in Fig. 7. 

Interestingly, this same effect has been observed for the addition of a rubber toughening agent to ethyl cyanoacrylate-based adhesives, as was reported previously. The rubber must contain enough latent acid functionality on the polymer backbone or in an additive to inhibit the thermally activated decomposition of the alkyl cyanoacrylate adhesive polymer. 

The important factors that affect the rubber toughening are (1) interfacial adhesion, (2) nature of the matrix, (3) concentration of the rubber phase, and (4) shape and size of the rubber particles. In the PS-XNBR blend containing OPS, due to the reaction between oxazoline groups of OPS and carboxylic groups of XNBR, the interfacial adhesion increases and as a result, the minor rubber phase becomes more dispersed. The immiscible blend needs an optimum interfacial adhesion and particle size for maximum impact property. In PS-XNBR, a very small concentration of OPS provides this optimum interfacial adhesion and particle size. The interfacial adhesion beyond this point does not necessarily result in further toughening. 

J. C. Hedrick, N. M. Patel, and J. E. McGrath, Toughening of Epoxy Resin Networks with Functionalized Engineering Thermoplastics, in Rubber Toughened Plastics, K. Riew (Ed.), American Chemical Society, Washington, DC, 1993. 

Dear, J.P. Combined Modeling and Experimental Studies of Rubber Toughening in Polymers, J. Mater. Set 38, 891-900, 2004. 

A.A. Collyer, Rubber Toughened Engineering Plastics, Chapman Hall, London (1994). 

An increasing variety of automotive parts is being made by thermoforming processes. Many of these products are made from rubber-toughened polypropylene, which are relatively stiff and can withstand a high level of physical abuse over a ivide range of temperatures. When such parts are used in high visibility areas, such as wheel arches, air dams, truck fenders, and... 

We have considerable latitude when it comes to choosing the chemical composition of rubber toughened polystyrene. Suitable unsaturated rubbers include styrene-butadiene copolymers, cis 1,4 polybutadiene, and ethylene-propylene-diene copolymers. Acrylonitrile-butadiene-styrene is a more complex type of block copolymer. It is made by swelling polybutadiene with styrene and acrylonitrile, then initiating copolymerization. This typically takes place in an emulsion polymerization process. 

Rubber toughened polystyrene is widely used in electronic and kitchen appliances. This type of application requires a good balance of stiffness, impact resistance, and ready coloration. Telephones, which are frequently dropped, are an excellent example of the benefits of rubber toughened polystyrene. The high surface gloss that we desire is obtained by minimizing the size of the rubber particles. Larger items, such as canoes, can be thermoformed from extruded sheet. 

In this report we will only consider type 3, i.e. mixtures of a rigid amorphous thermoplast with small amounts of an elastomer which is the underlying principle for all rubber toughened plastics to improve impact behavior. 

In order to obtain a finely sized dispersed phase in the PET matrix, the use of reactive compatibilization has been found to be important. Small dispersed rubber particles and a small interparticle distance are necessary to induce high toughness. For effective rubber toughening of PET, it is important that the rubber domains be less than 3 im in diameter (and preferably less than 1 xm) and that the interparticle distance be between 50-300 nm. 

Figure 14.6 Simplified structure for random ethylene-acrylic ester-glycidyl methacrylate terpolymers which are effective rubber tougheners for PET compounds. The ethylene-acrylic ester segments provide elastomeric properties while the glycidyl methacrylate functionalities enable reactive grafting to the PET matrix via the hydroxyl and carboxyl chain ends of the latter...

Figure 14.7 Schematic highlighting the microstructure of rubber-toughened PET and performance improvements when non-reactive elastomers are blended with reactive elastomers (adapted from Atofina literature entitled Lotader and Lotryl )...

Figure 14.8 Grafting reactions between PET end groups and glycidyl-methacrylate-containing rubber tougheners. This reaction is critical in ensuring that the reactive elastomeric toughener becomes grafted to the PET matrix and forms smaller, uniform domains of a rubber dispersed phase...

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