Rubber impact strength tests

Fig. 3.4. Solid dispersion of rubber particles in a glassy polymer matrix (sample prepared for the notched impact strength test).

An example of this improvement in toughness can be demonstrated by the addition of Vamac B-124, an ethylene/methyl acrylate copolymer from DuPont, to ethyl cyanoacrylate [24-26]. Three model instant adhesive formulations, a control without any polymeric additive (A), a formulation with poly(methyl methacrylate) (PMMA) (B), and a formulation with Vamac B-124 (C), are shown in Table 4. The formulation with PMMA, a thermoplastic which is added to modify viscosity, was included to determine if the addition of any polymer, not only rubbers, could improve the toughness properties of an alkyl cyanoacrylate instant adhesive. To demonstrate an improvement in toughness, the three formulations were tested for impact strength, 180° peel strength, and lapshear adhesive strength on steel specimens, before and after thermal exposure at 121°C. 

Bis(2,3-dibromopropyl) fumarate has been used as a fourth monomer in nitrile rubber- and graft-type ABS materials giving flame-resistant polymers. At least 10% bromine incorporation is required to pass the Underwriters Laboratories Subject 94 test. The graft-type materials fail at 7-10% bromine only because of dripping. Both types pass the ASTM D-635 test with 7% or more bromine. For the impact strength to be equivalent to that of conventional ABS, the fourth monomer must be present in both the rubber and resin phases. Thermal stability is marginal but can be improved with typical PVC stabilizers. 

ABS usually contains about 20wt% rubber, about 25% acrylonitrile, and about 55% styrene, having a Tg value of about 105C, a tensile modulus of 2.5GPa, and an impact strength of about 4 J (12.7 mm)-1 on an Izod test. However, owing to the many variations possible, the properties can vary considerably. As an example, Super ABS can have a notched Izod impact strength of up to 8 J (25 mm)-1. Also some or all of one of the comonomers may be replaced. Methylmethacrylate may replace acrylonitrile, as in MBS and MABS, with improvement in... 

Fig. 23 Flexural impact strengths of /S-modified rubber toughened PP plotted versus the amount of rubber content of the blends and the testing temperature. The arrows indicate samples that did not break. Data taken from Varga [165]...

To design a resin with the property enhancements of AN without the cross-linking problem, it was found that SMA copolymers and terpolymers could be blended with ABS resins to form miscible blends with properties of HHABS. A fundamental look at the miscibility of SMA copolymers with SAN copolymers indicated that the optimum thermodynamic interaction occurs when the AN content of the SAN is nearly equal to the MA content of the SMA [72]. Kim et al. also found low impact strengths at all modifier levels when blending SMA with SAN-g-polybutadiene (GRC = grafted rubber concentrate) [73]. Blends of SMA with SAN and GRC (SAN + GRC = emulsion ABS) exhibited ductility behavior similar to HHABS. The impact strengths of the polymers were 2-5 ft-lb/in, in a notched Izod test at ambient temperature. 

A few plastics which tend to be naturally brittle require an improvement in both their drop (impact) strength and their top loading (compression) strength. In the case of polystyrene, rubber is widely used as an impact modifier. Rigid PVC, particularly when used as a container, may suffer weakness when subjected to, say, a 3 4 foot drop test. Up to 15% of methyl methacrylate butadiene styrene (MBS) copolymer is usually added to improve impact strength. Chlorinated polyethylene has more recently been introduced as a PVC impact modifier. Vinyl acetate is frequently used as a modifier for PVC film. Polythene, LDPE-HOPE can have resistance to stress (environmental stress cracking), improved by the use either of rubber or polyisobutylene. These modifications have not as yet had any pharmaceutical applications. 

LLDPE and amine-terminated butadiene nitrile liquid rubber (ATBN) with di-peroxy initiator into the rubber tire powder. The compounded blends were molded into test specimens. The data showed about 50% better tensile and impact strength after compatibilization [Duhaime and Baker, 1991]. 

Based on the evidence so far, it seems probable that impact strength in rubber-modified plastics depends on the relative importance of crazing and shear yielding induced by the rubber particles,f as weU as on other parameters such as the rubber characteristics (below). As mentioned above, however, extrapolation from low-strain-rate to high-strain-rate tests cannot be made quantitatively. Research into the deformation mechanisms at high strain rates should be fruitful, though difficult to accomplish. 

Fig. 11.26 Impact strength of PA-6/EPR blends as a function of particle size (26 vol.% of EPR rubber notched Izod impact test at 20 °C) the different symbols refer to different manufacturing methods (From Gaymans (1994) reproduced with permission of Springer)...

Copolymers of acrylonitrile and lower acrylates have also been used as thickeners. The proportion of the acrylate in the copolymer was 60-90% by weight the preferred acrylates were the methyl through butyl esters. These authors also tested an extensive list of known and novel thickeners as comparative examples. The latter included nitrile rubber and vinyl acetate-vinyl chloride, methyl methacrylate-butadiene-styrene (MBS), and acrylonitrile-butadiene-styrene (ABS) copolymers. The copolymers of this invention were claimed to provide better stability, higher viscosity, less stringing, and better impact strength than do the thickeners of the prior art. The claims of this patent do not cover the disclosed copolymers. Polyvinyl ethers are another class of cyanoacrylate thickeners which have been disclosed but not claimed. ... 

Fig. 15. Effect of test temperature on the impact strength of PVC specimens containing various notch radii (21). Tb = brittle temperature. To convert kJ/m to fl lbf/in., divide by 2.10. Courtesy of The Plastics and Rubber Institute.

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