Stress crack resistance, environmental

Environmental stress crack resistance (ESCR) is an important property for many applications because it estimates the service life of polyethylene in any particular application. As pointed out by A. Lustiger [32], the term Environmental Stress Cracking was defined in 1959 by J.R Howard to 

The addition of crosslinking agents such as organic peroxides to polyethylene has also provided a method to alter the polyethylene structure during the fabrication process in order to provide a material that improves ESCR for many applications. Crosslinked polyethylene is an excellent container for gasoline and has completely replaced the metal-based gasoline container that was common many years ago. 

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Resistance to Chemical Environments and Solubility. As a rule, amorphous plastics are susceptible, to various degrees, to cracking by certain chemical environments when the plastic material is placed under stress. The phenomenon is referred to as environmental stress cracking (ESC) and the resistance of the polymer to failure by this mode is known as environmental stress cracking resistance (ESCR). The tendency of a polymer to undergo ESC depends on several factors, the most important of which are appHed stress, temperature, and the concentration of the aggressive species. 

For reasons that are not fiiUy understood, PPSF exhibits generally improved compatibiUty characteristics over either PSF or PES in a number of systems. An example of this is blends of PPSF with polyaryletherketones (39,40). These blends form extremely finely dispersed systems with synergistic strength, impact, and environmental stress cracking resistance properties. Blends of PPSF with either PSF or PES are synergistic in the sense that they exhibit the super-toughness characteristic of PPSF at PSF or PES contents of up to 35 wt % (33,34). The miscibility of PPSF with a special class of polyimides has been discovered and documented (41). The miscibility profile of PPSF with high temperature (T > 230° C) polysulfones has been reported (42). 

The very low density materials (VLDPEs) introduced in the mid-1980s are generally considered as alternatives to plasticised PVC (Chapter 12) and ethylene-vinyl acetate (EVA) plastics (see Chapter 11). They have no volatile or extractable plasticisers as in plasticised PVC nor do they have the odour or moulding problems associated with EVA. Whilst VLDPE materials can match the flexibility of EVA they also have better environmental stress cracking resistance, improved toughness and a higher softening point. 

The homopolymer finds a variety of uses, as an adhesive component, as a base for chewing gum, in caulking compounds, as a tackifier for greases, in tank linings, as a motor oil additive to provide suitable viscosity characteristics and to improve the environmental stress-cracking resistance of polyethylene. It has been incorporated in quantities of up to 30% in high-density polyethylene to improve the impact strength of heavy duty sacks. 

The styrene-based terpolymers were originally used to the extent of some 2-9% in order to reduce the notch sensitivity of the polycarbonate and to improve the environmental stress cracking resistance. More recently emphasis has been on alloys with 10-50% of SAN or ABS. Alloys of polycarbonates with ASA have also become available (Luran SC-BASF)... 

Environmental standards, 10 158 Environmental stress crack resistance (ESCR), 20 166... 

The launch of new resins being rare, progress on materials intended for medical applications is by way of formulation, alloys and modifications of existing resins. Thus, new radiation-stable polypropylene grades are available for the manufacture of cups, boxes, baskets, mixers, etc. that are radiation sterilized. And polyesters with better environmental stress cracking resistance are extending their potenti in the area of medical testing. 

High-impact grades present better impact resistances even at low temperature, higher flexibility and environmental stress cracking resistance (ESCR). The butadiene-styrene block copolymers are transparent but the alloys made of polystyrene and polybutadiene are not. 

LLDPE resins formulated for the blow molding applications have superior environmental stress-cracking resistance and low gas permeability. These features opened new bottle markets where such properties are important. A large variety of molded articles with a complex configuration... 

PDLCOM William Andrew, Inc., Plastics Design Library test data on the chemical compatibility and the environmental stress crack resistance of plastics... 

MPa (264 psi)J, good electrical properties, good environmental stress-crack resistance (relative to other amorphous plastics), and low flammability based on standard laboratory tests. 

Schellenberg J, Fienhold G (1998) Environmental stress cracking resistance of blends of high-density polyethylene with other polyethylenes. Polym Eng Sci 38(9) 1413-1419... 

Al-Saidi LF, Mortensen K, Almdal K (2003) Environmental stress cracking resistance behaviour of polycarbonate in different chemicals by determination of the time-dependence of stress at constant strains. Polym Degradat Stabil 82(3) 451—461... 

Soares JBP, Abbott RF, Kim JD (2000) Environmental stress cracking resistance of polyethylene the use of CRYSTAF and SEC to establish structure-property relationships. J Polym Sci Part B Polym Phys 38(10) 1267-1275... 

Table 12.12 Incorporation of PIB improves the environmental stress crack resistance of commercial polymers exposed to 50 50 CO-OA under a constant stress of lOOOpsi...

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