Creep Environmental Stress Cracking

From this table it will be noted that in terms of the mechanical and thermal properties quoted the copolymers are marginally inferior to the homopolymers. They do, however, show a marked improvement in resistance to environmental stress cracking. It has also been shown that the resistance to thermal stress cracking and to creep are better than with the homopolymer.This has led to widespread use in detergent bottles, pipes, monofilaments and cables. 

ISO 16770 2004 Plastics - Determination of environmental stress cracking (ESC) of polyethylene - Full-notch creep test (FNCT)... 

Limited UV resistance risks of environmental stress cracking heat and creep sensitivity low rigidity high shrinkage, difficult gluing. 

Mechanical properties of plastics can be determined by short, single-point quality control tests and longer, generally multipoint or multiple condition procedures that relate to fundamental polymer properties. Single-point tests include tensile, compressive, flexural, shear, and impact properties of plastics creep, heat aging, creep rupture, and environmental stress-cracking tests usually result in multipoint curves or tables for comparison of the original response to post-exposure response. 

Environmental stress-cracking, polyethylene, detergent, creep, molecular mass... 

Preliminary research has indicated that a PBT/PBA co-poly(ester ester) is susceptible to environmental stress cracking in water and in phosphoric acid solution, in both cases at 80°C. Time-to-Failure creep experiments were initiated to obtain quantitative data. These tests were performed in water and phosphoric acid solutions (pH = 1.6) at 80°C with notched tensile specimens under constant load (ranging from 0.6-7 MPa). The results have shown that the phosphoric acid solution decreases the lifetime when compared to tests done in water. Both environments decrease the lifetime tremendously when compared to creep tests in air. 

Environmental Stress Cracking (ESC), Thermoplastic Elastomer (TPE), Creep, Time-to-Failure, Hydrolysis, Co-poly(ester ester), Poly(butylene terephthalate), Poly(butylene adipate). 

The work discussed here has related not only to structure relationships but also to means of protection of the macromolec-ular material and the protective functions of these materials. There are many modes of failure, by chemical reaction, failure by fracture, environmental stress cracking and creep. Further there are complicating interactions arising from chemical reaction during relaxation of polymer networks, and in multiphase polymer systems and cos osites, failure at interfaces by adhesive failxire or stress-stress dilation. 

The polysulfones form another large group, and some of the commercially important structures are shown in Table 15.10. Poly(phenylene sulfone) tends to be too intractable for easy processing, and the copolymer structures are more useful. These are usually amorphous materials with high values, typically in the range of 465 to 560 K. They are thermally stable, show good mechanical properties — particularly creep resistance — and are resistant to attack by dilute acids and alkahs. They can, however, dissolve in polar solvents, and solvent attack may also cause environmental stress cracking. 

Polybutene-1, PB-1, or polybut-l-ene is another stereospecific (isotactic) polyolefin polymer, discovered by Prof. Giulio Natta in 1954. It is a linear high molecular weight crystalline thermoplastic polymer, with low density (0.91). The ethyl side groups create entanglement, which provides for the very good creep resistance of this polymer, which also has an abrasion resistance comparable to UHMWPE, and an excellent resistance to chemicals and environmental stress-cracking. 

Ayy Ayyer, R., Hiltner, A., Baer, E. A fatigue-to-creep correlation in air for application to environmental stress cracking of polyethylene. J. Mater. Sci. 42 (2007) 7004—7015. 

Up to now we have dealt with large stresses applied for short periods. Let s also consider material fracture imder conditions of low stresses for long duration—fracture in creep, fatigue, or environmental stress cracking (ESC). Creep under a static load was already discussed for the deformation of viscoelastic bodies, as shown in Figure 4-36. 

The application of a force to a material over a sustained period of time induces creep and if this force eventually leads to cracking, fracture or rupture, the process is termed stress cracking, static fatigue, or creep rupture and if the environment has speeded up the process, it is termed environmental stress cracking. 

An important application for polybntylene is plumbing pipe for both coimnercial and residential use. The exceUent creep resistance of polybntylene aUows for the manufacture of thiimer wall pipes compared to pipes made from polyethylene or polypropylene. Polybutylene pipe can also be used for the transport of abrasive fluids. Other applications for polybutylene include hot melt adhesives and additives for other plastics. The addition of polybutylene improves the environmental stress cracking resistance of polyethylene and the impact and weld line strength of polypropylene. Polybntylene is also used in pack aging applications. 

---