Stress cracking polypropylene

Polypropylene appears to be free from environmental stress cracking problems. The only exception seems to be with concentrated sulphuric and chromic acids and with aqua regia. 

It is less resistant to aliphatic hydrocarbons than polyethylene and polypropylene and in fact pipes may be solvent welded. At the same time the resistance to environmental stress cracking is excellent. 

Polypropylene It has similar chemical properties to polyethylene but is less susceptible to environmental stress cracking. It may also be used at somewhat higher temperatures. 

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. 

Neat polypropylenes absorb little water and are not very sensitive to it but can have some propensity to stress cracking in the presence of certain chemicals. Special grades are marketed for washing machines, dishwashers and so on. 

PP/PA (polypropylene/polyallomer). These plastics are similar to polyethylene, but each unit of their chains has a methyl group attached. They are translucent, autoclavable, and have no known solvents at room temperature. They are slightly more susceptible than polyethylene to strong oxidizing agents. They offer the best stress-cracking resistance of the polyolefins. Products made of polypropylene are brittle at ambient temperature and may crack or break if dropped from benchtop height. 

Blends of polyolefins (e.g., HPDE/LDPE, LDPE/ ethylene copolymers, PP/EPDM, PP/HDPE/EPDM, HDPE/butyl rubber) have been commercial since the late 1960 s and early 1970 s. Specific film formulations were commonly based on polyolefin blends to achieve the proper balance of processing, environmental stress crack resistance, modulus, toughness, cling, transparency, filler acceptance, printability, tear resistance, shrinkage characteristics, and permeability. Ethylene-propylene mbber (EPR, EPDM) was commonly incorporated into polypropylene as an impact modifier at moderate levels and as a flexibilizer at high levels. One of... 

Polypropylene One of the vinyl polymers with good flex life and good environmental stress crack resistance. 

Polypropylene Thermoplastic polymer of propylene. Has low density and good flexibility and resistance to chemicals, abrasion, moisture, and stress cracking, but decreased dimensional stability, mechanical strength, and light, fire, and heat resistance. Processed by injection molding, spinning, and extrusion. Used in fibers and films for adhesive tapes and packaging. Also called PP. 

Standard test method for environmental stress-cracking of ethylene plastics Insulating and sheathing materials of electric and optical cables - Common test methods - Part 4-1 Methods specific to polyethylene and polypropylene compounds - Resistance to enviromnental stress cracking - Measurement of the melt flow index - Carbon black and/or mineral filler content measurement in polyethy-lene by direct combustion - Measurement of carbon black content by thermogravimetric analysis (TGA) - Assessment of carbon black dispersion in polyethylene using a microscope... 

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. 

Polypropylene, PP, was blended with 5-20 wt% elastomers [styrene-butadiene, SBR, or butadiene-acrylonitrile, NBR] to produce materials useful for blow molding of bottles, free from brittleness and stress cracking. In a later patent, EPR, BP, and PIB, with a dicarboxylic acid anhydride, were used ... 

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