Chemicals, resistance solvent effect

Insufficient chemical resistance of a blend at times leads to its rejection for use in an aggressive chemical environment, although it possesses an excellent combination of mechanical properties. Thus chemical and solvent effects on polymer blends are important factors that frequently determine blends applicability. Attention has been given to chemical resistance of blends starting from the fundamental concept of the solubility parameters. Apart from the chemical and environmental restrictions, thermal resistance of a polymer blend is often a major criterion for its applicability. Thus, the thermal conductivity, heat capacity and heat deflection temperature of polymeric materials are discussed in separate sections. 

Despite their dull color, red iron oxide pigments find applications in different architectural and industrial coatings due to their excellent thermal stability, weather fastness, solvent resistance, chemical resistance, cost effectiveness and high hiding power. 

Surface Fluorination of Polymers. Fluorocarbon-coated objects have many practical appHcations because the chemically adherent surface provides increased thermal stabiHty, resistance to oxidation and corrosive chemicals and solvents, decreased coefficient of friction and thus decreased wear, and decreased permeabiHty to gas flow. Unusual surface effects can be obtained by fluorinating the polymer surfaces only partially (74). 

Modified alkyd resins In this group one finds styrenated alkyds, vinyl toluenated alkyds, oil-modified vinyl resins, acrylic alkyds, silicone alkyds and polyurethane alkyds. The modifying component usually has a number of effects. It always increases the molecular weight of the alkyd polymer, and may impart hardness, durability, or chemical resistance. It also affects the solubility of the polymer in solvents. 

Cured phenol-formaldehydes are resistant to attack by most chemicals. Organic solvents and water have no effect on them, though they will swell in boiling phenols. Simple resins are readily attacked by sodium hydroxide solutions, but resins based on phenol derivatives, such as cresol, tend to be less affected by such solutions. Simple phenol-formaldehyde polymers are resistant to most acids, though formic and nitric acids will tend to attack them. Again, cresol-based polymers have resistance to such attack. 

PVDC is appreciated for its barrier effect to water vapour, gases and aromas as well as its chemical resistance (except to certain solvents), its relative flexibility, fireproofing, the possibility of food contact for special grades, transparency, gloss, scalability (including by high frequency and ultrasound), printability. 

In the above equation T is the native protein and is in equilibrium with the metal complex, TM, which is resistant. Ti to Tn are the conformations which are susceptible to the particular condition which is impressed upon the protein. The various forms of T would be susceptible, in different degree to changes caused by heat, solvent effects, enzymolysis, etc., to give the products denatured forms (D), proteolytic fragments (P), and chemically modified forms (C). Possible combinations of these also could exist, such as C could rapidly undergo denaturation. There also is the possibility that different molecular forms of the metal complexes exist. These forms might have different susceptibilities, but the susceptibilities would not be the same as those of the metal-free proteins. 

Fillers often have a significant effect on the moisture resistance, the moisture-vapor transmission rate, and the solvent and chemical resistance of the cured adhesive bond. The effect, however, can be in either direction. Some fillers such as calcium carbonate tend to lower acid resistance, whereas others, such as silica or aluminum, may tend to lower alkali resistance. 

Many organic adhesives tend to be susceptible to chemicals and solvents, especially at elevated temperatures. Most standard tests to determine chemical resistance of adhesive joints last only 30 days or so. Unfortunately, exposure tests lasting less than 30 days are not applicable to many service life requirements. Practically all adhesives are resistant to these fluids over short time periods and at room temperatures. Some epoxy adhesives even show an increase in strength during aging in fuel or oil over these time periods. This effect is possibly due to either postcuring or plasticizing of the epoxy by the oil. 

Polyester coatings can be formulated as solvent-based as well as 100% solid coatings. In order to provide a non-sagging effect, proper selection of fillers is essential. Systems based on the reaction between maleic anhydride and bisphenol A offer greater chemical resistance over a wider range of pH. 

Chemical resistance Acids, bases, solvents 1 yr, 25°C No visible effect (14) ... 

Chemical test. Solubility is a very effective test to identify fibers. Polyolefins have excellent chemical resistance to most common solvents, and they can be easily distinguished from a polyester or nylon fiber by a simple solubility test. Functional groups can also be identified using a technique such as FTIR which wiU help identify the fiber type. 

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