Chemical Resistance Tests

Chemical Resistance Tests

According to the specific structure of the materials, there are chemicals that can be exposed to the product or equipment consisting of various substances naturally or manually, and its resistance to these chemicals is very important. Due to their light weight, easy processability and resistance to corrosion, good electrical and heat insulation properties; They are used in large quantities in many industries such as machinery, aircraft, electrical and electronics industries. However, plastics have different properties compared to metallic and other engineering materials.
Molecular weight, structure, degree of cross-linking, and functional groups of the skeleton of the polymers forming the plastic affect the physical and chemical properties of the plastic.
Thanks to the special structure of the material, products and fittings show resistance to chemicals.
In addition, chemicals, products, hot, cold, humid, watery, exposed to intense sunlight and so on. environments. The purpose of these tests is to see how resistant the materials that make up the products to these environments. These materials are subjected to various conditions that vary according to the tests. In the aging tests, the durability of the materials is observed by comparing the samples obtained before aging with the samples obtained before aging.

Appearance of plastics
Most plastics are colorless. Therefore, colorants are used to obtain the desired color. An opaque appearance can be obtained with pigments as well as a transparent appearance to soluble organic dyes. Some polymers such as polymethylmethocrylate are very clear.
Since polymethylmetarylate is also light, it is used both in place of optical glass and in vehicles such as aircraft.
Surface hardness of plastics
A disadvantage is that plastics are soft and less scratch resistant.
The hardness of the thermoplastics decreases, ie softens, with the increase of hot and added plasticizers.
In thermosets, temperature increase does not have a significant effect on hardness.
Plastics are less rigid than glass, ceramics and metals.
Density of plastics
Plastic materials, except wood, have a lower density than all other materials.
The density of the plastics is between 0,9 gr / cm3 and 2,5 gr / cm3.
Although their practical applications are by volume, they are sold by weight, which increases the validity of plastic where weight is first.
Thermal properties
The thermal property of plastics is one of the most important properties.
Although some plastics may be recommended for long-term use in the 100-180ºC range and most plastics exhibit softening over a wide temperature range, although other plastics such as polytetrafluoroethylene (PTEE) and polyphenylene sulfide have a service life up to 250ºC.
Softening and deflection temperature is the method that determines the use of high temperature plastics. However, it is worth noting that these temperatures are not the maximum operating temperatures of the material.
However, at low stresses or long-range loads, plastics can withstand these or higher temperatures. The softening temperature essentially provides information only in the pre-selection of the material.
An important feature of plastics is its thermal conductivity. Usually the heat conductivity of plastics is poor. The thermal conductivity of the metals is between 200-10.000x104 cal / cm.snºC.
The thermal conductivity of the plastics is between 2,0-8,0 cal / cm.snºCx104. Due to the low thermal conductivity of plastics, temperature growth caused by friction or repeated stresses causes heat build-up in the material.
This event causes thermal fatigue. In order to reduce thermal fatigue, additives are added to the plastic materials.
For this purpose, the most commonly used additives are metal powders (aluminum, copper, etc.) or plastics with various fibers (carbon fiber, glass fiber, etc.) having at least ten times higher thermal conductivity.
For example, the thermal conductivity of epoxides of 4-30 can be up to 800-2500 when supplemented with additives.
The thermal conductivity of plastics depends on the structural factors of the molecules, ie the degree of crystallinity and orientation. The degree of crystallinity and orientation increases, so does its thermal conductivity.
Another thermal property is thermal expansion.
The coefficient of thermal expansion, which is an important problem in the processing of plastic materials, is much larger than that of metals.
The addition of reinforcing fibers significantly reduces the thermal expansion of plastics. For example, the thermal expansion coefficient is reduced by half with the addition of 60% glass fibers to police tyrene.
Like thermal conductivity, thermal expansion varies with molecular weight and structural factors. The coefficient of thermal expansion decreases with increasing cross-link and bond density of the degree of crystallinity of the polymer.
The coefficient decreases in the direction of direction and increases in the upright direction.
In addition, the thermal expansion values ​​are different above or below the glass transition temperature and melt temperature (Tm) of plastics Tg.
Heat resistance of plastics is a very important factor. Generally, thermoplastics decompose at 65-120ºC when there is no load, and some varieties decompose at high temperatures such as 260ºC.
Therefore, they should be used under high pressure at high temperatures. Thermosets are harder and more heat resistant. If the temperature rises, they remain hard up to a certain temperature, but at high temperatures they become carbonized and decompose.
In general, thermosets can be exposed to a constant temperature between 150-230ºC; some special thermosets can withstand up to 260ºC. Filler materials such as asbestos and pine fillers increase the thermal resistance of plastics.

Chemical properties of plastics
Plastics are more resistant to chemicals than metals. Although thermoplastics are not affected by weak acid, base and salt solutions, they dissolve and swell in organic solvents. Thermoplastics are chemically affected by strong acids and bases.
Thermosets are the regions where decomposition is started during the contact of chemicals according to thermoplastics, cracks caused by bending, shrinkage and similar stresses during use in plastic.
The chemical resistance of the polymers depends on the type and concentration of the reagent, the polymeric structure, the temperature, the stress applied, the surface roughness and the morphology. Short-term polymer-chemical interactions are determined by tensile tests and long-term interactions are determined by friction tests.
Flammability properties of plastics
Plastics are very sensitive to flame. Generally, the rate of combustion of thermoplastics can be slowed down using additive. However, many plastics do not continue to burn after the flame has been removed.
The flammability of a plastic material can be measured, but generally this property depends on many factors related to the specific conditions of the fire. For example, solid PVC containing plasticizer extinguishes itself when flame is removed, whereas foam PVC without plasticizer continues to burn in the pile.
Although many test methods have emerged, it is based on the concept of Critical Oxygen Index (COI) which has been adopted in recent years.
Weathering of plastics
The degradation of the polymers over time is caused by chemical degradation of the material.
This phenomenon occurs under the influence of one or more factors.
The most important of these are thermal, mechanical, photochemical, radiation, biological and chemical factors.
Often, the conditions allow different wear to occur at the same time.
For example, an exposed polymer is exposed to UV radiation, oxygen and atmospheric emissions.
Likewise, the polymer is subjected to heat, mechanical forces and oxygen which can initiate wear during treatment.
Weathering of plastics; radiation is the result of chemical effects of abrasion, rain or hail erosion and air pollution caused by flying particles.
The resistance of thermoplastics to these factors varies from very good (acrylic and PVC) to weakness (polystyrene and cellulose acetate). Due to the water absorption and plasticizing effect, the durability of thermoplastics is poor.
However, the most important factor is the effect of UV radiation. In both cases the plastic material is loose; In addition, color loss occurs due to ultraviolet effect. The most resistant to UV rays are smartness.
Other plastics do not exhibit the same durability, but their properties can be improved by suitable additives such as carbon black. The effect of air is most common with pipes exposed to sunlight for a long time.
Additives such as antioxidants and stabilizers are added to increase the resistance of plastic materials against weather and climate effects.

The chemical resistance properties of plastic materials are tested in the following standards.
TS ISO 4433-1 Thermoplastic tubes - Resistance to chemical liquids - Classification - Part 1: Immersion test method
TS ISO 4433-2 Thermoplastic tubes - Resistance to chemical fluids - Classification - Part 2: Polyolefin tubes
TS ISO 4433-3 Thermoplastic pipes - Resistance to chemical liquids - Classification - Part 3: Polyurethane (pvc-U) with high impact resistance (pvc-U) and non-chlorinated poly (vinyl chloride) (pvc-C) pipes
TS ISO 4433-4 Thermoplastic pipes - Resistance to chemical fluids - Classification - Part 4: Poly (vinylidene fluoride) (pvdf) pipes
TS 11448 Plastic pipes and fittings chemical resistance - Classification

Example Chemicals are as follows.
Acetic acid
Nail polish remover
Acrylic acid
Alkyl alcohol
Alkyl benzene
Alkyl chloride
Amino acid
Ammonium chloride
Benzoic acid
Benzyl alcohol
Benzylidene aldehyde
Boric acid
Boron trifluoride
Brake Fluid
Bromo methane
Butyl acetate
Butyl phthalate
Butyric acid
Calcium chloride
Calcium hydroxide
Carbon dioxide
Carbon monoxide
Sodium hydroxide
Chlorine acetic acid
Chlorine benzene
Chlorine methane
Chlorine sulfonic acid
Chlorine trifluorethane
Chromic acid
Citric acid
Cleaning chemicals (acidic)
Cleaning chemicals (general)
Dibutyl ether
Dibutyl phthalate
Dichloro benzene
Diethyl ether
Diisopropyl ether
Dimethyl ether
Dimethyl sulfate
Ethyl acetate
Ethyl chloride
Ethylene chloride
Ethylene glycol
Ethylene oxide
Formic acid
Fuel oil, diesel
Fuel oil, gasoline
Transmission oil
Heating oil
Hydraulic oil
Hydrochloric acid
Hydrochloric acid
Hydrofluoric acid
Hydrogen chloride
Hydrogen peroxide
Hydrogen sulfide
Lactic acid
Lithium salts
Lubricating oils
Lubricating oils
Magnesium hydroxide
Magnesium salts
Magnesium sulfate
Manganese salt
Methyl chloride
Methyl ethyl ketone
Methyl format
Mineral oil
Natural gas
Nitric acid
Nitric acid
Oxalic acid
Phenyl ethanol
Phthalic acid
Potassium bromide
Potassium chloride
Potassium dichromate
Potassium hydroxide
Potassium nitrate
Potassium permanganate
Potassium sulfate
Propionic acid
Propionic acid
Rain water
Refrigerator oil
Silicone oil
Sodium carbonate
Sodium chlorate
Sodium hydrogen carbonate
Sodium hydroxide
Sodium hypochlorite
Sodium salts
Stearic acid
Stearic acid
Sulfur dioxide
Sulfuric acid
Trichlor methane
Neft oil
Uric acid
Vinyl acetate
Zinc chloride