Polymers in character recognition behavior under heat and combustion is relatively simple and at the same time sufficiently accurate method of determining the qualitative nature of the polymers. The method is based upon a visual observation of the behavior of the sample during its introduction into the upper part of the burner flame. As the sample is heated thermoplastics gradually soften and melt, and thermosets do not soften or melt. Therefore, with respect to heat can define a class of polymers (thermoplastics, thermosets). With further heating the sample is its sunbathing, accompanied by the release of degradation products, which have a specific smell to the individual polymers, allowing to determine the type of polymer.
Before proceeding to the examination of the polymer should be thoroughly acquainted with the relevant theoretical material, take samples of polymers, carefully inspect them to describe in detail their appearance (nature of the surface, color, hardness, transparency and the nature of the fracture and other features).
Capturing a sample Crucible Tongs, should make it into the flame; then carry out monitoring of heating, softening and sunbathing. At fire sample remove it from the burner; if it melts and shrinks in the heat soak up the ignition, but no more than 10 minutes. Swipe observing the illuminated material is flame burner, determine the color of the flame, burning behavior (quiet, heavy, with soot burnout, etc.), odor note of the combustion products and additional features (e.g., the ability to stretch in the yarn). To determine the odor of the product should extinguish the flames, and lightly brush the hands of direct air from the nose to the sample extinguished.
A comparison of the established features from the data given in Table application can determine the type of polymer in all samples taken for the experiment.
The approximate scheme of definition:
1. The sample does not ignite, retains its shape, there is a smell of formaldehyde. If, moreover, there is a smell:
a) ammonia – a urea-formaldehyde polymer;
b) sharp (fish) – melamine formaldehyde resin;
c) Phenol – phenol-formaldehyde resin.
2. The polymer is burning in the flames of the burner on and off when removed from the flame. If, moreover, appears:
a) the smell of burnt rubber, broad green border at the base of the flame – is chlorinated rubber; with a small green area overlapped yellow zone – a chloroprene;
b) The pungent smell of hydrogen chloride and green color – a derivative of polyvinyl chloride;
c) the sweet smell, the green color at the base of the flame, black ash – is polyvinyl chloride;
d) the smell of burnt milk – casein is;
d) the smell of acetic acid, sparks, molten resin in contact with the water forms a hard yellow-brown grain or cereal – cellulose acetate.
3. Polymer burn after removal of the flame; while there:
a) very fast burning, the smell of camphor – a celluloid; no smell of camphor – nitrocellulose;
b) the flame of the blue at the base, and, in addition, a strong sweet, fruity smell – is polymethyl methacrylate;
the smell of burned vegetables – it polyamides;
slightly sweet smell – polyvinyl formal;
the smell of rancid oil, spark – cellulose acetate butyrate;
c) flame with purple border, sparking the smell of acetic acid – is polivilatsetal;
d) a flame bright, yellow-white, smell: sweet (hyacinth) – a polystyrene or copolymers thereof; weak, a little sweet – a polyvinyl formal;
d) a flame surrounded by yellow-green border, long burning resin, a sweet smell; the molten resin, falling into the water, the disk image color light oak – is ethyl cellulose.
Determination of chemical resistance and hardness of the plastics
Overview
Chemical resistance is one of the important characteristics of plastics because of it depends largely on the choice of the major fields of application. Most plastics are characterized by high chemical resistance and are superior in this regard to traditional natural materials: metal, wood, and others. Chemical resistance due to structural features of the polymers, the presence or absence of functional groups capable of undergoing transformation in the environment of various reagents, availability and frequency of cross-linking, and others. The greatest chemical resistance towards acids and bases differ polymerization chain polymers which do not have reactive functional groups, polyolefins, polystyrene, halogen-containing polymers (polyvinyl chloride, perchlorovinyl, fluoroplastics). Recent in chemical resistance superior to the most resistant to hostile environments metal – gold that is dissolved in “aqua regia” (a mixture of nitric and hydrochloric acids), while fluoroplastics is kept essentially unchanged 24-hour refluxing the reagent.
Polycondensation polymers typically have heteroatoms in the main chain and have a lower chemical resistance in environments, which is caused by reaction of the polymer with reagents, accompanied by destruction of the circuit. Thus, in the polyamide in the acidic environment of the amide group is hydrolyzed in strong acids and alkalis.
Chemical resistance of carbon-chain polymers with functional groups depends on the chemical activity of the latter. In such polymers under the action of chemical agents interact functional groups while maintaining the main chain. Thus, polyacrylonitrile unstable in concentrated acids and alkalis because of saponification of the nitrile group and the formation of polyacrylic acid. The same happens with polymethylmethacrylate which complex groups due to hydrolysis converted into polymethacrylic acid; polyvinyl acetate under the same conditions turns into polyvinyl alcohol.
Soluble polymers as chemical resistance, depends on the characteristics of the structure, the presence of branching, crosslinking, presence of polar groups, the length of the macromolecule and other facts.
The smaller branches in the macromolecule, its length is longer and more polar groups, the higher the degree of intermolecular interaction, and lower the solubility of polymers. The solubility decreases with increasing regularity and frequency of macromolecules crosslinks. Crystalline polymers tend to have lower solubility than amorphous same chemical structure. Cured thermosetting resins are usually not soluble and do not swell in solvents.
Plastics are used as construction materials should have high chemical resistance with respect to the environment with which the articles are in contact during operation: soap-soda solution, solvents, acids, food media. Therefore, knowledge of the chemical resistance of plastics is required for a specialist. It allows you to set the correct choice of plastics for the manufacture of certain products.
Methods of determining the chemical resistance and hardness
1. Samples are placed in plastic tubes with an appropriate reagent and maintained therein for two hours at room temperature, periodic stirring with a glass rod or shaking. After soaking carefully poured reagent shake the tubes on a ceramic plate and external examination of samples set changes: dissolving, swelling, change in the nature of the surface, washing out the plasticizer, discoloration and other. Of course, the results give only an approximate idea of ​​the chemical resistance of plastics.
Accurate data on the chemical stability obtained with the test samples in standard sizes to change the weight, size, physical and mechanical properties under the conditions specified in the relevant standards.
2. To determine the hardness of plastics used Mohs’ scale of hardness (scale IPRA), consisting of a set of reference minerals, selected in such a way that each of them while pressing scratch the previous and, in turn, is drawn further.
The scale consists of 10 minerals (talc, gypsum, calcite, fluorite, apatite, feldspar, quartz, topaz, corundum, diamond), which are respectively assigned numbers from 1 to 10.
When testing the acute angle of one of the minerals from the pressure medium carried on the surface of the plastic test and examined for formation of scratches.
If no crack, the next line is applied to a solid material to produce visible to the naked eye, scratches, does not erase the finger.
The hardness of plastics indicate the serial number of the mineral, leave marks on the surface.
Method for determination of hardness with different mineralogical scale availability, simplicity, rapidity, but gives low results accuracy. However, this method allows us to characterize the relative hardness of the plastic.
More accurate results are obtained in tests by pressing a steel ball on the devices TSHSP, Brinell in accordance with approved standards, methods.