Dedicated to my dear mother, part-time best expert in separate sorting of plastics ...
If you, dear reader, have never arisen in your life for the question "what the hell is this plastic?", then you can not read the article :) But to the attention of everyone else - another article from the series "bookmark ! ". Today we have a topic - "Definition of plastics at home" and I continue to wikipedia Habr with useful information that I have left after completing my scientific and technical projects. Today, environmentalists, biotechnologists, polymer craftsmen, plastics processing engineers and all those who have had to sort plastics, glue plastics, solder plastics — automobile enthusiasts, home builders, and all interested parties — can safely go under the cat. Traditionally - at least FUN, a maximum of information, a Russian-language manual on plastics is simply not to be found, " I guarantee it ":)
... And finally the hands came to remember the Soviet children's novel of 1966, in which the practical recommendations for a child "who likes chemistry" are much more than in modern Belarusian chemistry textbooks taken together.
My old chemical friend Serezha came to me here and we started talking about my habrastaty. We smoothly switched from solvents of plastics to glue for all the same plastics and suddenly I couldn’t find the answer to “ but I didn’t understand what kind of plastic I had in my son’s machine to glue it according to your articles ”. And I decided to rectify the situation, to help all fathers, who were faced with the difficult task of repairing a plastic Chinese radio-controlled machine, donated to their children, and streamline the available information on the "reverse engineering" of plastic. Forewarned is forearmed. To find the best glue, you need to know what we glue :) By the way, the reader genseq also recommend my read the opus, all of a sudden it will help identify the plastic of the nanoporous sequencer;)
In fact, for the first time I encountered the concept of analysis of plastics in deep childhood when I read Vladimir Kiselyov’s book " a> "(if that, Children's Literature publishing house, Moscow, 1966 (!)). Very clean and bright novel, and most importantly, with the laboratory approaches that are vigorous for the child. Most of all I remember the episode with the distillation of organic glass, which I will mention in the text of the article ...
& lt; ... & gt; After school, I didn’t study with Kolya, but I went to Vita, where our guys were going to prepare today from an ink device — there are such ink devices made of transparent plastic — polymethyl methacrylate — a very valuable chemical for our experiments. To do this, it was necessary to build a special installation with a refrigerator and a condenser of the finished product. In the fridge, I suggested using dry ice, which the ice-maker always stays at our grocery store, and Vitya said that this was a valuable rationalization proposal & lt; ... & gt; In the meantime, we have prepared a device for the distillation of the fragments of an ink device into polymethyl methacrylate. To do this, we connected a flask of heat-resistant glass with a refrigerator, which was prepared from a box from under shoes. In this box we put dry ice. We connected the refrigerator with a glass tube to a condenser — a wide-mouth milk bottle.
Analysis and "reverse engineering" of polymers is a difficult, ungrateful task and it is quite difficult to implement in domestic conditions. Depending on the type of plastic and the functional additives that are present in it, you may need at least FTIR spectrometer (as noted in my article about solvents for plastics reader CactusKnight " at least the simplest Fourier transform infrared spectrometer, which in 30 seconds can get the spectra of plastics "), and better NMR , mass spectrometry , X-ray phase analysis or which is worse. Naturally, given the cost of such equipment (and the presence of specially trained personnel), it becomes clear that this pleasure is not cheap. But the fact is that more often for many practical purposes it is often enough to determine what class of plastics an unknown sample belongs to, without analysis of plasticizers, fillers, etc. (although important properties of plastic very often depend on them). To do this, you can and should use simple methods that, by and large, do not even require special chemical knowledge. Speaking about the limitations, in addition to the already mentioned additives, we can mention the analysis of complex copolymers and mixtures of polymers. Such things are very difficult to identify without involving serious instrumental methods of analysis.
Plastics are high molecular weight (polymeric) organic substances that are usually synthesized from low molecular weight compounds (monomers). They can be obtained both by chemical modification of high-molecular natural materials (cellulose, etc.), and from natural mineral raw materials (oil, natural gas, coal). The most important industrial methods for producing plastics from monomers can be classified by the mechanism of the polymer formation reaction, for example, polymerization or condensation. But since various chemically identical plastics can be obtained in different ways and from different types of raw materials, this classification will help little in analyzing unknown samples. But on the other hand, in addition to chemical research, the appearance of the plastic, as well as its behavior when heated, provides useful information for its accurate identification.
Physical interactions between individual macromolecules that make up the plastic “skeleton” are most often responsible for the useful properties of polymers that we know. These interactions are responsible for the adhesion of molecules, and therefore for strength, hardness, elasticity. Plastics consisting of linear threadlike molecules (several hundred nanometers long and several tenths nanometers in diameter) whose macromolecules are loosely linked (crosslinked) to each other, easily soften when heated. When the polymer material is heated above a certain temperature, the macromolecules, which are more or less oriented relative to each other at low temperatures, begin to slide past each other, forming a highly viscous melt. Depending on the degree of ordering of the macromolecule in the solid state, partially crystallized (partially ordered and amorphous (unordered) plastics can be distinguished. The degree of order greatly influences the behavior of the plastic during heating and its solubility. The picture below shows a schematic representation of the structure of plastics, showing the three main type of macromolecular structures:
Plastics, which soften when heated and have a flow in this state, are called thermoplastics . When cooled, such plastics become hard again. This process can be repeated many times. True, there are exceptions when the temperature at which the plastic begins to decompose is lower than the softening temperature. Plastic just does not have time to swim, because it breaks down into chemical components. By the way, solubility in organic liquids (described in detail in my previous article ), along with temperature effects, can serve as an indicator of linearity/branching polymer macromolecules. Because the solvents are embedded between the polymer chains, reduces the interaction forces between the macromolecules and allows them to move relative to each other. Important! Therefore, by the way, information from Habrastia and Solvents for plastics and protection from them can serve as an indicator for plastic type definitions are the same as all the methods described in the article below.
In contrast to thermoplastic materials, a different class of polymers, the so-called thermosetting materials, or thermosets have high thermal stability. Such substances are three-dimensional networks of tightly crosslinked macromolecules that can no longer melt or dissolve. Destruction of crosslinking can only be very high temperatures or aggressive chemical reagents.
Separately, you can mark elastic, rubbery elastomers , consisting of relatively weakly linked macromolecules. Such materials acquire a rigid structure during the vulcanization process. Due to the crosslinked structure, elastomers do not melt when heated to temperatures that are slightly lower than their decomposition temperature. Unlike chemically crosslinked elastomers, such as chemical rubber, stitching in so-called thermoplastic elastomers ("rubber for 3D printers) occurs through physical interactions between macromolecules. When heated, the forces of physical interaction between the molecules of the chain decrease, so that these polymers become ordinary thermoplastics. When when the physical interaction between molecules becomes stronger, the material behaves like an elastomer again. The table below lists the most important characteristics Whistles of the mentioned groups of polymeric materials. However, it should be remembered that pigments, plasticizer and various fillers (for example, soot or fiberglass) lead to significant deviations from these properties. Therefore, it is not always possible to identify polymeric materials only on the basis of these criteria. Densities are given as a guideline and These are rough approximations with an emphasis on solid monolithic materials (because foamed plastics differ dramatically in density from monolithic plastics).
In the piggy bank "physical properties". An approximate indicator of the hardness of plastic is its behavior when scratching with a nail: hard plastic scratches the nail; corneal plastics have approximately the same hardness with plastic; flexible or elastic plastic is scratched/pressed through with a fingernail.
If a mental experiment using a table did not produce results - it's time to read on and move on to more radical measures.
Start with a visual inspection. Manufacturers almost always with the help of stamping indicate the type of plastic products. Everyone probably met somewhere (often at the bottom of plastic packaging) such icons:
These are the so-called recycling codes - special characters used to designate the material from which the item is made, and to simplify the sorting procedure before sending it to recycling for recycling. At the moment, there are not many codes approved for a particular type of plastic. This is due to the fact that mixtures of various dissimilar materials (such as plastic + foil + paper) are increasingly being used. The triangle in which the numbers are indicated implies the possibility of recycling. Well, the numbers themselves - the type of plastic. Figures can be stamped without a triangle, but it is still possible to identify plastic by them. To do this, use the data from the table under the spoiler, with a list of approved IUPAC abbreviations for plastics.
|2||HDPE||Polyethylene, high density|
|4||LDPE||Polyethylene, low density|
|7||AB||Acrylonitrile-butadiene copolymer, nitrile rubber|
|10||ACS||Acrylonitrile-chlorinated polyethylene-styrene copolymer|
|11||AEPDS||Acrylonitrile-ethylene-propylene diene-styrene copolymer|
|12||AMMA||Acrylonitrile Methyl Methacrylate Copolymer|
|15||CAB||Cellulose Acetate Butyrate|
|16||CAP||Cellulose Acetate Propionate|
|18||CF||Cellulose formaldehyde resin|
|25||EAA||ethylene-acrylic acid copolymer|
|26||EBAK||Ethylene Butyl Acrylate Copolymer|
|28||EEAK||Ethylene ethyl acrylate copolymer|
|29||EMA||Ethylene-methacrylic acid copolymer|
|30||EP||Epoxides ; epoxy resin or plastic|
|31||ETFE||Ethylene-tetrafluoroethylene copolymer, Fluoroplast-40|
|32||EVA||Ethylene Vinyl Acetate Copolymer|
|33||EVOH||Ethylene-vinyl alcohol copolymer|
|36||LCP||Liquid Crystal Polymer|
|37||MABS||Methyl methacrylate-acrylonitrile-butadiene-styrene copolymer|
|38||MBS||Methyl methacrylate-butadiene-styrene copolymer|
|40||MF||Melamine formaldehyde resin|
|45||PAEK||Polyaryl ether ketone|
|53||PBAT||Polybutylene adipat/ terephthalate|
|61||PCT||Polycyclohexylene dimethyl terephthalate|
|65||PEC||Polyether carbonate or polybutylene succinate/carbonate|
|68||PEEK||Polyether ether ketone|
|72||LLDPE||Linear low density polyethylene|
|73||MDPE||Medium Density Polyethylene|
|79||UHMWPE||Ultrahigh-molecular weight polyethylene|
|81||VLDPE||Ultra High Density Polyethylene|
|82||PF||Phenol formaldehyde resin|
|86||PHB||Polyhydroxybutanoic acid polyhydroxybutyrate|
|92||PLA||Polylactic acid or Polylactide|
|103||PP-HI||High impact polypropylene|
|108||HIPS||High Impact Polystyrene|
|111||PTMAT||Polybutylene adipat/ terephthalate|
|117||PVC-C||Chlorinated polyvinyl chloride|
|118||PVC-U||Unplasticized polyvinyl chloride|
|131||UP||Unsaturated polyester resin|
|132||VCE||Vinyl Chloride Ethylene|
|133||VCEMAK||ethylene methyl acrylate vinyl chloride|
|134||VCEVAC||Vinyl chloride-ethylene vinyl acrylate|
|135||VCMAK||Vinyl Chloride Methyl Acrylate|
|136||VCMMA||Vinyl chloride methyl methacrylate|
|138||VCVAC||Vinyl chloride-vinyl acetate|
|139||VCVDC||Vinyl chloride-vinylidene chloride|
If the identification marks are not found - go to the physical tests. First, the simplest ones
Technically, the concept of density of plastics is used very rarely as a descriptive characteristic. This is due to the fact that many plastics contain all kinds of voids, pores and defects (which directly depends on the culture of production). True density can in principle be determined from the mass and volume using the “Archimedes method”, i.e. displacement of an equal volume of fluid. This method is quite suitable for granular or powder samples. For many materials it is much more convenient to use the so-called. flotation approach, when the sample floats in a liquid with the same density as it.
The density of the liquid used is measured using a hydrometer (ubiquitous alcohol-meters are a variation of a hydrometer with scale markings in percent by volume of alcohol).
Aqueous solutions can be used as model fluids
zinc chloride or magnesium chloride. If the density is below 1 g/cm 3 , methanol/ethanol/water mixtures are suitable.Restriction in the flotation method: the sample should not dissolve/swell in the liquid; the sample must be completely wetted; the sample should be completely absent air bubbles.
It is important to note that carbon black, fiberglass and other fillers can greatly influence the density index. For example, the density can vary depending on the content of the filler from 0.98 g/cm 3 (polypropylene weight. 10% talc) to 1.71 g/cm 3 (polybutylene terephthalate containing weight 50% fiberglass). Foamed polymers generally do not make sense to evaluate the density parameter, there is one air.
In the simplest case, if there are no exact methods for determining the density, you can immerse the test sample in methanol (density at 20 ° C = 0.79 g/cm 3 ), water (1 g/cm < sup> 3 ), a saturated aqueous solution of magnesium chloride (1.34 g/cm 3 ) or a saturated aqueous solution of zinc chloride (2.01 g/cm 3 ). Next, we look at the behavior of a piece of plastic in a liquid, it sinks or floats. This suggests that it is more dense or less than the density of the liquid in which it is immersed. To prepare 1 liter of saturated solution, approximately 1575 g of zinc chloride or 475 g of magnesium chloride are needed. We bring the salt weighed in advance with water to 1 l of the solution and dissolve with constant stirring. Anticipating the question "where do I get the reagents?" - I will answer with a quote from the same novel "The Girl and the Poultry":
But now I dreamed of only one thing - reagents. About chemical reagents. And I, and Vitya, and Seryozha, and even Zhenka Ivanov, recently did not go to the cinema, did not eat ice cream. We spent all the money on reagents. When I finish school, I will enter the university at the Faculty of Chemistry. But I will study there in absentia. And I will go to work in a chemical store. This is my dream, and I will do everything necessary to make it come true.
For these children, in 1966 it was much harder than you,%% username%:)
Having on hand some numbers, you can further estimate what type of polymer is hidden behind the sample. The table below shows the densities of the most common plastics.
|Density (g/cm 3 )||Material|
|0.80||Silicone rubber (filled silicone = & gt; up to 1.25)|
|0.89-0.93||Low Density Polyethylene LDPE|
|0.94-0.98||High density polyethylene HDPE|
|1.1-1.4||Epoxies, unsaturated polyester resins|
|1.19-1.35||Plasticized PVC (approximately 40% plasticizer)|
|1.20-1.22||Polycarbonate (base - bisphenol A)|
|1.26-1.28||Phenol formaldehyde resins (unfilled)|
|1.30-1.41||Phenol-formaldehyde resin filled with organic material (paper, cloth)|
|1.38-1.41||Hard Polyvinyl Chloride|
|1.47-1.52||Urea and melamine formaldehyde resins with organic fillers|
|1.47-1.55||Chlorinated polyvinyl chloride|
|1.5-2.0||Phenoplasts and aminoplasts with inorganic fillers|
|1.8-2.3||Polyester and epoxy resin with glass fiber filler|
In addition to density, one more non-destructive method of research can be the melting point.
As mentioned above, only plastics with the linear structure of macromolecular chains melt. Stitched "hard" plastic softening is not observed until the temperature at which thermal destruction occurs. Accordingly, this feature can, with some reservations, suggest that we have a cured thermoset material in front of us. In general, the melting point (and, by the way, glass transition temperatures too) are a fairly characteristic indicator for a particular type of polymer. True, the glass transition point is almost impossible to determine at home, it requires serious equipment ( DTA everything is there, measurement of the modulus of elasticity, etc.). But the melting point can be more or less accurately measured, as - watch GOST 33454-2015 . One of the most convenient options is the so-called. Kofler table, which gives accuracy up to 2-3 ° C. If there is no thermotable and it is not foreseen - everyone comes up with methods to the best of their ingenuity, there is a precedent with melting a piece of plastic on a glass ampoule with a mercury mercury thermometer :) (note mine is only for strong spirit guys, with a strong hand and a reliable burner, and the rest strongly discouraged)
The downside to temperature identification is the fact that temperature readings can be influenced by both the heating rate and the presence of certain additives, especially plasticizers. The most reliable indicators can be considered the melting point of partially crystallized polymers (for example, various polyamides). Temperature values for the most important plastics are given in the table below.
Data on absent polymers in the table can be found in the book A. Krause, A. Lange, M. Ezrin Plastics Analysis Guide .If this option does not work - it's time to move to the "heavy artillery."
Heavy artillery means of course destruction, which means smoke, soot, flames and unpleasant odors that you have to go through to determine your polymer. Traditionally, I urge all surveys to be carried out either in a workshop equipped with powerful supply and exhaust ventilation, or with a half mask with filter cartridges for “gases and vapors”.
So, when heated, all plastics undergo these or other changes. By the nature of these changes, you can quite accurately determine the type of polymer. For example, aromatic polymers and oligomers: polystyrene, polyethylene terephthalate, epoxy resins, etc. burn with a yellow, highly smoky flame. Blue flame is characteristic of oxygen-containing polymers and oligomers: polyvinyl alcohol, polyamides, polyacrylates. Green flame is observed when burning chlorine-containing polymers: polyvinyl chloride, polyvinylidene chloride. A perfect addition to the color of the flame can be the smell of "burning plastic", under the spoiler some examples.
|Phenolic resins||The smell of phenol|
|Cellulose Acetate||Vinegar or burning paper|
|Cellulose Acetobutyrate||Burning oil|
|Cellulose Nitrate||The smell of camphor and nitrogen oxides|
|Casein-based plastics||The smell of runaway milk, burnt bone, burning hair|
|Carbamide Resins||Formaldehyde and ammonia; fishy smell|
|Amino Resins||Fishy Smell|
|Polyamides||The smell of burning bone or burning hair|
|Polyethylene and polypropylene||Smell of burning paraffin (burning candle)|
|Polystyrene||Smell of domestic gas|
|Polyvinyl||Smell of hydrochloric acid|
|Soft PVC||Hydrochloric acid-like aromatic odor|
|Polyethylene terephthalate||Sweet, Strawberry Smell|
|Polymethyl methacrylate||Sweetish, fruity smell|
In the table below you can see the flame color/smell characteristics for the most common plastics.
The final stage available for home use may be pyrolysis (decomposition at high temperature) of plastic without air. All that is needed for this is to have a reliable gas burner, and a test tube with a stopper (in 1966 such a device was assembled by children from improvised means — see the beginning of the article).
About 0.1 g of the sample of the investigated plastic is placed in a test tube (or some kind of glass tube), closed with a tube with a vapor tube, and heated in a flame of a burner. In some cases, a pad of loose cotton wool or glass wool, which has been moistened with water, is inserted into the open end of the pyrolysis tube. At the open end of the tube should put a piece of wet pH indicator paper.
Heat the test tube slowly so that you can notice how the sample changes and smell the gas
exhausted . Depending on the reaction of pyrolysis gases with a wet indicator, three different groups of plastics can be distinguished: acidic, neutral or alkaline. The table below shows the plastics and the environment, which is formed by the gases arising from their decomposition, upon contact with water. Depending on the composition, some plastics can float up in pyrolysis dough in different groups, for example, phenol-formaldehyde resins or polyurethanes
|pH 0.5 - 4.0||pH 5.0 - 5.5||pH 8.0 - 9.5|
|Halogen-containing polymers (PVC, etc.)||Polyolefins (PE, PP)||Polyamides|
|Polyvinyl Esters||Polyvinyl alcohol||ABS polymers|
|Cellulose Ethers||Polyvinyl Acetals||Polyacrylonitrile|
|Polyethylene terephthalate||Polyvinyl Esters||Phenolic and cresol resins|
|Phenol formaldehyde resins||Styrene polymers (SAN, etc.)||Aminosmols (aniline-, melamine-, urea-formaldehyde resins|
|Polyurethane Elastomers||Polymethyl methacrylates|
|Unsaturated Polyester Resins||Polyformaldehyde|
|Vulcanized Fibers||Linear Polyurethanes|
And finally, dear reader, if you have read the rest of the article, you can safely consider yourself to have completed the “young polymer research” course and easily use plastic identification algorithms like the one below (the image is clickable).
That's all, divide and conquer
over your polymers ! Introduction to plastic identification is complete, subscribe to my Facebook / VKontakte notes to know more and be in the subject of recent surveys (or ask the main question of life, the universe and all that) !
Sergey Besarab ( Siarhei V. Besarab )
PS : when working with polymers and searching for information on the properties of these, I use the MatWeb: Online Materials Information Resource Polymer Properties Database , AZOM Materials Information , MatMatch , and of course the references listed in the list of references. What do you want!:)
He, J., Chen, J., Hellwich, K., et al . (2014). Abbreviations of polymer names (IUPAC Recommendations 2014). Pure and Applied Chemistry, 86 (6), pp. 1003-1015.
Vydrina TS Polymer Identification Methods Ekaterinburg, 2005
A. Krause, A. Lange, M.Ezrin Plastics Analysis Guide. Hanser Publishers, 1983.
Bark, L. S., Allen, N. S. Analysis of Polymer Systems. Applied Science Publishers Ltd., London, 1982.
Compton, T. R. Chemical Analysis of Additives in Plastics, 2 nd ed. Pergamon, Oxford, New York, 1977.
Ullmann's Polymers and Plastics: Products and Processes: Wiley-VCH
Haslam, J., Willis, H. A., Squirrel, D. C. M. Identification and Analysis of Plastics, 2 nd ed. Butterworth, London, 1972
Mitchell, J. Jr. Applied Polymer Analysis and Characterization. Hanser Publishers, Munich, Vienna, 1987.
Dietrich B. Methods for Identification of Plastics. Hanser
Schröder, E., Müller, G., Arndt K.-F. Polymer Characterization. Hanser Publishers, Munich, New York, 1989.
Verleye, G.A.L., Roeges, N.P.G., De Moor, M.O. Easy Identification of Plastics and Rubber. Rapra Technology Ltd., Strawbury, 2001.