Big encyclopedia of oil and gas. Atactic polypropylene: properties and applications

Polypropylene (PP)- a colorless polymer related to thermoplastics - synthetic materials that change their plasticity when heated. Melting temperature 160-170 С, density 900-910 kg / m 3, elongation without destruction 200-400%, insoluble in organic solvents. Resistant to hot water (up to 130C) and aggressive environments, except for strong oxidants (concentrated nitric and sulfuric acids). In thin films, it is practically transparent (96%).

For material characterized by high impact strength, resistance to repeated bending, good wear resistance. The material does not conduct heat well, does not conduct electric current. Thin films, fibers and filaments are produced from granular material by extrusion. Distinguish two main methods of film extrusion: Blown hose extrusion and flat slit extrusion. The first method produces a film sleeve that can be folded or cut. If the incision is made in one or more places along the sleeve, then a so-called half-sleeve is obtained. Cutting the sleeve lengthwise from both sides, you can get a web. In the second method (flat-slit extrusion), a film web is obtained. The film can be non-oriented and oriented.

Orientation of films (orientation of molecules in a material) is achieved by stretching them in a heated state during extrusion. Of the oriented films, the most widely used is biaxially oriented (BOPP) film.

This film has a tensile strength 3-4 times that of non-oriented material.

Such films are frost-resistant down to -50C, high strength, wear resistance and elasticity at the same time. Biaxially oriented films due to their ability to withstand significant mechanical loads, they are used for packaging various food products and other industrial goods on automatic lines. As a disadvantage of BOPP films, it is possible to note the weldability worse than that of films made of non-oriented PP.

Non-oriented film is produced mainly by blown tube extrusion, and biaxially oriented using flat-slit extrusion.

Differences between propylene and polyethylene

The difference between polypropylene and polyethylene and other types of plastics lies in the lower density category, with high level resistance to impact the environment(that is, to light, temperature and oxygen). The strength of this material is higher, so the abrasion resistance is also increased. A change in mechanical properties is observed during the aging process of the material. From this polypropylene protect stabilizers, which are introduced to protect the material not only during use, but also during manufacture. An important quality of polypropylene is water resistance. Resistance to aggressive media, as well as environmental factors is confirmed by many experiments.

The melting point of this material is significantly higher than that of polyethylene; therefore, it is subject to heat treatment with steam and hot water without loss of properties. Also, polypropylene is characterized by a low level of electrical conductivity. A feature of the material is also frost resistance.

All these properties of polypropylene allow you to successfully use it as a packaging material. Its high strength and durability, as well as resistance to environmental factors, allows it to be used as packaging for food.

Polypropylenes differ in molecular structure - it can be isotactic, syndiotactic and atactic polypropylene. The chemical and physical properties of different types of material differ. The main properties possessed by polypropylene can be reflected in the following table.

Polymers and materials made from them, household items, equipment are an important part of industry and human life in general. Natural resources, unfortunately, have been greatly depleted during their use. Therefore, people had to learn how to synthesize artificial materials that have a number of important technical characteristics. One of these is polypropylene. The chemical formula of this compound, the features of its properties and the structure of the molecule will be considered in the course of the article.

Polymers - general characteristics

This class of compounds includes those that have a very high value. After all, polymers are complex organic compounds consisting of repetitive monomer units, which can be from several tens to hundreds, thousands and millions.

Among all polymers, the following groups can be distinguished:

Natural origin - proteins, nucleic acids, ATP molecules, and so on.
Artificial - those that are created on the basis of natural, but have been chemically modified in order to improve technical characteristics. For example, artificial rubbers.
Synthetic - those that are created only by chemical reactions, synthesis in laboratories and industrial plants. Examples include synthetic fabrics and fibers, polyethylene, polyvinyl chloride, polypropylene, and others.

All designated groups of polymers are important industrial raw materials for the production and production of various equipment, household items, dishes, toys, furniture and other things.

Representatives of the most important synthetic polymers

The chemical formula of one of the most important representatives of synthetic polymers is written as (-CH 2 -CH 2 -) n. This is polyethylene. The areas of its use are known. These are household needs (household film), and industrial and food industries (packaging material). However, although it is the most common, it is far from the only representative that is extremely important for humans. You can also name such polymers as:

polyvinyl chloride;
polypropylene;
polyisobutylene;
polystyrene;
teflon;
polyvinyl acetate and others.

It is in the construction business, as well as for the manufacture of dishes, such a material as polypropylene plays an important role. Therefore, further we will consider precisely its features from a chemical point of view.

Polypropylene formula

From the point of view of the science of chemistry, the composition of a given substance can be expressed different kinds formulas. The first option is molecular notation. In this case, the polypropylene formula looks like this: (C 3 H 6) n. The last n denotes the degree of polymerization, that is, the number of structural starting units in the macrochain.

Such a record allows one to draw a conclusion about the qualitative and quantitative composition of the molecule. Polypropene consists of carbon and hydrogen atoms, and their number in the monomer unit is 3/6, respectively, and in the total chain depends on the index n. If we talk about the very structure of the compound, about the order of the bonds of atoms in the molecule, then another type of recording of the substance is needed.

Polypropylene: structural formula

The type of record that shows the order in which atoms are joined in a molecule is called a structural formula. For the substance we are considering, it will look like this: (-CH 2 -CH-CH 3 -) n. It is obvious that the generally accepted valence of atoms in organic chemistry is retained in this case as well. The formula of polypropylene or polypropene indicates which monomer unit is the basis of the compound. It is formed from propene (alkene) or propylene. His empirical formula: C 3 H 8.

Starting monomer

The monomer formula for polypropylene production is as follows: (—CH 2 —CH — CH 3 -). If this fragment is repeated several hundred times, then we get a whole macromolecule, which is the material in question. In addition, we have already indicated that, in general, an ordinary alkene, propene, should be considered the starting material. He is a polypropylene monomer. will be written as CH 3 -CH = CH 2. When the double bond is broken during polymerization, the desired fragment is formed. The same monomeric unit that repeats itself forms a polymer macromolecule.

Physical and chemical properties

The formula of polypropylene (-CH 2 -CH-CH 3 -) n makes it possible to judge its physical and chemical characteristics. Let's list the main ones.

Physical properties of this polymer: density 0.91 g / cm 3, hard, abrasion resistant, does not corrode. The color is white, opaque. There is no smell. It is insoluble in water and organic solvents at normal temperatures. When the index is over 100 0 С, it dissolves in hydrocarbon compounds. It begins to soften after 140 0 С, melts at 170 0 С. Possesses heat and frost resistance.
Chemical properties. In terms of activity, polypropene can be classified as an almost inert substance. It is capable of interacting only with particularly strong oxidants: fuming nitric, chlorosulfonic acids, oleum, active halogens (fluorine, chlorine). It does not interact with water at all, even at elevated temperatures. It reacts with oxygen only when irradiated with ultraviolet light, the process is accompanied by the destruction of the polymer. In organic solvents, it swells and dissolves with increasing temperature.

The indicated properties can be attributed to the technical characteristics of the material itself, which is used in industry. However, not all polypropylene is created equal. There are special stabilizing additives with which different grades of the polymer in question are created.

Material specifications

There are several basic properties that the polypropylene material possesses. Its characteristics are as follows:

When heated, it is capable of melting, preliminarily softening.
Does not have conductive properties.
Shock-resistant, durable.
Resistant to abrasion.
It ages when exposed to the sun and oxygen, but the process is quite slow.
As a polymer, it has a low molecular weight.
It is white, translucent, tasteless and odorless.
When burned, it does not emit harmful substances, it emits a light floral aroma.
It is flexible, durable, resistant to various kinds of dirt.
Possesses heat and frost resistance.

All the indicated properties of polypropylene as a material allow it to be used for various needs. It is easy to use, easy to maintain and use in practice in any branch of the national economy.

In total, there are three main types of this material:

attacking;
syndiotactic;
isotactic.

The main difference in them is, specifically, the arrangement of methyl groups in the chain. Also on specifications stabilizing additives, the number of monomer units in the macrostructure have an effect.

This material is produced either in the form of crystalline granular structures, or in the form of fibers, sheets.

Areas of use

Polypropylene material is used for the production of various films, packaging containers, food containers. It is from it that ordinary plastic cups and other items of disposable tableware are made. This material is used to make durable, chemical-resistant polypropylene sanitary pipes.

It is also used to create noise-proof materials. Duct tape is also a type of polypropylene.

Attactic material is used to manufacture:

mastic;
adhesives;
putty;
sticky tapes;
road surfaces and so on.

A large number of polypropylene sheets, fibers are used for the manufacture of toys, stationery, household and household items.

It is a waxy mass white(thin sheets are transparent and colorless). Chemically and frost-resistant, insulator, not sensitive to shock (shock absorber), softens when heated (80-120 ° C), solidifies when cooled, adhesion is extremely low. Sometimes in the popular mind it is identified with cellophane - a similar material of plant origin.

Receiving

For processing comes in the form of granules from 2 to 5 mm. Polyethylene is obtained by polymerizing ethylene:

High pressure polyethylene production

High pressure polyethylene(LDPE), or Low density polyethylene(LDPE) is formed under the following conditions:

temperature 200-260 ° C;
pressure 150-300 MPa;
the presence of an initiator (oxygen or organic peroxide);

in autoclave or tubular reactors. The reaction proceeds by a radical mechanism. The polyethylene obtained by this method has a weight average molecular weight of 80,000-500,000 and a degree of crystallinity of 50-60. The liquid product is subsequently granulated. The reaction takes place in the melt.

Production of medium-pressure polyethylene

Medium Density Polyethylene(ESD) is formed under the following conditions:

temperature 100-120 ° C;
pressure 3-4 MPa;
the presence of a catalyst (Ziegler-Natta catalysts, for example, a mixture of TiCl 4 and R 3);

the product falls out of solution in the form of flakes. The polyethylene obtained by this method has a weight average molecular weight of 300,000-400,000, a degree of crystallinity of 80-90%.

Getting low-density polyethylene

Low-pressure polyethylene(HDPE) or High density polyethylene(HDPE) is formed under the following conditions:

temperature 120-150 ° C;
pressure below 0.1 - 2 MPa;
the presence of a catalyst (Ziegler-Natta catalysts, for example, a mixture of TiCl 4 and R 3);

Polymerization proceeds in suspension according to the ion-coordination mechanism. The polyethylene obtained by this method has a weight average molecular weight of 80,000-3,000,000, a degree of crystallinity of 75-85%.

It should be borne in mind that the names "low pressure polyethylene", "medium pressure", "high density", etc. have a purely rhetorical meaning. So, polyethylene obtained by methods 2 and 3 has the same density and molecular weight. The pressure during polymerization at the so-called low and medium pressures is in some cases the same.

Other methods of producing polyethylene

There are other methods of ethylene polymerization, for example, under the influence of radioactive radiation, but they have not received industrial distribution.

Polyethylene modifications

The range of ethylene polymers can be significantly expanded by obtaining copolymers of ethylene with other monomers, as well as by obtaining compositions by compounding one type of polyethylene with another type of polyethylene, polypropylene, polyisobutylene, rubbers, etc.

Numerous modifications can be obtained on the basis of polyethylene and other polyolefins - graft copolymers with active groups that improve the adhesion of polyolefins to metals, paintability, reduce its flammability, etc.

Modifications of the so-called "cross-linked" polyethylene PE-C (PE-X) stand apart. The essence of stitching is that the molecules in the chain are connected not only in series, but also side bonds are formed that connect the chains to each other, due to this, the physical and to a lesser extent Chemical properties products.

There are 4 types of cross-linked polyethylene (according to the production method): peroxide (a), silane (b), radiation (c) and nitrogen (d). The most widespread is PEX-b, as the fastest and cheapest in production.

Molecular structure

High pressure polyethylene macromolecules ( n≅1000) contain side hydrocarbon chains C 1 -C 4, medium-pressure polyethylene molecules are practically unbranched, there is a greater proportion of the crystalline phase in it, therefore this material is denser; low pressure polyethylene molecules occupy an intermediate position. The large number of side branches explains the lower crystallinity and, accordingly, the lower density of LDPE compared to HDPE and PESD.

Indicators characterizing the structure of the polymer chain of various types of polyethylene:
Index	LDPE	ESD	HDPE
The total number of CH 3 groups per 1000 carbon atoms:
The number of end groups CH 3 per 1000 carbon atoms:
Ethyl branches
The total number of double bonds per 1000 carbon atoms
including:
vinyl double bonds (R-CH = CH 2),%
vinylidene double bonds (),%
trans-vinylene double bonds (R-CH = CH-R '),%
Crystallinity,%
Density, g / cm³

Low pressure polyethylene (HDPE)

Physicochemical properties of HDPE at 20 ° C:

Parameter

Meaning

Density, g / cm³

Breaking stress, kgf / cm²

under tension

under static bending

at cut

elongation at break,%

flexural modulus, kgf / cm²

tensile yield strength, kgf / cm²

elongation at the beginning of the flow,%

It is insoluble at room temperature and does not swell in any of the known solvents. At elevated temperatures (80 ° C) we will dissolve in cyclohexane and carbon tetrachloride. It can be dissolved under high pressure in water overheated to 180 ° C.

Over time, it degrades with the formation of cross-chain links, which leads to increased brittleness with a slight increase in strength. Unstabilized polyethylene undergoes thermal oxidative degradation (thermal aging) in air. Thermal aging of polyethylene proceeds by a radical mechanism, accompanied by the release of aldehydes, ketones, hydrogen peroxide, etc.

Low-pressure polyethylene (HDPE) is used in the construction of waste disposal sites, storage facilities for liquid and solid substances that can pollute soil and groundwater.

Processing

Polyethylene (except ultramolecular) is processed by all methods known for plastics, such as extrusion, blow molding, injection molding, and pneumatic molding. Extrusion of polyethylene is possible on equipment with an installed "universal" worm.

Application

Plastic wrap (especially packaging, such as bubble wrap or scotch tape),
Containers (bottles, jars, boxes, cans, garden watering cans, seedling pots)
Polymer pipes for sewerage, drainage, water and gas supply.
Polyethylene powder is used as hot melt glue.
Armor (armored panels in body armor)
Hulls for boats, all-terrain vehicles

Details of technical equipment, dielectric antennas, household items, etc.; Low-tonnage grade of polyethylene - the so-called "ultra-high molecular weight polyethylene", characterized by the absence of any low molecular weight additives, high linearity and molecular weight, is used for medical purposes as a replacement for cartilage tissue of joints. Despite the fact that it compares favorably with HDPE and LDPE in its physical properties, it is rarely used due to the difficulty of its processing, since it has a low MFR and is processed only by casting.

n CH 2 = CH (CH 3) → [-CH 2 -CH (CH 3) -] n

International designation - PP.

The parameters required to obtain polypropylene are close to those at which low-pressure polyethylene is obtained. In this case, depending on the specific catalyst, any type of polymer or mixtures thereof can be obtained.

Polypropylene is produced in the form of white powder or granules with a bulk density of 0.4-0.5 g / cm³. Polypropylene is produced stabilized, dyed and unpainted.

Molecular structure

By the type of molecular structure, three main types can be distinguished: isotactic, syndiotactic and atactic. Isotactic and Syndiotactic are generated randomly;

Physical and mechanical properties

Unlike polyethylene, polypropylene is less dense (density 0.91 g / cm 3, which is the lowest value in general for all plastics), harder (resistant to abrasion), more heat-resistant (begins to soften at 140 ° C, melting point 175 ° C), hardly undergoes stress corrosion cracking. Possesses high sensitivity to light and oxygen (sensitivity decreases with the introduction of stabilizers).

The tensile behavior of polypropylene, even more than polyethylene, depends on the rate of application of the load and on the temperature. The lower the stretching rate of polypropylene, the higher the value of the mechanical properties. At high tensile rates, the tensile breaking stress of polypropylene is well below its tensile yield strength.

Indicators of the main physical and mechanical properties of polypropylene are shown in the table:

The physical and mechanical properties of polypropylene of different grades are shown in the table:

Physical and mechanical properties of polypropylene of various grades

Indicators / brand

01P10 / 002

02P10 / 003

03P10 / 005

04P10 / 010

05P10 / 020

06P10 / 040

07P10 / 080

08P10 / 080

09P10 / 200

Bulk density, kg / l, not less

Melt flow rate, g / 10 min

Elongation at break,%, not less

Yield strength at break, kgf / cm², not less

Cracking resistance, h, not less

Heat resistance according to the NIIPP method, ° C

Polyethylene (PE): physicochemical and consumer properties, consumption structure, polyethylene applications

Polyolefins are the most common type of polymers produced by polymerization and copolymerization of unsaturated hydrocarbons (ethylene, propylene, butylene and other alpha-olefins). About 50% of the ethylene produced in the world is used for the production of polyethylene.

The chemical structure of a polyethylene molecule is simple and is a chain of carbon atoms, to each of which two hydrogen molecules are attached.
Polyethylene (PE) [–CH2-CH2–] n exists in two modifications, differing in structure and, therefore, in properties. Both modifications are obtained from ethylene CH2 = CH2. In one form, the monomers are linked in linear chains with a degree of polymerization (DP), usually 5000 or more; in the other, branches of 4-6 carbon atoms are randomly attached to the main chain. Linear polyethylenes are produced using special catalysts; polymerization proceeds at moderate temperatures (up to 150 ° C) and pressures (up to 20 atm.).
Polyethylene is a thermoplastic polymer, opaque in a thick layer, crystallizes in the temperature range from minus 60 ° C to minus 369 ° C; not wetted with water, at room temperature does not dissolve in organic solvents, at temperatures above 80 ° C first swells and then dissolves in aromatic hydrocarbons and their halogen derivatives; PE is resistant to the action of aqueous solutions of salts, acids, alkalis, but at temperatures above 60 ° C sulfuric and nitric acids quickly destroy it. Short-term processing of PE with an oxidizing agent (for example, a chromium mixture) leads to oxidation of the surface and wetting it with water, polar liquids and adhesives. In this case, PE products can be glued.
Ethylene can be polymerized in several ways, depending on this, polyethylene is divided into: high pressure polyethylene (LDPE) or low density (LDPE); low density polyethylene (HDPE) or high density (HDPE); and also for linear polyethylene.
LDPE is polymerized in a radical way under pressure from 1000 to 3000 atmospheres and at a temperature of 180 degrees. Oxygen serves as the initiator.
HDPE is polymerized at a pressure of at least 5 atmospheres and a temperature of 80 degrees using Ziegler-Natta catalysts and an organic solvent.
Linear polyethylene (also called medium-pressure polyethylene) is produced at 30-40 atmospheres and a temperature of about 150 degrees. Such polyethylene is, as it were, an "intermediate" product between HDPE and LDPE in terms of properties and qualities.
Not so long ago, a technology began to be applied, which uses the so-called metallocene catalysts. The meaning of the technology lies in the fact that it is possible to achieve a higher molecular weight of the polymer, which, accordingly, increases the strength of the product.
In terms of their structure and properties (despite the fact that the same monomer is used), LDPE, HDPE, linear polyethylene differ, and, accordingly, are used for different tasks. LDPE is a soft material, HDPE and linear polyethylene have a rigid structure.
Differences also appear in density, melting point, hardness, and strength.
Comparative characteristics high and low pressure polyethylene (LDPE and HDPE)

The main reason for the differences in the properties of PE is the branching of macromolecules: the more branches in the chain, the higher the elasticity and less crystallinity of the polymer. The branching complicates a denser packing of macromolecules and prevents the achievement of a degree of crystallinity of 100%; along with the crystalline phase, there is always an amorphous phase containing insufficiently ordered sections of macromolecules. The ratio of these phases depends on the method of obtaining PE and the condition of its crystallization. It also determines the properties of the polymer. LDPE films are 5-10 times more permeable than HDPE films.
The mechanical properties of PE increase with increasing density (degree of crystallinity) and molecular weight. In the form of thin films, PE (especially a low density polymer) has greater flexibility and some transparency, and in the form of sheets it becomes more rigid and opaque.
Polyethylene is shock-resistant. Frost resistance can be noted among the most important properties of polyethylene. They can be operated at temperatures from -70 ° C to 60 ° C (LDPE) and up to 100 ° C (HDPE), some brands retain their valuable properties at temperatures below -120 ° C.
Polyethylenes, being saturated hydrocarbons, are resistant to many aggressive media (acids, alkalis, etc.) and organic liquids.
A significant disadvantage of polyethylene is its rapid aging. The aging period is increased due to special additives - antioxidants (phenols, amines, carbon black).
The melt viscosity of LDPE is higher than HDPE, so it is easier to process into products.
In terms of electrical properties, PE, as a non-polar polymer, belongs to high-quality high-frequency dielectrics, the dielectric constant and dielectric loss tangent change little with a change in the frequency of the electric field, temperature ranging from minus 80 ° C to 100 ° C and humidity. However, the catalyst residues in HDPE increase the dielectric loss tangent, especially with a change in temperature, which leads to some deterioration of the insulating properties.
Low pressure polyethylene PEHD
Light elastic crystallizing material with heat resistance of certain brands up to 110 ° C. Allows cooling down to -80 0С. Melting temperature of grades: 120-135 0С. Glass transition temperature: approx. -20 0С. Gives a shiny surface.
It is characterized by good impact resistance and higher heat resistance compared to LDPE.
Properties are highly dependent on the density of the material. An increase in density leads to an increase in strength, stiffness, hardness, and chemical resistance. At the same time, with an increase in density, the impact resistance at low temperatures, elongation at break, and permeability to gases and vapors decrease.
High creep is observed under prolonged loading. Has a very high chemical resistance (more than LDPE). It has excellent dielectric characteristics. Biologically inert. Easily recyclable.

Indicators (23 0С)	Values for unfilled stamps
Density	0.94-0.97 g / cm3
Vicat heat resistance (in liquid medium, 50 0С / h, 50N)
Tensile yield strength (50 mm / min)
Tensile modulus (1 mm / min)
Tensile Elongation (50mm / min)
Charpy impact strength (notched sample)
Ball indentation hardness (358 N, 30s)
Specific surface electrical resistance	10 ^ 14-10 ^ 15 Ohm
Water absorption (24h, humidity 50%)

HDPE polyethylene (high density) is used mainly for the production of containers and packaging. Abroad, about a third of the polymer produced is used for the manufacture of blow molded containers (containers for food products, perfumery and cosmetic products, automotive and household chemicals, fuel tanks and barrels). It should be noted that in comparison with other areas, the use of HDPE for the production of packaging films is growing at an outstripping pace. PE ND is also used in the production of pipes and pipeline parts, where such advantages of the material as durability (service life - 50 years), simplicity of butt welding, low cost (on average 30% lower than in metal pipes).
High pressure polyethylene

Other designations: PE-LD, PEBD (French and Spanish designations).
Light elastic crystallizing material with no load heat resistance up to 60 ° C (for some brands up to 90 ° C). Allows cooling (various grades in the range from -45 to -120 ° C).
Properties are highly dependent on the density of the material. An increase in density leads to an increase in strength, stiffness, hardness, and chemical resistance. At the same time, with an increase in density, impact resistance at low temperatures, elongation at break, fracture toughness, and permeability to gases and vapors decrease. Prone to stress cracking. Does not differ in dimensional stability.
It has excellent dielectric characteristics. Has a very high chemical resistance. Not resistant to fats, oils. Not UV resistant. Differs in increased radiation resistance. Biologically inert. Easily recyclable.
Characteristics of the brand assortment
(minimum and maximum values for industrial brands)

Application examples

LDPE polyethylene (low density) is used mainly in the production of food, technical, agricultural films and for insulation of pipelines. IN last years abroad the most actively growing volume of consumption and production of linear low density polyethylene, which in a number of foreign countries has largely displaced from the main market segments (film production) LDPE.
Linear polyethylene LLDPE

Other designations: PE-LLD, L-LDPE
Lightweight elastic crystallizing material. Heat resistance up to 118 0С. Has greater resistance to cracking, impact strength and heat resistance than low density polyethylene (LDPE). Biologically inert. Easily recyclable. Provides less warpage and greater dimensional stability than LDPE.
Characteristics of the brand assortment
(minimum and maximum values for industrial brands)

Application examples

Package. Containers (including for food products), containers.
Sevilen: TU 6-05-1636-97
Sevilen, a copolymer of ethylene with vinyl acetate, is a high molecular weight compound related to polyolefins. It is obtained by a method similar to the method for the production of low density polyethylene (high pressure).
Sevilen is superior to polyethylene in transparency and elasticity at low temperatures, has increased adhesion to various materials.
The sevilen property depends mainly on the vinyl acetate content (5-30 wt.%). With increasing vinyl acetate content, crystallinity, breaking tensile stress, hardness, heat resistance decrease, while coke density, elasticity, transparency, adhesion increase.
Sevilen with a vinyl acetate content of up to 15% (grades 11104-030, 11306-075) is processed by the same methods as low-density polyethylene, but processing by extrusion and injection molding is carried out at a lower temperature.
Sevilen grades 11104-030, 11306-075 can be used to make blown products, hoses, gaskets, toys. From the same grades of sevilen, weather-resistant, transparent films are obtained, which, in comparison with polyethylene films, have a lower melting point.
High adhesion properties of sevilen and good compatibility with waxes make it possible to use it as a coating for paper and cardboard in the production of containers. For these purposes, Sevilen is used with a vinyl acetate content of 21-30 wt. % (grades 11507-070, 11708-210, 11808-340).
An important area of using sevilen is the preparation of hot melt adhesives on its basis. Hot melt adhesives do not contain solvents, at room temperature they are solids... They are used in molten form at a temperature of 120 - 200C.
To obtain hot melt adhesives, Sevilen is used, containing 21-30 wt.% Of vinyl acetate (grades 11507-070, 11708-210, 11808-340). Sevilen-based hot melt adhesives are widely used in printing, furniture, footwear and other industries.
Sevilen combines well with various fillers, which leads to a wide distribution of filled products.
Table of quality indicators of sevilen brands TU 6-05-1636-97

The name of indicators	Sevilen 11104-030	Sevilen 11205-040	Sevilen 11306-075	Sevilen 11407-027	Sevilen 12206-007	Sevilen 12306-020
Density, g / cm2
Melt flow rates, g / 10 min, within: at t = 190 0С
The spread of the melt flow rate within the batch,%
Mass fraction of vinyl acetate,% within
Number of inclusions, pcs. no more
Breaking strength, MPa (kgf / cm2), not less
Elongation at break,%, not less
Adhesive strength, N / mm (kgf / cm), not less
Resistance to thermal oxidative aging, h, not less, for recipes 02, 03, 06
Resistance to thermal oxidative aging, h, not less, for recipes 05.07				not standardized	not standardized	not standardized
Redesign method		extrusion, casting	extrusion, casting, compounding	extrusion	extrusion, casting	extrusion, casting

The complex of physical, mechanical, chemical and dielectric properties of PE determines its consumer properties and allows it to be widely used in many industries (cable, radio engineering, chemical, light, medicine, etc.).
PE consumption structure,%

Insulation of electrical wires... High dielectric properties of polyethylene and its mixtures with polyisobutylene, low permeability to water vapor allow it to be widely used for insulating electrical wires and making cables used in various communications (telephone, telegraph), signaling devices, dispatch telecontrol systems, high-frequency installations, for winding wires motors operating in water, as well as for insulating submarine and coaxial cables.
Polyethylene insulated cable has advantages over rubber insulation. It is lighter, more flexible and has greater electrical strength. A wire covered with a thin layer of polyethylene can have a plasticized polyvinyl chloride top layer that provides good mechanical protection against damage.
In the production of cables, LDPE is used, crosslinked with small amounts (1-3%) of organic peroxides or irradiated with fast electrons.
Films and sheets. Films and sheets can be made of PE of any density. In the production of thin and elastic films, LDPE is more widely used.
Films are made by two methods: extrusion of molten polymer through an annular slot followed by blowing or extrusion through a flat slot followed by stretching. They are produced with a thickness of 0.03-0.30 mm, a width of up to 1400 mm (in some cases up to 10 m) and a length of up to 300 m.
In addition to thin films, sheets with a thickness of 1-6 mm and a width of up to 1400 mm are made from PE. They are used as lining and electrical insulating materials and are processed into technical products for household use by the method of vacuum forming.
Most of the LDPE products serve as packaging material, competing with other films (cellophane, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyethylene terephthalate, polyvinyl alcohol, etc.), a smaller part is used for the manufacture of various products (bags, bags, boxes and boxes for other types of containers).
Films are widely used for packaging frozen meat and poultry, in the manufacture of balloons and balloons for meteorological and other studies of the upper atmosphere, protection against corrosion of oil and gas pipelines. IN agriculture transparent film is used to replace glass in greenhouses and greenhouses. The black film is used to cover the soil in order to retain heat when growing vegetables, fruit and berry and legumes, as well as for lining silo pits, the bottom of reservoirs and canals. More and more plastic sheeting is used as a material for roofs and walls in the construction of premises for storing crops, agricultural machines and other equipment.
Household items are made of polyethylene film: raincoats, tablecloths, curtains, napkins, aprons, kerchiefs, etc. The film can be applied on one side to various materials: paper, fabric, cellophane, metal foil.
Reinforced polyethylene film is more durable than conventional film of the same thickness. The material consists of two films, between which there are reinforcing threads made of synthetic or natural fibers or a rare glass fabric.
Tablecloths are made from very thin reinforced films, as well as films for greenhouses; from thicker films - bags and packaging material. Reinforced film, reinforced with a rare glass cloth, can be used for the manufacture of protective clothing and used as a lining material for various containers.
On the basis of PE films, adhesive (adhesive) films or tapes can be made, suitable for repairing high-frequency communication cable lines and for protecting steel underground pipelines from corrosion. Polyethylene films and tapes with an adhesive layer contain on one side a layer of low molecular weight polyisobutylene, sometimes mixed with butyl rubber. They are produced with a thickness of 65-96 microns, a width of 80-I50 mm.
LDPE and HDPE are also used to protect metal products from corrosion. The protective layer is applied by flame and vortex spraying methods.
Pipes. Of all types of plastics, PE has found the greatest application for the manufacture of extrusion and centrifugal casting of pipes, characterized by lightness, corrosion resistance, insignificant resistance to fluid movement, ease of installation, flexibility, frost resistance, ease of welding.
The continuous method produces pipes of any length with an internal diameter of 6-300 mm and a wall thickness of 1.5-10 mm. Polyethylene pipes small diameters are wound on drums. By injection molding, fittings are manufactured for pipes, which include bent pipes bent at an angle of 45 and 90 degrees; tees, couplings, crosses, branch pipes. Large diameter pipes (up to 1600 mm) with a wall thickness of up to 25 mm are produced by centrifugal casting.
Due to their chemical resistance and elasticity, polyethylene pipes are used to transport water, solutions of salts and alkalis, acids, various liquids and gases in the chemical industry, for the construction of internal and external water supply networks, in irrigation systems and sprinkler installations.
LDPE pipes can operate at temperatures up to 60 ° C, and HDPE pipes - up to 100 ° C. Such pipes do not collapse at low temperatures (up to - 60 ° C) and when water freezes; they are not subject to soil corrosion.
Molding and injection molding... Extruded or extruded polyethylene sheets can be made into various articles by stamping, bending, or vacuum forming. Large-sized items (boats, baths, tanks, etc.) can also be made of polyethylene powder by sintering it on a heated mold. Separate parts of the products can be welded using a hot air jet heated to 250 ° C.
Valves, hoods, containers, parts of fans and pumps for acids, agitators, filters, various containers, buckets, etc. can be made by molding and welding.
One of the main methods of processing PE into products is injection molding. Bottles made of polyethylene with a volume of 25 to 5000 ml, as well as dishes, toys, electrical products, lattice baskets and boxes, are widely used in the pharmaceutical and chemical industries.
The choice of a particular technological process is determined primarily by the need to obtain a branded assortment with a certain set of properties. The suspension method is appropriate for the production of polyethylene of pipe grades and grades of polyethylene intended for processing by the extrusion method, as well as for the production of high molecular weight polyethylene. With the involvement of mortar technologies, LLDPE is obtained for high-quality packaging films, grades of polyethylene for the manufacture of articles by casting and rotational molding. The gas-phase method is used to produce a branded range of polyethylene intended for the manufacture of consumer goods.

Plastics

Chains of polypropylene molecules.

Household items made in whole or in part of plastic

Plastics(plastic masses) or plastic- organic materials based on synthetic or natural high molecular weight compounds (polymers). Plastics based on synthetic polymers are extremely widely used.

The name "plastics" means that these materials, under the action of heat and pressure, are able to form and maintain a given shape after cooling or hardening. The molding process is accompanied by the transition of the plastically deformable (viscous-flow) state to the glassy state.

History

The first plastic was produced by the English metallurgist and inventor Alexander Parks in 1855. Parkes named it parkesin (later another name was spread - celluloid). Parkesin was first presented at the Great International Exhibition in London in 1862. The development of plastics began with the use of natural plastic materials (for example, chewing gum, shellac), then continued with the use of chemically modified natural materials (such as rubber, nitrocellulose, collagen, galalite) and finally came to fully synthetic molecules (Bakelite, epoxy resin, polyvinyl chloride, polyethylene and others).

Parkesin was the trademark of the first man-made plastic and was made from cellulose treated with nitric acid and a solvent. Parkesin was often called artificial ivory. In 1866, Parkes created the Parkesine Company to mass-produce the material. However, in 1868 the company went bankrupt due to poor product quality as Parks tried to cut production costs. Parkesin's successor was xylonite (another name for the same material), produced by the company of Daniel Spill, a former employee of Parks, and celluloid, produced by John Wesley Hyatt.

Types of plastics

Depending on the nature of the polymer and the nature of its transition from the viscous to the glassy state during the molding of products, plastics are divided into

Thermoplastics ( thermoplastic plastics) - when heated, they melt, and when cooled, they return to their original state.
Reaktoplasts ( thermosetting plastics) - differ in higher operating temperatures, but when heated they are destroyed and during subsequent cooling do not restore their original properties.

Receiving

The production of synthetic plastics is based on the reactions of polymerization, polycondensation or polyaddition of low molecular weight starting materials extracted from coal, oil or natural gas. In this case, high molecular weight bonds are formed with a large number of starting molecules (the prefix "poly-" from the Greek "many", for example, ethylene-polyethylene).

Processing methods

Casting / injection molding
Pressing
Vibration shaping
Foaming
Casting
Welding

Mechanical restoration

Plastics, in comparison with metals, have increased elastic deformation, as a result of which higher pressures are used when processing plastics than when processing metals. As a rule, it is not recommended to use any lubricant; only in some cases mineral oil is allowed for finishing. Cool the product and tool with a jet of air.

Plastics are more fragile than metals, therefore, when processing plastics with cutting tools, it is necessary to use high speeds cutting and reduce the feed. Tool wear when processing plastics is much greater than when processing metals, which is why it is necessary to use tools made of high-carbon or high-speed steel or hard alloys. The blades of cutting tools should be sharpened as sharply as possible, using fine-grained wheels for this.

Plastic can be processed on a lathe, can be milled. For sawing, band saws, circular saws and silicon carbide discs can be used.

Welding

The connection of plastics to each other can be carried out mechanically using bolts, rivets, gluing, dissolving, followed by drying, as well as by welding. From the above joining methods, only by welding it is possible to obtain a joint without foreign materials, as well as a joint that, in terms of properties and composition, will be as close as possible to the base material. Therefore, welding of plastics has found application in the manufacture of structures, which are subject to increased requirements for tightness, strength and other properties.

The process of welding plastics consists in the formation of a joint due to the contact of heated surfaces to be joined. It can occur under certain conditions:

Elevated temperature. Its value should reach the temperature of the viscous-flow state.
Tight contact of the welded surfaces.
The optimum welding time is the holding time.

It should also be noted that the temperature coefficient of linear expansion of plastics is several times higher than that of metals, therefore, in the process of welding and cooling, residual stresses and deformations appear, which reduce the strength welded joints plastics.

The strength of plastic welded joints is greatly influenced by the chemical composition, orientation of macromolecules, ambient temperature and other factors.

Various types of plastic welding are used:

Welding with gas heat carrier with and without additive
Extruded welding
Contact heat flash welding
Contact heat penetration welding
Welding in a high frequency electric field
Ultrasonic welding of thermoplastics
Friction welding of plastics
Radiation welding of plastics
Chemical welding of plastics

As with metal welding, when welding plastics, you should strive to ensure that the material weld and the near-weld zone in terms of mechanical and physical properties differed little from the base material. Fusion welding of thermoplastics, like other methods of their processing, is based on the transfer of the polymer first to a highly elastic and then to a viscous-flow state and is possible only if the surfaces of materials (or parts) to be welded can be transferred to a viscous melt state. In this case, the transition of the polymer to a viscous-flow state should not be accompanied by the decomposition of the material by thermal destruction.

Many plastics produce harmful fumes and gases when welding. For each gas there is a strictly defined maximum available concentration in the air (MPC). For example, for carbon dioxide the maximum permissible concentration is 20, for acetone - 200, and for ethyl alcohol - 1000 mg / m³.

Plastics based materials

Furniture plastics

The plastic used to make furniture is made by impregnating paper with thermosetting resins. Paper making is the most energy and capital intensive step in the entire plastic manufacturing process. Two types of paper are used: the basis of the plastic is kraft paper (thick and unbleached) and decorative (to give the plastic a picture). Resins are classified into phenol-formaldehyde, which is used to impregnate kraft paper, and melamine-formaldehyde, which is used to impregnate decorative paper. Melamine formaldehyde resins are made from melamine and are therefore more expensive.

Furniture plastic consists of several layers. The protective layer - overlay - is practically transparent. Made of high quality paper, impregnated with melamine-formaldehyde resin. The next layer is decorative. Then several layers of kraft paper, which is the basis of the plastic. And the last layer is compensating (kraft paper impregnated with melamine-formaldehyde resins). This layer is present only in American furniture plastics.

Finished furniture plastic is made of strong tinted sheets with a thickness of 1-3 mm. In terms of properties, it is close to getinax. In particular, it does not melt when touched by the tip of a soldering iron, and, strictly speaking, it is not a plastic mass, since it cannot be cast in a hot state, although it lends itself to changing the shape of the sheet when heated. Furniture plastic was widely used in the 20th century for finishing subway car interiors.

Plastic marking system

Identification of plastics.

To ensure the disposal of disposable items in 1988, the Society of Plastics Industry developed a labeling system for all types of plastics and identification codes. Plastic marking consists of 3 arrows in the shape of a triangle, inside which there is a number indicating the type of plastic. Often, when marking products under the triangle, letter marking is indicated (marking in Russian letters is indicated in brackets):

PET or PETE (PAT, PET) - Polyethylene terephthalate. Usually used for the production of containers for mineral water, soft drinks and fruit juices, packaging, blisters, upholstery. Such plastics are potentially hazardous for food use.
PEHD or HDPE (HDPE) - High density polyethylene, low pressure polyethylene. Production of bottles, flasks, semi-rigid packaging. Considered safe for food use.
PVC (Pvc) - Polyvinyl chloride. It is used for the production of pipes, tubes, garden furniture, flooring, window profiles, blinds, containers for detergents and oilcloth. The material is potentially hazardous for food use as it may contain dioxins, bisphenol A, cadmium.
LDPE and PELD (LDPE) - Low density polyethylene, high pressure polyethylene. Production of tarpaulins, garbage bags, bags, films and flexible containers. Considered safe for food use.
PP (PP) - Polypropylene... It is used in the automotive industry (equipment, bumpers), in the manufacture of toys, as well as in the food industry, mainly in the manufacture of packaging. Considered safe for food use.
PS (PS) - Polystyrene. It is used in the manufacture of insulation boards for buildings, food packaging, cutlery and cups, boxes and other packaging (cling film and foam), toys, dishes, pens, and so on. The material is potentially hazardous, especially in case of fire, as it contains styrene.
OTHER or O- others. This group includes any other plastic that cannot be included in the previous groups. This is mainly polycarbonate. Polycarbonate is not toxic to the environment, but may contain bisphenol A, which is hazardous to humans. It is used to make hard transparent products such as baby horns.

[Plastic waste and recycling

The suspension of plastic particles resembles zooplankton, and jellyfish or fish can mistake them for food. Large quantities of durable plastic (bottle caps and rings, disposable lighters) end up in the stomachs of seabirds and animals, in particular sea turtles and black-footed albatrosses. In addition to directly harming animals, floating waste can absorb organic pollutants from water, including PCBs (polychlorinated biphenyls), DDT (dichlorodiphenyltrichloromethylmethane), and PAHs (polyaromatic hydrocarbons). Some of these substances are not only toxic - their structure is similar to the hormone estradiol, which leads to hormonal disruption in a poisoned animal.

Sorted plastic for recycling

Plastic recycling methods:

In December 2010, Ian Bayens and colleagues at the University of Warwick proposed a new technology to recycle virtually all plastic waste. The machine, using pyrolysis in a fluidized bed reactor at a temperature of about 500 ° C and without access to oxygen, decomposes pieces of plastic waste, while many polymers decompose into the original monomers. The mixture is then separated by distillation. The final products of processing are wax, styrene, terephthalic acid, methyl methacrylate and carbon, which are raw materials for the light industry. The use of this technology allows you to save money by eliminating waste disposal, and, taking into account the receipt of raw materials (in the case of industrial use), it is a quickly payback and commercially attractive way to dispose of plastic waste.

Phenolic resin-based plastics, as well as polystyrene and polychlorinated biphenyl, can be decomposed by white rot fungi. However, this method is commercially ineffective for waste disposal - the process of destruction of plastic based on phenolic resins can take many months.

With incomplete combustion of polypropylene and polyethylene, carbon monoxide (CO) and water are formed, with full combustion - carbon dioxide (CO2) and water.

Physiological action, toxicity

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The melting point of polypropylene ranges from 165 to 175 C, which, in combination with sufficiently high strength characteristics and excellent chemical resistance in many corrosive environments, significantly expands the possibilities of using it in the chemical industry as a structural and protective material.

Dependence of the crystallization temperature on the time of nucleation at the initial moment (/ and at the end

The melting point of polypropylene is about 165 C, however, under normal conditions, crystallization occurs at temperatures below 150 C. In this case, crystallization occurs at more high temperatures ah and the orientation of the polymer chains.

Due to the heterogeneity of molecules and different sizes of crystallites, the melting point of polypropylene varies from 160 to 175 C. The heat capacity of polypropylene is greatly influenced by the presence of impurities and contact with some metals, for example, copper or its alloys. Therefore, when installing polypropylene pipelines for hot water supply, fittings containing copper elements should not be used.

It is shown that the introduction of chlorine causes an increase in the melting point of polypropylene.

Property dependency.

In a wide temperature range - between the glass transition temperature of polyisobutylene and the melting point of polypropylene - the mixtures exhibit highly elastic properties.

This small change in chemical structure leads to the fact that the melting point of polypropylene exceeds the melting point of polyethylene by 30 - 50 C.

Dependence of the melting point on the amount of chlorine in the polymer. | The dependence of the intrinsic viscosity on the amount of chlorine in the polymer.

For this purpose, it is proposed to carry out the polymerization of gaseous polypropylene under the action of complex catalysts: triethylaluminum titanium trichloride, supported on particles of a powdered polymer, or at temperatures above the melting point of polypropylene, when the formed polymer flows down from the catalyst support.

The temperature in the screw is 80 - 100 C higher than in the melt water or on the die, and the temperature at which the fiber is formed is 80 - 120 C higher than the melting temperature of polypropylene. With insufficiently careful stabilization of polypropylene during molding, thermo-oxidative destruction of the polymer occurs, and the intensity of this process is the greater, the higher the molecular weight of the initial polymer.

For rational heating of the melt above the melting point of polypropylene, it is advisable to choose larger distances between the die holes than when spinning fibers from melts of polyamides or polyesters.

In the same works of Flory, it is assumed that for polypropylene, in which the helical form of macromolecules found in the crystalline state has high internal stability, the forces of intermolecular interaction do not play a decisive role in the initiation of crystallization processes. It is noted that the melting point of polypropylene (169 C) is very high compared to the melting point of polyethylene (137 C), the molecules of which have a flat zigzag structure.

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Depending on the amount of isotactic part that is contained in polypropylene, as well as the molecular weight, the properties of this material can vary within wide limits. The greatest industrial interest is used by polypropylene, the molecular weight of which is from 80 to 200 thousand, and the content of the isotactic part is from 80 to 98 percent.

In many of its properties, polypropylene resembles.

Physical and mechanical properties

The density of polypropylene, in contrast to the density of polyethylene, is lower (this indicator is 0.90 g / cm 3, which is the smallest among all types of plastic), it is harder (greater resistance to abrasion), and also has the highest value of heat resistance (its softening begins at a temperature of 140 degrees Celsius, it melts at 175 ° C), is practically not susceptible to stress corrosion cracking. Polypropylene is highly sensitive to oxygen and light (a decrease in sensitivity occurs during the introduction of stabilizers).

How polypropylene will behave during stretching is even more dependent on temperature, as well as the speed at which the load is applied. The lower the rate of stretching of a given material, the higher the indicator of its mechanical properties will be. At high rates, the stretching that breaks the stress during stretching of polypropylene is substantially lower than its yield point during stretching.

The physical and mechanical properties of various grades of this material can be seen in the table:

Chemical properties

Propylene is a hydrocarbon with three carbon atoms. During the stepwise polymerization reaction, a polymer is formed from it, in which methyl groups are also attached to the polymer chain.

Three types of polypropylene are formed - syndiotactic, isotactic and attack. The difference between these polymers is the positioning in the space of methyl groups. In isotactic polypropylene, each of the methyl groups is positioned on one side of the polymer; in syndiotactic polypropylene, they can be positioned from different sides, and in the attactic, the positioning is random.

Polypropylene is a chemical resistant material. Only strong oxidants such as nitric fuming acid, chlorosulfonic acid, oleum and halogens can have a significant effect on it. Sulfuric acid at a concentration of 58%, as well as 30% hydrogen peroxide in room conditions have an insignificant effect. The destruction of polypropylene occurs only as a result of prolonged contact with these reagents at temperatures from 60 degrees Celsius.

Polypropylene is a waterproof material (up to a temperature of 130ºC), and is also resistant to aggressive environments (for example, alkalis and acids, some brands can come in contact with food, used for the manufacture of goods and packaging, for example, polypropylene tape, as well as used in medical -biological industry); but it is affected by strong oxidants (H2SO4, HNO3, chromium mixture).

In organic solvents, this material swells slightly at room temperature. At a temperature,exceeding 100ºC, polypropylene dissolves in aromatic hydrocarbons such as toluene, benzene. Information on the resistance of this material to the effects of certain chemicals can be seen in the table.

Due to the presence of tertiary carbon atoms, this material is more sensitive to the effects of oxygen, especially at higher temperatures. This is the reason why polypropylene is more prone to aging when compared to polyethylene. Aging of the material proceeds more rapidly and is accompanied by a rather sharp deterioration in the mechanical properties of polypropylene. For this reason, the material is used only in a stabilized form. Stabilizing agents are used to protect polypropylene from degradation both during processing and during operation. This material, to a lesser extent than polyethylene, is subject to cracking resulting from the influence of aggressive environments. It can withstand standard stress cracking tests carried out in a variety of environments. At a temperature of 50 degrees Celsius, the indicators of resistance to cracking in a 20% aqueous OP-7 solution of an emulsifier for polypropylene, the melt flow value of which is from 0.5 to 2.0 g / 10 min, which is in a state of stress, is over 2 thousand hours.

Polypropylene is a waterproof material. Even after six months of contact with water (in room conditions), its water absorption is not higher than 0.5%, and at a temperature of 60 degrees Celsius, this figure is less than two percent.

Thermophysical properties

The melting point of polypropylene is higher than that of polyethylene, which means that its decomposition temperature is also higher. Pure isotactic polypropylene begins to melt at 176ºC. The highest temperature for use of propylene is from 120 to 140 ° C. All polypropylene products can withstand boiling and steam sterilization without changing their mechanical properties or shape.

Polypropylene has a higher heat resistance than polyethylene, but is inferior to this material in terms of frost resistance. The temperature of its frost resistance or fragility ranges from -5 to -15 ° C. To increase the frost resistance of isotactic polypropylene, ethylene units can be introduced into its macromolecule (for example, during the copolymerization of ethylene with propylene).

Indicators of the main polypropylene thermophysical properties are shown in the table: