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PVC or polypropylene which is better? Polyethylene and polypropylene pipes - what is the difference? Polypropylene (PP). Properties guide and application overview

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

Receipt

It is supplied for processing in the form of granules from 2 to 5 mm. Polyethylene is produced by polymerization of ethylene:

Production of polyethylene high pressure

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 follows 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 occurs in the melt.

Production of medium pressure polyethylene

Medium pressure polyethylene(PESD) 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, and a degree of crystallinity of 80-90%.

Production of polyethylene low pressure

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 occurs 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, and a degree of crystallinity of 75-85%.

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

Other methods for producing polyethylene

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

Modifications of polyethylene

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

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

The modifications of the so-called “cross-linked” polyethylene PE-S (PE-X) stand out. The essence of cross-linking is that the molecules in the chain are not only connected sequentially, but also lateral bonds are formed that connect the chains to each other, due to this the physical and, to a lesser extent, chemical properties of the products change quite significantly.

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

Molecular structure

Macromolecules of high-density polyethylene ( n≅1000) contain side hydrocarbon chains C 1 -C 4, the molecules of medium pressure polyethylene are practically unbranched, there is a larger proportion of the crystalline phase in it, so this material is more dense; low-density 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 various types polyethylene:
Index	LDPE	PESD	HDPE
Total number of CH 3 groups per 1000 carbon atoms:
Number of CH3 end groups per 1000 carbon atoms:
Ethyl branches
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’), %
Degree of crystallinity, %
Density, g/cm³

Low Density Polyethylene (HDPE)

Physico-chemical properties of HDPE at 20°C:

Parameter

Meaning

Density, g/cm³

Breaking stress, kgf/cm²

when stretched

with static bending

when cutting

relative elongation at break, %

modulus of elasticity in bending, kgf/cm²

tensile yield strength, kgf/cm²

relative elongation at the beginning of the flow, %

At room temperature insoluble and does not swell in any known solvent. At elevated temperatures (80 °C) it is soluble in cyclohexane and carbon tetrachloride. Under high pressure it can be dissolved in water superheated to 180 °C.

Over time, it destructs with the formation of transverse interchain bonds, which leads to increased fragility against the background of a slight increase in strength. Unstabilized polyethylene in air is subject to thermal oxidative destruction (thermal aging). Thermal aging of polyethylene occurs through a radical mechanism, accompanied by the release of aldehydes, ketones, hydrogen peroxide, etc.

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

Recycling

Polyethylene (except for supermolecular polyethylene) is processed by all methods known for plastics, such as extrusion, extrusion blowing, injection molding, and pneumatic molding. Polyethylene extrusion is possible on equipment with a “universal” worm installed.

Application

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

Parts 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 additives, high linearity and molecular weight, is used for medical purposes as a replacement cartilage tissue 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 processing it, since it has a low MFI and can only be processed by casting.

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

International designation – PP.

The parameters required to produce polypropylene are close to those at which low-density polyethylene is obtained. In this case, depending on the specific catalyst, any type of polymer or mixture 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 available stabilized, painted and unpainted.

Molecular structure

Based on the type of molecular structure, three main types can be distinguished: isotactic, syndiotactic and atactic. Isotactic and syndiotactic are formed randomly;

Physical and mechanical properties

Unlike polyethylene, polypropylene is less dense (density 0.91 g/cm 3, which is the lowest value for all plastics), harder (abrasion resistant), more heat resistant (begins to soften at 140 ° C, melting point 175 ° C), is almost not subject to corrosion cracking. It is highly sensitive 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 load application and temperature. The lower the rate of stretching of polypropylene, the higher the value of the indicators mechanical properties. At high speeds tensile strength, the tensile failure stress of polypropylene is significantly lower than its tensile yield strength.

Key indicators physical and mechanical properties polypropylene are given in the table:

The physical and mechanical properties of polypropylene of different grades are given 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

Resistance to cracking, h, not less

Heat resistance according to the NIIPP method, °C

Polyethylene (PE): physical, chemical and consumer properties, consumption structure, areas of application of polyethylene

Polyolefins are the most common type of polymers obtained by polymerization and copolymerization reactions of unsaturated hydrocarbons (ethylene, propylene, butylene and other alpha-olefins). About 50% of the world's ethylene is used to produce polyethylene.

The chemical structure of the polyethylene molecule is simple and consists of a chain of carbon atoms, each of which is attached to two hydrogen molecules.
Polyethylene (PE) [–CH2-CH2–]n exists in two modifications that differ 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) of typically 5000 or more; in the other, branches of 4-6 carbon atoms are attached to the main chain in a random manner. Linear polyethylenes are produced using special catalysts; polymerization occurs at moderate temperatures (up to 150 0C) 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; is not wetted by water, does not dissolve in organic solvents at room temperature, at temperatures above 80 ° C it first swells and then dissolves in aromatic hydrocarbons and their halogen derivatives; PE is resistant to aqueous solutions of salts, acids, and alkalis, but at temperatures above 60 °C, sulfuric and nitric acids quickly destroy it. Short-term treatment of PE with an oxidizing agent (for example, a chromium mixture) leads to oxidation of the surface and wetting of it with water, polar liquids and adhesives. In this case, PE products can be glued together.
Ethylene can be polymerized in several ways, depending on this, polyethylene is divided into: high-density polyethylene (LDPE) or low-density polyethylene (LDPE); low-density polyethylene (HDPE) or high-density polyethylene (HDPE); and also for linear polyethylene.
LDPE polymerizes radically under pressure from 1000 to 3000 atmospheres and at a temperature of 180 degrees. The initiator is oxygen.
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 like an “intermediate” product between HDPE and LDPE in terms of properties and qualities.
Not long ago, technology began to be used that uses so-called metallocene catalysts. The meaning of the technology is that it is possible to achieve a higher molecular weight of the polymer, which, accordingly, increases the strength of the product.
In their structure and properties (despite the fact that the same monomer is used), LDPE, HDPE, linear polyethylene are different, and, accordingly, are used for different tasks. LDPE soft material, HDPE and linear polyethylene have a rigid structure.
Differences also appear in density, melting point, hardness, and strength.
Comparative characteristics of high and low pressure polyethylene (LDPE and HDPE)

The main reason that causes differences in the properties of PE is the branching of macromolecules: the more branches in the chain, the higher the elasticity and the less crystallinity of the polymer. Branching makes it difficult for macromolecules to pack more closely and prevents the degree of crystallinity from reaching 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 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. Among the most important properties Polyethylene can be noted for its frost resistance. They can be used 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 that of 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; dielectric constant and dielectric loss tangent change little with changes in the frequency of the electric field, temperature in the range from minus 80 ° C to 100 ° C and humidity. However, catalyst residues in HDPE increase the dielectric loss tangent, especially with temperature changes, which leads to some deterioration in insulating properties.
Low pressure polyethylene PEHD
Light elastic crystallizing material with heat resistance of some brands up to 110 0C. Allows cooling down to -80 0C. Melting point of grades: 120-135 0C. Glass transition temperature: approx. -20 0С. Gives a shiny surface.
Characterized by good impact strength and greater 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, rigidity, hardness, and chemical resistance. At the same time, with increasing density, impact resistance at low temperatures, elongation at break, and permeability to gases and vapors decrease.
High creep is observed under prolonged loading. Has very high chemical resistance (more than LDPE). Has excellent dielectric characteristics. Biologically inert. Easily recyclable.

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

HDPE (high density) polyethylene is used primarily for the production of containers and packaging. Abroad, approximately a third of the produced polymer is used for the manufacture of containers by blow molding (containers for food products, perfumes and cosmetics, automotive and household chemicals, fuel tanks and barrels). It is worth noting that, compared to other areas, the use of HDPE for the production of packaging films is growing at a faster pace. ND PE is also used in the production of pipes and pipeline parts, where such advantages of the material as durability (service life - 50 years), ease of butt welding, low cost (on average 30% lower than metal pipes).
High pressure polyethylene

Other designations: PE-LD, PEBD (French and Spanish designation).
Lightweight, elastic, crystallizing material with heat resistance without load up to 60°C (for certain brands up to 90°C). Allows cooling (various brands 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, rigidity, hardness, and chemical resistance. At the same time, with increasing density, impact resistance at low temperatures, elongation at break, crack resistance, and permeability to gases and vapors decrease. Prone to cracking under loading. Does not differ in dimensional stability.
Has excellent dielectric characteristics. Has very high chemical resistance. Not resistant to fats and oils. Not resistant to UV radiation. It is characterized by increased radiation resistance. Biologically inert. Easily recyclable.
Characteristics of the branded assortment
(minimum and maximum values for industrial grades)

Application examples

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

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

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 compound related to polyolefins. It is produced by a method similar to the method for producing low-density polyethylene (high pressure).
Sevilen is superior to polyethylene in transparency and elasticity at low temperatures, and has increased adhesion to various materials.
The properties of Sevilen depend mainly on the content of vinyl acetate (5-30 wt.%). With increasing vinyl acetate content, crystallinity, tensile stress, hardness, and heat resistance decrease, while density, elasticity, transparency, and adhesion increase.
Sevilen with a vinyl acetate content of up to 15% (grades 11104-030, 11306-075) is processed using 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, and toys. From the same grades of Sevilen, weather-resistant, transparent films are obtained, which have a lower melting point compared to polyethylene films.
The high adhesive 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. % (brands 11507-070, 11708-210, 11808-340).
An important area of use of Sevilen is the preparation of hot melt adhesives based on it. Hot melt adhesives do not contain solvents and are solids at room temperature. They are used in molten form at a temperature of 120 – 200C.
To obtain hot melt adhesives, use Sevilen containing 21-30 wt.% vinyl acetate (grades 11507-070, 11708-210, 11808-340). Hot melt adhesives based on Sevilen are widely used in the printing, furniture, footwear and other industries.
Sevilen combines well with various fillers, which makes filled products widely available.
Table of quality indicators of Sevilen grades 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 fluidity indicators, g/10 min, within: at t=190 0С
Variation in melt flow rate within a batch, %
Mass fraction of vinyl acetate, % within
Number of inclusions, pcs. no more
Tensile 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, no less, for formulations 02, 03, 06
Resistance to thermal-oxidative aging, h, not less, for formulations 05.07				not standardized	not standardized	not standardized
Reprocessing 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.).
Structure of PE consumption, %

Insulation electrical wires . The 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 means communications (telephone, telegraph), signaling devices, dispatch telecontrol systems, high-frequency installations, for winding wires of engines operating in water, as well as for insulating submarine and coaxial cables.
A cable with polyethylene insulation has advantages over rubber insulation. It is lightweight, more flexible and has greater electrical strength. A wire coated with a thin layer of polyethylene may have upper layer from plasticized polyvinyl chloride, forming a good mechanical protection from damage.
In the production of cables, LDPE is used, cross-linked with small quantities (1-3%) of organic peroxides or irradiated with fast electrons.
Films and sheets. Films and sheets can be made from PE of any density. When producing thin and elastic films, LDPE is more widely used.
Films are produced by two methods: extrusion of molten polymer through an annular slit followed by blowing or extrusion through a flat slit followed by drawing. They are produced in thicknesses of 0.03-0.30 mm, widths up to 1400 mm (in some cases up to 10 m) and lengths 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 a lining and electrical insulating material and processed into products for technical and household purposes using the vacuum molding method.
Most of the products made from LDPE 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, sacks, linings for drawers, boxes, etc.) other types of containers).
Films are widely used for packaging frozen meat and poultry, in the manufacture of balloons and cylinders for meteorological and other research. upper layers atmosphere, corrosion protection of main oil and gas pipelines. IN agriculture transparent film is used to replace glass in greenhouses and greenhouses. Black film is used to cover the soil in order to retain heat when growing vegetables, fruits and legumes, as well as for lining silage pits, the bottom of reservoirs and canals. Polyethylene film is increasingly being used as a material for roofs and walls in the construction of buildings for storing crops, agricultural machinery and other equipment.
Household items are made from polyethylene film: raincoats, tablecloths, curtains, napkins, aprons, scarves, 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 rare glass fabric.
Tablecloths and films for greenhouses are made from very thin reinforced films; from thicker films - bags and packaging material. Reinforced film reinforced with rare glass fabric can be used to make protective clothing and used as a lining material for various containers.
Based on PE films, sticky (adhesive) films or tapes can be made, suitable for repairing high-frequency cable lines and for protecting steel underground pipelines from corrosion. Polyethylene films and tapes with sticky 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 80-150 mm.
LDPE and HDPE are also used for protection metal products from corrosion. The protective layer is applied using 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, low resistance to fluid movement, ease of installation, flexibility, frost resistance, and ease of welding.
The continuous method produces pipes of any length with internal diameter 6-300 mm with a wall thickness of 1.5-10 mm. Polyethylene pipes are not large diameter are wound on drums. Pipe fittings are manufactured by injection molding, which includes elbow pipes bent at an angle of 45 and 90 degrees; tees, couplings, crosses, pipes. Large diameter pipes (up to 1600 mm) with wall thicknesses 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 chemical industry, for the construction of internal and external water supply networks, in irrigation systems and sprinkler systems.
Pipes made from LDPE can operate at temperatures up to 60 0C, and from HDPE - up to 100 0C. Such pipes do not collapse at low temperatures (up to – 60 0C) and when water freezes; they are not subject to soil corrosion.
Molding and injection molding products. From polyethylene sheets obtained by extrusion or pressing, you can make various products stamping, pattern bending or vacuum forming. Large items (boats, bathtubs, tanks, etc.) can also be made from polyethylene powder by sintering it on a heated mold. Individual parts of products can be welded using a jet of hot air heated to 250 0C.
Forming and welding can be used to produce valves, caps, containers, parts of fans and pumps for acids, stirrers, filters, various containers, buckets, etc.
One of the main methods for processing PE into products is the injection molding method. Polyethylene bottles 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 one or another technological process is determined primarily by the need to obtain a branded assortment with a certain set of properties. The suspension method is suitable for the production of pipe grades of polyethylene and grades of polyethylene intended for processing by extrusion, as well as for the production of high molecular weight polyethylene. Using solution technologies, LLDPE is produced for high-quality packaging films, polyethylene grades for the manufacture of products using casting and rotational molding methods. The gas-phase method produces a branded range of polyethylene intended for the manufacture of consumer goods.

Plastics

Chains of polypropylene molecules.

Household items made wholly or partly of plastic

Plastics(plastic masses) or plastics- organic materials based on synthetic or natural high-molecular compounds (polymers). Exclusively wide application produced plastics based on synthetic polymers.

The name “plastics” means that these materials are capable of being formed under the influence of heat and pressure and retaining a given shape after cooling or hardening. The molding process is accompanied by a transition from a plastically deformable (viscous-flow) state to a glassy state.

Story

The first plastic was produced by the English metallurgist and inventor Alexander Parkes in 1855. Parks called it parkesin (later another name became widespread - celluloid). Parkesine 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 completely synthetic molecules (bakelite, epoxy resin, polyvinyl chloride, polyethylene and others).

Parkesine was the trademark of the first artificial plastic and was made from cellulose treated with nitric acid and a solvent. Parkesine 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 Bad quality products 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 Hiatt.

Types of plastics

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

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

Receipt

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

Processing methods

Casting/Injection Molding
Pressing
Vibroforming
Foaming
Casting
Welding

Mechanical restoration

Plastics, compared to 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 is the use of mineral oil allowed during final processing. Cool the product and tool with a stream of air.

Plastics are more brittle than metals, therefore, when processing plastics with cutting tools, it is necessary to use high cutting speeds and reduce 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. Blades cutting tools it is necessary to sharpen, if possible, more sharply, using fine-grained wheels for this.

Plastic can be processed on a lathe or milled. Band saws, circular saws and carborundum wheels can be used for sawing.

Welding

Plastics can be connected to each other mechanically using bolts, rivets, gluing, dissolving followed by drying, and also by welding. From the listed methods connections, only by welding it is possible to obtain a connection without foreign materials, as well as a connection 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 that are subject to increased requirements for tightness, strength and other properties.

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

Fever. Its value must reach the temperature of the viscous-flow state.
Close contact of welded surfaces.
The optimal 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, during the welding and cooling process, residual stresses and deformations arise, which reduce the strength of welded joints of plastics.

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

Various types of plastic welding are used:

Welding with gas coolant with and without additive
Welding with extrudable filler
Resistance thermal flash welding
Contact-thermal penetration welding
Welding in electric field high frequency
Ultrasonic welding of thermoplastics
Friction welding of plastics
Radiation welding of plastics
Chemical welding of plastics

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

To ensure that food, as we all know, remains fresh and beneficial features, they require special packaging. Of the most popular materials that are used to make packaging, two can be distinguished: polyethylene and polypropylene. And each of them has its own characteristics. You can read more about the use of polypropylene packaging at the link, but for now let’s look at the basic properties of each material.

Polyethylene packaging: advantages and disadvantages

Depending on the source raw material, the properties of the polyethylene film will depend. In addition, density also affects the strength of plastic bags. In most cases, such bags are characterized by a low level of strength, and therefore are used for temporary storage and transportation of food products. Low price is the main advantage of plastic packaging, which makes it affordable in our time. However, this type of packaging has many disadvantages compared to polypropylene.

Among the disadvantages of polyethylene are the following:

The lack of the required level of elasticity is the main disadvantage. In other words, such packaging is easy to tear, so it is used for products that do not require a long shelf life.
Under mechanical stress, such bags lose their attractive appearance.
Low level of strength even for bags created under high level pressure.

Polyethylene in the refrigerator

Many people think that any food can be stored in plastic in the refrigerator. This is far from true: food can be stored in polyethylene, but you need to use special bags that are resistant to low temperatures. Ordinary plastic bags at low temperatures can release toxic substances in the same way as when heated. If you freeze vegetables or fruits for the winter, even clean and high-quality ones, in such packaging, it can cause food poisoning.

Polypropylene packaging: advantages and disadvantages

Polypropylene bags have many significant advantages, which we will discuss further.

First of all, it is worth highlighting the excellent reliability and durability indicators, which allows you to create high-quality and reliable packaging.
In addition, high-density polypropylene helps protect food from negative impact environmental factors. Therefore, most manufacturers choose polypropylene for packaging long-term food products.
The strength of polypropylene helps protect products from deformation when dropped.
Excellent strength indicators allow you to efficiently and compactly store goods in a car and transport them over long distances. Therefore, polypropylene packaging is used by most product manufacturers and warehouse owners to move them to the end consumer.
Polypropylene allows you to print various inscriptions on its surface, namely information about a specific type of product. In other words, you can create ready-made packaging from polypropylene, ready for sale.
It is also worth highlighting the transparency of polypropylene, which allows you to evaluate the quality of food products and at the same time preserve their beneficial properties.
An excellent level of elasticity is another significant advantage of polypropylene. In other words, such packaging is not deformed under mechanical impact. Polypropylene bags are difficult to tear without the use of sharp objects.
The use of polypropylene when packaging products allows you to make high-quality and airtight seams. In other words, food products retain their freshness and beneficial properties for a long time.
It is also worth highlighting the excellent resistance of polypropylene to high temperatures.

Features of the use of polypropylene

Polypropylene film, as well as duplex polypropylene laminates in web form, are commonly used for automatic product filling on vertical or horizontal packaging machines; in this case, the seams of the packaging are formed by welding thermoelements at a constant temperature.

Transparent biaxially oriented polypropylene film with a thickness of 20, 25, 30, 35 and 40 micrometers; used for packaging bulk grocery products (cereals, sugar, salt, tea and other products), bakery products and baked goods, cookies, crackers, group packaging of sweets and other confectionery products, industrial goods (covering boxes, packaging for textiles and knitwear) and in many other cases.

Pearl polypropylene, 30 and 35 micrometers thick; has all the same properties as transparent polypropylene, but in addition, thanks to the foamed microstructure, it also perfectly reflects light and has a reduced specific gravity, making it very economical to use; pearl polypropylene also withstands low temperatures well without becoming brittle when the polymer crystallizes; That is why it is successfully used for packaging ice cream, glazed cheese curds and other products that require storage at low temperatures.

Final comparison

These materials are similar in properties. Polypropylene is a less elastic material. At the same time, it has high barrier properties. Bags made from polypropylene film are glossy and “crispy”, but they do not withstand cold well. So, let's take a look at the main characteristics of polymer packaging in order:

Economic characteristics

Polyethylene packaging is much cheaper than its polypropylene counterparts. Savings, with the same parameters, can sometimes reach 50% of the cost. Polyethylene is considered the most economical packaging material.

Physical and technical characteristics

Appearance. The properties of propylene film provide the bags with high presentation characteristics. Glossy polypropylene bags compare favorably with their duller (sometimes cloudy) plastic counterparts. Very often, packaging loses its presentation due to frequent unloading and loading operations, careless attitude when displaying goods on display, or showing them to customers. Due to their properties, polypropylene bags are most often very resistant to various logistics manipulations. All types of polyethylene are significantly inferior to polypropylene in terms of resistance to creasing.
Strength and durability. The choice of material and design of the package greatly depends on the product being packaged and the method of application of the packaging. Polypropylene is a fairly durable material. Bulk products, as well as goods with sharp edges, are often packaged in it. However, due to less elasticity, polypropylene bags have a weak point - the side (cut) weld. Often, during unloading and loading operations, bags of products packaged in polypropylene are thrown. Cut welds often cannot withstand such loads. The solution is to change the package design or material. Bags with a flat rear “Euro-seam” are more resistant to such loads. Due to the design. Plastic bags– stronger due to elasticity.
Temperature resistance. All polypropylene products can withstand boiling and can be sterilized by steam without any change in their shape or mechanical properties. Polypropylene is not so resistant to freezing. Due to low temperatures, the material completely loses its elasticity and becomes quite brittle. In this regard, you need to choose the right package design to minimize risks and losses. Polyethylene films have more low temperature melting. At the same time, they are more resistant to freezing.

The main part of the construction market products is represented by materials made from polyvinyl chloride and polypropylene. Therefore, when arranging communications it becomes very difficult actual question: " - what's better?". This question can be answered by taking a closer look at the products and their specifications.

Polyvinyl chloride, which appeared on the construction raw materials market at the end of the 20th century, was originally a raw material for the production of linoleum. Later they even tried to use it in the manufacture of dishes. However, due to the fact that this material contains toxic substances released during combustion, production kitchen utensils stopped abruptly. At the same time, PVC began to be actively used in.

Polystyrene, invented several decades later than polyvinyl chloride, became the main raw material in the production of plastic tableware, lining for household appliances and electrical insulation. Later, PP (PP), like PVC, found its application in the manufacture of collectors and others.

Representing the same category of raw materials (plastic), polypropylene and PVC difference still have. Accordingly, the pipes made from them also differ.

Main characteristics and advantages of materials

It is worth noting that in many respects it is much inferior to polypropylene materials. How exactly do PP collectors differ from polyvinyl chloride collectors, we suggest that you familiarize yourself in more detail below.

Maximum permissible temperature conditions

Temperature chart.

First of all, polypropylene products can boast of increased heat resistance (up to +140⁰С with a minimum value of +95⁰С). As practice shows, such pipes have demonstrated excellent performance indicators and have proven themselves in hot water supply (including centralized). Used even at critical operating temperatures, polypropylene products with a reinforced frame do not soften, and therefore do not deform.

Well, of course, functionality. All the valuable qualities of polypropylene collectors allow them to be used in a wider range. Almost universal polypropylene is in many ways superior to polyvinyl chloride products, and therefore is more in demand than PVC. Recycled polyethylene and polypropylene, the differences of which are clearly demonstrated above, have found their application in various spheres of life, although products made from polyvinyl chloride are still less in demand.

Video about the rules for choosing polypropylene pipes:

Polyethylene and polypropylene are actively used for systems internal sewerage. These modern materials resistant to corrosion and oxidation. They are easy to install and serve long time given that correct operation. Let's take a closer look at the technical characteristics and installation features of sewerage pipes made of polyethylene and polypropylene.

Polyethylene pipes for sewerage

Polyethylene is the result of the polymerization of ethylene gas in the presence of catalysts at elevated temperature and pressure. Physical properties materials depend on the reaction conditions:

1. If high temperature and pressure are maintained, the output is low-density polyethylene (LDPE).

2. For more low rates temperature and pressure – high density polyethylene (HDPE).

Standards

Polyethylene corrugated pipes for sewerage are not regulated by GOSTs. Their production is coordinated with specific customers. The production of polyethylene pipes for the arrangement of internal communications is regulated by GOST 22689.2-89.

What points are regulated by the standards? This:

length and diameter of sewer pipes;
possibility of using both HDPE and LDPE in production;
requirements to symbols pipes (for example, TK 30-5000 - PVD GOST 22689.2; interpretation - “sewage pipe made of high-pressure polyethylene with a diameter of 30 millimeters and a length of five meters”);
length and diameter of sockets for connecting polyethylene pipes;
typical sizes of adapters, turns, connecting parts of all types (tees, couplings, crosses, etc.).

Limitations within the standard:

installation of polyethylene pipes only in conditions of gravity sewerage;
maximum operating temperature - +45° C (short-term increase to +60° C is possible).

Advantages of polyethylene pipes for sewerage

1. Long service life (from fifty years).

2. High reliability and resistance to corrosion, chemical influences, water hammer, and external aggressive factors.

3. No need for expensive maintenance.

4. Low price (compared to steel and cast iron pipes).

5. Low weight, due to which the installation of polyethylene pipes does not present any particular difficulties.

The only disadvantages include restrictions regarding the scope of their application (see above).

Types of polyethylene pipes

1. LDPE pipes (made of high-density polyethylene).

Characteristics:

low weight, which facilitates transportation, installation and dismantling;
resistance to aggressive factors;
simplicity and high reliability of connections.

2. HDPE pipes for sewerage (made of low-density polyethylene).

They are most often used for pipelines in areas with cold water supply.

3. PE pressure pipes for sewerage (most often made of PE-80 polymer).

Their scope of application is pressure sewerage systems.

4. Corrugated polyethylene pipes.

Most often used for arrangement external sewerage. Performed in two layers:

the upper one – corrugated – provides high strength and resistance to external influences;
internal – smooth – ensures unhindered movement of liquid, low likelihood of blockages.

Main characteristics:

high chemical resistance (PE-80 and PE-63 polyethylene is used in production);
high strength, possibility of installation at a depth of up to twenty meters underground (provided by external rigid rings).

Features of installation of polyethylene pipes

Various types of connections are used.

1. Bell-shaped.

Stages of work:

selection of pipes and fittings according to the project and taking into account the dimensions (when choosing the length, you need to take into account those sections that will be inserted into the socket);
removing external chamfer from pipes; cleaning the inside (there should be no burrs, scuffs, or other irregularities);
inserting the pipe into the socket manually (you need to leave a compensation gap of 1 cm);
When drawing up a project, it is important to provide for laying the pipeline at a slope.

2. Welded.

For these types of connections, you need a special machine for welding polyethylene pipes. Main structural elements:

bushings on which pipes are put;
heating plates.

The essence of welding is to melt the ends of the pipes and connect them.

3. Couplings.

Type of connections used during installation corrugated pipes. Slide-on couplings are used to assemble the pipeline, and rubber seals are used to seal the joints.

Thus, polyethylene pipes are perfect for arranging both internal and external sewage systems. For interior works – smooth pipes, for external ones - corrugated.

Polypropylene pipes for sewerage

The area of their application is internal non-pressure sewerage.

Polypropylene pipes are made from stabilized polypropylene by hot extrusion.

Advantages of polypropylene sewer pipes

1. Increased resistance to chemicals.

2. Excellent hydraulics, perfect smooth surface.

3. Resistance to corrosive processes.

4. Light weight, no overgrowing of the section.

5. Ability to withstand impacts even at sub-zero temperatures.

6. Ability to withstand hot water flow for a long time.

7. Safety for humans and the environment.

Polypropylene pipes are manufactured in accordance with GOST 26996.

Differences between polypropylene and polyethylene

The distinctive characteristics of polypropylene pipes are dictated by the properties of the source material. Polypropylene (vs. polyethylene)

more resistant to abrasion;

less dense;

more resistant to high temperatures (maximum operating temperature - +75 - +90° C);
highly sensitive to light and oxygen.

Types of polypropylene pipes

1. Pipes for arranging a “cold” pipeline – PN-10.

2. Pipes for arranging “cold” and “hot” pipelines – PN-20.

When used in sewer systems With cold water service life is 50 years; With hot water- 25 years. If the temperature exceeds the permissible values (indicated on the labels), the pipe lengthens. Therefore, during installation, compensators and various sliding supports are installed.

3. Reinforced polypropylene pipes(PN-25).

For use only in heating systems. Service life depends on pressure and temperature. So, at a temperature of up to seventy degrees and a pressure of 8 atmospheres - up to fifty years.

Installation features

Stages of work:

1. Drawing up a water supply project and selecting components (fasteners, fittings, etc.).

2. Selecting places for attaching the water supply to the walls, drilling holes.

3. Welding polyethylene pipes into a single structure (first cut the pieces to the required length, install couplings and tees).

4. Installation of water supply.

If you need to connect pipes different diameters, then adapters are used.

Thus, polypropylene pipes are suitable for equipping hot and cold water supply systems, heating, air conditioning, etc.

04:43:38 - 25.02.2019

What is polypropylene?

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Polypropylene is a material that is obtained by polymerizing propylene using metal complex catalysts.

Polypropylene has the international name PP. The material is obtained under conditions close to the conditions for the production of low-density polyethylene. The type of polymer and their mixtures are prepared depending on the catalyst used. The produced polypropylene is a white powder or granules. Polypropylene is delivered to the consumer dyed, stabilized or undyed.

Currently, polypropylene can have three main types of molecular structure: syndiotactic, isotactic and atactic. Syndiotactic and isotactic structures can have varying degrees of perfection of spatial regularity. Stereoisomers of a material can have different physical, mechanical and chemical properties. As for atactic polypropylene, it is a rubber-like material that is characterized by high fluidity, a density of about 850 kg/m³, a melting point of around 80 degrees Celsius, and excellent solubility in diethyl ether.

The physical and mechanical properties of polypropylene compare favorably with those of polyethylene. The density of polypropylene is only 0.91 g/cc, which is the minimum among plastics. At the same time, the material has a higher hardness, it is resistant to abrasion, and has higher heat resistance. Polypropylene begins to soften only at temperatures above 140 degrees Celsius, and its melting point reaches 175 degrees. Polypropylene is practically not subject to corrosion cracking.

Other characteristics of polypropylene include high sensitivity to oxygen and light. Sensitivity can be reduced by introducing appropriate stabilizers. The behavior of polypropylene largely depends on the temperature and speed of load application. The value of the mechanical properties of polypropylene will be higher, the lower the rate of stretching of the material. At high rates of stretching of the material, the failure stress will be significantly lower than the tensile yield strength of polypropylene.

The chemical properties of polypropylene deserve special attention. The material from which shopping bags are made has high chemical resistance. Only strong oxidizing agents have a significant effect on it. Even concentrated sulfuric acid and 30% hydrogen peroxide have little effect at room temperature. Only prolonged contact with these environments at a temperature of 60 degrees Celsius leads to the destruction of the polymer.

As for organic solvents, when polypropylene is exposed to them at room temperature, slight swelling of the material is observed. At temperatures above 100 degrees Celsius, polypropylene dissolves in toluene, benzene and other aromatic hydrocarbons.

Chemical formula of polypropylene

Polypropylene is a water-resistant material. Even with prolonged contact with water at room temperature, for example, for six months, the water absorption of polypropylene does not exceed 0.5%. At a temperature of 60 degrees Celsius, the water absorption of the material reaches only 2%.

As for the thermophysical properties of polypropylene, the melting point of the material is much higher compared to polyethylene. Consequently, polypropylene has more high temperature melting. For pure isotactic polypropylene it is 176 degrees Celsius. The maximum operating temperature of the material is 120-140 degrees Celsius. Each polypropylene product can withstand boiling and can also be exposed to steam without changing its mechanical properties and shape.

Polypropylene has less frost resistance compared to polyethylene (others packing materials for moving). The temperature of its fragility ranges from -5 to -15 degrees Celsius. To increase frost resistance, ethylene units are introduced into the macromolecule of isotactic polypropylene.

Processing of the material involves molding using extrusion, pneumatic and vacuum molding methods, as well as injection, extrusion-blow, injection-blow, and compression molding. In some cases, injection molding technology is used.

Polypropylene bags

Currently, polypropylene is used in the production of various films, including packaging films, containers, bags, pipes, household items, parts of technical equipment, and non-woven materials. Polypropylene can act as an electrical insulating material, a material for arranging noise and vibration insulation of interfloor ceilings in floating floor systems

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