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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 polyethylene 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 low temperatures can also release toxic substances 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 factors external environment. 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 does not deform under mechanical influence. 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 are stronger due to their 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 a lower melting point. At the same time, they are more resistant to freezing.

Polyethylene and polypropylene are the most common plastics. They are used in many areas of human activity:

• production of films and packaging materials;
• pipe production;
• production of thermal insulation materials, etc.

It is perhaps even difficult to imagine an industry where they are not used. However, although their properties are largely similar, there are also differences. So, what is the difference between polyethylene and polypropylene? Let's look at it below.

The differences are chemical

Both materials have the word "poly" in their names, which means "many" in Greek. In our country, most scientific terms are borrowed from Greek or Latin - this has been the custom for a long time. That is, “polyethylene” means “a lot of ethylene,” and “polypropylene” means “a lot of propylene.” What are ethylene and propylene?

Under normal conditions, both of these chemical compounds are flammable gases. The formula of ethylene is C 2 H 4, the formula of propylene is C 3 H 6. They occupy the first and second lines of the class of compounds, which is called “alkenes”, or “acyclic unsaturated hydrocarbons”. Their general formula– СnН2n, that is, there are always twice as many hydrogen atoms (H) in the molecule of any alkene as there are carbon atoms (C). This means that the third in the row will have the formula C 4 H 8, the fourth – C 5 H 10, etc.

Polyethylene granules

We've dealt with ethylene and propylene, let's move on. What is the difference between polyethylene and polypropylene, and how is a popular packaging material made from flammable gases? In the production of polyethylene and polypropylene it is used special process. It is called "polymerization". Its essence is that long chains are obtained from gas molecules, consisting of a huge number of “bricks”, each of which is a C 2 H 4 unit (for polyethylene) or C 3 H 6 (for polypropylene). Material made from such polymer chains has properties that are fundamentally different from the properties of the original molecules, although the chemical formula remains almost the same: (C 2 H 4) n and (C 3 H 6) n, where n is the number of units in a polyethylene molecule or polypropylene.

Performance comparison

These materials are neighbors in the alkene group, so they have a lot in common in terms of physical properties. But propylene still has generally higher strength characteristics. For example, on the Brinell hardness scale, polyethylene has an indicator of 1.4-2.5 kgf/mm², and polypropylene – 6.0-6.5 kgf/mm². For other indicators, the differences are not so noticeable. The areas of application of both materials also have many similarities.

They are used in the production of packaging materials, plastic dishes, and pipes. Foamed polymers are in demand as a thermal insulation material. They are widely used for the production of copolymers (they contain various structural units, for example, polyethylene and polypropylene or some other polymer). Production of dielectrics, household items, decorative items - the list of areas where you cannot do without them would take a long time.

One of the modifications of polyethylene - ultra-high molecular weight high-density polyethylene - has very high strength characteristics. In this regard, the material is used where special strength is required. For example, when creating body armor, helmets, armor panels. In a number of parameters, its characteristics are higher than those of Kevlar, which is also used for the manufacture of body armor.

Table

The table below will most fully answer the question of what is the difference between polyethylene and polypropylene.

	Polyethylene	Polypropylene
Chemical formula	(C 2 H 4) n	(C 3 H 6) n
Strength (Brinell)	1.4-2.5 kgf/mm²	6.0-6.5 kgf/mm²
Chemical properties	Resistant to most acids, destroyed only when exposed to nitric acid (at least 50 percent saturation) and some other caustic substances	A noticeable destructive effect is exerted by: concentrated nitric acid, chlorosulfonic acid, and some other caustic substances
Melting temperature	+103-137 degrees Celsius (different brands)	+130-171 degrees Celsius (different brands)
Application area	Construction, production of packaging materials, plastic utensils, dielectrics, armor panels (ultra-high molecular weight polyethylene) and much more	Containers, various films (including packaging), pipes, threads, fibers and much more

TYPES OF POLYMER PIPES. DIFFERENCE BETWEEN POLYETHYLENE AND POLYPROPYLENE PIPES, PVC PIPES, POLYBUTENE PIPES. MARKING OF POLYMER PIPES.

The choice of pipes for water supply, heating and sewerage systems in our time is quite large.
But quite recently, almost exclusively steel and cast iron pipes were used for these purposes. Polymer materials appeared in human life relatively recently - in the middle of the 20th century. We all quickly got used to plastic bags and bags, greenhouse film and colored basins. Somewhat later, disposable tableware, plastic furniture and even plastic teapots appeared. Today we are already offered window frames and pipes made of polymers. But for the most part, Russian consumers doubt the reliability and durability of polymer pipes. Colored polymer pipes, wound into coils like noodles, look too frivolous compared to the usual high-quality thick and heavy steel and cast iron pipes.

But let's look at the statistics. What does the European consumer prefer? More than 80% of pipes installed in new or majorly renovated houses are copper and polymer pipes, used in approximately equal quantities.

To understand the positive and negative properties of polymer pipes, you need to start with polymers. Unlike metals and asbestos cement polymers - organic substances with all their advantages and disadvantages, being closely related to natural high-molecular materials - wood, leather and wool.

Polymers have a number of advantages:

• They have universal chemical resistance and are not subject to corrosion;
• Despite their lightness (their density is 5-8 times lower than the density of steel), they are quite strong and elastic;
• Polymers are easily processed into products, i.e. take a given shape and are well painted;
• The thermal conductivity of polymers is significantly lower than that of metals, which, in particular, reduces heat loss when transporting hot liquids.

However, polymers are not without significant disadvantages:

• When heated, the strength of polymers decreases. Like all organic substances, they burn, and under the influence of ultraviolet rays they age (become brittle and collapse);
• Disadvantages include a large (10 times more than steel) coefficient of thermal expansion; however, the elasticity of polymers partially compensates for this disadvantage.

Technologists producing products from polymers are trying, and not without success, to enhance their advantages and reduce their disadvantages. In the second half of the 20th century, the chemical industry mastered the production of dozens of polymers, but 5-7 of the most important ones found mass application, including in the production of pipes.
The undisputed leaders are polyethylene (PE), polypropylene (PP) And polyvinyl chloride (RUS).
These polymers belong to the group of thermoplastics. They are capable of transforming into a plastic-viscous state when heated, and hardening when cooled.
Pipes from such polymers are produced by extrusion (extrusion) using a heated screw (an example of a simple extruder, but only without heating - home meat grinder). The pipes are obtained with a very smooth surface (the roughness of polymer pipes is approximately 10 times lower than that of steel pipes).

Polyethylene pipes

Polyethylene pipes are most widespread. Initially they were made from ordinary polyethylene (remember transparent plastic film). Such pipes lost strength when heated to 50-60°C and quickly aged. They could only be used to supply cold water.

In the 80s Chemists have learned to bind linear polyethylene molecules to each other - “cross-linking”. This “cross-linked” polyethylene has increased strength, heat resistance, and resistance to UV radiation. They can be used to transport water at temperatures up to 95°C. Having gained increased heat resistance, “cross-linked” polyethylene has lost its ability to be welded. In product labeling, “cross-linked” polyethylene is designated PE-X (the letter X indicates that the polymer is “cross-linked”). Pipes from cross-linked polyethylene make up more than half of the total production of polymer pipes.

Pipes made of cross-linked polyethylene PE-X can be used not only for cold, but also for hot water supply and heating (central and floor).

Polypropylene pipes

Polypropylene (PP) It ranks second in terms of use in pipe production. The physical, mechanical and thermal properties of this polymer are close to cross-linked polyethylene, but unlike the latter, it is more rigid. Therefore, polypropylene pipes are produced in the form of measured sections, which is somewhat less convenient during transportation and requires large quantity connecting elements during installation. At large companies this problem has been solved: they offer different variants complex connection systems - low-temperature welding and using metal components.

PVC pipes

Polyvinyl chloride (PVC)- a polymer very widely used in construction; in the production of pipes it follows polyethylene and polypropylene. It is usually used in unplasticized form. The presence of chlorine in PVC causes concern among environmentalists and limits the use of such pipes for water supply. A positive property of polyvinyl chloride is its reduced flammability and increased chemical resistance compared to other polymers. It is also less sensitive to UV radiation, so the main areas of application for PVC pipes are drainage systems and sewerage.

Polybutene pipes

Polybutene (PB)- a polymer, like polyethylene and polypropylene, from the group of polyolefins. Biologically harmless. Pipes made of polybutene are more elastic than those made of polypropylene. Polybutene is characterized by high strength properties, resistance to UV irradiation and increased heat resistance, approaching in this respect “cross-linked” polyethylene.

Polybutene pipes have proven themselves in hot water supply and heating networks (in particular, for installing heated floors). At 70°C and a system operating pressure of 0.3 MPa, a 50-year service life of RV pipes is guaranteed. Maximum temperature operation of such pipes +95°C. Like polypropylene, polybutene pipes can be welded, which allows these pipes to be used for internal wiring.

Marking of polymer pipes

Polymer pipes are marked according to the type of polymer ( RE,RE-X,RR etc.), by outer diameter and nominal pressure (PN).
The outer diameters of pipes (in mm) for internal wiring are presented in the following row: 10; 12; 16; 25; 32; 40; 50, etc.
In addition to diameter, pipes are marked by wall thickness.

The nominal pressure is usually expressed in bars: 1 bar = 0.1 MPa. By nominal pressure we mean constant internal water pressure at 20°C, which the pipe can withstand without failure for 50 years (for example, PN=10, PN=12.5 or PM=20).
To assess the level of these parameters, we can recall that the operating water pressure in the water supply system is no more than 0.6 MPa (6 bar). Maximum pressure that the pipe can withstand a short time, several times higher than nominal. At temperatures above 20°C, the trouble-free operation life of polymer pipes at a constant pressure is reduced or may remain the same - 50 years, but subject to a lower operating pressure.

Characteristics of some materials used for the production and connecting parts of polymer pipes

Indicators	The meaning of indicators for the material
	HDPE (PVP)	HDPE (PSP)	PVD (PNP)				PVDF	PA (plasticized)
Density, g/cc
Tensile yield strength, MPa
Elongation at break, %
Modulus of elasticity, MPa
Linear expansion coefficient
Calculated permissible stress of pipes, MPa

Currently widely used in various industries, as well as in Everyday life. That is why in many situations it is necessary to pre-select the polymer for certain temperature indicators of their operation.

For example, the melting point of polyethylene ranges from 105 to 135 degrees, so it is possible to identify in advance those areas of production where this material will be appropriate for use.

Features of polymers

Each plastic has at least one temperature, which makes it possible to evaluate the conditions of its immediate use. For example, polyolefins, which include plastics and plastics, have low melting points.

In degrees depends on the density, and the operation of this material is allowed at parameters from -60 to 1000 degrees.

In addition to polyethylene, polyolefins also include polypropylene. The melting point makes it possible to use this material at low temperatures; the material becomes brittle only at -140 degrees.

Melting of polypropylene is observed in the temperature range from 164 to 170 degrees. From -8°C this polymer becomes brittle.

Templen-based plastic can withstand temperatures of 180-200 degrees.

The operating temperature of plastics based on polyethylene and polypropylene is in the range from -70 to +70 degrees.

Among plastics that have a high melting point, we highlight polyamides and fluoroplastic, as well as nylon. For example, softening of caprolon occurs at a temperature of 190-200 degrees, melting of this plastic mass occurs in the range of 215-220°C. Low temperature melting of polyethylene and polypropylene makes these materials in demand in chemical production.

Features of polypropylene

This material is a substance obtained by the reaction of a thermoplastic polymer. The process is carried out using metal complex catalysts.

The conditions for obtaining this material are similar to those under which polyethylene can be produced. low pressure. Depending on the chosen catalyst, any type of polymer, as well as its mixture, can be obtained.

One of the most important characteristics of the properties of this material is the temperature at which this polymer begins to melt. Under normal conditions, it is a white powder (or granules), ranging up to 0.5 g/cm³.

Depending on the molecular structure, polypropylene is usually divided into several types:

• atactic;
• syndiotactic;
• isotactic.

Stereoisomers have differences in mechanical, physical, chemical properties. For example, atactic polypropylene is characterized by high fluidity; the material is similar to rubber in external parameters.

This material dissolves well in diethyl ether. Isotactic polypropylene has some differences in properties: density, resistance to chemical reagents.

Physico-chemical parameters

The melting point of polyethylene and polypropylene is high, so these materials are now widely used. Polypropylene is harder, has higher abrasion resistance, and can withstand temperature changes well. Its softening begins at 140 degrees, despite the fact that the melting point is 140°C.

This polymer is not subject to corrosion cracking and is resistant to ultraviolet radiation and oxygen. When stabilizers are added to the polymer, these properties are reduced.

Currently, various types of polypropylene and polyethylene are used in industrial sectors.

Polypropylene has good chemical resistance. For example, when it is placed in organic solvents, only slight swelling occurs.

If the temperature rises to 100 degrees, the material can dissolve in aromatic hydrocarbons.

The presence of tertiary carbon atoms in the molecule explains the resistance of the polymer to elevated temperatures and exposure to direct sunlight.

At 170 degrees, the material melts, its shape is lost, as well as the main specifications. Modern heating systems are not designed for such temperature values, so it is quite possible to use polypropylene pipes.

With a short-term change in temperature level, the product is able to maintain its characteristics. With prolonged use of polypropylene products at temperatures above 100 degrees, their maximum service life will be significantly reduced.

Experts advise buying reinforced products that are minimally subject to deformation when the temperature rises. Additional insulation and an internal aluminum or fiberglass layer will help protect the product from expansion and increase its service life.

Differences between polyethylene and polypropylene

The melting point of polyethylene differs slightly from Both materials, when heated, soften and then melt. They are resistant to mechanical deformation, are excellent dielectrics (they do not conduct electric current), are lightweight, and are not able to interact with alkalis and solvents. Despite the many similarities, there are some differences between these materials.

Since the melting point of polyethylene is lower, it is less resistant to ultraviolet radiation.

Both plastics are in a solid state of aggregation, odorless, tasteless, and colorless. Low-density polyethylene has toxic properties, propylene is absolutely safe for humans.

The melting point ranges from 103 to 137 degrees. Materials used in manufacturing cosmetics, household chemicals, decorative flowerpots, dishes.

Polymer differences

As the main distinguishing characteristics of polyethylene and polypropylene, we highlight their resistance to pollution, as well as strength. This material has excellent thermal insulation characteristics. Polypropylene is the leader in these indicators, so it is currently used in larger volumes than foamed polyethylene, the melting point of which is less important.

Cross-linked polyethylene

The melting point of cross-linked polyethylene is significantly higher than that of conventional material. This polymer is a modified structure of bonds between molecules. The basis of the structure is ethylene, polymerized under high pressure.

It is this material that has the highest technical characteristics of all polyethylene samples. The polymer is used to create durable parts that can withstand various chemical and mechanical loads.

The high melting point of polyethylene in the extruder determines the areas of use of this material.

Cross-linked polyethylene has a wide-cell network structure of molecular bonds, formed when cross chains consisting of hydrogen atoms appear in the structure, which are combined into a three-dimensional network.

Technical specifications

In addition to high strength and density, cross-linked polyethylene has original properties:

• melting at 200 degrees, decomposition into carbon dioxide and water;
• increase in rigidity and strength with a decrease in elongation at break;
• resistance to aggressive chemicals, biological destroyers;
• "shape memory".

Disadvantages of cross-linked polyethylene

This material gradually deteriorates when exposed to ultraviolet irradiation. Oxygen, penetrating its structure, destroys this material. In order to eliminate these shortcomings, the products are covered with special protective shells made from other materials, or a layer of paint is applied to them.

The resulting material has universal properties: resistance to destroyers, strength, high melting point. They allow the use of cross-linked polyethylene for the manufacture of hot or cold water supply pipes, insulation of high voltage cables, and the creation of modern building materials.

Finally

Currently, polyethylene and polypropylene are considered one of the most popular materials. Depending on the process conditions, it is possible to obtain polymers with specified technical characteristics.

For example, by creating a certain pressure, temperature, or choosing a catalyst, you can control the process and direct it towards the production of polymer molecules.

The production of plastics that have certain physical and chemical characteristics has made it possible to significantly expand the scope of their use.

Manufacturers of products made from these polymers are trying to improve technology, increase the service life of products, and increase their resistance to temperature changes and exposure to direct sunlight.

In order to answer this question, you need to know the properties of materials, as well as understand the areas of application of each.

Both materials are obtained in completely different ways:

Polypropylene or PP by polymerization of propylene molecules;

Cross-linked polyethylene or PE-X (PEX) by chemical or physical cross-linking of ethylene molecules.

Properties and characteristics

Density	0.933-095 g/cm3
Melting temperature
Frost resistance
Thermal conductivity	0.3-0.4 W/mK
Tension at break

Both materials have good wear resistance and practically identical tensile strength. However, if PP has greater resistance to cracking, then under sudden load changes it performs worse than PEX. In addition, cross-linked polyethylene has greater flexibility: the minimum bending of pipes made from it is 5D (using a 3D spring), versus 8D for polypropylene. Pipes made from both materials have memory properties, which means they can regain their shape when heated to 100 °C.

The melting point of cross-linked polyethylene is 30-40 °C higher than PP, but they are used in lower temperature conditions. Maximum working temperature is the same for both and equals 90 °C. And it is already necessary to clarify what the service life will be for pipes made of cross-linked polyethylene or polypropylene when used in different temperature conditions. But the lower limit is very different. If for polypropylene the critical temperature is -15-20 °C, then cross-linked polyethylene retains impact resistance down to -50 °C.

With a sharp change in physical or thermal loads, the properties of polypropylene are reduced. The same service life high temperatures polypropylene will be lower than cross-linked polyethylene. In this case, it is necessary to take into account the pressure and temperature in the system, as well as differences, which can also affect the service life.

Both materials have high levels of microbiological and physiological neutrality and are not subject to corrosion. However, in terms of chemical resistance to various reagents and solvents, PP is slightly inferior to PEX. If in polypropylene for additional protection stabilizers are added, the cross-linked polyethylene is protected by an additional layer of anti-diffusion coating. The chemical neutrality of pipes made from both materials is also facilitated by the smoothness of the inner surface. The roughness coefficient is the same for PEX and PP and is equal to 0.0007 mm. They can also be used for drinking water supply systems only if there is a certificate of admissibility for installation in drinking water supply systems.

Due to the higher density and physical and chemical properties of the material, PEX does not allow either liquids or gases to pass through, which allows it to be safely used in pressure gas and water supply systems.

What conclusion can be drawn?

PE-X and PP pipes are quite strong and elastic and can cope even with the aggressive coolant of domestic systems. However, while polypropylene pipes perform well in more static systems, XLPE pipes can withstand sudden changes within the system.

PN 10 - for cold water supply (up to +20°C) and heated floors (up to +45°C), nominal operating pressure 1 MPa (10.197 kgf/cm2);

PN 16 - for cold water supply and hot water supply (up to +60°C), nominal operating pressure 1.6 MPa (16.32 kgf/cm2);

PN 20 - for hot water supply (temperature up to +80°C), nominal pressure 2 MPa (20.394 kgf/cm2);

PN 25 (reinforced) – for hot water supply and central heating (up to +95°C), nominal pressure 2.5 MPa (25.49 kgf/cm2).