月: 2023年1月

What Is Steel Pipe?

A steel pipe is a tubular object made of steel. Steel is classified into the following two types according to the manufacturing method:

1. Seamless Steel Pipe

Seamless steel pipe refers to steel pipe that has no seams in the tube. To manufacture a seamless steel pipe, a cylinder made of steel, called a billet, is first heated to about 1200°C. Then, using a special tool, the center of the heated cylinder is pushed open and a hole is drilled through it. This process (Mannesmann method) is used to produce seamless steel pipe.

2. Welded Steel Pipe

Welded steel pipes are manufactured using steel strip, which is a rolled steel sheet. This steel strip is heated, oxidized, and bent into a cylindrical shape.

Uses for Steel Pipes

Steel pipe is versatile and used in a wide range of areas.

One of the most common uses for steel pipe is piping. Pipes are used to transport liquids and gases.

Other uses for steel pipe include stair railings, gardening materials, and fences.

Features of Steel Pipes

In addition to the classification by manufacturing method described above, steel pipes can be divided into the following three types according to material:

1. Stainless Steel Pipe

Stainless steel pipes are manufactured using alloy steel containing 10.5% or more chromium. Among steel pipes, stainless steel pipes are the most frequently used. The reason for this is that stainless steel pipes have high pressure resistance and can be made lighter. Stainless steel pipes are also superior in that they are rust-resistant and can be used for a long period of time.

2. Carbon Steel Pipes

Carbon steel pipes are made from carbon steel, an alloy of iron and carbon. The advantage of using carbon steel pipe is its relatively low price. Therefore, it is widely used as piping for transporting oil, gas, water, etc.

3. Alloy Steel Pipes

Alloy steel pipes are manufactured from alloys such as nickel, molybdenum, and chromium added to the carbon steel mentioned above.

What Is Steel Casting?

Steel casting involves pouring molten steel into a mold to solidify into a specific shape and size. Known for their strength and tenacity, cast steel products are used in mechanical structures subjected to large forces. Unlike cast iron, which contains graphite, cast steel generally has less than 2.1% carbon.

Uses of Steel Castings

Steel castings are divided into carbon steel castings and alloy steel castings. Carbon steel castings are used in motors, power plant machinery, and railroad parts, while low-alloy steel castings improve strength and resistance, used in brackets, gears, and automotive parts. High-alloy steel castings, with added nickel, chrome, and manganese, are utilized in high-temperature and pressure environments like turbine casings and pump parts.

Principles of Steel Casting

Traditional sand casting involves making a sand mold from a wooden mold, pouring molten steel, and breaking the mold post-cooling. Other methods include full mold (using styrofoam), lost wax (for precision casting), and shell molding (suitable for mass production). The steel casting process encompasses design, modeling, molding, melting, casting, cutting, heat treatment, finishing, and inspection. Casting simulation ensures optimal metal flow and solidification, while heat treatment is crucial for achieving the desired metallurgical structure.

What Is a Ball Valve?

A ball valve is a valve with a spherical (ball-shaped) valve plug with a hole drilled in the center, which is inserted into a seat in the body (valve box).

By rotating the ball of the valve body 90 degrees, the fluid flow is shut off and the flow path is closed. Ball valve is defined in the Glossary of Terms for valves (JIS B0100) as “a general term for a valve in which a spherical valve plug rotates inside a valve housing with a valve rod as its axis. The valve plug can be a full-surface or half-surface sphere. The valve plug can be either a full-surface ball or a half-surface ball.

The ball of the valve plug does not remain in the flow path when the valve is open, resulting in a small pressure drop, and is used for fully open or fully closed valves, not for flow control.

Uses of Ball Valves

Figure 1. Example of Ball Valve Use

Ball valves are widely used in household and general industrial applications because of their ease of operation, simple structure, and compact size. Ball valves are generally used in the fully open or fully closed position because fluid accumulates between the body (valve plug) and the ball (plug) when used at the ball’s mid-position opening angle. Therefore, this valve is used as a shutoff valve for shutoff purposes.

The ball (plug) of a ball valve can be opened or closed by turning the handle attached to the stem (valve stem) 90 degrees, which has the advantage of easy operation and short operating time. In addition, since the ball does not remain in the flow path during valve opening, pressure loss is reduced.

The flow path has a few steps and can be used for piping fluids containing slurries and solids. The slurry is a mixture of solids and liquids, such as finely ground coal or ore, mixed with water to form mud, which is used for conveying.

Principle of Ball Valves

Figure 2. Ball Valve Opening and Closing Valve Status and Fluid Flow

In a ball valve, the ball (valve plug) and seat (valve seat) inside the body (valve box) make surface contact to close the fluid. In this condition, the center of the ball bore is at 90 degrees to the center of the body opening. When the ball is rotated 90 degrees, the center of the ball hole becomes concentric with the center of the body opening, and the fluid flows.

The force required for this open/close operation is proportional to the frictional resistance between the ball’s spherical surface and the seat. The larger the nominal diameter of the valve, the greater the force required to open and close the valve. Therefore, valves with larger nominal diameters use rotating handles equipped with gear actuators (reduction gears).

Many ball valves are full-bore port valves with a small difference in flow path area between the inside of the body and the inlet/outlet piping, and feature an extremely small pressure loss when fully open because the flow path is almost straight.

Structure of Ball Valves 

Figure 3. Structure of Ball Valve

Ball valves are mainly composed of a body (valve box), a disc (valve plug), a stem (valve stem), and a handle. A ball valve is operated by a handle or an actuator.

The handle is attached to the stem and transmits rotation to the stem. When the valve is open, the rotation of the handle causes the ball to rotate 90 degrees, and when the valve is closed, the ball rotates in the opposite direction.

Types of Ball Valves

1. Classification by Opening/Closing Operation Method

Figure 4. Operation and Drive System of Ball Valve

Ball valves have the following three main types of operation and drive methods for opening and closing.

• Manual Type
  Rotation of stem by the handle, etc.
• Air-Actuated Type
  Rotates the stem with a pneumatic actuator
• Electric Type
  Rotate stem with electric actuator

2. Classification by Bore Shape

Ball valves are available in the following three bore shapes. The bore is the inside diameter of the flow path in the body.

• Standard Bore
  The bore diameter is one size smaller than the valve’s nominal diameter (pipe inner diameter).
• Reduced Bore
  The bore diameter is at least one size smaller than the valve’s nominal diameter (pipe bore).
• Full Bore
  The bore diameter is almost the same as the nominal diameter of the valve (pipe I.D.)

3. Classification by Ball Support Method

Figure 5. Ball Support Method

Ball valves are available in the following two types of rotating ball support methods.

Floating Type (Floating Ball Type)
In the floating type, the ball is supported by a seat mounted inside the body. The square end of the stem fits into the ball groove and rotates the ball.

The groove of the ball is parallel to the fluid flow direction when fully closed, and the ball slides slightly and is pressed against the seal by the fluid pressure to ensure sealing. Typically used for low pressure (up to JIS20K, CL300) and small bore (up to DN200).

Trunnion Type (Fixed Ball Type)
In the trunnion type, the upper part of the ball is supported by the stem (valve stem) and the lower part by the trunnion (rotating shaft). The upper and lower parts of the ball are supported by the rotating shaft, making it less susceptible to fluid pressure. The seat is pushed by a spring built into the seat holder, which contacts and seals the ball. It is generally used for high pressure (JIS 30K, CL600 or higher) and large bore (DN250 or higher).

4. Classification by Body Material

• Grey cast iron JIS G5501 FC200
• Spheroidal graphite cast iron JIS G5502 FCD400
• Carbon steel forgings for pressure vessels JIS G3202 SFVC 2A
• High temperature and high pressure cast steel JIS G5151 SCPH2, SCPH21
• Stainless steel castings JIS G5121 SCS13A, SCS14A
• Copper and copper alloy castings JIS H5120 CAC401 Bronze castings Class 1
• Copper and copper alloy rods JIS H3250 C3771 Brass for forging

Body materials are selected based on the following requirements. For details, refer to each manufacturer’s catalog, etc.

• Fluid type, pressure, temperature, flow velocity, and presence/absence of impurities
• Corrosion resistance required or not
• Applicable regulations and standards

5. Classification by Sheet Material

In general, ball valve seats are either soft seals made of resin or carbon fiber, or metal seats made of metal.

Soft Seals
PTFE (Teflon) or PTFE filled with carbon or other agents. Maximum service temperatures are approximately 150°C for PTFE alone and 300°C for PTFE filled with carbon or other agents.

PTFE sheets are characterized by chemical resistance, low frictional resistance, and excellent operability. There are also carbon fiber sheets with a maximum operating temperature of approximately 500°C.

Metal Sheet
Carbon steel or stainless steel material is thermal-sprayed with a high-hardness nickel alloy on the ball contact surface of the sheet. In this case, the same thermal spray is also applied to the ball side.

The metal sheet has a maximum operating temperature of up to about 500°C and applies to high-temperature fluids, powders, slurries, and viscous fluids that are difficult to handle with soft sheets.

What Is Polyurethane?

Polyurethane is a polymer with urethane bonds obtained by reacting isocyanate groups with hydroxyl groups.

By changing the type and composition of the primary raw materials and the molding method, polyurethane can be made spongy, flexible like rubber, or hard like rubber tires.

Figure 1. Polyurethane synthesis reaction formula

Uses for Polyurethane

Polyurethane can be divided into two broad categories in terms of appearance: foam-based, which is porous, and non-foam-based, which is rubber-like. Since the uses for each are quite different, they are described separately below.

1. Foam-Based

Foam-based polyurethane comes in two types: soft foam and hard foam. Soft foam, in particular, is used in various applications, from everyday items to industrial uses. Soft foam applications include sponges used in kitchens, cushions for headphones and other devices, rollers for industrial equipment, and soundproofing materials.

Rigid polyurethane foam applications are often used in construction sites as heat insulators.

2. Non-foam Type

Non-foamed polyurethane has high elasticity and toughness and is used as elastic structural materials such as rubber and elastomers, as well as fibers, paints, and adhesives.

As elastomers, they are used in tires, belts, gaskets, rollers, machine parts, and automobile bumpers. Polyurethane fibers, called spandex, are also widely used in clothing such as jackets, pants, swimwear, sportswear, etc., due to their high elasticity.

Composition of Polyurethane

Figure 2. Typical examples of raw materials that make up polyurethane

The raw materials used to make polyurethane include diisocyanates, which have bifunctional isocyanate groups in their molecules, polyols, which have hydroxyl groups in their molecules, and low molecular weight diols.

While there are only a few types of diisocyanates used in polyurethane, there is a very wide range of polyols, which are the raw materials for the hydroxyl group component. This is because polyols themselves are polymers with molecular weights ranging from several hundred to several thousand, and they are composed of a wide range of monomer combinations.

The low molecular weight diols are typical examples of hydroxyl group components, and their dimers are also used as low molecular weight diols. Triols with three hydroxyl groups and alcohols with a single hydroxyl group are also used to adjust the molecular weight.

Characteristics of Polyurethane

The characteristics of polyurethane vary greatly depending on the type of raw material used in the mixture. In general, polyurethanes have excellent mechanical strength (elasticity and toughness) and the following characteristics:

1. Advantages

• High mechanical strength, excellent elasticity and toughness, and high tensile strength. Maintains elasticity even at high hardness.
• Excellent abrasion resistance and aging resistance.
• Excellent oil and solvent resistance, and good adhesion.
• Excellent low-temperature properties and good weather resistance.
• Highly resilient to compression. 

2. Disadvantages

• Poor heat resistance; continuous use temperature is limited to 80°C to 100°C.
• Easily hydrolyzed and weak in water.
• Toxic gases are generated by combustion.

These characteristics vary greatly depending on the combination of raw materials used. For example, hardness and strength differ greatly depending on the ratio of polyol and low molecular weight diol used. In addition, the polyol component contributes significantly to weather resistance and hydrolysis resistance. Therefore, it is important to design molecules that match the required performance.

Other Information on Polyurethane

Production Methods for Polyurethane Foam

Figure 3. Reaction Formula for Urethane Foam Foaming

Polyurethane foam is a sponge-like molded product produced by foaming polyurethane during the molding process. There are multiple methods of manufacturing polyurethane foam, including slab molding, in which a mixture of raw materials is foamed without being placed in a mold and then cut into the shape of the product. Other methods are mold molding, where a mold is used to form the product into the required shape, and laminate molding, which is useful for producing large insulation boards.

1. Soft Foam-Based Polyurethane
In soft foam polyurethane, water is added as a foaming agent to the raw material polyol, and the isocyanate groups react with the water to produce carbon dioxide gas. At the same time, resinification by the reaction of polyol, low molecular weight diol, and isocyanate proceeds, so that each bubble of carbon dioxide gas cures in a continuous state to form a porous foam.

During the reaction with water, the isocyanate becomes an amine. However, due to the extremely high reactivity of amines, it immediately reacts with another isocyanate group to form a urea bond. For this reason, the composition of soft foam-based polyurethane contains not only urethane bonds but also many urea bonds.

2. Rigid-Foam Polyurethanes
Rigid-foam polyurethane uses a low-boiling physical foaming agent that evaporates from the reaction heat during urethane conversion. The bubbles of rigid foam are independent bubbles to obtain a high thermal insulation effect.

What Is Polyester?

Polyester is a general term for polymers formed by ester bonds.

Polyethylene terephthalate (PET) is a typical example. By changing the alcohol or carboxylic acid that forms the ester bond, the properties of the resulting polyester can be changed. It is used in various applications, but typical examples include materials for clothing, bedding, and curtains.

Uses of Polyester

Typical applications for polyester include polyethylene terephthalate (PET) for PET bottles, polyester fibers, and cable protectors for electronic devices and automotive parts. Polytrimethylene terephthalate (PTT) is also used as a polyester fiber.

Another type of polyester is unsaturated polyester, which has unsaturated bonds in the molecule. FRP is used in a wide range of industries, including aircraft and other transportation components, construction materials, sporting goods, and space-related components, such as rockets.

Production Process of Polyester

Figure 1. Production process for polyethylene terephthalate (PET)

There are two methods of polyester production: direct polymerization, in which a divalent alcohol and a divalent carboxylic acid are dehydrated and condensed to form an ester bond. The second method is ester exchange, in which a dicarboxylic acid ester and a divalent alcohol undergo an ester exchange reaction. 

Various polyesters can be made by changing the divalent alcohol and divalent carboxylic acid used in the dehydration-condensation process, and their physical properties also change, resulting in different applications. For example, polyethylene terephthalate with two alcohol carbons is used as a material for fleece and other clothing, while polybutylene terephthalate with four alcohol carbons has high durability and stretchability and is used for sportswear and swimwear.

Polyester has different properties depending on their molecular structure. Their common characteristics are high strength, abrasion resistance, and elasticity. On the other hand, its disadvantages are that it is easily electrified and has low heat resistance.

Other Information on Polyester

1. Differences Between Polyester and Nylon

Nylon is a polymer similar to polyester, but its chemical structures are very different. Polyester is formed by ester bonds, while nylon is formed by amide bonds.

Polyester fibers are characterized by their firmness, elasticity, resistance to wrinkling, and resistance to acids and alkalis. In contrast, Nylon fibers are lightweight and dry quickly. Polyester fibers are similar in appearance and feel to cotton and wool, and are used in women’s and men’s clothing. Nylon fibers, on the other hand, are used for innerwear and stockings as well as a material for automobile airbags.

2. Unsaturated Polyester

Figure 2. Three-dimensional crosslink formation reaction of unsaturated polyester

Unsaturated polyester is a thermosetting resin and differs from thermoplastics, such as PET, PEN, PBT, and PTT in this respect. Specifically, a mixture of polyester resin having unsaturated bonds in the molecule and vinyl monomer is made into a final product by three-dimensional cross-linking of the polyester resin with the vinyl monomer through heating.

3. Physical Properties and Applications of Unsaturated Polyesters

Figure 3. Comparison of physical properties of thermosetting resins

Unsaturated polyesters are particularly excellent in moldability due to their low viscosity during molding. When composited with glass fiber or carbon fiber, its toughness increases, so it is used for automobile bodies, ships, and other applications requiring strength. The weak point is that the ester bonds in the main chain are hydrolyzed by alkali, resulting in a decrease in molecular weight and low alkali resistance.

What Is Polyethylene?

Polyethylene is a type of plastic resin sometimes abbreviated as PE. It is a resin composed only of carbon and hydrogen atoms and basically produces only water and carbon dioxide when burned.

The amount of branched chains and molecular weight of polyethylene vary depending on the manufacturing process. Low-density polyethylene (LDPE), which is highly branched and has low crystallinity, is transparent and soft. High-density polyethylene (HDPE), which has fewer branches and higher crystallinity, has excellent impact resistance. Ultra-high-molecular-weight polyethylene (UHMW-PE), which has excellent mechanical properties, is also available.

Uses of Polyethylene

Polyethylene is a polymer obtained by polymerizing ethylene (C2H4). It is used in a wide range of applications due to its advantages, such as easy processing and low cost.

Polyethylene has different properties depending on its density. Low-density polyethylene (LDPE) has good processability and is used for wrapping film, tube containers for mayonnaise and other products, and plastic bags.

High-density polyethylene (HDPE) is impact-resistant and is used in plastic bags, buckets, other sundries, and kerosene tanks, among others. There is also ultra-high-molecular-weight polyethylene (UHMW-PE), which has excellent mechanical properties and is used in separators for lithium-ion batteries.

Structure and Characteristics of Polyethylene

Polyethylene is obtained by polymerizing ethylene (C2H4), which has a carbon-carbon double bond. It has a simple structure consisting only of carbon and hydrogen atoms.

The difference between low-density polyethylene and high-density polyethylene introduced earlier is density. The manufacturing process for both is different. In the case of low-density polyethylene, a large number of branched molecular chains are produced during the polymerization reaction. This makes it difficult for the polymers to align with each other, resulting in lower crystallinity and lower density.

On the other hand, high-density polyethylene does not produce branched chains during the polymerization reaction, and linear polymers are easily aligned, resulting in a high degree of crystallinity and density.

LDPE and HDPE, which have different higher-order structures, have very different physical properties: LDPE is easy to process, transparent, and soft, but has low heat resistance. HDPE, on the other hand, has high heat resistance, chemical resistance, and impact resistance, but is cloudy white like a plastic bag and less transparent than LDPE.

Polyethylene Toxicity and Environmental Impact

Polyethylene is an inert substance, which means that even if it enters the body, it is eliminated without causing chemical reactions. In addition, polyethylene is composed only of carbon and hydrogen atoms, so when it burns, it basically produces only carbon dioxide and water. On the other hand, since polyethylene is used in large quantities throughout the world, there are concerns about the environmental impact of incinerating all unneeded polyethylene. For this reason, polyethylene has recently been recycled and reused. However, the recycling rate is still not high enough, and technological development for polyethylene reuse is still underway.

What Is a Polyolefin?

A polyolefin is the generic term for polyethylene and polypropylene. These materials are formed from monomers known as olefins, which are compounds containing double bonds between carbon atoms and are also referred to as alkenes.

Both polyethylene and polypropylene, as polyolefins, possess unique characteristics. However, they have the following in common: (1) lightweight due to their low density, (2) excellent moisture resistance, which prevents the permeation of water vapor in the air, and (3) only carbon dioxide and water are produced when burned because they are composed of only carbon and hydrogen atoms. Only carbon dioxide and water are produced when polyolefin is burned.

Types and Uses of Polyolefins

Polyolefins are a generic term for resins whose raw material compounds are olefins.

Polyethylene is classified into low-density polyethylene (LDPE), high-density polyethylene (HDPE), and ultra-high-molecular-weight polyethylene (UHMW-PE). UHMW-PE is used in separators for lithium-ion batteries.

Polypropylene is a milky white resin used in a wide range of industries, including food trays, home appliance parts, and automotive parts.

Structure of Polyolefins

The raw material for polyethylene, which is classified as polyolefins, is ethylene, while the raw material for polypropylene is propylene. Both of these raw materials have double bonds. Hydrocarbons with such double bonds, or alkenes, used to be called olefins. As a remnant of this name, polyethylene and polypropylene made from olefins are called polyolefins.

LDPE and HDPE are manufactured in different ways. Due to the difference in manufacturing methods, the number of molecular chains with branches and molecular weight differs, resulting in LDPE and HDPE having different physical properties. In the case of polypropylene, physical properties vary depending on the stereo-regularity of the methyl groups in the side chains, with higher stereo-regularity resulting in higher hardness and strength.

Characteristics of Polyolefins

The following are some characteristics common to both polyethylene and polypropylene, also known as polyolefins.

The first characteristic is that they are lightweight. Polyolefins have a density of less than 1 g/cm3, which is small among resins.

The second feature is excellent moisture resistance. Polyolefins have a low water absorption rate, so they are used to prevent the permeation of water vapor from the air, such as in lids.

The third characteristic is that no harmful compounds are produced when they are burned. Since polyolefins are composed of only carbon and hydrogen atoms, only water and carbon dioxide are produced when they are burned. However, it should be noted that if the polymer is partially modified or additives are added, other compounds may be produced during combustion.

What Is Polystyrene?

Polystyrene is a polymer compound obtained by polymerizing styrene, which is chemically synthesized from crude oil or naphtha.

It is also known as polystyrene or styrene resin. Polystyrene was first industrialized in Germany in the 1930s. It was later industrialized in the U.S., but production stalled for a while because the country was in the midst of World War II.

Full-scale production began after the war when Japan began importing styrene monomer in 1957.

Uses of Polystyrene

Polystyrene are versatile plastic that can be used for various applications, including plastic parts inside home appliances, food packaging materials, letter cases, computer housings, CD cases, ballpoint pen shafts, and other items requiring high transparency and rigidity. It is also used for diffusion plates and light guide plates for LCD displays. The applications are wide-ranging.

Foamed polystyrene, to which a foaming agent is added, can be easily formed during the molding process and is used in products that take advantage of its heat-insulating properties. It is used for cup noodle containers, containers for boxed lunches and prepared foods at supermarkets, as well as insulation materials for building materials.

Types of Polystyrene

Types of polystyrene include general polystyrene, expanded polystyrene, impact-resistant polystyrene, and biaxially oriented polystyrene sheet.

1. General-Use Polystyrene

General-use polystyrene is made exclusively from styrene, is inexpensive, and is used in many applications due to its well-balanced physical properties. It has excellent transparency, and good dimensional accuracy, and can be easily colored. Since styrene is the only raw material, it is easy to recycle.

On the other hand, it has weaknesses such as a low heat resistance temperature of 60-80°C, low-impact resistance, and high resistance to acids and alkalis, but low oil resistance.

2. Foamed Polystyrene

Expanded polystyrene is a material that foams and expands when heated during the molding process of the final product. It is more commonly known as expanded polystyrene. When polystyrene is manufactured, a foaming agent is added to the raw material, which causes it to expand when heated during the molding process. Since it is a foaming material, it has high heat insulation properties and is lightweight, making it widely used in everything from daily necessities to building materials. 

3. Impact-Resistant Polystyrene

Impact-resistant polystyrene is made by adding rubber components such as polybutadiene during the polymerization of polystyrene, thereby improving the impact resistance of general-use polystyrene. While the impact resistance is 5 to 10 times higher than that of general-purpose polystyrene, there are disadvantages, such as lower rigidity and transparency. Moldability and chemical resistance are equivalent to those of general polystyrene.

Blends of this impact-resistant polystyrene with general-use polystyrene exhibit properties intermediate between these two, and a wide variety of grades are available. 

4. Biaxially Oriented Polystyrene Sheet

A biaxially oriented polystyrene sheet is obtained by further stretching the extruded polystyrene sheet in two axial directions. Biaxial stretching results in molecular orientation, which improves strength and impact resistance without compromising transparency and chemical resistance. It is mainly used as a food packaging material, such as transparent lids for boxed lunches sold in supermarkets and convenience stores.

Other Information on Polystyrene

How Polystyrene Is Manufactured

Polystyrene can be produced industrially through bulk polymerization, solution polymerization, emulsion polymerization, and suspension polymerization. Styrene, the raw material, is obtained by thermal synthesis of benzene and ethylene.

1. Mass Polymerization Method
This is a method in which styrene monomer is polymerized by adding an initiator to the monomer and heating it as it is.

2. Solution Polymerization Method
This method involves dissolving styrene monomer in a reaction-inert organic solvent, adding a polymerization initiator, and heating for polymerization.

3. Emulsion Polymerization Method
This method involves mixing styrene monomer, surfactant, water-soluble polymerization initiator, and water, emulsifying the mixture in water, and then polymerizing it by heating. 

4. Suspension Polymerization Method
Styrene monomer, suspension stabilizer, polymerization initiator, and water are mixed, and polymerized by heating while suspended and dispersed in water.

What Is Polypropylene?

Polypropylene is a plastic synthesized by polymerizing propylene (molecular formula: C3H6, structural formula: CH2=CH-CH3).

Polypropylene was discovered in 1954 by Mr. Natta of Italy, who discovered that it could be synthesized using a titanium-based organometallic compound called Ziegler-Natta catalyst. In Japan, industrial mass production began in 1962.

Among commodity resins, polypropylene can be produced at a lower cost and is second only to polyethylene in production volume. With a specific gravity of 0.9, it is small, scratch-resistant, strong, and chemical-resistant. It is used in a wide range of applications, from household materials such as packaging materials and food containers to automotive and medical supplies.

Polypropylene is classified as a thermoplastic resin that softens when heated above its glass transition point or melting point.

Uses of Polypropylene

Polypropylene is used in an extremely wide range of applications, taking advantage of its characteristics.

1. Food Containers

Food containers are a typical application for polypropylene. Polypropylene is a crystalline resin with high heat resistance and low dielectric constant, so it does not generate heat even when exposed to high frequencies in microwave ovens. This feature is used not only in general-purpose food containers but also in Tupperware for storing food ingredients for repeated use.

2. Automotive Applications

Next, automotive applications are attracting attention. Polypropylene is beginning to be used for bumpers and lamp housings, where metal materials have been used in the past, due to its low specific gravity and high strength. In the future, the replacement of electric vehicles with electric vehicles is expected to accelerate the development of lightweight automotive parts made of polypropylene. 

3. Physical and Chemical Equipment and Medical Equipment

Polypropylene is a nonpolar polymer composed only of carbon and hydrogen, making it highly resistant to organic solvents, acids, and alkalis. Therefore, polypropylene is used in laboratory equipment and measuring instruments that come in contact with solvents, as well as syringes for syringes in the medical field. 

4. Medical and Carpet Fibers

Polypropylene is nonpolar, as mentioned above, and therefore has poor dyeability and printability. However, recent technological advances such as surface treatment have made this possible, and polypropylene is increasingly being used as a quick-drying material.

Properties of Polypropylene

Polypropylene can be easily crystallized and has excellent heat resistance and mechanical strength. Molded products have high surface hardness and are not easily scratched. It is also possible to make grades with the desired strength by blending glass fibers and fillers.

Water resistance is as low as 0.01%, making it suitable for use in food containers, pipes, and other applications that are exposed to water for long periods of time. On the other hand, it has several drawbacks, the first of which is poor adhesion and printability. As a non-polar resin, it is incompatible with polar adhesives and does not wet well with inks.

The second problem is low weather resistance.

Polypropylene deteriorates and oxidizes when exposed to ultraviolet rays, resulting in a decrease in mechanical strength and bleaching. However, the addition of UV absorbers and antioxidants can compensate for these shortcomings.

Other Information on Polypropylene

Polypropylene Molding Methods

Polypropylene is a thermoplastic resin, which means that it becomes fluid when heated above its melting point. There are a wide variety of molding methods, including injection molding, extrusion, blow molding, and vacuum molding. Injection molding using molds enables mass production of products at a lower cost than other methods.

Polypropylene crystallizes easily, so if a flat product is desired, ribs should be placed where performance is not a problem, or the mold temperature and cooling conditions should be carefully controlled. Polypropylene sheets produced by extrusion molding or press molding can be easily bent or cut, making it possible to manufacture parts with a variety of shapes.

In recent years, it has also been used as a material for 3D printers that do not require molds.

What Is Polyvinyl Chloride (PVC)?

Polyvinyl chloride, also known as PVC, is a synthetic resin.

By adding additives such as plasticizers, various properties can be obtained. For this reason, it is used as a raw material for a wide variety of products, including hard plastics, soft plastics, and rubber.

Uses of PVC

PVC is used in various applications because it is inexpensive, easy to process, and can develop a variety of properties by changing additives. PVCs are broadly classified into rigid PVC and flexible PVC, each of which has different applications.

1. Rigid PVC

Rigid PVC has a plasticizer content of 10% or less. Major applications include signboards and signs, pipes and fittings for water and sewage pipes, piping materials for corrosive gases and chemicals, and conduits for electric wires and wiring.

2. Flexible PVC

Flexible PVC contains 25~50% plasticizer. It is mainly available in sheet form (0.2mm or thicker), film form (0.2mm or thicker), leather (with fabric backing), and extruded forms. The applications for each are as follows:

• Sheet Form: Handbags, belts, slippers, cushioned flooring, floating bags
• Film: Raincoats, boots, disposable gloves, umbrellas, food packaging, agricultural film, and clothing
• Leather: Vehicle interiors, furniture, bags, clothing
• Extruded: Textiles, electrical wire sheathing, flexible gas pipes, garden hoses

Properties of PVC

The molecular structure of PVC is polymers formed by the polymerization of vinyl chloride monomers. Most products are straight polymers made solely from PVC monomers. Copolymers copolymerized with other monomers such as vinyl acetate and ethylene vinylidene chloride are also available.

PVC products are produced by blending the above PVC polymers with stabilizers, plasticizers, colorants, and other additives using various processing and molding methods. The main feature of PVC is that by changing the type and amount of additives, a wide range of functions can be achieved, such as hard plastic, soft plastic, and rubber.

Characteristics of PVC

The following is a comparison of PVC’s characteristics with those of other general-purpose plastics, such as polyethylene (PE), polypropylene (PP), and polystyrene (PS).

1. Advantages

• Possessing carbon-chlorine bonds, polyvinyl chloride (PVC) has excellent chemical stability. It also has excellent flame resistance and durability.
• Compared to other resins, it has low crystallinity and contains a polar group called a carbon-chlorine bond, making it miscible with various substances.
• It exhibits high resistance to acids, bases, and most inorganic chemicals. When it comes to organic solvents, it dissolves in solvents containing aromatic rings, like toluene, ketones such as acetone, and cyclic ethers like tetrahydrofuran. However, it maintains a relatively high resistance to other types of chemicals.

2. Disadvantages

• Compared to resins such as polyethylene, it is inferior in impact resistance. It is brittle and cracks easily, especially at low temperatures. However, it is possible to increase impact resistance by adding plasticizers.
• When soft PVC products are used for a long period of time, the additives inside may ooze or volatilize on the surface.

Other Information on PVC

1. How PVC Are Manufactured

PVC is made by polymerization of vinyl chloride monomers, and industrial manufacturing methods include suspension polymerization, precipitation polymerization, and emulsion polymerization.

Suspension Polymerization
Vinyl chloride monomer, polymerization initiator, and water are mixed and heated for polymerization in a pressurized polymerization tank. After the reaction, a slurry of PVC resin dispersed in water is obtained. After removing the remaining monomer, the powdered PVC powder is obtained by dehydration and drying.

Precipitation Polymerization
This is a method in which polymerization is carried out in a solvent in which the vinyl chloride monomer is dissolved but PVC is not. When the vinyl chloride monomer, initiator, and solvent are mixed and polymerized at a low temperature, PVC precipitates. This mixture is filtered to obtain a low-polymerization PVC powder.

Emulsion Polymerization
This is a method of polymerization in which vinyl chloride monomers, surfactants, water, and a water-soluble initiator are mixed. The monomer is emulsified in water and polymerized in the emulsion droplets. To recover the polymer after polymerization, the emulsifying and dispersing effect of the surfactant is eliminated by the addition of salt or acid, and the polymer is agglomerated, followed by dehydration and drying to obtain PVC powder.

2. Safety of PVCs

PVCs are widely used for daily necessities such as food and toys. For this reason, various laws and regulations set standards, and industry associations have established voluntary standards to ensure the safety of PVCs.

For example, for products that come in contact with food such as plastic wrap, some laws require that the amount of residual vinyl chloride monomer be less than 1ppm. Also, the use of phthalate esters used in plasticizers is prohibited by certain laws. In addition, PVC used in blood bags and other products is subject to various standards.