This article gives complete industry insights on plastic materials.
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Plastics are synthetic compounds composed of polymers, which are lengthy molecules made up of carbon atom chains. A polymer consists of numerous repeating units known as monomers. The chain structures are interspersed with atoms such as hydrogen, nitrogen, oxygen, and sulfur.
Plastics are categorized into thermoplastics and thermosets, each with distinct responses to heat. Thermoplastics can be reheated and reshaped multiple times, making them recyclable. In contrast, thermoset plastics do not soften once set, making them non-recyclable. They are formed from extensive polymer chains that are heated and compressed into rigid, cross-linked structures, which prevents them from softening upon reheating.
Prior to the advent of plastics during the mid-first industrial revolution, products for various uses were made from natural and readily available materials. Wood was abundant, making it a common choice. For centuries, metals like iron and bronze were produced through rudimentary methods, and similar techniques were employed to create glass.
The arrival of plastic marked a transformative shift in manufacturing both everyday and industrial products. As a versatile, moldable, and resilient material, plastic captured the interest of scientists and inventors eager to refine and advance its applications.
Different plastic formulations can be engineered to exhibit a wide range of properties, characteristics, and strengths. Through various chemical processing methods, plastic can be adjusted to achieve diverse levels of strength, toughness, resilience, hardness, and heat resistance.
Originally, the term "plastic" described materials that were "pliable and easily shaped," specifically referring to polymers, which translates to “of many parts.” Natural polymers, such as cellulose, which forms plant cell walls, were known long before synthetic versions were created. With the advent of synthetic polymers derived from petroleum and fossil fuels, scientists were able to create polymers with chains significantly longer than those found in nature.
In 1856, Alexander Parkes introduced a flexible material named Parkesine, made by combining nitrocellulose, alcohol, camphor, and oil. This innovation is recognized as the inception of the modern plastic industry. Parkes' discovery inspired further advancements by scientists and inventors who sought to refine and enhance his formula, leading to the development of the plastic materials we use today.
John Wesley Hyatt built upon Parkes' work in 1869, aiming to find a substitute for ivory in billiard balls. By treating cellulose nitrate with camphor, Hyatt created a plastic that could be molded to mimic ivory's appearance and properties. To facilitate large-scale production, Hyatt collaborated with Charles Burrough to develop machinery for mass-producing his new material.
The advent of fully synthetic plastics came with Bakelite, developed in 1907 by Leo Baekeland. Bakelite, formed from the reaction between phenol and formaldehyde, marked a significant milestone in the industry. It was widely used for products like sealants, lacquers, and moldable materials due to its successful mass production.
During the 20th century, various types of plastics emerged, with a significant increase in production during World War II. Plastics were heavily utilized in the military for synthetic fabrics, vehicle components, and containers to replace rubber. After the war, production adapted to meet consumer demand, leading to the rapid growth of the plastics industry, which has become a global necessity.
Fish paper, also known as fiber paper, vulcanized fiber, or red fiber, was developed alongside plastics and patented in England by Thomas Taylor in 1859. It is made from vulcanized cellulose fibers that have been treated with zinc chloride, acids, or bases and then pressed into sheets. The sheets are laminated to achieve thicknesses ranging from 0.093 inches (2.4 mm) to 0.375 inches (9.5 mm).
Fish paper is lightweight, malleable, and offers superior resistance to both heat and cold compared to many plastics. It maintains its strength even at very low temperatures and is available in sheets, rolls, or coils. Due to its remarkable durability, fish paper is primarily used as an insulation material.
Plastic materials were once hailed as a "wonder material" due to their superiority over steel in many aspects of engineering design. Plastics offer numerous advantageous properties that metals often lack, and their lower production costs make them ideal for mass manufacturing. However, the primary concern with plastics is their environmental impact.
Below are some of the advantages of plastics.
Plastics excel in formability, allowing them to be molded, cast, rolled, pressed, stamped, extruded, and more. They can be shaped into intricate designs that other materials might find challenging or impossible to achieve. Additionally, the dies and tools required for shaping plastics are generally simpler to produce.
Unlike metals, plastics do not corrode or degrade in the same manner. Metals are prone to rust, which compromises their structural integrity and can lead to contamination issues, particularly in food and pharmaceutical products.
Plastics have densities ranging from 0.8 to 1.5 times that of water, making them considerably lighter compared to metals and glass. In contrast, steel has a density about 7.8 times that of water, while glass and ceramics have densities approximately 2 to 3 times that of water. Despite their lower density, plastics can be used in many of the same applications as metals and glass, with some engineered to achieve a high strength-to-mass ratio.
Different types of plastics possess distinct mechanical properties, which can be enhanced by incorporating special additives. These additives, such as glass and carbon fibers, can improve the flexibility and strength of the plastic. The addition of these fibers to a plastic matrix results in a composite material with superior tensile and flexural strength.
Plastics are composed of long, chain-like molecules that can form either crystalline or amorphous structures. These structures contribute to their natural elasticity. Plastics are less prone to brittle fracture and cracking, although tearing can be a concern. This issue can be addressed by incorporating additives or using a polymer base with high tensile strength.
Plastics can be produced in clear, translucent, or opaque forms and can be colored by adding pigments. They also offer a range of surface finishes and textures, eliminating the need for costly secondary processing.
Plastics are known for their chemical and wear resistance, which contributes to their long service life under normal conditions. Additives can further improve their durability by providing resistance to oxidation and ultraviolet radiation. However, the longevity of plastics poses an environmental challenge, as they can accumulate and negatively impact ecosystems if not properly managed.
Similar to glass and metals, certain types of plastics can be recycled. Traditionally, plastics are recycled by heating and melting them into raw materials for new products. This method applies primarily to thermoplastics. For other types of plastics, advanced processes are being developed, which chemically convert them into monomers used as fuels for energy generation.
Plastics are relatively easy to form and require less energy for production compared to metals and glass. They can be easily shaped when heated, needing only moderate pressure. Plastics can also be formed using compressed air. The melting temperature of plastics is lower than that of metals and glass, allowing them to be injected and molded with less costly dies and tools.
The production of plastic goods begins with creating raw plastics, which possess the fundamental properties of their base polymers. These raw plastics are produced in petrochemical plants, where feedstocks are transformed into raw plastics via polymerization. The raw plastics are then delivered to manufacturing and fabrication facilities in liquid, powder, or pellet form, with the pellets being processed into the final products.
Polymerization is the process of creating macromolecules known as polymers by linking hundreds to thousands of unit molecules called monomers. This process is facilitated by the presence of double bonds and active functional groups in organic compounds, which enable the formation of long-chain molecules.
There are various polymerization methods designed to produce specific types of polymers, including bulk, solution, suspension, and emulsion polymerization. Each method involves distinct chemical mechanisms for carrying out the reaction.
Polymerization processes can generally be classified into two categories: step growth (or condensation) polymerization and chain growth (or addition) polymerization. Addition polymerization involves an additional reaction, while condensation polymerization occurs through the reaction of monomer molecules.
The type of polymer formed by condensation polymerization depends on the types of monomers. When the monomers have reactive groups, the polymer has low molecular weight. Two reactive monomer groups create linear polymers, while more than two reactive groups result in three-dimensional polymer networks.
Polymerization can involve one or multiple types of monomer feedstocks. Using a combination of different monomers is a common approach to enhance the properties of raw plastics. Polymers created from more than one type of monomer are known as copolymers.
After polymerization, plastics are further processed by incorporating an initial set of additives. Stabilizers and antioxidants are among these additives, protecting the raw plastic from degradation due to exposure to air, light, or heat. This helps stabilize the plastic for additional processing and storage.
To achieve the desired properties in commodity plastics, they are blended and compounded with various formulations. These formulations can impart specific physical, mechanical, electrical, Durometer hardness, and chemical properties. In addition to stabilizers and antioxidants, other additives include processing aids, performance enhancers, and aesthetic modifiers.
Manufacturing and fabrication plants then introduce another set of additives, such as pigments, fillers, and reinforcing materials. These additives ensure that the plastic meets the final specifications set by the manufacturer to suit its intended application.
Plastic polymers are generally categorized into two main types: thermoplastics and thermosetting polymers.
Thermoplastic Polymers: Thermoplastic polymers or thermoplastics have polymer molecules that can be repeatedly rearranged by heating and cooling. Heating thermoplastics liquifies or softens them, but no chemical change takes place during this process. This is because of the absence of cross-linking that is evident in thermosetting polymers. Subsequent cooling returns the material to its solid state. This heating and cooling process allows the plastic to be formed into different shapes.
Thermosetting Polymers: Plastics made from these types of polymers have functional groups that form the cross-links between the molecules. Thermosetting polymers or thermosets cannot be softened through heating. Once heated, they undergo a chemical reaction that permanently changes their properties. Processing thermosets includes an additional process called curing. Curing is the process of creating crosslinks between polymer chains, finalizing the properties of the plastic.
In addition to being classified as thermosetting or thermoplastic, plastics are divided according to the type of polymer used in producing the raw resin.
Polyethylene (PE): Polyethylene is the most extensively used plastic material. PE has many desirable characteristics, such as easy processability, toughness, and flexibility, which are all retained even at low temperatures. PE is odor and toxin-free and has excellent clarity, good water barrier properties, good electrical insulation properties, and a low cost. It has two main types: high-density polyethylene (HDPE) and low-density polyethylene (LDPE).
Polypropylene (PP): PP is a polymer that can have a wide range of properties, which depend on its molecular weight, morphology, crystalline structure, additives, and copolymerization. It can be made into polymers with a high degree of crystallinity, resulting in higher tensile strength and hardness comparable to HDPE. Moreover, it can withstand higher temperatures without loss of strength or degradation. The disadvantage of using PP is its susceptibility to UV degradation and oxidation.
Polyurethane (PU): PU is produced from polyester or polyether polyols, diisocyanate compounds, curatives, and additives. They are suitable for making high-performance, engineering-grade products. Their mechanical properties can vary from soft and flexible to hard and rigid.
Polyvinyl Chloride (PVC): PVC is a plastic that can be formulated with different stabilizers, plasticizers, impact modifiers, processing aids, and other additives. It can be made into rigid or flexible plastic by modifying the amount of plasticizers. Moreover, they offer better clarity than other versatile plastics. However, PVCs have the potential to release harmful pollutants, acids, and toxins during processing or degradation. Its compounding ingredients are now being regulated by FDA, EPA, and other organizations.
Polyethylene Terephthalate (PET): PET, specifically biaxally oriented PET, is known for its low permeability to moisture, carbon dioxide, and alcohol. It also has an excellent intrinsic viscosity. The downside of using PET, however, is its affinity for water. It tends to absorb water, which makes processing difficult as the resin needs to be dried before extrusion.
Polystyrene (PS): PS is another versatile plastic modified by copolymerization and additives. They can be made into flexible, rigid, or cellular (foam) plastic forms. PS is generally prone to oxidation. Thus, repeated recycling is not recommended. Furthermore, their sensitivity to oxidation causes their color to become yellowish.
Polyamide (PA): PA is considered an engineering plastic characterized by its high toughness, high impact strength, resistance to solvents, abrasion resistance, and ability to be modified to possess heat resistance. PA production mostly goes into the manufacturing fibers. Only about 10% of PA production volume is used in plastic forming processes.
Acrylonitrile Butadiene Styrene (ABS): ABS is a common plastic material characterized by good hardness and rigidity with some degree of toughness. Protective coatings are usually applied due to the material‘s poor resistance to UV and merely adequate resistance to most acids and alkalis.
Polycarbonate (PC): PC is easily processed by different molding methods, with injection molding and sheet extrusion being the most common. Polycarbonates are known for their high impact strength, heat resistance, good electrical insulation, transparency, good water barrier properties, and inherent flame retarding properties.
Polytetrafluoroethylene (PTFE): PTFE is one of the most common types of fluorocarbon polymers. It has many desirable characteristics, such as low coefficient of friction, self-lubrication, chemical resistance, and hydrophobicity. This makes PTFE desirable as a coating material. Its hydrophobic property also prevents the growth of microbes, which further extends its applications to manufacturing food and drugs.
Polymethyl Methacrylate (PMMA): This type of plastic is also known as acrylic. It is a type of thermoplastic with distinctive properties such as superb transparency, lightness, tensile and flexural strength, and UV resistance. They are commonly used as a substitute for transparent glass. Examples of their applications are windows, lenses, safety barriers, and screens.
Single Use: Of the broad spectrum of plastics, single-use plastics have raised the greatest amount of worldwide concern. In essence, they are a form of disposable plastics designed to be used once and thrown away. Items that fall into this category include plastic bags, plastic stirrers, straws, soda and water bottles, and food packaging. Of the 300 million tons of plastic produced each year, half of it is single-use.
Small single-use plastic items are often conveniences that are used to mix coffee, bring a purchase home, or display new merchandise. Other forms of single-use plastics play a more vital role, such as surgical gloves and tools, breathing masks, and other items for medical care. Regardless of the material, these items can only be used once for safety and protection. The original reason for the development of single-use plastics was to prevent the spread of disease, cut labor costs, and serve as a means for keeping items fresh for a longer period of time.
The flexibility, cost-effectiveness, and safety provided by single-use plastics are the main reasons they are so widely used. With rising concerns for environmental impact, several multinational companies have developed methods for recycling and repurposing single-use plastics, from making paving materials for roads to producing outdoor buildings. Every company and country are doing their part to make use of these convenient and vital materials.
Thanks to their excellent formability, various fabrication methods have been developed for plastics. They can be easily molded, cast, extruded, stretched, or spun, and typically flow to match the profile of the mold or die without requiring extreme heat or pressure. Following the initial fabrication processes, plastics can also undergo secondary operations such as trimming, cutting, grinding, drilling, gluing, and welding, much like metals.
Below are the primary fabrication processes used for plastic materials.
Injection molding is a widely used method for shaping plastics. It involves injecting molten plastic into a closed mold or chamber. The process consists of four main operations:
Injection molding is typically used for creating plastic parts that are open on one side. It is not ideal for producing closed, hollow items like plastic bottles on its own. To manufacture such products, an inert gas is introduced into the mold, which is partially filled with molten plastic. The gas forces the plastic to adhere to the mold's surface, forming a hollow structure. This technique is called gas-assisted injection molding.
Casting is a fundamental technique where liquid plastic is poured into a mold without applying pressure. This method is applicable for both thermosetting plastics and thermoplastics. The casting process includes:
Unlike injection molding, casting is not ideal for creating hollow components. It is primarily used for manufacturing straightforward, solid forms. Furthermore, extra machining is often necessary to eliminate excess material from gates, risers, and runners, as well as to address any flashes.
Blow molding creates hollow plastic items by expanding a heated plastic material within a mold. The primary steps involved in blow molding include:
Blow molding is divided into two primary categories: extrusion blow molding and injection blow molding. In extrusion blow molding, the plastic is extruded into a hollow tube with one end open. Conversely, injection blow molding involves injecting plastic into a core mold to form the preform, which is then expanded using air to conform to the mold. Both methods utilize air pressure to shape the preform inside the mold.
Rotational molding, often known as "roto molding," is a method used to create hollow and seamless plastic items. Unlike processes that involve high pressure for extrusion or injection, roto molding forms the product by distributing the melted plastic onto the interior surfaces of the mold through rotation. The process can be outlined as follows:
Because rotational molding does not require high pressures, the molds used are relatively low-cost. This makes it possible to manufacture larger items with a lower investment. Additionally, rotational molding can produce double-walled components without the need for further processing.
Compression molding forms plastic resin by applying pressure between two molds. This technique is particularly suited for creating large products from thermosetting plastics. The steps involved in the process are outlined below:
Compression presses are usually designed to close downward, although upward-closing models are also available. The mold is equipped with internal heating elements that soften the plastic charge, enabling it to conform to the mold's shape. Additionally, the heat facilitates the curing process of the plastic. During curing, gases may be released from the plastic, which are removed through a process known as degassing.
Plastic extrusion is the process of forcing molten plastic through a die, producing a product with a continuous shape. This is a common method of producing films, sheets, rods, and tubes. Extrusion is also combined with other processes such as blow molding, where the plastic is first processed and fed by an extruder, followed by a molding process. The operations involved in plastic extrusion are outlined below:
Plastic extrusion encompasses various processes tailored to specific products, such as sheet extrusion and blown-film extrusion. Additionally, extrusion is utilized for coating and jacketing wires and cables.
Traditional extrusion methods involve a hopper, throat, and a screw or auger to feed resin or pellets through the barrel to the die or profile. This approach is widely recognized and standard in the industry.
Earlier extrusion techniques did not use a screw or auger; instead, they employed a ram. This method is still used today for extruding certain plastics like PTFE and UHMW to create products such as sleeves, rods, blocks, tubing, and lining sheets. In ram extrusion, powder serves as the raw material, which is gravity-fed into the extrusion chamber, sintered, and then pushed through the die by a hydraulic ram. Despite these differences, the process shares similarities with traditional extrusion.
Ram extrusion comes in two forms: horizontal and vertical. Both involve forcing powder through a die with a ram. Similar to powder metallurgy, the quality of the extruded products depends on factors such as the extruder design, powder properties, extrusion rate, applied pressure, and sintering temperature.
Calendering is a manufacturing technique that heats and rolls plastic material into films, sheets, or laminated coatings. Originally popular for processing rubber, this method is increasingly being used for thermoplastics as well. The process generally includes the following stages:
Calendering is particularly effective for creating multilayered products. Materials such as textiles or paper can be introduced alongside the plastic sheet or film during the final rolling stages. This method produces a double-ply product that merges the durability of the base material with the surface and barrier properties of the plastic.
Thermoforming involves heating thin plastic sheets to their optimal forming temperature and then stretching them over a mold. This secondary forming process does not use raw plastic resin but rather employs sheets or films that have been produced through earlier processes like extrusion or calendering. The procedure typically includes the following steps:
There are four primary techniques for shaping a thermoformed product into a three-dimensional form: vacuum forming, pressure forming, mechanical forming, and twin sheet forming. Each method utilizes different approaches to apply pressure and shape the plastic. In vacuum, pressure, and twin sheet forming, compressed air is used to press the plastic sheet against the mold. In contrast, mechanical thermoforming involves two dies that press together to shape the plastic.
Thermoforming is generally limited to producing parts with relatively thin walls. Additionally, the process can result in defects such as uneven thickness, webbing, and warping.
In plastic fabrication, spinning is a technique used to twist and stretch short strands of plastic into continuous fibers. These fibers are then used to produce synthetic textiles, ropes, and cables. The typical spinning process includes the following steps:
The steps mentioned above are the general operations for plastic fiber spinning. Spinning can be further divided into three main types: melt, dry and wet spinning. These processes differ in how the dimensional stability of the fiber is attained.
Plastic fabrication is the process of designing, manufacturing, and assembling a product made out of plastic material or composites that contain plastic. There are numerous plastic fabrication methods known today, considering the wide variety of products made out of plastic...
Blow molding is a type of plastic forming process for creating hollow plastic products made from thermoplastic materials. The process involves heating and inflating a plastic tube known as a parison or preform. The parison is placed between two dies that contain the desired shape of the product...
Plastic bottles are bottles made of high or low-density plastic, such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polycarbonate (PC), or polyvinyl chloride (PVC). Each of the materials mentioned has...
Plastic channels are plastic products that have linear extruded profiles. They have a constant cross-sectional shape across their axis. They are long and narrow structures, and their depth is relatively short. These products serve a variety of functions and uses...
Plastic extrusion, also known as plasticating extrusion, is a continuous high volume manufacturing process in which a thermoplastic material -- in a form of powder, pellets or granulates -- is homogeneously melted and then forced out of the shaping die by means of pressure...
A plastic rod is a solid plastic shape made by the process of plastic extrusion or plastic co-extrusion. These have a contrast of plastic tubing and hollow plastic profiles. Plastic rods are found in various industries, including...
Plastic trim products are extruded linear profiles that can be made to any length. Because of its ability to attach, hold, and seal, plastic trim has many applications. Plastic, HDPE, LDPE, butyrate, PVC, acrylic, and...
Rotational molding, commonly referred to as "rotomolding", is a plastic casting technique used to produce hollow, seamless, and double-walled parts. It uses a hollow mold tool wherein the thermoplastic powdered resin is heated while being rotated and cooled to solidify...