Omar Khalid
Plastics are classified into two types based on their surface energy: low surface energy (LSE) plastics and high surface energy (HSE) plastics. The surface energy of a material refers to the chemical makeup of a material that influences its level of molecular attraction. Low surface energy materials have a weak potential attraction, making them difficult to bond. Some examples of low surface energy plastics include polyolefin, polyethylene, and polypropylene. On the other hand, high surface energy materials have a stronger affinity between molecules, making them easier to bond. Some methods to improve the surface energy of plastics and make them more amenable to adhesion include corona, flame, or plasma surface treatment. The plastic with the highest surface energy mentioned in the sources is Polycarbonate, with an energy rating of 42 Dyme/cm.
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What You'll Learn
- Low-density polyethylene (LDPE) plastics are flexible and impact-resistant
- Polypropylene (PP) is a rigid plastic with high chemical resistance
- Polycarbonate has an energy rating of 42 Dynes/cm
- Polytetrafluoroethylene (PTFE) has an energy rating of 18 Dynes/cm
- Polyvinyl chloride (PVC) is used for industrial chemicals and automotive products
Low-density polyethylene (LDPE) plastics are flexible and impact-resistant
The flexibility and impact resistance of Low-Density Polyethylene (LDPE) plastics are among the many characteristics that make them a popular choice for manufacturing. LDPE is a thermoplastic made from the monomer ethylene, which was first produced in 1933. It is defined by a density range of 917–930 kg/m3, which is lower than that of High-Density Polyethylene (HDPE). This lower density gives LDPE its flexibility, allowing it to bend, stretch, and resist impact.
LDPE's flexibility and impact resistance are due to its chemical structure. Its molecules have more branching than HDPE, resulting in weaker intermolecular forces and lower tensile strength. This means that LDPE is less crystalline and, therefore, more flexible. This flexibility is retained even in very cold temperatures. Additionally, LDPE's high corrosion and chemical resistance make it durable and impact-resistant. It can withstand exposure to diluted or concentrated chemicals without breaking down.
The production of LDPE involves a radical polymerization process, requiring extreme heat (up to 570 Kelvin) and high pressure (up to 3,000 atm). Despite its popularity, LDPE has some disadvantages. It may crack or break when holding heavier objects, and it has a maximum temperature limit of 221 degrees Fahrenheit before it starts to melt. LDPE also has high gas permeability, allowing gases like carbon dioxide to pass through easily. Furthermore, it has poor UV resistance, struggling to maintain its shape and integrity when exposed to UV rays.
LDPE is commonly used in the manufacturing of various containers, bottles, tubing, plastic bags, and other packaging materials. Its flexibility and impact resistance make it suitable for producing plastic goods like cling wrap, juice containers, and garbage containers. LDPE is also used in agricultural films, wiring, and cables due to its low water absorption and corrosion resistance. However, it is important to note that LDPE is not as easily recyclable as some other plastics, and it emits greenhouse gases at a higher rate.
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Polypropylene (PP) is a rigid plastic with high chemical resistance
Polypropylene, also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is the second-most widely produced commodity plastic, with global demand estimated at around 45 metric tons. The versatility of polypropylene stems from its unique properties, including its rigidity, toughness, durability, and high chemical resistance.
Polypropylene is a rigid plastic with excellent fatigue resistance and elasticity, contributing to its reputation for toughness and durability. Its rigidity is enhanced by the presence of the methyl group, which increases the crystalline melting point, making polypropylene stiffer and more resistant to creep than other plastics like polyethylene. This rigidity, combined with its high chemical resistance, makes polypropylene ideal for applications requiring toughness and the ability to withstand wear and tear.
The chemical resistance of polypropylene is due to its non-polar nature and high softening point. It can withstand temperatures up to 160°C without melting, compared to polyethylene, which anneals at around 100°C. This high-temperature stability allows polypropylene to resist chemical corrosion and degradation, making it suitable for applications in the medical and automotive sectors. For example, polypropylene is used in medical components and plastic packaging for food and drink products, ensuring safety and durability.
The high chemical resistance of polypropylene also extends to its ability to resist oxidation and degradation caused by contact with certain materials, such as copper. Additionally, polypropylene has a slippery, tactile surface that resists adhesion, making it suitable for applications where non-stick properties are desirable. However, its low surface energy can pose challenges in certain applications, such as coating and bonding, where surface treatments may be required to improve adhesion.
In summary, polypropylene (PP) is a rigid plastic with high chemical resistance, making it a versatile and widely used material in various industrial and domestic applications. Its rigidity, toughness, and resistance to chemicals and wear and tear contribute to its popularity and adaptability in multiple sectors, including packaging, automotive, medical, and electrical industries.
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Polycarbonate has an energy rating of 42 Dynes/cm
Polycarbonate is a durable material with high impact resistance and the ability to undergo large plastic deformations without cracking or breaking. This makes it ideal for applications requiring transparent or electrically non-conductive parts, such as eyewear lenses and automotive components. Polycarbonate has an energy rating of 42 dynes/cm, which is considered a high surface energy (HSE).
HSE plastics, such as polycarbonate, are characterised by their sturdiness and ease of moulding into complex shapes. They find common use in reusable containers and lab equipment, like test tubes. The high surface energy of polycarbonate facilitates better adhesion, printing, or coating compared to low surface energy plastics. This is because the higher energy value indicates a stronger affinity between molecules, making them more receptive to adhesives, inks, or coatings.
The energy measurement of 42 dynes/cm for polycarbonate is significantly higher than that of other plastics. For instance, polypropylene (PP), commonly used in bottle caps and medical devices, has a surface energy of just 29 dynes/cm. Similarly, polyethylene (PE) and low-density polyethylene (LDPE), used for their flexibility and impact resistance in household chemicals, have slightly higher surface energies than PP but still fall below 40 dynes/cm.
The dividing line between low surface energy (LSE) and HSE plastics is generally considered to be around 40 dynes/cm. Polycarbonate, with its energy rating of 42 dynes/cm, sits just above this threshold, contributing to its versatility and ease of processing. This energy rating also impacts the behaviour of liquids on its surface. For instance, a drop of water will spread more easily on a high surface energy material like polycarbonate due to the strong attraction between molecules.
Overall, polycarbonate's energy rating of 42 dynes/cm positions it within the HSE category, making it a versatile and valuable plastic for a range of applications where its unique properties are advantageous.
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Polytetrafluoroethylene (PTFE) has an energy rating of 18 Dynes/cm
Polytetrafluoroethylene (PTFE), commonly known as Teflon, is a synthetic fluoropolymer with the brand name Teflon by Chemours, a spin-off from DuPont, which originally invented the compound in 1938. It is a fluorocarbon solid, a high-molecular-weight polymer consisting wholly of carbon and fluorine. PTFE has a low surface energy of 18 Dynes/cm, which makes it difficult to bond, print, or coat. However, this property also contributes to its non-stick and low-adhesive characteristics, making it suitable for applications such as non-stick cookware.
The low surface energy of PTFE is due to its molecular structure, with a core of carbon atoms shielded by fluorine atoms. This structure results in strong carbon-carbon and carbon-fluorine bonds, contributing to its chemical resistance and stability. PTFE's fluorine sheath protects the carbon-carbon bonds from chemical attack, further enhancing its stability. Additionally, the low interchain forces between the molecules allow them to slide past each other with ease, contributing to its low friction coefficient.
PTFE's exceptional chemical resistance and thermal stability make it a high-performance material. It is virtually inert to all known solvents, acids, and bases, and it has a high melting point of approximately 330°C. This makes PTFE ideal for use in containers and pipework for reactive and corrosive chemicals, as well as in high-temperature applications. PTFE is also hydrophobic, meaning it repels water and water-containing substances due to the low electric polarizability of fluorine.
While PTFE's low surface energy makes it challenging to work with in certain applications, various surface treatment techniques can be employed to enhance its adhesion, printing, and coating properties. For example, corona, plasma, and laser treatments can increase the surface energy and roughness of PTFE, improving its ability to bond with other materials. These treatments modify the surface chemistry, creating polar groups that enhance adhesion and allowing PTFE to be used in a wider range of applications.
PTFE has revolutionized cookware and engineering plastics with its non-stick and low-adhesive properties. Its discovery and subsequent development have paved the way for innovative products, such as non-stick pans and high-performance hoses, showcasing the significance of understanding and manipulating surface energy in materials science and engineering.
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Polyvinyl chloride (PVC) is used for industrial chemicals and automotive products
Polyvinyl Chloride (PVC) is a widely used plastic polymer with a range of applications, including industrial chemicals and automotive products. Its versatility, durability, chemical resistance, and affordability make it a popular choice across various industries.
PVC is a synthetic polymer derived from the vinyl chloride monomer. It can be modified by blending it with additives such as plasticizers, stabilizers, lubricants, and pigments to enhance specific properties for different applications. One of its notable characteristics is its high heat resistance, making it suitable for industrial chemical handling, hot water pipes, and fire sprinkler systems.
In the automotive industry, PVC is used for various components, including automotive underbody coating and cable and wire insulation. Its corrosion resistance and strength make it an ideal material for these applications. Additionally, PVC is used in the production of blood bags, medical tubing, and IV bags, showcasing its versatility and safety for medical devices.
The versatility of PVC extends to its ability to be manufactured in different forms, such as foam PVC, which is lightweight and rigid, making it suitable for signage, display boards, and prototyping. Clear PVC offers excellent clarity and transparency, making it ideal for packaging, display cases, and protective covers.
While PVC has numerous advantages, it is important to note that it has been the subject of controversy due to the link between vinyl chloride monomer exposure and cancer. Environmentalists and health advocates have raised concerns about the potential ill effects of exposure to certain substances within PVC. However, industry officials maintain that these substances are carefully controlled and released in trace amounts that have not been proven harmful.
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Frequently asked questions
Surface energy is the chemical makeup of a material that influences its level of molecular attraction. A higher value indicates a stronger affinity between molecules.
The simplest way to determine the surface energy of a plastic is through the Wetting Method. If water droplets are sprinkled on the plastic and they spread out, the plastic has high surface energy. If the droplets remain spherical, the plastic has low surface energy.
Polyolefin, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are examples of plastics with low surface energy.
High-density polyethylene (HDPE) and polycarbonate are examples of plastics with high surface energy.
Surface treatments such as applying heat, oxidation, chemicals, corona treatments, or plasma treatments can increase the surface energy of plastics by altering their chemical structure.
