Alexei Volkov
Crosslinked plastic and super linear are two types of polymers with distinct characteristics. Crosslinking refers to the formation of bonds between polymer chains, resulting in increased molecular weight and enhanced physical and mechanical properties. On the other hand, linear polymers like polyethylene form a class of materials known as thermoplastics, which can be moulded into various shapes. They are characterized by long strings of carbon-carbon bonds. This comparison raises an interesting question: is crosslinked plastic denser than super linear? To answer this, we need to delve into the specific properties and behaviours of these materials under different conditions.
| Characteristics | Values |
|---|---|
| Durability | Cross-linked plastic is more durable than linear plastic |
| Cost | Cross-linked plastic is more expensive than linear plastic |
| Ease of production | Linear polyethylene requires compromises in production that cross-linked polyethylene does not |
| Environmental stress cracking resistance | Cross-linked plastic resists environmental stress cracking more than 15 times longer than linear plastic |
| Izod impact toughness | Cross-linked plastic has Izod impact toughness more than 5 times better than linear plastic |
| Crack growth resistance | Cross-linked plastic has crack growth resistance more than 10 times better than linear plastic |
| Flexibility | Cross-linked polymers are more elastic than linear polymers |
| Tensile strength | Cross-linked plastic has superior tensile strength compared to linear polyethylene |
| Resistance to fracture | Cross-linked plastic has superior resistance to fracture compared to linear polyethylene |
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What You'll Learn
Cross-linked plastic is more expensive
Cross-linked polyethylene, for example, is formed through a plastic molding process called rotational molding or rotomolding. This process involves placing a weighed amount of non-crosslinked resin powder, which already contains the materials required for later crosslinking, into a mold. The mold is then closed and rotated inside an oven, causing the powder to coat the inside surfaces as it fuses together and crosslinks. Finally, the mold is cooled, and the part solidifies.
The initial low molecular weight of the non-crosslinked resin is advantageous in the early stages of processing, helping the resin particles uniformly fill the mold, melt, and fuse together. However, it is only after the part is fully formed that crosslinking occurs, enhancing the physical and mechanical properties of the plastic. This additional processing time and the additives required for crosslinking contribute to the higher cost of crosslinked parts.
The advantages of cross-linked plastic lie in its superior performance and durability. Crosslinking dramatically increases the molecular weight and improves the physical properties of the polymer, resulting in plastic with better impact resistance, tensile strength, and resistance to fracture compared to linear polyethylene. Crosslinked parts also exhibit greater resistance to environmental stress cracking, higher Izod impact toughness, and better resistance to crack growth.
Therefore, despite the higher cost, cross-linked plastic is preferred in applications where long-term performance and durability are crucial, such as in the manufacturing of kayaks or specific types of storage tanks.
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Cross-linked plastic is more durable
The advantages of crosslinked polyethylene are particularly evident in the rotomolding process. During rotomolding, non-crosslinked resin powder is placed into a mold, heated, fused, crosslinked, and then solidified. The initial low molecular weight of the non-crosslinked resin helps the resin particles uniformly fill the mold, melt, and fuse together. However, it is the subsequent crosslinking that builds molecular weight and enhances the physical and mechanical properties of the final product.
Cross-linked plastics are often used in applications where durability is a key requirement, such as in the manufacture of kayaks. For instance, Jackson Kayak chooses to build their whitewater kayaks out of cross-linked plastic to ensure their products are as durable and functional as possible.
While cross-linked plastic offers superior durability, it does come at a cost. The additives required for crosslinking and the longer processing times associated with cross-linked parts generally make them more expensive to produce than linear alternatives.
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Cross-linked plastic is more impact-resistant
Cross-linked plastic is often used in applications where impact resistance and durability are crucial, such as in the manufacturing of kayaks and storage tanks. For example, Jackson Kayak chooses to construct their whitewater kayaks from cross-linked plastic to ensure the most durable and functional kayaks possible. The raw material for cross-linked plastic is more expensive, but the resulting product is superior in terms of long-term performance and resistance to environmental stress.
The process of crosslinking involves creating bonds between the polymer chains, which increases the molecular weight and improves the physical properties of the plastic. This is achieved through various methods, including the use of peroxides and crosslinking agents, as well as electron bombardment. The initial low molecular weight of the non-crosslinked resin during the early stages of processing allows for uniform filling, melting, and fusion within the mold.
On the other hand, linear polyethylene, or high-density polyethylene (HDPE), is created by heating thermoplastic resin to form a fluid plastic that hardens and cures into a linear structure. The molecules in HDPE are connected like a rope, twisted together but not tied. While HDPE tanks are generally cheaper due to material costs and molding parameters, they lack the impact resistance, tensile strength, and resistance to fracture offered by cross-linked plastic.
The advantages of cross-linked plastic are evident in the plastic molding process called rotational molding or rotomolding. During this process, the non-crosslinked resin powder is placed into a mold, which is then rotated inside an oven. As the mold heats up, the powder coats the inside surfaces, fuses together, crosslinks, and solidifies as the mold cools. This process enhances the physical and mechanical properties of the plastic, resulting in improved impact resistance.
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Cross-linked plastic has higher tensile strength
Cross-linked plastics, or polymers, are formed by the creation of bonds between polymer chains. These bonds are as strong and stable as the principal bonds along the polymer backbone. Crosslinking increases the length of the polymer chains, and therefore the physical properties of the plastic, beyond what can be achieved without crosslinking. Crosslinking can be achieved through several methods, including the use of peroxides and crosslinking agents, and electron bombardment.
Cross-linked plastics have several advantages over linear plastics. Cross-linked plastics have been shown to resist environmental stress cracking more than 15 times longer when compared to linear plastics (>1000 hours vs 72 hours in ASTM D-1693). The Izod impact toughness of cross-linked plastics is more than 5 times better than that of linear plastics (17.0 vs 3.3 ft-lb in ASTM D-265). Additionally, the resistance to crack growth is 10 times better in cross-linked plastics (>1000 hours vs <10 hours in ASTM F-1473).
The advantages of cross-linked plastics are particularly evident in the plastic molding process called rotational molding or rotomolding. During this process, a weighed amount of non-crosslinked resin powder is placed into a mold, which is then closed and rotated inside an oven. As the mold heats up, the powder fuses together, crosslinks, and then solidifies as the mold is cooled. Crosslinking builds molecular weight and enhances the physical and mechanical properties of the plastic.
Cross-linked plastics have a higher tensile strength than linear plastics. This is due to the increased crosslink density in cross-linked plastics, which leads to a higher Young's modulus and a higher ultimate stress. The higher crosslink density also results in a higher strain concentration under the same tensile strain, which further reduces the fracture strain.
Overall, the superior performance of cross-linked plastics in terms of tensile strength and other properties makes them ideal for long-term applications, such as in kayaks, artificial joints, power cable insulation, and plumbing applications.
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Cross-linked plastic is less crystalline
Cross-linked plastics are formed by adding bonds between polymer chains, resulting in increased molecular weight and enhanced physical and mechanical properties. This process improves the impact resistance, tensile strength, and resistance to fracture compared to linear polyethylene. Cross-linked plastics are also more expensive due to the additional processing time and additives required for crosslinking.
Linear polyethylene, on the other hand, is created by heating thermoplastic resin to form a fluid plastic that hardens and cures into a linear structure. The molecules in linear polyethylene are connected like a rope, with individual threads twisted together but not tied. This results in a lower molecular weight and inferior physical properties compared to cross-linked plastics.
The key difference between cross-linked and linear plastics lies in their molecular structure. Cross-linked polymers contain branches that connect polymer chains, making the polymer more elastic. These branches make it difficult for the polymer molecules to pack in a regular array, leading to reduced crystallinity. In contrast, linear polymers have a more ordered structure, allowing the molecules to pack in a more regular array, resulting in higher crystallinity.
The reduced crystallinity in cross-linked plastics is a direct consequence of the branching and crosslinking of polymer chains. The introduction of branches and crosslinks disrupts the regular arrangement of molecules, leading to a less ordered structure. This decrease in crystallinity can impact the optical, mechanical, and thermal properties of the material.
While cross-linked plastics exhibit superior performance in terms of durability and toughness, the reduced crystallinity may affect their transparency and surface finish. The exact impact of reduced crystallinity on the properties of cross-linked plastics can vary depending on the specific polymer and processing conditions. However, the overall improvement in physical and mechanical characteristics makes cross-linked plastics a preferred choice for applications requiring long-term performance and impact resistance.
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Frequently asked questions
Crosslinked plastic is a type of plastic formed by creating bonds between polymer chains. These bonds tie the polymers together, increasing molecular weight and enhancing physical and mechanical properties.
Super linear plastic, or linear plastic, is a type of plastic made up of long strings of carbon-carbon bonds. The molecules are connected like a rope, twisted together but not tied.
Yes, crosslinked plastic is denser than super linear plastic due to the formation of bonds between polymer chains, resulting in increased molecular weight and enhanced physical properties.
Crosslinked plastic offers superior impact resistance, tensile strength, and resistance to fracture compared to super linear plastic. It also has higher resistance to environmental stress cracking and better toughness.
Crosslinked plastic is commonly used in applications where durability and long-term performance are required, such as in the construction of kayaks and rotational molding processes. It is known to be more expensive than super linear alternatives.
