PLASTIC

Plastics are nothing but synthetic organic high polymers. It is important to know the general outstanding properties of plastics to make best use of this an engineering material. It should also be noted that each plastic material has its own peculiar properties to suit the various uses. Hence the success of plastic as an engineering material for a particular purpose will depend upon the correct choice of the variety.

PROPERTIES OF PLASTIC MATERIALS

Following are the general properties of plastics.

1. STRENGTH

The plastics are sufficiently strong and can be used for load bearing structural members. The strength of plastics can further be increased by reinforcing them with various fibrous materials.

Plastic as structural material has not gained much popularity because of the following resins.

  • High cost of construction
  • High temperature susceptibility
  • Poor stiffness
  • Being subjected to creep under constant load
2. WEATHER RESISTANCE

The plastics, prepared from phenolic resins, are only good in resisting weather effects. Certain plastics are seriously affected by ultraviolet light.

3. FIRE RESISTANCE

Plastics, being organic in nature, are combustible. But the resistance to fire temperatue depends upon the plastic structure.

  • Cellulose acetale plastics burn slowly.
  • Polyvinyl chloride (PVC) plastics are non-inflammable.
  • Phenol formaldehyde and urea formaldehyde plastics are used as fire proofing materials.
4. DURABILITY

Plastics generally possess sufficient durability, provided they offer sufficient surface hardness. Thermoplastic varieties are found to be attacked by termites and rodents.

5. DIMENSIONAL STABILITY

Plastics easily maintain its shape and do not go under plastic deformations.

6. CHEMICAL RESISTANCE

Plastics offer great resistance to moisture, chemicals and solvents. Many plastics are found to possess excellent corrosion resistance. Plastics are used to convey chemicals.

7. THERMAL RESISTANCE

The plastics have low thermal conductivity and therefore foamed or expanded varieties of plastics are used as thermal insulators.

8. WORKING CONDITIONS

All operations like drilling, sawing, punching, clamping etc are carried out easily on plastics, just like wood.

9. MOISTURE RESISTANCE

This property depends upon variety of plastics used, for example, cellulose plastics are considerably affected by the presence of moisture, whereas polyvinyl chloride plastics offer high resistance to moisture.

10. DUCTILITY

Plastics, generally, have low ductility and hence plastic structural members may fail without prior warning.

11. MISCELLANEOUS PROPERTIES

In addition to above properties, plastics have following qualities.

  • Plastics are available in variety of colors, both opaque and transparent.
  • Plastics possess excellent insulating property, so used as electric insulators.
  • Plastics are clean, light and shining, so they need not be given any finish such as painting, polishing etc.
  • Normally thermo-plastics have low melting point and cannot be used where temperature or heat condition persists.
  • They possess good optical and sound absorption qualities.

Thermoset and Thermoplastics

Though thermoset plastics and thermoplastics sound similar, they have very different properties and applications. Understanding the performance differences can help you make better sourcing decisions and improve your product designs.

The primary physical difference is that thermoplastics can be remelted back into a liquid, whereas thermoset plastics always remain in a permanent solid state. Think of thermoplastics as butter – butter can be melted and cooled multiple times to form various shapes. Thermoset is similar to bread in that once the final state is achieved, any additional heat would lead to charring.

Thermoset

 Curing Process

plastics5

Thermoset plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product remelting when heat is applied, making thermosets ideal for high-heat applications such as electronics and appliances.
Features & Benefits

Thermoset plastics significantly improve the material’s mechanical properties, providing enhances chemical resistance, heat resistance and structural integrity. Thermoset plastics are often used for sealed products due to their resistance to deformation.

Pros
  • More resistant to high temperatures than thermoplastics
  • Highly flexible design
  • Thick to thin wall capabilities
  • Excellent aesthetic appearance
  • High levels of dimensional stability
  • Cost-effective
Cons
  • Cannot be recycled
  • More difficult to surface finish
  • Cannot be remolded or reshaped

Thermoplastics

 Curing Process

thermoplastics

Thermoplastics pellets soften when heated and become more fluid as additional heat is applied. The curing process is completely reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be remolded and recycled without negatively affecting the material’s physical properties.

Features & Benefits

There are multiple thermoplastic resins that offer various performance benefits, but most materials commonly offer high strength, shrink-resistance and easy bendability. Depending on the resin, thermoplastics can serve low-stress applications such as plastic bags or high-stress mechanical parts.

Pros
  • Highly recyclable
  • Aesthetically-superior finishes
  • High-impact resistance
  • Remolding/reshaping capabilities
  • Chemical resistant
  • Hard crystalline or rubbery surface options
  • Eco-friendly manufacturing
Cons
  • Generally more expensive than thermoset
  • Can melt if heated

Uses

  • Flooring

Plastic materials like polyvinyl chloride (PVC) and polyethylene are used to make flooring less prone to wear and tear. It also decreases the sound pollution level and can be cleaned easily. 

  • Roofing

To protect the outer surface of the roof from damage, two layers of different plastic materials are required. The upper part is made of colored thermoplastic.

  • Insulation

Polyurethane spray is frequently used for insulation when constructing green or low energy buildings.

  • Wall

The type of pre-fab, composite wall board can be transferred to the work place easily for a particular task and provide good support to columns and other associated essentials during renovation.  

  • Pipes

Commonly made up of polyvinyl chloride (PVC), CPVC, acrylonitrile butadiene styrene (ABS) or polyethylene, plastic pipes are flexible and very light in weight, making them easy to install.  All of these plastic materials are also highly chemical and water resistant, making them suitable for many extreme environments.

  • Windows

Polycarbonate is used to manufacture building windows. This plastic material is strong, clear and very light in weight.

  • Doors

Some construction projects use doors made from a stiff polyurethane foam core with a fiber reinforced plastic (FRP)coating. The sandwich structure of these doors makes them incredibly strong.

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