Physical Properties of Polymeric Materials

August 18, 2024

A thermoplastic, also known as thermosoft plastic, is a type of plastic polymer that becomes pliable or mouldable at a high temperature and hardens when cooled.

The polymer chains are bonded together via intermolecular forces, which reduce as the temperature increases, producing a viscous liquid. Thermoplastics may be reshaped in this state and are commonly utilised to manufacture parts using polymer processing techniques like injection moulding, compression moulding, calendering, and extrusion.

Physical Properties of Polymer

The structure, kind of monomer units from which polymers are generated, and other elements all influence the qualities of a polymer. The following are some of the physical and chemical properties of polymers:

Tensile Strength – A polymer’s tensile strength is its ability to stretch without breaking. This feature of polymers determines their physical strength and durability.

Melting and Boiling Points – Polymers have extremely high melting and boiling points. Longer chains mean stronger intermolecular forces, and thus higher melting and boiling points.

Hardness – Hard polymers are resistant to hard substances penetrating them. They are employed in the construction of electronics and can tolerate wear and tear as well as scratches.

Density-Based on density differences, polymers are classed as high-density polymers or low-density polymers.

Heat Capacity / Heat Conductivity — This determines how effective a polymer is as a heat insulator. A polymer’s heat conductivity is determined by the stiffness of its molecules.

Thermal Expansion – This property determines how much a polymer expands or shrinks when exposed to heat or cold.

Crystallinity – Because polymers with less crystallinity are brittle, they are more useful. The sort of organisation of polymeric chains determines this feature.

Elasticity– Polymers with weak intermolecular linkages stretch more and are more pliable.

Physical Properties of Polymeric Materials

1. Gas permeability

Gas permeability is usually expressed in terms of air permeability or coefficient of permeability.

1) Gas permeability

It refers to the volume of gas permeating through 1m2 area of plastic film of certain thickness under 0.1MPa air pressure (under standard condition) within 24 hours, m3.

2) Permeability coefficient

Under the standard condition, the volume of gas permeating through the plastic film of unit area and unit thickness in unit time and under unit pressure difference.

Test standard: GB/T 1038-2022 plastic film and sheet gas permeability test method (differential pressure method)

2. Moisture permeability

Water vapor permeability is expressed by the amount or coefficient of water vapor permeability.

1) Water vapor permeability

The mass of water vapor that passes through 1m2 of film within 24h under the difference in vapor pressure between the two sides of a film of a certain thickness.

2) Moisture Permeability Coefficient

The amount of water vapor that passes through a unit area and a unit thickness of a film under a unit time and a unit pressure difference.

Test standard: GB/T 1037-2021 Experimental method for water vapor permeability of plastic films and sheets (cup method).

3. Water permeability

Water permeability (water permeability) is determined by placing the test sample under a certain water pressure and for a certain period of time, and observing the degree of water permeability of the test sample directly with the naked eye.

Test standard: HG/T 2582-2022 Determination of water permeability of rubber or plastic coated fabrics.

4. Water absorption

Water absorption refers to the amount of water absorbed by immersing a specimen of a specified size into simmering water at a certain temperature for 24h.

Test standard: GB/T 1034-2008 Water absorption test method for plastics

5. Density and relative density

1) Density

The mass per unit volume of the material at the specified temperature. The unit is kg/m3 or g/cm3 or g/mL.

2) Relative density (relative density)

The ratio of the mass of a certain volume of a substance to the mass of a reference substance of the same volume at the same temperature. The relative density at temperature t~ is expressed as dtt. When the reference substance is water, it is called relative density.

Density at temperature t and relative density can be converted by the following formula:

Density and relative density at temperature t

Where St is the relative density of the specimen at temperature t℃; pt is the density of the specimen at temperature t℃; pw is the density of water at temperature t℃.

Test standard: GB/T 1033-2008 Plastic density and relative density test method

6. Shrinkage

Mold shrinkage (mold shrinkage) is often expressed as molding shrinkage or molding shrinkage.

1) Molding shrinkage

The extent to which the size of a molded part is smaller than the size of the corresponding cavity, usually expressed in mm/mm.

2) Molding shrinkage

Also known as metrological shrinkage, it is the percentage of the ratio of the part size to the corresponding mold cavity size, often expressed in %.

Test standard:

GB/T 15585-1995 Determination of injection molding shrinkage of thermoplastics

GB/T 17037.4-2003 Preparation of thermoplastic injection molding specimens Part 4: Determination of molding shrinkage

JG/T6542-1993 Determination of shrinkage of thermosetting molding plastics.

Author:

Ms. Tina

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sales@honyplastic.com

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