Sage-Tips

What factor affects the mechanical properties of polymers?

Numerous factors affect various mechanical properties of polymers, in- cluding molecular weight, processing, extent and distribution of crystallinity, composition of polymer, and use temperature.

Why is molecular weight important for polymers?

Why is Molecular Weight Important in Polymers? As the molecular weight increases, mechanical properties generally increase. Every polymer has an ideal molecular weight at which the balance of different properties (such as processability, strength, brittleness etc.) is optimized.

What determines the mechanical properties of a polymer sample?

These properties can be measured through tensile testing. For crystalline or semicrystalline polymers, anisotropy plays a large role in the mechanical properties of the polymer. The crystallinity of the polymer can be measured through differential scanning calorimetry.

How does a polymers molecular structure affect its characteristics?

Polymers consist of very long molecules that contain chains of carbon. They too are held together by very strong covalent bonds. There are greater intermolecular forces between the long chains compared with smaller simple molecules. This means that polymers have a higher melting point than many other organic molecules.

How does molecular weight affect TG?

A polymer with long chains (high molecular mass) has less free volume than one with short chains. Thus, low molecular mass gives lower values of Tg , and higher molecular mass causes Tg to approach Tg,∞ asymptotically.

What is the molecular weight of polymer?

A polymer’s molecular weight is the sum of the atomic weights of individual atoms that comprise a molecule. It indicates the average length of the bulk resin’s polymer chains. All polymer molecules of a particular grade do not have exactly same molecular weight. There is a range or distribution of molecular weights.

What is molecular weight in polymers?

How does changing the molecular weight distribution affect the processability of plastics?

The low-molecular weight portion of the distribution has a similar effect as a plasticizer, that is, it reduces the brittleness and lowers the melt viscosity which improves the processability, whereas the high-molecular weight portion causes processing diffculties because of its huge contribution to the melt viscosity.

What are the effects of molecular weight of polymers on their glass transition temperature?

Low molecular weight values result in lower glass transition temperatures whereas increasing values of molecular weight result in an asymptotic approach of the glass transition temperature to Tg,∞ .

How do the properties of polymers depend on molecular weight?

Almost all properties of a polymer depend on the molecular weight and its distribution, that is, low and high molecular weight polymers will have vastly different mechanical and thermo-physical properties.

How does the molecular weight affect the impact properties of polycarbonate?

A High molecular weight increases the viscosity of the material – makes it harder to process the material using conventional methods. The longer the chains, the harder it is to get them to flow because they are more tangled. This table shows the influence of melt flow on the impact properties of polycarbonate.

What is the effect of high molecular weight on chemical resistance?

A High molecular weight increases the chemical resistance – to a point. It takes more damage to the main chains of the molecules before it will affect the strength of the material. A High molecular weight increases the viscosity of the material – makes it harder to process the material using conventional methods.

What happens to the molecular weight during the course of molding?

Molecular weight can decrease during the course of molding. Examples could be – Plasticizer in rigid PVC. Regrind in nylon. The world of polymers continues to grow and offers many design, cost and performance advantages to choose from.