How does crystallinity affect density?

Crystallinity defines the degree of long-range order in a material, and strongly affects its properties. The more crystalline a polymer, the more regularly aligned its chains. Increasing the degree of crystallinity increases hardness and density.

What increases crystallinity?

Crystallinity is usually induced by cooling a melt or a dilute solution below its melting point. The later can result in the growth of single crystals. Narrow molecular weight, linear polymer chains, and high molecular weight increase the crystallinity.

How does crystallinity affect polymer properties?

Crystallinity: The crystallinity of the polymer increases strength, because in the crystalline phase, the intermolecular bonding is more significant. Hence, the polymer deformation can result in the higher strength leading to oriented chains.

What is difference between LDPE and HDPE?

LDPE is softer and more flexible than HDPE. It also has a lower melting point (115° C) and is more transparent. HDPE is rigid and durable and offers greater chemical resistance. Its higher melting point (135° C) allows it to withstand higher temperatures than LDPE.

What determines crystallinity?

The degree of crystallinity of cellulose is expressed in terms of the crystallinity index (CrI); this is determined by the ratio of the crystalline peak to valley (amorphous region) in the diffractogram based on a monoclinic structure of cellulose [175].

How do you calculate crystallinity?

Polymer crystallinity can be determined with DSC by quantifying the heat associated with melting (fusion) of the polymer. This heat is reported as Percent Crystallinity by normalizing the observed heat of fusion to that of a 100 % crystalline sample of the same polymer.

What is crystallinity percentage?

Percent crystallinity as obtained by X-ray measurements is defined as the ratio of intensity from the crystalline peaks to the sum of the crystalline and amorphous intensities: percent crystallinity = Icrystalline / (Icrystalline + Iamorphous)

Why is it difficult to 100% crystallinity in polymers?

For XRD a crystal is defined as perfect 3-D order. This corresponds to the strictest definition of a crystal. For a semi-crystalline polymer, for instance, 100% crystallinity is never obtained by this definition since there are large interfacial regions where some degree of disorder is present.

Does any polymer ever become 100% crystalline?

Almost no polymer is 100% crystalline and, in fact, most polymers are only around 10-30% crystalline. There’s a way we can find out how much of a polymer sample is amorphous and how much is crystalline. This method has its own page, and it’s called differential scanning calorimetry.

Which is stronger LDPE or HDPE?

LDPE is softer and more flexible than HDPE. HDPE is rigid and durable and offers greater chemical resistance. Its higher melting point (135° C) allows it to withstand higher temperatures than LDPE. Its more crystalline structure also results in greater strength and opacity of the material.

Which is better HDPE or PP?

Density is a key factor that differentiates HDPE from PP. Because HDPE has a lower density, it can be more rigid. Thanks to its lower density, though, PP, can be used when moulding parts with lower weight. Like HDPE, Polypropylene offers good chemical resistance.

How does crystallinity of plastic affect its properties?

The degree of crystallinity (amount of structurally ordered regions) in a plastic has a direct bearing on the materials mechanical, optical, chemical and thermal properties. For example, when an amorphous plastic is at room temperature (21°C), the polymer chains are in a highly disordered and tangled state.

How to determine the percent crystallinity of a polymer?

It is also possible to determine the percent crystallinity of a polymer using DSC measurements. In this case, you will need to know the specific heat capacities of purely crystalline and purely amorphous samples of the polymer in order to complete the calculations.

How is the crystallinity of a polymer related to mass transfer?

Crystallinity is a measurement of the degree of structural order of the molecules in a polymer. It has an inverse relationship with the permeability of polymer composites. The mass transfer of a gas or aroma in a semicrystalline polymer is primarily a function of the amorphous phase, resulting in the permeation of the gas or aroma.

How to find the density of an amorphous crystal?

∆∆∆∆V amorphous totally crystalline amorphous partially crystallin e vv v v C − − % = Dilatometry Example: Nylon How would you find the density (i.e. specific volume) of this crystal given the size and shape? amorphous totally crystalline amorphous partially crystallin e vv v v C − − % =