What increases crystallinity?

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 do you increase the degree of crystallinity?

Increase in concentration which can occur via solvent evaporation, induces interaction between molecular chains and a possible crystallization as in the crystallization from the melt. Crystallization from solution may result in the highest degree of polymer crystallinity.

What effect does branching have on a polymer?

Branching makes the polymers less dense and results in low tensile strength and melting points.

What makes a polymer more crystalline?

The more crystalline a polymer, the more regularly aligned its chains. Increasing the degree of crystallinity increases hardness and density. HDPE (high density poly(ethene)) is composed of linear chains with little branching. Molecules pack closely together, leading to a high degree of order.

How does crystallinity affect solubility?

Crystallinity decreases solubility. 4. The rate of solubility increases with short branches, allowing the solvent molecules to penetrate more easily.

Which polymer is more likely to crystallize?

Linear polymers are more likely to crystallize that branched ones. In addition, polymers having isotactic structures will normally have a higher degree of crystallinity that those having atactic structures.

How does crystallinity affect hydrolysis?

The correlation between the CrI and the initial hydrolysis rate (Fig. 5) shows a continuous decrease in rate as crystallinity increases. At higher degrees of crystallinity, cellulose samples are less amenable to enzymatic hydrolysis, less reactive and less accessible.

What is the effect of branching?

The effect of long chain branching depends on the differences in their chemical structure from that of the main chain and to a lesser extent on the degree of long chain branching. The physical characteristics of the polymer show the sharpest changes when tree-like branching occurs.

Are branched polymers more viscous?

For example, at low loads (shear stresses) linear polymers and their melts flow like newtonian fluids and possess a lower viscosity as compared with branched polymers, whereas at high loads the character of flow deviates from that of a newtonian flow, so that the viscosity of a branched polymer is lower than that of a …

What is the crystallinity of polymer materials?

The crystallinity of a polymer refers to the degree as to which there are regions where the polymer chains are aligned with one another. However, in order for this to occur, some degree of stereoregularity is required.

How does branching affect solubility?

Solubility. The solubility decreases with increase in mass because the hydrocarbon part becomes larger and resists the formation of hydrogen bonds with water molecules. The solubility of isomeric alcohols increases with branching because the surface area of the hydrocarbon part decreases with branching.

Are branched polymers soluble?

Branched polymers are often soluble in one or more solvents because it is possible to separate the polymer chains. Cross-linked polymers are insoluble in all solvents because the polymer chains are tied together by strong covalent bonds. Linear and branched polymers form a class of materials known as thermoplastics.

What is the effect of branching on polymer properties?

The effect of branching on the polymer properties depends on the number and length of the branches. Short branches interfere with the formation of crystals, that is, they reduce the amount of crystallinity whereas long branches undergo side chain crystallization because they are able to form lamellar crystals of their own.

How does crystallinity affect interchain hydrogen bonding?

Since the crystallinity is the result of interchain hydrogen bonding, changes in crystallinity reflect decreases or increases in this bonding. Although water alone cannot break the interchain hydrogen bonds, decrystallization can be brought about by many reagents.

What is the effect of degree of branching on density?

degree of branching as well as the length of the branches affects the density which can vary considerably. Typically, the higher the density of the polymer the higher the degree of crystallinity and the stiffer, harder, and stronger the polymer. Today, many grades of polyethylene are

How does crystallinity affect the properties of a plastic?

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.