How is crosslink density calculated?

How is crosslink density calculated?

The cross-link density resulting from chemical cross-link chains can then be calculated by dividing the polymer density by Mc. Intramolecular cyclization in finite species causes the delayed gel point relative to the predictions of Flory-Stockmayer [25].

Does crosslinking increase density?

The bulk density increases with the increase of crosslink density for crosslinked polymers. The higher the temperature is, the more discrete the bulk density distribution is. The distribution of the bulk density with various temperatures for different crosslink densities.

What is crosslink formation?

Crosslinking is the general term for the process of forming covalent bonds or relatively short sequences of chemical bonds to join two polymer chains together.

What is a physical crosslink?

Physical cross linking is the formation of a bond between polymer chains through weak interactions. Most of the times, these interactions tend to be ionic bonds. E.g. sodium alginate gels form ionic bonds upon exposure to calcium ions. This cross linking involves bridge formation between alginate chains.

How do you test a polymer for crosslinking?

The cross-link density of a polymer can be determined by using ASTM-D2765 as a method guideline. The method determines the gel content and swell ratio for a known mass of polymer extracted in an appropriate solvent at a specific temperature for a specific amount of time.

What is the major purpose of cross-linking in polymers?

Introduction. Chemical cross-linking has been widely used to alter the physical properties of polymeric materials, the vulcanization of rubber being a prototypic example. Linking of polymer chains through chemical linkages gives a material a more rigid structure and potentially a better-defined shape.

How does cross-linking affect strength?

Strength and modulus tend to increase as the cross-linking agent concentration is increased, up to about 50%, after which the values level out or begin to fall. Water absorption drops with increasing cross-linking agent over the whole range of concentrations.

How does the crosslink density influence its swelling in solvent?

An increase in crosslink density results in a decreased swelling and vice versa. If the hydrogel is mechanically constrained to a surface, it can experience various wrinkling and buckling conformations upon swelling, as the stresses associated with its confinement are relieved.

How do I confirm crosslinking?

From swelling study crosslink density is measured. Also by using Dynamic Mechanical Thermal Analyzer, you get crosslink density. NMR will also be helpful. Preliminary observation can be made by observing extent of swelling (Solvent up take), which will vary according to crosslink density.

What is the importance of cross-linking?

What are the two types of cross-linking?

There are three different types of crosslinkers – homobifunctional, heterobifunctional, and photoreactive crosslinking reagents. How do these types of crosslinkers differ from one another and how do you know which one to use for your specific application?

Why is hydrogel swelling important?

Both studies suggested that the swelling ratio of hydrogel composites, which is related to the hydrogel mesh size, may affect nutrient transport and drug delivery throughout the hydrogels and thus influence the proliferation and differentiation of encapsulated cells.

What causes polymer swelling?

The swelling is defined as a penetration of a solvent into the polymer network that causes an abrupt change in the volume (Gugliuzza and Drioli 2007), moving the boundary from unsolvated glassy region to solvated and expanding rubbery domain.

What increases cross-linking?

9.4. The first is through free radical or oxidizing reactions assisted by an increased temperature and the presence of air. UV light or other radiation sources may also promote crosslinking. Another mechanism is a chemical reaction such as through the condensation of an alcohol or an amine with a carboxylic acid.

What increases cross linking?