Cross-linking is the formation of connections between the long-chain molecules in a polymer. It causes the polymer structure to be permanently altered. If the amount of cross-linking is low, the polymer is transformed into an elastomer; if cross-linking is significant, the polymer is transformed into a thermoset.
What determines the degree of crosslinking in a gel?
Nov 11, 2021 · What physical changes occur during crosslinking? Crosslinking agents tie together carbon atoms from different chains of the polymer, transforming what were once viscous linear segments into an insoluble gel network that no longer melts or flows like a typical thermoplastic. How does cross linking affect a polymers viscosity?
What is crosslinking in chemistry?
Apr 04, 2020 · What physical changes occur during cross linking? Crosslinking . Crosslinking is an irreversible change that occurs through a chemical reaction, such as condensation, ring closure, addition, and so on.
What factors affect the covalent modification and crosslinking of proteins?
Aug 22, 2001 · Polymer elasticity stems from the interactions during deformation of the polymer chains held together through physical or chemical crosslinking. Increasing the polymer chain length and/or decreasing the amount of crosslinks can …
What is the overview of crosslinking and protein modification?
Cross-linking by glutaraldehyde and transglutaminase prevented size increases in alkaline pH. Microgel plasticity and elastic modulus were unaffected by treatments. Microgels treated with glutaraldehyde were found to have much greater stability to urea, sodium dodecyl sulfate, and reducing agents when compared to other samples.
What occurs during crosslinking?
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.
Is cross-linking a physical or chemical change?
Summary – Physical vs Chemical Cross Linking The term cross linking is common in chemistry and biology. The key difference between physical and chemical cross linking is that physical cross links occur through weak interactions whereas chemical cross links form through covalent bonding.Apr 12, 2021
How does cross-linking affect the physical properties of a polymer?
A cross-link is a chemical bond between polymer chains other than at the ends. Cross-links are extremely important in determining physical properties because they increase the molecular weight and limit the translational motions of the chains with respect to one another.Mar 5, 2021
What is physical crosslinking?
Radiation or physical crosslinking processes rely on the use of an external source of high-energy radiation to create intermediate excited transition state species, which can decompose and create hydrogen atoms and organic free radical species.
What are the effects of cross linking in polymers quizlet?
The effect of cross-linking in polymers is that it significantly reduces the solubility of a polymer, highly cross-linked polymers are almost impossible to dissolve in any solvent. Also, the more cross-links present in a polymer, the more dense and structurally rigid the material will be.
How cross linking in polymers affects the chemical and physical properties of materials?
By cross-linking, the structure of a polymer solution can be fixed. The resulting polymer networks (or gels) show elastic behavior and, depending on the system, good mechanical properties. Polymer networks are able to swell by uptaking water or organic solvents.
How does cross linking affect a polymers viscosity?
Cross-linker increases the viscosity of gelling agents by connecting the separate gel polymers together. Cross-linker significantly increases the viscosity of linear gel by increasing the molecular weight of the base polymer by linking multiple molecules together.
Why does cross linking increases the elasticity of a polymer?
At first, adding cross-links between polymer chains makes the polymer more elastic. The vulcanization of rubber, for example, results from the introduction of short chains of sulfur atoms that link the polymer chains in natural rubber. As the number of cross-links increases, the polymer becomes more rigid.
How does crosslinking occur?
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. Epoxides undergo ring opening. Some two-component systems may be cured at room temperature but other systems require an elevated temperature. Some additional information on crosslinking was provided above under binder types.
How does crosslinking improve mechanical competence?
Crosslinking improves the mechanical competence (e.g., Young's modulus, yield stress) and decreases the degradation rate of CG scaffolds independent of the chemical and microstructural characteristics. 3,56,57 The three most common crosslinking techniques are the physically based dehydrothermal (DHT) and ultraviolet (UV) processes and the chemically based carbodiimide (EDAC) process. DHT and EDAC in particular have been used extensively for in vitro and in vivo applications. 5,56 DHT processing involves heating of the CG material under vacuum for a specified amount of time (typically 105–120 °C, <50 mTorr, 24–48 h) to remove residual moisture and introduce covalent crosslinks within the CG struts. Increasing the DHT crosslinking temperature and duration has been shown to increase compressive modulus by up to twofold and tensile modulus by up to 3.8-fold. 56,58 While increased crosslink density was correlated with increasing compressive modulus, higher denaturation levels led to higher tensile modulus, but also led to reduced ultimate stress and strain to failure. 58 EDAC processing utilizes carbodiimide chemistry to translate carboxyl (COOH) groups into unstable amine-reactive esters. This intermediate can be stabilized by N -hydroxysulfosuccinimide (NHS), leading to the formation of stable amide crosslinks. 59 Increasing the ratio of EDAC and NHS to COOH increases the degree of crosslinking. 56,59 Both DHT and EDAC methods maintain the integrity of the open pore structure of the material by introducing crosslinks within the CG struts only. 56
How does crosslinking a binder polymer increase stiffness?
Crosslinking the binder polymer can increase stiffness and waterproofness of the bonded nonwoven by providing covalent bonds between polymer chains, which reduce their mobility. The crosslinking potential of a binder system can be classified as follows:
What is crosslinking in thermosetting?
thermosetting. The most well-known example of crosslinking is the vulcanisation of natural latex or butadiene polymers with sulphur, an accelerator and zinc oxide. The process is complicated and the crosslinked product tends to discolour.
What is ionic crosslinking?
Ionic crosslinking has been applied to durable press in recent years, where it offers an alternative to traditional covalent crosslinking. In the ionic crosslinking process, cellulose must undergo a carboxymethylation process to form anionic cellulose (Borsa et al., 1999 ), followed by a cationization process to form the crosslinking structure ( Sahin et al., 2009 ). Ionic crosslinking can be carried out either by treating cellulose with sodium chloroacetate plus cationic glycerin/cationic chitosan, or by treating with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHTAC) plus BTCA ( Hashem et al., 2003 ). Research on this topic has focused on different routes and different reagents for the cationization process ( Hashem et al., 2005; Bilgen et al., 2006; Hauser and Tabba, 2001 ).
What is XLPE used for?
These properties make XLPE useful especially for extruded hot-water pipe, foam insulation, large containment tanks, and wire and cable coverings. For power-cable coverings or insulation, XLPE withstands higher temperatures from electrical overloads and short circuits than alternative materials such as PVC.
What are the advantages of thermoplastic?
The advantages are an easier process related to thermoplastic, with higher cadences, avoiding deburring operations typical of thermosets as well as an increased resistance to temperatures as high as 450 °C. Some successful automotive applications are fixings, air ducts or resonators.
