2 plastic layer aging factors
The effect of molecular structure of resin on the brittleness of plasticized layer
The brittleness of the plasticized layer is essentially determined by the nature of the adhesive. The adhesive for producing the adhesive paper is phenolic resin or melamine resin. These two resins are phenol and melamine under certain conditions. It is formed by condensation with formaldehyde.
Phenol and formaldehyde are subjected to addition reaction under basic catalysis to form a hydroxymethyl derivative of phenol, and then polycondensation reaction is carried out to form an initial linear structure phenolic resin. The linear structure of the resin has a certain softness. The resin has a degree of polymerization of 2 to 10 per molecule and a molecular weight of 200 to 1300. As the reaction proceeds, the final resin in an insoluble and infusible state is finally formed. The melamine resin is formed by the addition reaction of melamine with formaldehyde under neutral or weak alkaline conditions to form dimethylol and trimethylol melamine. As the reaction proceeds, the final insoluble and infusible resin is formed. . From the two types of resins, they are all network-shaped macromolecules with a bulk structure. The network-like macromolecules of this shape have high degree of cross-linking, which makes the flexibility of the molecules become small and the brittleness becomes very large. At the same time, a large amount of hydrogen bonds exist in the molecules of the melamine resin, so the resin does not have elasticity, and the structure of the resin is liable to be broken under the action of external force, and since there is still a free methylol group in the cured resin, With the extension of time, the free methylol group will gradually decrease, resulting in a micro-gap in the resin structure, which will also increase the brittleness of the resin.
2.2 Factors affecting the surface crack of the plasticized layer
From the molecular structure of the phenolic resin and the melamine resin, it can be seen that they all have a free methylol group, and some of these methylol groups gradually decrease with time, forming a micro-gap on the resin structure, which is a plasticized layer. One of the causes of cracks. In addition, since the methylol has a strong affinity for water, it can adsorb moisture. During the use of bamboo plywood, the surface plasticized layer resin will repeatedly expand and contract with changes in air humidity and use environment, so that the resin interior Produces large internal stresses. When such internal stress exceeds the bonding force inside the resin, cracking of the surface is caused. At the same time, the methylol groups in the molecular structure of the resin also undergo a slow polycondensation with each other, causing shrinkage, causing some of the internal binding of the molecules to be broken, forming cracks on the surface of the plasticized layer.
2.3 Factors affecting the peeling and deformation of the surface plasticized layer
In the bonding interface between the substrate and the plasticized layer, since the bamboo material and the cured adhesive have strong reactive groups such as hydroxyl groups, the adhesive and the bamboo have some weak bonds, and the polarities are strong. It is possible for water molecules to replace these weak bonds and to block the active groups of the bamboo and the adhesive, so that the desorption of the bamboo and the adhesive occurs, and the surface plasticized layer is separated from the substrate. At the same time, moisture may enter the interior of the adhesive molecule, which mainly enters the low cross-linking density zone in the adhesive molecule. This part of the water has two effects: one is to reversibly plasticize the molecular structure of the region. Second, it has a destructive effect on the molecular structure of the region. The plasticizing effect can increase the molecular mobility of the adhesive system, reduce the internal stress and tend to balance; the destruction causes the chemical structure of the system to be destroyed, and the rubber layer produces micro-cracks and other defects.
During the hot pressing process, the bamboo curtain plywood is compressed by heat and compressed by the action of high temperature and high pressure, and the adhesive is solidified. When the adhesive is cured, shrinkage stress is generated due to volume shrinkage. During the cooling process, bamboo plywood generates internal stress due to the difference in thermal expansion coefficient between the bamboo and the surface plasticized layer. These internal stresses weaken the bond between the rubber layer and the bamboo. In the use of bamboo plywood, also due to the difference in the coefficient of swelling and shrinkage between bamboo and adhesive, internal stress occurs during the process of moisture absorption and desorption, and the repeated action of this internal stress exacerbates the understanding of adsorption and promotes the adhesive. The damage to the substrate causes the surface plasticized layer to peel off from the substrate. The deformation of the surface of the plasticized layer is due to the fact that some parts of the plasticized layer are peeled off from the substrate; on the other hand, due to the deformation of the substrate, the deformation of the substrate is the main reason. The basic component of bamboo curtain plywood is bracts, and the current clam processing is mostly manual. Therefore, the thick book of bracts is very uneven. During the hot pressing process, the compression state of the bracts is also very different, resulting in unloading. The large difference in rebound between the bucks after pressing reduces the flatness of the plate surface macroscopically. At the same time, during the use of bamboo plywood, due to the difference in dry shrinkage between the bracts and the bracts and between the batt and the adhesive, a large intraplate stress is generated, which causes the plate surface to deform and the flatness to decrease.
The effect of molecular structure of resin on the brittleness of plasticized layer
The brittleness of the plasticized layer is essentially determined by the nature of the adhesive. The adhesive for producing the adhesive paper is phenolic resin or melamine resin. These two resins are phenol and melamine under certain conditions. It is formed by condensation with formaldehyde.
Phenol and formaldehyde are subjected to addition reaction under basic catalysis to form a hydroxymethyl derivative of phenol, and then polycondensation reaction is carried out to form an initial linear structure phenolic resin. The linear structure of the resin has a certain softness. The resin has a degree of polymerization of 2 to 10 per molecule and a molecular weight of 200 to 1300. As the reaction proceeds, the final resin in an insoluble and infusible state is finally formed. The melamine resin is formed by the addition reaction of melamine with formaldehyde under neutral or weak alkaline conditions to form dimethylol and trimethylol melamine. As the reaction proceeds, the final insoluble and infusible resin is formed. . From the two types of resins, they are all network-shaped macromolecules with a bulk structure. The network-like macromolecules of this shape have high degree of cross-linking, which makes the flexibility of the molecules become small and the brittleness becomes very large. At the same time, a large amount of hydrogen bonds exist in the molecules of the melamine resin, so the resin does not have elasticity, and the structure of the resin is liable to be broken under the action of external force, and since there is still a free methylol group in the cured resin, With the extension of time, the free methylol group will gradually decrease, resulting in a micro-gap in the resin structure, which will also increase the brittleness of the resin.
2.2 Factors affecting the surface crack of the plasticized layer
From the molecular structure of the phenolic resin and the melamine resin, it can be seen that they all have a free methylol group, and some of these methylol groups gradually decrease with time, forming a micro-gap on the resin structure, which is a plasticized layer. One of the causes of cracks. In addition, since the methylol has a strong affinity for water, it can adsorb moisture. During the use of bamboo plywood, the surface plasticized layer resin will repeatedly expand and contract with changes in air humidity and use environment, so that the resin interior Produces large internal stresses. When such internal stress exceeds the bonding force inside the resin, cracking of the surface is caused. At the same time, the methylol groups in the molecular structure of the resin also undergo a slow polycondensation with each other, causing shrinkage, causing some of the internal binding of the molecules to be broken, forming cracks on the surface of the plasticized layer.
2.3 Factors affecting the peeling and deformation of the surface plasticized layer
In the bonding interface between the substrate and the plasticized layer, since the bamboo material and the cured adhesive have strong reactive groups such as hydroxyl groups, the adhesive and the bamboo have some weak bonds, and the polarities are strong. It is possible for water molecules to replace these weak bonds and to block the active groups of the bamboo and the adhesive, so that the desorption of the bamboo and the adhesive occurs, and the surface plasticized layer is separated from the substrate. At the same time, moisture may enter the interior of the adhesive molecule, which mainly enters the low cross-linking density zone in the adhesive molecule. This part of the water has two effects: one is to reversibly plasticize the molecular structure of the region. Second, it has a destructive effect on the molecular structure of the region. The plasticizing effect can increase the molecular mobility of the adhesive system, reduce the internal stress and tend to balance; the destruction causes the chemical structure of the system to be destroyed, and the rubber layer produces micro-cracks and other defects.
During the hot pressing process, the bamboo curtain plywood is compressed by heat and compressed by the action of high temperature and high pressure, and the adhesive is solidified. When the adhesive is cured, shrinkage stress is generated due to volume shrinkage. During the cooling process, bamboo plywood generates internal stress due to the difference in thermal expansion coefficient between the bamboo and the surface plasticized layer. These internal stresses weaken the bond between the rubber layer and the bamboo. In the use of bamboo plywood, also due to the difference in the coefficient of swelling and shrinkage between bamboo and adhesive, internal stress occurs during the process of moisture absorption and desorption, and the repeated action of this internal stress exacerbates the understanding of adsorption and promotes the adhesive. The damage to the substrate causes the surface plasticized layer to peel off from the substrate. The deformation of the surface of the plasticized layer is due to the fact that some parts of the plasticized layer are peeled off from the substrate; on the other hand, due to the deformation of the substrate, the deformation of the substrate is the main reason. The basic component of bamboo curtain plywood is bracts, and the current clam processing is mostly manual. Therefore, the thick book of bracts is very uneven. During the hot pressing process, the compression state of the bracts is also very different, resulting in unloading. The large difference in rebound between the bucks after pressing reduces the flatness of the plate surface macroscopically. At the same time, during the use of bamboo plywood, due to the difference in dry shrinkage between the bracts and the bracts and between the batt and the adhesive, a large intraplate stress is generated, which causes the plate surface to deform and the flatness to decrease.
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