Phenolic Resin

Phenoic formaldehyde resin (PF) are a varied group of synthetic resins produced through the reaction of phenolic compounds and aldehydes. These resins were first noted in the 1870s, with Bayer creating the first synthesis. Later, through continued study, L.H. Baekeland, an American scientist, created a useful phenolic resin system in 1909. He then started the Bakelite Company, which began the industrial production of phenolic resins. These resins are now common in molding compounds, styling products, insulation, coatings, encapsulation materials, and refractory materials.     1.Synthesis of Phenolic Resins   Phenolic resins are made from a variety of raw materials, resulting in varying types and properties. Phenol-formaldehyde resin is the industrial resin people use most. It is created from phenol and formaldehyde using a two-step process involving addition and polycondensation. Depending on the specific material requirements, the reaction process and rate of the addition and polycondensation reactions can be controlled by varying the synthesis process conditions of phenolic resins to produce resins with varying molecular structures, viscosities, solids contents, and residual carbon content.   2. Classification of Phenolic Resins   The molecular structure of phenolic resins can be changed by controlling the synthesis settings. These settings affect the addition and polycondensation reactions. Based on these molecular structures, phenolic resins can be classified as thermoplastic phenolic resins and thermosetting phenolic resins. 2.1 Thermoplastic Phenolic Resin ( Novolac )   Thermoplastic Phenolic Resin (such as Phenolic Resin 2402) are linear phenolic resins characterized by their straight-chain molecular arrangement.They are primarily produced by reacting excess phenol (P) with formaldehyde (F) under acidic conditions. Thermoplastic Phenolic Resin are created through a two-stage reaction: first, an addition reaction, then a polycondensation reaction. Because the reaction takes place in an acidic environment, the addition mostly results in monomethylol groups forming at the ortho and para locations on the benzene ring (see Figure 2). The second stage, polycondensation, mainly involves the dehydration of the produced monomethylolphenol with the phenol monomer. Furthermore, under acidic conditions, the rate of the polycondensation reaction is much faster than the addition reaction. Furthermore, the presence of phenol in the reaction system is greater than that of formaldehyde. This causes the hydroxymethyl groups generated during the addition process to rapidly react with the excess phenol in the system to form linear macromolecules, resulting in the absence of active hydroxymethyl functional groups in the reaction product molecules. The structural formula is shown in Figure 4. 2.2 Thermosetting Phenolic Resin ( Resole )   Thermosetting phenolic resin (such as Phenolic resin for electronic materials) is a relatively reactive intermediate product synthesized by reacting for a certain period of time under the action of an alkaline catalyst and heat at a molar ratio of formaldehyde to phenol greater than 1. Therefore, if the synthesis process is not controlled, it can easily react violently, leading to gelation and even cross-linking reactions, ultimately forming insoluble and infusible macromolecules.   The synthesis process of thermosetting phenolic resin is also divided into two steps. The initial stage involves an addition reaction where hydroxymethyl groups are formed on the benzene ring, specifically at the ortho and para positions, leading to the creation of monomethylolphenol. Because the reaction activity of the active hydrogen atoms at the ortho and para positions on the benzene ring is much greater than that of the hydroxyl group on the hydroxymethyl group under alkaline conditions, the resulting hydroxymethyl group is not easily polycondensed.The active hydrogen atoms on the benzene ring can react with more hydroxymethyl groups, leading to the creation of dimethylol and trimethylolphenol. Figure 5 shows this addition reaction. Next, a polycondensation reaction occurs where the polymethylol groups react with active hydrogen atoms on the phenol monomer. This creates a methine bridge, or the hydroxymethyl groups dehydrate to form an ether bond. As this polycondensation keeps happening, it makes a branched resol phenolic resin.   The curing mechanism of thermosetting phenolic resins is quite complex. Currently, the most widely accepted theory is based on the active hydroxymethyl groups present in the molecular structure of thermosetting phenolic resins. During heating, these hydroxymethyl groups react in two ways: with active hydrogen atoms on the benzene ring to form methylene bonds, or with other hydroxymethyl groups to form ether bonds.   3.The Bonding Mechanism of Phenolic Resins as Binders   Four main ideas exist to explain how polymer adhesives stick things together: mechanical interlocking, diffusion, electronic attraction, and adsorption. For phenolic resin systems, mechanical interlocking is key.   The sticking process for phenolic resins occurs in two steps. At the start, the resin goes into all the small holes and uneven areas on the surface of what it's bonding to. For this to happen, the resin needs to be able to wet the surface well. Next, the phenolic resin hardens. During this process, molecules join together to form a network. This lets the resin molecules get stuck in the holes and uneven spots, creating a strong grip that holds the resin and the surface together tightly.   Website: www.elephchem.com Whatsapp: (+)86 13851435272 E-mail: admin@elephchem.com

Carbon foam, a functional carbonaceous material with a honeycomb structure, not only boasts excellent properties such as low density, high strength, oxidation resistance, and adjustable thermal conductivity, but also boasts excellent processability. Therefore, it can be used as a thermal conductor, insulator, catalyst carrier, biosolidifier, and absorber. It holds broad application prospects in military applications, energy-saving building insulation, chemical catalysis, biological wastewater treatment, and energy. Carbon foam can be sorted into two kinds—one that lets heat pass through easily (thermally conductive) and another that stops heat from passing through (thermally insulating). The difference lies in how much the original carbon material has been turned into graphite. Mesophase pitch and phenolic resin are two typical carbonaceous precursors for producing high- and low-thermal-conductivity carbon foams, respectively. Currently, both thermosetting and thermoplastic phenolic resins are high-quality carbonaceous precursors for producing low-thermal-conductivity carbon foam. Using phenolic resin as the raw material, a phenolic resin foam can be produced by adding a blowing agent and a curing agent and foaming at normal pressure. Carbon foam is then produced by high-temperature carbonization. The compressive strength of this carbon foam is below 0.5 MPa, which restricts how it can be used.   When Phenolic Resin 2402 is used as the raw material, the pores of the carbon foam produced at different foaming pressures are all nearly spherical (Figure 6). Since no foaming agent is added, the foaming process follows a self-foaming mechanism, whereby the matrix material undergoes a cracking reaction at a certain temperature, generating corresponding small molecular gases. As gases form, they gather and grow into pores. The viscosity, structure, volume, shape, and gas production rate of the base material change as cracking gas is produced. This means the structure of pores in carbon foam depends on the base material's viscosity, gas production rate, volume, how quickly its viscosity changes, and outside pressure within the foaming temperature range. At foaming temperatures between 300 and 425°C, 2402 phenolic resin makes lots of cracking gas (Figure 3(a)) and has low viscosity (<2×104Pa·s, Figure 4(d)). Because of this, surface tension causes the pores to be round. When the foaming pressure is 1.0 MPa, the low outside pressure causes bubbles to merge and grow, leading to larger pore sizes (500-800 μm). Also, the larger pores mean the carbon foam has thinner connections and many pores are close to becoming open cells (Figure 6(a)).   When the foaming pressure goes up to 3.5 MPa, the pore size of the carbon foam goes down (300-500 μm), the connections get thicker, and the pore structure is more consistent (Figure 6(b)). If the foaming pressure keeps increasing to 5.0 MPa, the pore size keeps going down, but the consistency of the pore structure starts to get worse (Figure 6(c)). At a foaming pressure of 6.5 MPa, the pore structure of the carbon foam keeps getting worse, but the pore density goes up (Figure 6(d)).   When the foaming temperature goes above 425°C, the viscosity of the 2402 phenolic resin quickly goes up. The foaming pressure clearly has an important impact on how consistent the pore structure is and how dense the carbon foam is. If the foaming pressure is less than the pressure inside the bubble, the cracking gas produced later can still overcome the base material's viscosity and keep gathering and growing in the already formed bubble. This results in a fairly consistent pore structure in the bubble, but no new bubbles will form. But, if the foaming pressure is high enough, the cracking gas produced later can only form new, smaller bubbles at the connections of the already formed bubbles or in the base material, which makes the pore structure of the foamed carbon worse and increases the pore density.   Conclusion (1) The way thermoplastic phenolic resin (resin for refractory) foams is based on its own reaction. How well it foams depends on the conditions (pressure, temperature, and time). It's also influenced by how the molecules interact, considering their size, distribution, how they lose weight when heated, and how their viscosity changes with temperature. Viscosity and temperature are key. (2) When heated to 300-420°C, 2402 Phenoic formaldehyde resin breaks down fast, making a lot of gas. If the material's viscosity is below 2×104 Pa·s at this point, the resulting foamed carbon has good bubbles that are round and evenly spaced. (3) Lower pressures when foaming help make foamed carbon with consistent pores. Higher pressures stop the gas from clumping together and getting bigger, which causes more bubbles to form. This makes the pore structure uneven and increases how many bubbles there are.   Website: www.elephchem.com Whatsapp: (+)86 13851435272 E-mail: admin@elephchem.com