The Define Of Bakelite
The chemical name of bakelite is phenolic plastic, which is the first variety of plastics to be put into industrial production. Phenolic and aldehyde compounds can be prepared by polycondensation reaction under the action of acidic or basic catalysts. Fully mix phenolic resin with sawdust, talcum powder (filler), urotropine (curing agent), stearic acid lubricant), pigment, etc., and heat and knead in a mixer to obtain bakelite powder . The bakelite powder is heated and pressed in a mold to obtain a thermosetting phenolic plastic product.
The condensation products of phenols and aldehydes are commonly known as phenolic resins, which are often referred to as synthetic resins obtained by the condensation reaction of phenol and formaldehyde, and were the first thermosetting resins to be synthesised.
Although phenolic resins are the oldest class of thermosetting resins, but because of its easy availability of raw materials, easy synthesis, and phenolic resins have good mechanical strength and heat resistance, especially with outstanding instantaneous high temperature ablation resistance, and the resin itself has a wide range of modified room, so phenolic resins are still widely used in the manufacture of glass fibre reinforced plastics, carbon fibre reinforced plastics and other composite materials.
Phenolic resin composites are particularly important in the aerospace industry (space vehicles, rockets, missiles, etc.) as structural materials for instantaneous high temperature and ablation resistance. By controlling the synthesis conditions (e.g. the ratio of phenol to aldehyde, the type of catalyst used, etc.), two different types of phenolic resins can be obtained:
One is known as thermosetting phenolic resins, which are resins containing light methyl reactive groups that can be further reacted, and if the synthesis melon is not controlled, the bulk polycondensation reaction will continue until a non-melting, insoluble cured resin with a three-way network structure is formed, hence the name first-order resin.
The other type of resin, known as thermoplastic phenolic resins, is a linear resin that does not form a three-way network structure during the synthesis process and a curing agent must be added during the further curing process. The synthesis and curing principles of these two types of resin are not the same, and the molecular structures of the resins are also different.
Modified phenolic resins
The purpose of modifying phenolic resins is mainly to improve its brittle or other physical properties, to improve its bonding properties to fiber reinforced materials and to improve the molding process conditions of composite materials.
Modifications are generally carried out by the following means:
- 0 Blocking the phenolic group. The phenolic groups of phenolic resins do not generally participate in chemical reactions during the resin manufacturing process. The phenolic light groups left in the resin molecular chain tend to absorb water, which reduces the electrical properties, alkali resistance and mechanical properties of the cured product, while the phenolic light groups tend to generate wake or other structures under the action of heat or ultraviolet light, resulting in uneven colour changes.
- @Introduce other components. The introduction of components that react chemically with the phenolic resin or are more compatible with it, separating or surrounding the light base, thus changing the curing speed and reducing water absorption.
The introduction of other polymer components can combine the advantages of two polymer materials.
1.polyvinyl acetal modified phenolic resin
Industry – the most used polyvinyl acetal modified phenolic resin, it can improve the resin to the bonding force of glass fibres, improve the brittleness of phenolic resin to increase the mechanical strength of the composite, reduce the curing rate and thus help to reduce the molding pressure. The phenolic resin used as a modifier is usually a phenol formaldehyde resin synthesised with ammonia or magnesium oxide as a catalyst. The modified polyvinyl acetal is a polymer containing varying proportions of light, acetal and acetal side chains, the properties of which depend on:@ the molecular weight of the polyvinyl acetal, @ the relative content of light, acetal and acetal groups in the polyvinyl acetal molecular chain;0 the chemical structure of the aldehyde used. As a result of the addition of polyvinyl acetal, the concentration of phenolic resin in the resin mixture is reduced accordingly, slowing down the curing rate of the resin and making low-pressure molding possible, but the heat resistance of the product is reduced.
2.Polycoolamine modified phenolic resins
Phenolic resins modified by polycoolamine improve the impact toughness and adhesion of phenolic resins, and improve the fluidity of the resin, but still maintain the advantages of phenolic resins. The polycoolamine used for modification is a class of light methyl polycoolamine, the use of light methyl or active hydrogen in the synthesis of the resin process or in the resin curing process to form a chemical bond to achieve the purpose of modification.
3.Epoxy-modified phenolic resin
The composite material made from a mixture of 40% first-order thermosetting phenolic resin and 60% diphenol propane epoxy resin can combine the advantages of the two resins and improve their respective disadvantages, thus achieving the purpose of modification. This mixture has the excellent bonding properties of the epoxy resin, improving the brittleness of the phenolic resin, and the excellent heat resistance of the phenolic resin, improving the disadvantages of the epoxy resin which is less heat resistant. This modification is through the light methyl group in the phenolic resin and epoxy resin in the light group and epoxy group for chemical reaction, and phenolic .
4.Organic silicone aldehyde resin
Organosilicone resins have excellent heat and moisture resistance. The heat resistance and water resistance of phenolic resin can be improved by using silicone monomer linear phenolic resin in the phenol light group or light methyl to react. The use of different silicone monomers or their blends modified with phenolic resins can result in modified phenolic vinyl resins with different properties and a wide range of selectivity. The composite material prepared with silicone modified phenolic resin can work under 200~260% for quite some time, and can be used as instant high temperature resistant material, used as ablative material for rockets, missiles, etc.
5.Boron-modified phenolic resin
Due to the introduction of inorganic elements in the molecular structure of phenolic resin, phenolic resin than phenolic resin heat resistance, instantaneous high temperature resistance and mechanical properties more excellent. Boron-modified phenolic resins are much better than ordinary phenolic resins in terms of heat resistance, instantaneous high temperature resistance and ablative corrosion resistance. They are mostly used in rockets, missiles and space vehicles and other space technology fields as excellent ablation-resistant materials.
6.Xylene-modified phenolic resin
Xylene modified phenolic resin is the introduction of hydrophobic structure of the xylene ring in the molecular structure of phenolic resin, thus modifying the water resistance, alkali resistance, heat resistance and electrical insulation properties of the phenolic resin has been improved.
7.Diphenyl ether formaldehyde resin
Diphenyl ether formaldehyde resin is made of diphenyl ether instead of phenol and formaldehyde condensation, diphenyl pay formaldehyde resin glass fibre reinforced composites have excellent heat resistance, can be used as H-class insulation materials, it also has good radiation resistance, moisture absorption is also very low.
The History of Bakelite
One day in 1905, the German chemist Beyer, doing experiments on phenol and formaldehyde in a flask, found that a kind of sticky stuff was produced inside, he washed it with water, but it wouldn’t come off. He finally managed to get the “nasty” piece off and, relieved, Beyer threw it in the waste bin. A few days later Beyer was about to dump the contents of the waste bin, when he caught a glimpse of the piece again, its surface smooth and shiny, with an attractive sheen. After some experimentation, it turned out that what was once “annoying” was now “delightful”.
It is impervious to water, does not deform when heated, is mechanically strong and easy to work with, and has good insulation properties, which is ideal for the fledgling electrical industry. As a result, it was used extensively in the production of electric switches, light switches, lamp heads, telephones and other electrical appliances, for which it was given the name “Bakelite”. To this day, Bakelite is still one of the most important, most produced and most commonly used plastics.
The Advantages Of Bakelite
Bakelite has high mechanical strength, good insulation, heat and corrosion resistance, so it is often used in the manufacture of electrical materials, such as switches, lamp heads, headphones, telephone cases, instrument cases, etc., from which “Bakelite” is named.
The Disadvantages Of Bakelite
The disadvantage of phenolic resin is poor mechanical properties, but also not resistant to oil and chemical corrosion, in order to overcome the above defects, people have modified phenolic resin in phenolic resin by adding different fillers can get different functions of modified phenolic plastic, such as adding asbestos, mica in the ingredients, can increase its acid resistance, alkali resistance, wear resistance, can be used as materials for chemical equipment and motors, automotive parts, adding glass fiber can Adding glass fibre can increase the hardness and can be used as machine parts, etc. After modification with nitrile rubber, the oil resistance and impact strength are greatly improved; after modification with PVC, the mechanical strength and acid resistance can be improved.
Phenolic plastic (bakelite) properties and uses
Heat resistance: From a practical point of view, the use temperature of phenolic plastics with various fillers is: inorganic filler 160 ℃; organic filler 140 ℃; the maximum use temperature of glass fiber and asbestos filler is 170 ~ 180 ℃.
Corrosion resistance: Machining phenolic resin without fillers is hardly attacked by inorganic acids, insoluble in most hydrocarbons and chlorides, and insoluble in ketones and ethanol. However, it is not resistant to corrosion by concentrated sulfuric acid, nitric acid, high temperature chromic acid, fuming sulfuric acid, alkali and oxidizing agents. Phenolic plastic also has the above-mentioned characteristics, but when studying its corrosion resistance, the corrosion resistance of the filler must also be taken into account.
Modification of phenolic plastics: The main disadvantages of phenolic plastics are brittleness, poor arc resistance, and dielectric properties that change with frequency. Therefore, in production applications, modification methods are used to make up for the shortage of machining bakelite . The use of phenolic resin (mainly thermoplastic) and other types of polymer blending applications can improve the performance of phenolic plastics.
Commonly used polymer compounds are: polyamide resin, polyvinyl chloride resin, nitrile rubber, polypropylene resin and so on. For example, after mixing with polyvinyl chloride, it can improve its mechanical strength, heat resistance, dielectric properties, acid resistance, water resistance, etc., and has good colorability. Bakelite powder based on phenolic resin and nitrile rubber can greatly improve the impact strength of the parts.
Bakelite powder made with a mixture of phenolic resin and polyamide resin and inorganic fillers (such as mica and feldspar) has higher dielectric properties, and its products can be used under high temperature, high frequency and high pressure conditions.
Uses: Widely used as electrical insulation materials, furniture parts, machine tool accessories, mechanical operating parts, valve hand wheels, handles, handles, handles, handles, daily necessities, handicrafts, etc. In addition, it is also used as asbestos phenolic plastic for acid resistance, rubberized paper for insulation, rubberized cloth, phenolic foam for insulation and sound insulation and honeycomb plastic.
Bakelite powder
Bakelite powder, also known as gum wood powder, has good insulating properties and is used in the manufacture of electrical appliances and everyday industrial products etc. It is a phenolic plastic with mainly wood powder as filler, which is pressed.
The physical and chemical properties of Bakelite
When formaldehyde/phenol (molar ratio less than 1, thermoplastic products can be obtained, called thermoplastic phenolic resin, i.e. linear phenolic resin, which does not contain further condensation groups, plus the curing agent and heating can be transformed. For example, hexamethylenetetramine as a curing agent, curing temperature 150C, mixed with fillers made of moulding powder commonly known as Bakelite powder. When formaldehyde / phenol (molar ratio) is greater than 1, in the alkali-catalyzed first to get a stage A resin, i.e. thermosetting phenolic resin, soluble in organic solvents, A stage resin contains further condensation of light methyl, so no need to add curing agent that can be cured: heating under the reaction to get B stage resin, also known as semi-soluble phenolic resin, insoluble and non-melting but can be dissolved and softened. A further reaction gives the insoluble, non-melting, bulk structure of Phase C resins, also known as insoluble phenolic resins. Stage A resins are also self-curing when stored for long periods of time. The curing of thermosetting phenolic resins is divided into two forms: room temperature curing and heat curing. Room temperature curing can be used non-toxic room temperature curing agent NL, can also use benzene sulfonyl chloride or petroleum sulfonic acid, but the latter two materials are more toxic, irritating
