The chemical name of bakelite is phenolic plastics, which is the first variety of plastics put into industrial production. Because of its high mechanical strength, good insulation, heat resistance and corrosion resistance, it is often used in the manufacture of electrical materials, such as switches, lamp caps, earphones, telephone cases, instrument cases, etc.
Phenolic resin can be prepared by condensation polymerization of phenols and aldehydes with acid or basic catalyst. Bakelite powder was obtained by mixing phenolic resin with sawdust, talc (filler), urotropine (curing agent), stearic acid (lubricant), pigment, etc. and heating in a mixer. Thermosetting phenolic resin products were obtained by heating and pressing bakelite powder in mold. The disadvantages of phenolic resin are poor mechanical properties, oil resistance and chemical corrosion resistance,
People have modified phenolic resin, adding different fillers in phenolic resin can get modified phenolic plastics with different functions. For example, adding asbestos and mica in ingredients can increase its acid resistance, alkali resistance and wear resistance, which can be used as materials for chemical equipment and accessories for motor and automobile; adding glass fiber can increase hardness, which can be used as machine parts, etc.; using nitrile rubber After modification, the oil resistance and impact strength are greatly improved; after modification with PVC, the mechanical strength and acid resistance are improved.
The characteristics of bakelite are non absorbent, non-conductive, high temperature resistant and high strength. It is often used in electrical appliances. Because of its high insulation and good plasticity, it is called “bakelite”. Bakelite is made of powdered phenolic resin, mixed with sawdust, asbestos or clay, and then pressed out in a mold at high temperature. Among them, phenolic resin is the first synthetic resin in the world.
Phenolic plastic (bakelite): the surface is hard, brittle and fragile. There is a sound of wood when knocking. It is mostly opaque and dark (brown or black). It is not soft in hot water. It is an insulator, and its main component is phenolic resin.
When the formaldehyde / phenol (molar ratio) is less than 1, the thermoplastic product can be obtained, which is called thermoplastic phenolic resin, that is, linear phenolic resin. It does not contain further condensation groups, and can be cured only by adding curing agent and heating. Such as hexamethylene tetramine as curing agent, curing temperature 150 ℃, mixed with filler made of molding powder, commonly known as bakelite powder. When the formaldehyde / phenol (molar ratio) is greater than 1, the thermosetting phenolic resin, which is soluble in organic solvents, can be obtained first under the catalysis of alkali. The resin in stage a contains hydroxymethyl which can be further condensed, so it can be cured without adding curing agent. The resin in stage B, also known as semi soluble phenolic resin, can be obtained under the reaction of heating, which is insoluble and insoluble, but can swell and soften. Further reaction can obtain insoluble and insoluble structure c resin, also known as insoluble phenolic resin. The resin at stage a can also self cure after long-term storage.
The curing forms of thermosetting phenolic resin can be divided into room temperature curing and heat curing.
Non toxic room temperature curing agent NL, benzene sulfonyl chloride or petroleum sulfonic acid can be used for room temperature curing, but the latter two materials are more toxic and irritating.
The main purpose of phenolic resin modification is to improve its brittleness or other physical properties, improve its adhesion to fiber reinforced materials and improve the molding process conditions of composites. Generally, the modification is carried out by the following ways:
① Blocking phenol hydroxyl. Phenolic hydroxyl group of phenolic resin does not take part in chemical reaction in the process of resin manufacturing. The phenolic hydroxyl left in the molecular chain of the resin is easy to absorb water, which reduces the electrical properties, alkali resistance and mechanical properties of the cured products. At the same time, phenolic hydroxyl groups are easy to form quinones or other structures under the action of heat or ultraviolet light, resulting in uneven color changes.
② Introduce other components. In order to change the curing speed and reduce the water absorption, the components which have chemical reaction with phenolic resin or good compatibility with phenolic resin are introduced to separate or surround hydroxyl groups. The introduction of other polymer components can combine the advantages of the two polymer materials.
① The molecular weight of polyvinyl acetal;
② The relative content of hydroxyl group, acetyl group and acetal group in the molecular chain of polyvinyl alcohol acetal;
③ The chemical structure of the aldehyde used. Due to the addition of polyvinyl acetal, the concentration of phenolic resin in the resin mixture decreases correspondingly, which slows down the curing rate of the resin and makes low-pressure molding possible, but the heat resistance of the product decreases.
Modified phenolic vinegar resins with different properties can be obtained by modifying phenolic resin with different organosilicon monomers or their mixed monomers, which have wide selectivity. The composite prepared by silicone modified phenolic resin can work at 200 ~ 260 ℃ for a long time, and can be used as instantaneous high temperature resistant material for rocket, missile and other ablative materials.
The water resistance, alkali resistance, heat resistance and electrical insulation properties of the modified phenolic resin were improved.
First, the brand must be recognized when purchasing: At present, there is a flood of goods in the market, and toxic materials that have been eliminated or banned by the state have also flooded into the homes. Ordinary consumers should choose brand products with high reputation, good reputation, high degree of anti-counterfeiting and international quality system certification.
Second, the waterproof parts should be comprehensive: the floor and wall of the bathroom (return height is not less than 1.8 meters or full), the floor and wall of the kitchen, balcony (return height is not less than 0.3 meters), all of the first floor residential Floor and wall (return height 0.3 m), the ground floor and all walls of the basement should be waterproof and moisture-proof.
Third, the thickness of the waterproof layer should be enough: the thickness of the waterproof layer directly affects its waterproof life. If the thickness of the waterproof layer is reduced, it is equivalent to reducing its waterproof life. cnc machining
Fourth, the construction process should be meticulous: the joint between the wall and the ground, the yin and yang angle, the water pipe, the floor drain and the surrounding of the sanitary ware and the trench in the laying of the cold and heat pipe are the key waterproof parts, and the construction must be meticulous.
5. Closed water test after completion: After the waterproof construction is completed, seal the door and the drain, and store the water for 24 hours indoors to check if there is any leak.
6. If leakage is found, even if remedial measures are implemented.