[Weekly Topic] Special lecture on polymer materials: “Plastics” – Learn a little every day (1) Engineering plastics “Enhance your knowledge””

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This post was last edited by tclz007 on 2013-12-9 at 19:04. Starting this month, learning activities will be carried out in the field of polymer materials; we hope that fellow enthusiasts will come to participate, offer good suggestions, engage actively in learning, and those who conduct in-depth discussions will receive substantial financial rewards as well as attractive bonuses~~! To encourage everyone to come and participate in discussions more actively, as well as to study more diligently, the top ten participants each time will receive a “Motivation Reward for Active Learning”. Some people might think that it’s terrifying to spend their working days doing nothing, performing menial tasks without knowing what to do or what to learn, day after day, year after year, with no vision for their future We must start working hard from now on; even if we learn a little knowledge every day, it will add up over time and help us enrich ourselves. We need to set clear goals – only by filling our minds first can we enrich other aspects of our lives as well. . . . . . It only takes a short ten-odd minutes per day, and you will see the future! ! ! (Anyway, I have learned it; whether you learn it or not is up to you. Besides those experts like Hai Chuan, there are still others who know it.) . . ) Enough talk – let’s start with the basics today~~! Types of plastics and their main properties. Types of engineering plastics and their main properties. Name (code), main properties, examples of applications. Thermoplastics: Polyethylene (PE); High-pressure polyethylene – soft, transparent, non-toxic ； Low-pressure polyethylene is rigid, wear-resistant, corrosion-resistant, and has good electrical insulation properties. High-pressure polyethylene: films, hoses, plastic bottles ； Low-pressure polyethylene: Used in chemical processing equipment, pipes, gears that do not require high load-bearing capacity, bearings, etc. Polypropylene (PP) has higher strength, hardness, and elasticity than polyethylene; it has a low density, good heat resistance, excellent electrical insulation properties and corrosion resistance. However, it lacks toughness, is not wear-resistant, and ages easily. It is used in flanges, gears, fan impellers, pump impellers, handles, television (radio) casings, as well as in chemical pipes, containers, medical devices, etc. Polyvinyl chloride (PVC) boasts high strength and good corrosion resistance. Soft polyvinyl chloride, which features a high elongation rate; its products are soft, and it offers good corrosion resistance and electrical insulation properties. It is used in exhaust gas treatment towers, gas and liquid transfer pipes, centrifugal pumps, ventilators, and connectors ； Soft PVC: films, raincoats, acid- and alkali-resistant hoses, cable insulation, insulating layers, etc. Polystyrene (PS): good corrosion resistance and electrical insulation properties as well as high transparency; it has relatively high strength and stiffness, but poor heat and wear resistance, weak impact resistance, and is flammable and prone to cracking – used for spools, bobbins, and yarn tubes ； Instrument parts, equipment enclosures ； Storage tanks, pipes, elbows ； Lamp shade, transparent window ； ABS plastic, used in electrical insulating materials and similar applications, boasts high strength and impact toughness, as well as good wear and heat resistance. It also exhibits high chemical stability and insulation properties, is easy to shape, and has good machinability. However, its performance under extreme temperatures is poor; it is flammable and opaque. It is used for gears, bearings, dashboard enclosures, refrigerator linings, as well as various containers, pipes, interior decoration panels in aircraft, window frames, and soundproofing materials. It can also be used to manufacture car body parts such as fenders, handrails, and heating/air conditioning ducts. Polyamide (PA) (nylon or nylon fiber) features good strength, toughness, wear resistance, corrosion resistance, vibration damping capacity, and self-lubricating properties. It is easy to shape, and is non-toxic and odorless. Nylon 610, 66, 6, etc., which have high creep values, poor thermal conductivity, high water absorption, and large shrinkage during molding, are used for manufacturing small parts such as gears and worm gears ； Aromatic nylon is used to manufacture wear-resistant parts at high temperatures, insulating materials, and space suits, among other things. It should be noted that nylon experiences significant changes in its properties and dimensions after absorbing water. Polycarbonate (PC) has high tensile and bending strengths, good impact toughness and creep resistance, as well as high heat and cold resistance and dimensional stability. It is highly transparent, has low water absorption, offers good insulation properties and formability, but has poor chemical stability. It is used for insulating components such as washers, gaskets, sleeves, and capacitors ； Instrument enclosure, guard ； In the aviation and aerospace industries, PTFE (the \"king of plastics\") is used to manufacture signal lights, windshields, cockpit covers, helmets, etc. Its excellent chemical resistance, good performance in high and low temperatures, low coefficient of friction, low water absorption, low hardness and strength, as well as moderate compressive strength, and relatively high cost make it suitable for use in anti-friction sealing components, chemical-resistant parts, heat exchangers, and insulating materials in high-frequency or humid environments, such as in chemical pipelines, electrical equipment, and filters for corrosive substances. PMMA (acrylic glass) has a light transmittance of 92%; its relative density is half that of glass. It offers high strength and toughness, resistance to ultraviolet rays and atmospheric aging, is easy to shape, but has low hardness and is not wear-resistant. It dissolves easily in organic solvents, and has poor heat resistance and thermal conductivity as well as a high coefficient of expansion. It is used for aircraft cockpit covers, turret observation ports, instrument lamp covers, and optical lenses, as well as bulletproof glass, screens for televisions and radars, car windshields, and protective covers for instruments and equipment. Thermosetting plastics: Phenolic plastics (PE) possess certain strength and hardness, high wear and heat resistance, good insulation and corrosion resistance. They have high stiffness, low moisture absorption, minimal deformation, simple manufacturing processes, and are inexpensive. The disadvantage is that it is brittle and not suitable for use in plugs, switches, telephones, instrument panels, car brake pads, internal combustion engine cranks, pulleys, silent gears in textile machines and instruments, acid-resistant pumps used in the chemical industry, as well as various household items. Epoxy plastic (EP) has a high specific strength, good toughness, as well as resistance to heat, cold, corrosion, and electrical insulation. It is also waterproof, moisture-proof, and mold-resistant, with excellent formability and dimensional stability. Toxic and expensive; plastic molds, precision measuring tools, encapsulated electrical components, formulations for aircraft paint, oil tanker paint, coating materials for canned goods, printed circuit boards, etc. Plastic is made from resins (natural or synthetic) as the main component, with various additives added to improve its performance and processability. It is called plastic because it is usually molded under heating and pressure conditions. Classification of plastics 1. Classification by the properties of the resin: Thermoplastic plastics: Plastics that can be repeatedly heated to soften and cooled to harden within a specific temperature range. Such as polyethylene plastic, polyvinyl chloride plastic. Thermosetting plastics: Plastics that can be cured into materials that are neither meltable nor soluble when exposed to heat or other conditions. Such as phenolic plastics, epoxy plastics, etc. 2. Classified by the scope of plastic use: General-purpose plastics refer to plastics that are produced in large quantities, have a wide range of applications, good formability, and are inexpensive. Such as polyethylene, polypropylene, polyvinyl chloride, etc. Engineering plastics: refer to plastics that can withstand certain external forces, possess good mechanical properties and dimensional stability, and retain their excellent characteristics at high and low temperatures, making them suitable for use as components in engineering structures. Such as ABS, nylon, polyaluminum, etc. Special plastics: Generally refer to plastics with special properties (such as heat resistance, self-lubrication, etc.) that are used in applications with specific requirements. Such as fluoroplastics, silicones, etc. Basic properties of plastics 1. Light weight and high specific strength. Plastics are lightweight; the density of most plastics ranges from 0.9 to 2.3 grams per cubic centimeter, which is only 1/8 to 1/4 of that of steel and about 1/2 of that of aluminum. The density of various foam plastics is even lower, ranging from 0.01 to 0.5 grams per cubic centimeter. Strength per unit mass is called specific strength, and the specific strength of some reinforced plastics is close to or even exceeds that of steel. For example, alloy steel has a tensile strength of 160 MPa per unit mass, while plastics reinforced with glass fibers can achieve values of 170–400 MPa. 2. Excellent electrical insulation properties. Almost all plastics possess excellent electrical insulation properties, such as very low dielectric loss and good arc resistance, properties that are comparable to those of ceramics. 3. Excellent chemical stability. Generally, plastics exhibit good resistance to chemical substances such as acids and bases. In particular, polytetrafluoroethylene has even better chemical resistance than gold; it can withstand the corrosion of highly corrosive electrolytes such as aqua regia, which is why it is known as the \"king of plastics\". 4. Good anti-friction and wear resistance. Most plastics possess excellent anti-friction, wear-resistant, and self-lubricating properties. Many friction-resistant parts made from engineering plastics take advantage of these properties of plastics; by adding certain solid lubricants and fillers to the wear-resistant plastics, it is possible to reduce their coefficient of friction or further enhance their wear resistance. 5. Light transmission and protection performance. Most plastics can be used to make transparent or translucent products, among which polystyrene and acrylate plastics are as transparent as glass. The chemical name for plexiglass is polymethyl methacrylate, and it can be used as an material for aircraft glass. Plastic films such as polyvinyl chloride, polyethylene, and polypropylene possess good light transmission and heat retention properties, and are widely used as agricultural films. Plastics possess various protective properties, which is why they are commonly used for protective packaging, such as plastic films, boxes, barrels, bottles, etc. 6. Excellent shock absorption and noise reduction performance. Certain plastics are flexible and elastic; when subjected to frequent mechanical impacts and vibrations from the outside, viscous internal friction is generated, converting mechanical energy into heat energy. For this reason, they are used in engineering as materials for shock absorption and noise reduction. For example, bearings and gears made of engineering plastics can reduce noise, and various foam plastics are widely used as excellent materials for damping sound. The excellent properties of the aforementioned plastic enable it to be widely used in industrial and agricultural production as well as in people’s daily lives ； It has evolved from being a substitute for materials such as metals, glass, ceramics, wood, and fibers in the past, to becoming an indispensable material in modern life and advanced industries. However, plastics also have their drawbacks. For example, their heat resistance is inferior to that of materials such as metals; generally, plastics can only be used at temperatures below 100°C, with a few types being usable around 200°C ； The thermal expansion coefficient of plastics is 3 to 10 times greater than that of metals, making their dimensional stability susceptible to changes in temperature ； Under load, plastics will slowly exhibit viscous flow or deformation, a phenomenon known as creep ； Furthermore, plastics undergo aging in the atmosphere, under sunlight, due to prolonged stress, or as a result of certain substances, which causes a decline in their performance. These disadvantages of plastics more or less affect or limit their applications. However, with the development of the plastics industry and deeper research into plastic materials, these shortcomings are being gradually overcome, and new plastics with excellent properties as well as various plastic composites are continually emerging. Welcome everyone to listen. I have started broadcasting, and I hope those who, like me, want to gain knowledge every day will listen. Let’s learn together every day and discuss~~! Special Lecture Series: Special Lectures on Polymer Materials – “Plastics”; Learn a Little Every Day (6) Polystyrene – “Improve Yourself” http://bbs.hcbbs.com/thread-1257966-1-1.html Special Lectures on Polymer Materials – “Plastics”; Learn a Little Every Day (5) Polystyrene – “Improve Yourself” http://bbs.hcbbs.com/thread-1257435-1-1.html Special Lectures on Polymer Materials – “Plastics”; Learn a Little Every Day (4) ABS Plastic – “Improve Yourself” http://bbs.hcbbs.com/thread-1257228-1-1.html Special Lectures on Polymer Materials – “Plastics”; Learn a Little Every Day (3) Polyvinyl Chloride – “Improve Yourself” http://bbs.hcbbs.com/thread-1256914-1-1.html Special Lectures on Polymer Materials – “Plastics”; Learn a Little Every Day (2) Polyethylene – “Improve Yourself” http://bbs.hcbbs.com/thread-1256622-1-1.html Special Lectures on Polymer Materials – “Plastics”; Learn a Little Every Day (1) Engineering Plastics – “Improve Yourself” http://bbs.hcbbs.com/thread-1256345-1-1.html [Special Lectures] Special Lectures on Polymer Materials – “Plastics”; Continuously Updated http://bbs.hcbbs.com/thread-1256917-1-1.html