Synthetic Fibers and Advanced Materials

This lesson surveys the world of synthetic fibers, advanced polymers, and inorganic/organic hybrid materials that have shaped the materials revolution of the 20th and 21st centuries.

Basic Knowledge

Major synthetic fibers:
・Nylon (aliphatic polyamide): Carothers, 1935; stockings and parachutes
・Polyester (PET): clothing and plastic bottles
・Acrylic fiber (polyacrylonitrile): sweaters and artificial leather
・Vinylon: polyvinyl acetate treated with formalin; developed uniquely in Japan (Ichiro Sakurada, 1939); reinforcing material for ropes and hoses
・Polypropylene fiber: lightweight; artificial turf and carpets
・Aramid fiber (Kevlar): aromatic polyamide; bulletproof vests and rocket components
・Carbon fiber (CFRP): PAN or pitch carbonized as the raw material; aircraft, sporting goods, and automobile weight reduction

Advanced polymers:
・Conductive polymers: polyacetylene and PEDOT (Hideki Shirakawa, 2000 Nobel Prize); organic LEDs, organic solar cells, and antistatic applications
・Liquid-crystal polymers: the basis of liquid-crystal displays
・Superabsorbent polymers: cross-linked sodium polyacrylate; disposable diapers and desert greening
・Ion-exchange resins: ultrapure-water production and water treatment
・Biodegradable plastics: PLA (polylactic acid), PHB, and PHA; measures against marine plastics
・Shape-memory polymers: return to their original shape when the temperature changes
・Self-healing polymers: heal damaged areas by themselves; research is advancing worldwide

Inorganic/organic hybrids:
・Silicones (Si-O-Si backbone + organic groups): heat resistance and water repellency; medical seals and lubricating oils
・MOFs (metal-organic frameworks): metal ions + organic linkers; extremely high surface area (5000 m²/g); gas storage and catalysis
・Nanocomposites: polymers + nanoparticles (clay, carbon nanotubes, and graphene); improved mechanical strength and electrical conductivity
・Organic-inorganic perovskites (CH₃NH₃PbI₃, etc.): next-generation solar cells, with efficiency approaching that of silicon solar cells
2D materials: graphene (one layer of C atoms; Geim and Novoselov, 2010 Nobel Prize), MoS₂, and h-BN (hexagonal boron nitride), at the forefront of modern electronic materials.

Further Study (Principles and Applications)

Carbon fiber: A strategic material in which Japan holds 70% of the world market. Toray, Teijin, and Mitsubishi Chemical are major manufacturers. It is used in 50% of the body of the Boeing 787, F1 chassis, golf clubs, tennis rackets, fishing rods, and bicycles.
Organic LEDs (OLEDs): Organic dye molecules emit light when an electric current passes through them; they are widely used in smartphones, televisions, and lighting. They are expanding in fields where flexibility, contrast, and color reproduction surpass LCDs. Japanese companies such as Sumitomo Chemical and JOLED have also accumulated substantial technological expertise.
Perovskite solar cells: A Japanese technology originating in the Miyasaka laboratory at Toin University of Yokohama in 2009. They are lightweight, low-cost, and flexible and can be produced by coating. They are a next-generation candidate alongside silicon solar cells, and their conversion efficiency rose sharply from 3.8% to 26% in 10 years.
Graphene: A single-layer sheet of carbon atoms in a honeycomb structure. Its electrical conductivity exceeds that of copper, its mechanical strength is 200 times that of steel, its thermal conductivity is comparable to diamond, and it is almost transparent. Applications in smartphones, flexible devices, seawater desalination membranes, and medical diagnostics are being researched.
SDGs and advanced materials: They are directly connected to “Goal 9: Industry, innovation, and infrastructure” and “Goal 12: Responsible consumption and production.” Biomaterials, recycled materials, low-energy manufacturing processes, and carbon-capture materials (CO₂ adsorption by MOFs) are at the forefront of research.

Points to Note (Common Confusions and Frequent Mistakes)

① Carbon fiber CFRP means Carbon Fiber Reinforced Plastic; the matrix is epoxy resin or another material, and the reinforcing material is carbon fiber. ② Aramid means aromatic polyamide; commercial names include Kevlar (DuPont) and Twaron. Nylon is an aliphatic polyamide, and the difference in strength is large (aramid is about five times stronger). ③ Organic LEDs and liquid-crystal displays: OLEDs emit light themselves, whereas LCDs use a backlight and liquid-crystal shutters; their contrast and power consumption differ. ④ The perovskite crystal structure is an ABX₃-type crystal derived from CaTiO₃. CH₃NH₃PbI₃ in solar cells is one example.

Practice

1. Describe the characteristics of carbon fiber CFRP and its significance in reducing aircraft weight.
2. Explain how conductive polymers such as polyacetylene conduct electricity from the perspective of conjugated double bonds.
3. Explain the structure of graphene and why its strength, electrical conductivity, and thermal conductivity are all excellent.