Adhesives, Surfactants and Rubbers
Next: Colorants
Welcome to the second part of what can be made locally by the Unfactory concept. Again you can read this more with the mind of getting an overview of all uses.
Adhesives
Epoxies have the biggest share in the adhesives markets and different epoxy compounds can be developed to suit many different uses. Epoxies are thermoset plastics (cannot be remoulded after heating). They are the typical two-part glues found in normal hardware stores and supermarkets.
The most commercially important epoxy resins are glycidyl ethers, amines and esters. They are all made from epichlorohydrin. Another important class are epoxy novolac resins made by condensing phenol or creosol with formaldehyde in presence of acid catalysts.
They can be used as adhesives for wood, metal, glass, stone, and some plastics. They can be made flexible or rigid, transparent or opaque/coloured, fast setting or slow setting. High-performance epoxies are also used the construction of aircrafts, automobiles, bicycles, boats, golf clubs, skis, snowboards and any applications where high strength bonds are required.
Surfactants
Surfactants are compounds that lower the surface tension between materials. Surfactants can act between two liquids, gas and a liquid, or between a liquid and a solid. Detergents are a common category of surfactants. The term itself comes from words surface active agent.
Surfactants get their properties normally by being amphiphilic. This means that it contains both a hydrophobic group (one that is repelled by water) and a hydrophilic group (one that is attracted to water and tends to be dissolved in water).
They get absorbed in the air-water interface. At the interface, they align themselves so that the hydrophobic part is in the air and hydrophilic part is in water. This will cause the decrease in surface tension or interfacial tensions (that’s basically just naming convention – surface tensions are between liquid and gas (usually air) and interfacial tension is between any two substances like liquid-liquid, liquid-solid or solid-air).
The commercially most significant type of surfactants is currently linear alkyl benzene sulfonate (LAS). It is used in cleaners and detergents.
Surfactants are in products such as detergents, fabric softeners, emulsions, soaps, paints, adhesives, inks, anti-fogs, ski waxes, snowboard wax, deinking of recycled papers, in flotation, washing and enzymatic processes even laxatives.
Shampoos are usually made by combining a surfactant like sodium lauryl sulfate or sodium laureth sulfate with a co-surfactant like cocamidopropyl betaine in water.
For a low-tech alternative, a much older method of making soap is to mix wood ash with fats and water. A technique invented in Mesopotamia some two thousand years BC. The fats can either be plant or animal based. In the Middle Ages the most expensive soap was made with olive oil and known as Castile white.
To probe further: https://blog.biolinscientific.com/what-are-surfactants-and-how-do-they-work and https://www.essentialchemicalindustry.org/materials-and-applications/surfactants.html
Rubbers
Rubbers are polymer chain of simple monomers. Most of them are either gases or low-viscosity liquids but polymerisation turns them into a form of liquids that have extremely high viscosity.
Rubbers also contain other substances such as curatives that cross-link the polymer chains into a network. Curatives are used in the vulcanisation process to harden the rubbers. Most common curatives are sulfur type for unsaturated rubbers and peroxides for saturated. Accelerator chemicals are used to control the curation process.
Reinforcement agents like silica and carbon black improve performance like tensile strength. Fillers are used to reduce cost, change colour and increase hardness. Plasticisers are used again to control properties such as plasticity or decrease the viscosity.
The general-purpose rubbers are natural rubber, styrene-butadiene rubber (SBR), butadiene rubber, isoprene rubber and ethylene-propylene rubber. They are used mostly in tyres and mechanical goods (like gaskets).
SBR are synthetic rubbers derived from styrene and butadiene. They have good resistance to abrasion and tolerate aging when protected by additives. SBR competes with natural rubber and is used widely in pneumatic tires. Other uses include shoe heels and soles, gaskets and even chewing gum.
Polybutadiene rubber (PBD) is made from the polymerisation of the monomer 1,3-butadiene. It has a high resistance to wear and is used especially in the manufacture of tires. It’s also used as additive to improve the toughness (impact resistance) of plastics such as polystyrene and acrylonitrile butadiene styrene (ABS).
Isoprene rubber is synthetically produced by polymerisation of 1-methyl-1,3-butadiene. It has good mechanical properties and are used in anti-vibration mounts, drive couplings, bearings and adhesives. For tire use it is usually blended with SBR and PBD to improve performance.
Ethylene propylene rubber (EPR) is a copolymer of ethylene, propylene and a small amount of other monomers. It is resistant to heat, oxidation, ozone and the weather and it is also colourfast. It also has excellent electrical insulation, compression, and low temperature properties. It is used in electrical cable insulation and in flexible rubber goods such as hoses or weatherstripping.
Castable urethane are available in wide range of hardness and chemical compositions. Castable urethanes are used when making rubber wheels and printing rolls. They have good toughness, tear resistance, high load bearing ability etc. They are usually processed by machine dispensing or hand mixing and pouring to a mold.
As a natural low-tech alternative to synthetic fuel-based rubbers are naturally rubber from rubber tree or Guayule. Guayule is a perennial woody shrub in the aster family and is native to the rangeland area of the Chihuahuan Desert. Natural rubber, ethanol and non-toxic adhesives can be extracted from it.
Next: Colorants