Polymers are a wide group of naturally created and synthetic substances constructed from large macromolecules. These macromolecules are generally repeating chains of smaller molecules or monomers. These long-chain chemicals are naturally and synthetically derived. They demonstrate a wide range of properties, fundamental chemistries, and applications that are key to all life and most human activities, ancient and modern. This article will discuss polymers, their properties, types, and applications.
What Is Polymer?
A polymer is a class of natural and synthetic substances composed of very large molecules. Natural polymers are the major building blocks of living organisms, including: proteins/polyamides, polynucleotides (RNA, DNA), and lignins (coniferyl alcohol compounds). Various natural and man-made minerals also qualify as polymers. These include: diamond, quartz, concrete, and silicone rubbers. Man-made polymers are a broad collection of diverse chemistries/monomers that are induced to catalyze by various means. These result in polymers as diverse as LSR (liquid silicone rubber) and LCP (liquid crystal polymer).
What Are the Other Terms for Polymers?
Polymers are also called plastics. This term derives from the highly plastic behavior of some of the earliest materials such as polyethylene, which can undergo very large plastic deformations under load before a fracture occurs. Polymers are also often referred to as resins (or synthetic resins) because of the natural tree resin origins of some of the (primitive) natural polymer materials used for thousands of years.
What Are Polymers Made Of?
Polymers are made of repeating steps of simpler compounds called monomers. Many chemicals have the potential to be polymerized into chains that make a material whose properties differ extremely from the monomer—these are polymers. Monomers can be organic chemical gases, oily liquids, amino acids, sugars, alcohols, and many more chemical types.
What Are the Properties of Polymers?
Polymer properties fall into a group of categories. Although, some polymers do not easily categorize and polar opposite properties can exist within a property class, from divergent materials. Discussed below are the mechanical, chemical, optical, and electrical properties of polymers:
What Are the Mechanical Properties of Polymers?
The mechanical properties of polymers are:
- Polymers have the ability to stretch and deform under load and recover unaltered when the load is removed. Most polymers show some elastic behavior; some are extremely elastic.
- Polymers have the ability to permanently or viscously stretch and deform under load. Some polymers are crystalline and brittle, however.
- Polymers cover a spectrum of strengths from almost liquid to near-light-metal strengths. Natural polymers generally have low strength, when compared with synthetic resins.
What Are the Chemical Properties of Polymers?
The chemical properties of polymers are:
- Many polymers are highly durable molecules that are resistant to many or all forms of natural, environmental, and chemical degradation. Others, particularly natural polymers, are extremely delicate and fragile. Many polymers are susceptible to organic acids, triggering depolymerization and breakdown. Other polymers are highly soluble in organic solvents such as chloroform, acetone, alcohols, etc.
- Most synthetic polymers are hydrophobic to some degree, although some are soluble in water, which can be a useful property. Many natural polymers are hydrophilic and affected by water, though rarely fully soluble.
What Are the Optical Properties of Polymers?
The optical properties of polymers are:
- Polymers range from highly amorphous to highly crystalline.
- Crystalline polymers are generally opaque at optical frequencies.
- Amorphous polymers are often transparent at visible light frequencies. Transparency in amorphous polymers varies from cloudy/colored translucency to glass-like transparency.
- Biaxial stretching can induce transparency in various polymers that are not naturally transparent.
What Are the Electrical Properties of Polymers?
Almost no polymers are naturally conductive. Many are highly effective dielectrics that are widely used in the electricity and electronics sectors for isolators and insulators. High breakdown voltages predominate in polymers. A few polymers have shown unusual electrical properties including: poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)), polyacetylene (PA), polyaniline (PANI), and polypyrrole (PPy).
What Are the Types of Polymers?
Polymers generally fall into large families, with some exceptions that are isolated chemically and unrelated to any of the families. The general types of polymers are natural polymers and synthetic polymers.
Natural Polymers
Natural polymers vary significantly by source. In their natural state, there can be many variants within a nomenclature that are closely related but can be differentiated by small properties and chemical identifiers. Some of the natural polymers are listed below:
1. Cellulose in Paper and Trees
Cellulose in the cell walls of fibrous growth is a toughening/stiffening agent that gives cells bulk and allows them to contribute to building tall and strong structures in plants. Various types of cellulose are differentiated by the plant source. Once extracted and refined, the raw material loses much of its variety and can be treated as a uniform material.
2. Starches in Plants Such As Potatoes and Maize
Starches are abundant biopolymeric materials. They are used in plants to store energy in a water-stable form, consisting of α-glucose polymers. Natural starches show poor strength and thermal stability. When extracted and purified, starches can be used as organic feedstock to manufacture bio-sourced polymers such as polylactic acid (PLA). They can also be used as feedstock for industrial alcohol production, which can then be used in the manufacture of alcohol-based polymers such as polyvinyl alcohol, and PVA.
3. Proteins, Such As Hair, Nails, Tortoiseshell
The protein from hair/shell, etc. is generally keratin. This can be dissolved by a variety of methods, to make feedstock for bio-sourced polymers, often including cellulose as a modifier. Large source keratin materials have long been used as-is as viable materials for product making: tortoiseshells and horns for combs, spectacle frames (horn rims), and decorative objects. Cow horns were traditionally used for waterproof storage (gunpowder) and as drinking vessels.
4. Wool From Animals
Wools are an excellent source of high-quality keratin. They are used as feedstock for several biosource polymers such as keratin dialysate and photoactive keratin films (combined with methylene blue) and are being used in medical applications.
5. Silk From Insects
Silk from the silkworm has long been known as a strong material. It is now understood to be made from two proteins: sericin and fibroin. Spider silk is similar, constructed from alanine and glycine. It is impossible to harvest in useful quantities, but the synthesis of similar materials from plant source matter is suggesting the development of bulk polymers that may be applicable to single-use plastic applications.
6. DNA
DNA (and RNA) are by nature long-chain polymers made of short proteins (amino acids).
7. Pitch or Tar
Pitch/tar/asphalt/bitumen is a family of viscoelastic materials. They are both natural and synthetic, are thermoplastic polymers, and have wide applications.
8. Natural Rubber and Lacquer
Natural rubbers are derived from the sap of a range of plants and exist as a method for carrying nutrients and fluids in the plant. They have another valuable property which is their hardening when exposed to air. They form a natural and waterproof/infection-proof barrier when the plant is injured. It is in this state that the natural monomer forms a natural polymer: latex.
Latex is exploited in various forms to make rubber compounds to promote aggressive cross-linking and greater chemical stability. Lacquers such as shellac are derived from the excretion of beetles. They can be dissolved in various solvents to make them applicable as coatings. As the solvent evaporates, the lacquer hardens.
Synthetic Polymers
Synthetic polymers are materials that are engineered for particular properties and industrially polymerized, from synthesized and natural monomers. The polymerizations can require high pressures and temperatures, catalysts, energetic reactions, and large industrial plants in many cases. Listed below are some examples of synthetic polymers:
1. Nylon
Nylons vary in the manufacturing method, molecular weight, and precise monomer class but they are all polymer chains constructed from polyamides. They are tough and chemically resilient engineering polymers with relatively poor cosmetics and a slippery, low-energy surface. Most nylon is manufactured as fibers for clothing, ropes, and webbing.
2. Polyethylene
Polyethylenes, like the nylons, are differentiated by molecular weight. The differences are generally related to the degree and complexity of side branching in the chains. The monomer is solely ethylene gas. Polythenes range from soft low density (plastic bag) material to UHMW (ultra-high molecular weight) engineering grades. Polythene is used for food containers, pipes, and engineering parts. For more information, see our guide on Polyethylene.
3. Polyester
Polyesters are generally amorphous materials, used as fibers and films. These are among the most widely used synthetic polymers. For more information, see our guide on Polyester.
4. Teflon™
PTFE, polytetrafluoroethylene is an advanced synthetic polymer based on fluorines and is representative of a larger family of related polymers. These materials have very low surface energy, making them ideal for applications where chemical and abrasion resistance are critical.
5. Epoxy
Epoxy resins are generally two-part materials that either co-polymerize when mixed, or undergo a catalytic reaction triggered by one part upon the other. Epoxies are thermoset polymers that are self-catalyzing and formed/applied as liquids that harden and hold their shape as firm (usually hard) solids.
6. Silicone
Silicone rubbers are mostly made as two-part, thermoset polymers that undergo a catalytic reaction when mixed. The resultant materials are generally elastomers, with low to moderate tear resilience but high compressive strength. They’re capable of withstanding high temperatures—up to 300 °C in some cases. For more information, see our guide on Silicone.
7. Slime
Slime is an unusual material that uses borax as a cross-linking agent. It transforms PVA (polyvinyl acetate) into a stable and super elastic material that behaves as both a fluid and a solid. When mixed with glue, borate activator ions cross-link with the glue’s protein molecules, turning them into larger molecules that find it more difficult to slide past each other. You have now made a new polymer. This makes slime very sensitive to strain rate. It allows the display of brittle behavior, despite being almost a liquid.
8. Polystyrene
Polystyrene (PS) is a very widely used polymer with very useful properties. It can be foamed (with a refrigerant gas) to make a soft, fragile but highly shock-resilient and insulating material (expanded PS). It can be used without copolymerization as a low-cost, somewhat brittle transparent solid. And it can be alloyed with synthetic rubbers (acrylonitrile and butadiene) to make an opaque, rigid, and strong polymer, ABS, with a near-universal application. For more information, see our guide on Polystyrene.
What Are the Applications of Polymers?
The applications of polymers are listed below:
1. Clothing
Polymers are widely used in synthetic fiber manufacture for textiles, for diverse uses. Examples of polymers used in clothing are: nylon, aramid, polyester (PET), and PVA.
2. Money
Various countries have moved away from paper currency and now manufacture money from polymer films, generally polypropylene. This is a growing trend as it makes currency that serves for longer, stays cleaner, and isn’t implicated in contamination and poisonings.
3. Personal Protective Equipment
Disposable smocks, shoe covers, and coveralls are generally made from non-woven polypropylene fabrics. Disposable gloves are made from latex or nitrile rubber. Filter masks are made from a wide range of polymer fibers and non-woven polymer fabrics. Face shields are generally made from assorted polymers, with the transparent part being PET.
4. Medical Applications
The medical applications for polymers are wide-ranging. Examples are: natural polymers for drug delivery systems, bioinert synthetic polymers for stents, and single-use devices for blood collection/diagnostics.
5. Household Items
Polymers of various types are widely used in the typical developed-world home. Examples are: polyethylene food containers, ABS knife handles, films for food covering, and heat-resistant seals for oven doors.
6. Car Parts
The automotive sector uses polymers in most areas. Some examples are: brake reservoirs, suspension bladders, door handles, and bumpers.
7. Paints
Many paints are based on polymers. Acrylics are widely used, as are alkyd resins as well as natural and synthetic resins in varnish.
8. Glues
Glues are one of the earliest broad uses for natural polymers. They are made from hoof (keratin), fish waste (proteins), and tree sap (pitch). Synthetic substitutes range from polyvinyl acetate to polyester resins, and cyanoacrylates to polyurethane.
9. Lubricants
Several synthetic polymers have very low surface energy combined with toughness. This makes them slippery and strong (self-lubricating). PE, nylon, and POM are extensively used as bearing materials.
10. Constructions
Polymers are widely used in construction as adhesives, concrete modifiers, roofing materials (bitumen), window frames, and seals.
11. Packaging and Containers
Various synthetic polymers are widely used in packaging as rigid and film materials. Examples are: PET, PP, PS, and paper (cellulose).
12. Electronics
Large numbers of polymers serve a range of purposes in electronics. These include: dielectrics, component enclosures, coatings, circuit boards, wire insulators, and structural parts.
What Are the Advantages of Polymers?
The advantages of polymers are listed below:
- Easy and well-understood processing methods.
- Generally low cost of materials.
- Potential for high strength.
- High elasticity.
- Chemical stability.
- Thermal stability.
- Great cosmetic quality.
What Are the Disadvantages of Polymers?
The disadvantages of polymers are:
- Low tensile strength.
- Ductility and plasticity under load.
- Thermal sensitivity.
- Chemical sensitivity.
- Poor abrasion resilience.
- Environmental burden.
Are Polymers Biodegradable?
It depends. Natural polymers are almost all biodegradable, though some, such as amber, are durable. Few synthetic polymers are highly biodegradable, though many newly developed materials aim for biodegradability or compostability. Half-lives for synthetic polymers depend on the type of attack, but in landfill, this can be decades or centuries in some cases.
Are Polymers Water Soluble?
Yes, polymers are water-soluble. Most natural and some synthetic polymers are soluble in water. Other natural polymers are hygroscopic or softened by water absorption. Some synthetic polymers absorb moisture and nylon actually requires up to 8% water to reduce brittleness.
Are Polymers Elastic?
Yes, polymers are elastic. The most elastic polymers are natural and synthetic rubbers, offering a huge elastic extension of several hundred percent in some cases. Many polymers have very high structural integrity and low distortion under loads, making them both elastic and stiff.
What Are the Differences Between Polymer and Plastic?
All plastics are polymers, but not all polymers are plastics. Plastics refers to synthetic polymers that are rigid, semi-rigid, elastic, and made of long-chain polymeric molecules. Polymers are a much broader family, including materials that seem to have no relationship to plastics.
What Are the Differences Between Polymers and Metals?
Polymers are complex chemicals. They are mainly constructed from organic chemicals, though a few synthetic and natural polymers have essentially mineral origins. Metals are generally atomic in nature—forming crystalline microstructures that make their properties varied according to processing methods. Polymers are generally much weaker than metals, though weak metals (lead, antimony, etc.) can be considerably weaker than stronger polymers (POM, nylon, etc.).
Summary
This article presented polymers, explained what it is, and discussed its various applications. To learn more about polymers, contact a Xometry representative.
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