Plastic materials are generally considered all the polymers based on chains of molecules mainly based on carbonium and hydrogen atoms. There is a very wide variety of plastics, from several points of view: mechanical, thermal, electrical, aesthetical, processing method.
The first level of distinction from the industrial point of view is the thermal behavior: thermoplastics are generally injection moulded, while thermosets are compressed and shaped.
Categorizations
The thermoplastic polymers can be catgorized by several point of views:
- Thermal behavior
- Crystalline grade (amorphous or semi-crystalline)
- Use (commodity polymers, technopolymers, super-polymers)
- Origin (fossil chemical synthesis, biological chemical synthesis, recycling)
- Homogeneity (omopolymer, copolymer)
- Molecular family (polyolephins, poliammides, etc.)
Thermal behavior
All type of plastics are divided into three major type of materials:
| Thermoplastic | Thermoset | Elastomer |
|---|---|---|
| The polymers are formed of chains which formed two types of structure namely amorphous and semi crystalline. Once the polymer is formed, thermoplastic can be reused over and over again. No strong chemical bonds exist among chains. | The polymers are cross linked and undergoes both physical and chemical changes when heated. Once polymer is formed, it cannot be melted to be remolded | The polymers had rubber-like properties with elangation up to 100% or more |
 |
Thermoplastics
A thermoplastic is a type of plastic made from polymer resins that becomes a homogenized liquid when heated and hard when cooled. When frozen, however, a thermoplastic becomes glass-like and subject to fracture. These characteristics, which lend the material its name, are reversible. That is, it can be reheated, reshaped, and frozen repeatedly. This quality also makes thermoplastics recyclable.
There are dozens of kinds of thermoplastics, with each type varying in crystalline organization and density. Some types that are commonly produced today are polypropylene, polyethylene, polyvinylchloride, polystyrene, polyethylenetheraphthalate and polycarbonate.
Crystalline grade
Amorphous & Semi-Crystalline properties
| Amorphous | Semi-crystalline |
|---|---|
| Low mold shrinkage | Higher mold shrinkage |
| Limited chemical resistance | Good chemical resistance |
| High coefficient of friction | Example |
| Can be tough and brittle | Tough |
Amorphous & Semi-Crystalline materials
| Amorphous | Semi-crystalline | |
|---|---|---|
| ABS | Acetal | |
| Acrylic | Cellulose butyrate | |
| Cellulose propionate | Liquid crystal polymer (LCP) | |
| Polyamide-imide | Nylon | |
| Polyarylate | Polyester (PBT) | |
| Polycarbonate | Polyetheretherketone (PEEK) | |
| Polyetherimide | Polyethylene | |
| Polyethersulfone | Polyethylene terephthalate (PET) | |
| Polyphenylene oxide | Polyphenylene sulfide | |
| Polystyrene | Polypropylene | |
| Polyurethane | - | |
| Polyvinyl chloride (PVC) | - | |
Categorization based on Use
| Commodity | Technopolymers | Super-polymers |
|---|---|---|
| Low cost/volume (1€/kg[1]) | Medium cost/volume (2-4 €/kg[1]) | High cost/volume (4-30€/kg[1]) |
| Low processing temperature
(180-240°C) |
Medium processing temperature
(250-320°C) |
High processing temperature
(280-400°C) |
| Low processing cost and complexity | Medium processing cost and complexity | High processing cost and complexity |
| Examples: LDPE, PP, PS, ABS, PVC,
PET |
Examples: PA, PC, POM, PBT | Examples: PEEK, PPSU, PBI |
Categorization based on origin
| Chemical synthesis by fossils | Chemical synthesis by biologicals | Recycling |
|---|---|---|
| Originated from fossil oil, natural gas
or coal |
Originated from agricultural production
or scrapped materials |
Originated from plastics recycled from
industry or individuals |
| High envoironmental impact | Low envoironmental impact and
eventually biodegradable |
Medium-low envoironmental impact |
| High homogeneity and properties
stability, full variety of grades |
Medium homogeneity and stability,
generally limited to low mechanical properties |
Medium-low homogeneity and low property
stability (especially for individuals recycling waste collection), dark color |
Categorization based on homogeneity
| Homopolymer | Copolymer |
|---|---|
| One only polymer type | Two or more polymer types |
| Typically strictly fixed
properties |
Smoothened properties |
| Examples: PP-homo | Examples: PP-copo (99% PP + 1% LDPE) |
Categorization based on molecular family
The most common and clear way of describing a material is to use its molecular family, that describes most of the properties of it within a defined window. This is happening because most of the properties are given by the properties of the monomer and how it tends to link with the composants of the same chain and its counterparts on other chains.
For example the family of polyammides contains PA6, PA66, PA12: all of them have very good mechanical properties, similar behavior with chemical agents, etc. that can be clearly distinguished from those of the polyethilene family (LDPE, HDPE).