Plastics Molding & Manufacturing/Plastic Charactheristic

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 categorized 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)	Medium cost/volume (2-4 €/kg)	High cost/volume (4-30€/kg)
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 polyethylene family (LDPE, HDPE).