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.

CategorizationsEdit

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 behaviorEdit

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
 

ThermoplasticsEdit

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 gradeEdit

Amorphous & Semi-Crystalline propertiesEdit

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 materialsEdit
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 UseEdit

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 originEdit

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 homogeneityEdit

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 familyEdit

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).

  1. a b c 2019