What is the difference between thermoplastics and thermosets?

Among many types of plastics divided into several families, we can divide them into two categories: thermoplastics and thermosets. Since some plastics belong to the two categories depending on the modifications made in the initial chemical structure.

Thermosets

They are curing resins, much used in crafts such as polyester resin, or in small maintenance in civil construction such as epoxy resin.

After polymerization and rigid, this resin does not return to its original state, that is, it does not soften even with the heat - it is the so-called "cure", an attempt to heat the thermoset in order to fuse it fatally will lead to degradation. The cure is an irreversible chemical reaction called reticulating, also known by the term crosslinking; and occurs more easily and quickly in the presence of heat and may occur at room temperature. It is noteworthy that this type of reaction is exothermic (releases heat), so even at room temperature the heating of the plastic material occurs naturally.

The crosslinking that occurs during the reaction is caused by the bonding of atoms between / through two linear polymers, resulting in a rigid three-dimensional chemical structure. In the figure below it is possible to see an example of a polymerization reaction of styrene-polyester copolymer, used in craftwork.

Crosslinking reaction
The thermosets as well as the thermoplastics can be fiber reinforced and loaded with other fillers. They are quite rigid even without the addition of reinforcements, however, it is that story of glass: the harder the more fragile; making them to be used in more specific applications such as where thermoplastics do not withstand heat and in exclusively manual work applications. In addition, the fact that the thermoset cannot be reprocessed adds a further disadvantage, with waste destined for the production of loads in the form of powder.

Thermoplastics

Unlike thermosets, thermoplastics do not cure and can be easily melted with heat (between 135° C and 250°C [275°F and 482°F] depending on the polymer) and cured again with cooling at room temperature. They can be reprocessed several times, but obviously, they lose properties at each recycling and can also degrade due to the high number of re-cycles.

Compared to thermosets, they have much lower thermal and dimensional stability, but have a much easier and economical processability.

Below is a table with examples of the main families of polymers, thermoplastics and thermosets, their best-known trade names and manufacturing companies.

THERMOSETS
Family Commercial name Manufacturer
Alkyds Uradil DSM
Epoxies D.E.R. Dow
Araldite Huntsman Advanced Materials
Phenolic Bakelite Union Carbide
Diallyl Phthalate (DAP) Daiso DAP Daiso
Melanins Cymel Allnex
Polybutadienes Ricon Total Cray Valley
Polyesters Laminac Island Pyrochemical Industries
Paraplex Rohm and Haas
Silicones Xiameter Dow Corning
Ureas Urecoll Basf
THERMOPLASTICS
Family/Polymer Commercial name Manufacturer
ABS Terluran Styrolution
Acetalics Delrin DuPont
Acrylics Plexiglas Evonik
Aramids Nomex DuPont
Cellulosics Tenite Eastman Chemical
Ethocel Dow
Ionomers Surlyn DuPont
Polyamides (Nylons) Zytel DuPont
Technyl Solvay
Polycarbonates Lexan Sabic
Polyesters (PBT) Valox Sabic
Celanex Celanese

Bibliography:
HARPER, Charles A.; PETRIE, Edward M. Plastics Materials and Process: A Concise Encyclopedia. Hoboken: John Wiley & Sons, Inc., 2003.
WIEBECK, Hélio; HARADA, Júlio. Plásticos de Engenharia: Tecnologia e Aplicações. São Paulo: Artliber Editora, 2005.
Article posted in May 25, 2017
About the author: Daniel Tietz Roda is Plastics Technologist graduated from the FATEC/ZL and Mechanical Design Technician from ETEC Aprígio Gonzaga, in São Paulo, Brazil. Roda worked 5 years with technical assistance and development of plastics in industries and nowadays is the publisher of this website.
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