Mechanical / thermal / chemical / moisture / electrical / biological / ageing / processing / optical / appearance / HSE / Price
Specifications and the choice of thermoplastic material
There is a wide range of thermoplastic materials with variants that has individual properties and price. For the non experts it is very easy to get lost and make the wrong choice of material.

Before selection of material it is important to map the properties required for the end product. Below we have made some examples of issues to be considered when a product specification profile is to be made.

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Mechanical
The mechanical properties for the different thermoplastics ranges from the stiff, brittle to the impact resistant, soft and flexible qualities etc. Thermoplastics can be used for many applications even where other materials as metal, three or rubber are used today. Doe to the fact that the properties for the different materials are widely spanned, it is very important in advance to map all the required mechanical properties.

 

Issues for a specification profile
static load dynamic load
load duration pressure
tension impact strain
elasticity hardness
vibration shape stability
abrasion damping

 

Aktuelle mekaniske egenskaper
density [g/cm3] hardness [Shore, Rockwell]
Brinell test of hardness [N/mm2] tensile strength [N/mm2]
tension elongation [%] flexural stress [N/mm2]
breaking strength [N/mm2] elongation at break [%]
elasticity module [N/mm2] brittle hardness [J/m]
friction coefficient wear [um/km]

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Thermal
Most thermoplastics will have a change to the mechanical and chemical properties with alternating temperatures. Ie in low temperatures soft profiles from PVC can become hard and brittle causing them to break by normal use. The defining of the products operating temperature is of great importance. If the product will be exposed to higher or lower temperatures for a shorter period, these temperatures and the duration of the exposure will need to be defined.

Thermal exposure must bee judged together with demand for mechanical and chemical properties, as they will change dependant on the temperatures.

Issues for a specification profile
maximum utility temperature maximum utility temperature, short duration
lowest utility temperature thermal conductivity

 

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Chemicals
Many thermoplastics has a excellent resistance to even strong chemicals. These properties does vary significantly within the different qualities. Swelling, disintegration, changes to the electrical properties, stress cracking etc can be the effect of exposure to chemicals.

If a product is to be exposed to chemicals, it is important to establish what type of chemicals this might be. The chemicals can typically range from acids basics, solvents to simple detergents.

For all the thermoplastics there are comprehensive documentation of the chemical resistance. Feel free to contact Parma Plast to find the ultimate material for your chemical environment.

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Moisture
Some of the thermoplastics will absorb water. Often this effect will not have any practical implications. There can be a negative effects or some products as shaft bushings, water sealing, or electrical insulation.

Specifications to be considered:

Issues for a specification profile
Type of moisture exposure Humidity
Barrier properties  

 

Other properties
Vannopptak [%]  

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Electrical
Many thermoplastics has good properties as an electrical insulator. Thermoplastics are commonly used for numerous electrical applications as insulation, encapsulations etc. As the electrical properties for some of the thermoplastics can change significantly exposed to humidity, the electrical specification will have to be clearly defined.

 

Issues for a specification profile
Insulating properties Dielectric properties

 

Issues for the electrical properties
Dielectric constant [Î r] Dielectric loss [tand ]
Dielectric strength [MV/m] Surface resistant [ohm]
Specific resistance [ohm cm]  

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Biologic environment
Thermoplastics can in certain environments as seawater, dirt, hot and humid etc. be exposed to microbes, fungi or other micro-organism that can attack or grow on the thermoplastics and hence change the materials properties.

There is additives to avoid or limit the microbe effect. Feel free to contact us for a discussion of your requirements.

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Ageing
Some thermoplastics can after some time in use become weakened by the influence of their environment. (For example temperatures, moisture, weather and wind, sunlight, microbes etc.) The thermoplastic can become yellow, brittle, and in time it might crack. Many of the thermoplastics can be used for out door applications in harsh environments over a long period of time without significant reduction of the physical properties by adding pigments with a good light-resistance, UV stabilisers etc. The exposure to sunlight or similar is important to specify.

Some combinations of materials in direct contact can have a mutual negative influence. Softeners in one material can migrate to the other material and in time create stress cracking.

Some additives is intended to migrate to prevent algae growth etc. on the surfaces. This type of additives will be consumed over time and they are a factor for the total lifetime of the material.

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Post processing
Plastic materials are very often post processed in some manner. The post processing can be varnishing, gluing, welding, drilling, milling, punching, polishing, laminating etc. It is highly recommended that the post processing is considered in the material specifications.

 

Issues for the specification profile
Mechanical machining (drilling, cutting, punching, milling, grinding etc) Gluing
Welding Surface treatment

Parma Plast will help directing you to the right process, joining methods, type of glue, welding temperatures etc.

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Optical
The transparency will vary with the different thermoplastics. Some are opaque (non transparent) and others are transparent but with individual clearness. Some materials will be more scratch resistant than others, some are impact resistant and expensive, while others are brittle and inexpensive. These product requirements should be considered:

 

Issues for a specification profile
opaque / transparent light passage
refraction index  

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Appearance
Thermoplastics can in addition to the geometric design be delivered with a variety of surface qualities. The surfaces can be dull, glossy or half glossy. Numerous additives for dying can be applied.

 

Issues for a specification profile
Surface quality Colour and structure.

A standardised code is used when specifying colours ie RAL or Pantone.

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HSE
In light of HSE there are some issues to be considered when choosing thermoplastic materials. One important issue is the fire technical properties as they are individual for the specific thermoplastic. Some are very combustible and some are very difficult to ignite. A fire in thermoplastics will often create much fumes. The most common combustion gas is carbon monoxides. Dependant on what plastic material that is burning, other toxic gasses like HCL, NO, HCN etc. can be emitted. Specifications for the material combustibility, fire propagation, fume emission and the toxicity of the combustion products should be considered. Many thermoplastics can be added fire-resistive components to make them more incombustible.

Materials to be in contact with food or to be used for children's toys etc are under strict regulations. A great choice of thermoplastic materials are already approved by authorities for contact with food.

Issues for a specification profile
Combustibility Fire propagation
Fume emission Toxicity of the combustion products
Decomposition properties Approval for nutritional use

 

Relevant properties
Oxygen index Combustion products

Parma Plast can supply HMS datasheets for all thermoplastics / products.

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Cost
It is important to establish the optimum relation between price and quality as the cost of the individual thermoplastic may vary significantly. To achieve this optimum relation it is recommended to focus on specifying the quality profile based on the input above. Your requirement profile will be carefully processed by Parma Plast in order to specify the material quality that will best meet your requirements. When the relevant thermoplastic materials are established they can be judged by price (for comparable volume). The presented register will explain the relations between the selected group of materials and is to be used as a guideline only. The individual materials will also have individual post-processing cost. This will not be reflected here.

Thermoplastics approximate prices

 

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