Formulating Thermoplastic Compounds

A Basic Introduction to Formulating Thermoplastic Compounds.

In order to achieve the right aesthetics and mechanical performance for any plastic article it’s important to design the most cost- effective formula.
The first task is to choose the most suitable polymer for the application. The properties of Thermoplastics can be very diverse, and pricing can vary tremendously, especially for some of the more exotic high-performance polymers.

Thermoplastics can generally be classified into three groups, Commodity grades, Engineering grades and High-Performance grades.

Commodity grades- Are thermoplastics made in vast quantities for applications where exceptional mechanical properties are not generally required. E.g., Milk bottles, Food Packaging, Carrier bags, Household products etc. Costs for these types of polymers are generally cheaper when compared to engineering plastics and high-performance grades.

Polyethylene, Polypropylene, PVC, Polyethylene Terephthalate(PET) and Polystyrene are some good examples of commodity grades.

Engineering grades- The mechanical properties of these types of thermoplastics are generally superior to commodity grades. Certain grades can handle heat and stress well, when in use, and because of their high mechanical strength can often be used as metal replacements. The Automotive, Aerospace, Building Construction and Electronics industries all benefit from the use of these types of polymers.

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Acrylonitrile Butadiene Styrene (ABS), Polycarbonate, Polyamides (Nylon) are some of the more common engineering grades.

High-Performance grades- Thermoplastics that fall into this group have a variety of exceptional properties. Their ability to withstand high temperatures, chemical attack and their excellent mechanical strength make them ideal candidates for use within the Aerospace, Automotive and Electronics industries. Some good examples of high- performance grades are Poly Ether Ketone (PEEK), Polysulfone (PSU), and Polyphenylene Sulfide (PPS)

When the polymer with the most suitable properties has been selected for the end article, further modifications can be made during a compounding process. This often involves the addition of colourants and or additives and fillers to achieve the desired look and finished product properties.

When it comes to colouring thermoplastics compounds, care must be taken to ensure the colourants selected for the formula, are compatible with the chosen polymer, and that their properties such as heat stability, light and weather fastness are all at the desired level to suit the end application.

Performance enhancing additives can also be compounded into the polymer of choice to further enhance their outdoor UV performance, Antistatic properties, Conductivity, Surface Frictional properties, Antimicrobial, Flame Retardancy, Heat Stability, etc.

Fillers are often added to thermoplastic compounds to drastically modify the mechanical/performance properties or aesthetics required for the end article. The most commonly used fillers are; Magnesium Silicate (Talc) Calcium Carbonate (Chalk) Mica, Glass fiber or beads, Aluminum Trihydrate, Magnesium Hydroxide, these last two fillers are specifically used to improve flame retardancy. The other fillers are mainly used to improve stiffness, mechanical strength, surface hardness, or change visual appearance.

Fully formulated compounds tend to be used for applications where the technical properties are paramount. They just need to be processed as supplied under the recommended processing conditions. Flame retardant compounds, Talc/Chalk/Glass filled compound and Conductive compounds are some of the most common grades supplied to the end converters.

There is another process whereby natural thermoplastic polymers can be modified and that’s by using a masterbatch. A masterbatch is a concentration of colourants, additives or a combination of both that’s added into the natural polymer during processing at a specified addition rate. Whilst this method is often cheaper than the fully compounded route, the end converter must ensure that he uses the recommended addition rate, and that their equipment is fully capable of achieving a homogenous mix. Failure to achieve this can lead to mechanical failures and inconsistencies in the colour appearance.

Polymer chemists, Plastic engineers and experienced Colour Chemists should always be consulted when designing plastic applications in order for the right solution to be reached.

Author: 

Pravin S Mistry - Global CEO of PREA Ltd and International Polymer Consultancy - Plastics, Composites, Rubber, Adhesives, Polyurethane... focuses globally on:

• Mergers & Acquisitions, buying selling companies
• Recruitment- Full time and Interim
• Interim CEO / MD
• Polymer Consultancy
   

He personally has worked for over 40 years in the industry - UK, USA, Mainland Europe, Asia... in the polymer other manufacturing industries as Divisional Managing Director and CEO for multinational companies. Early career roles include Operations Director, Technical Director, Technical Quality Manager , Chemical Engineer, Laboratory Technician.

Thermoplastic Elastomers or TPEs combine the look and feel of a thermosetting elastomer with the processing power of thermoplastics. While elastomers are employed when flexibility is a primary concern, thermoplastic uses are broader and place more emphasis on the specific material’s properties. However, with the right process of injection molding or extrusion, manufacturers can create flexible materials that also take on important thermoplastic-type properties. This is a major advantage of TPE materials.

Uses of thermoplastic elastomers vary between industries. It’s important to pick a TPE material that is compatible with the application where it will be used.

This article will review 7 uses of thermoplastic elastomers, review their advantages, and examine how they’re processed. The table below shows some of the common uses of TPE:

1. Thermoplastic Elastomers is Used For Automotive Parts

Many automotive parts are made of thermoplastic elastomers. They find their way into seats and interiors, weather seals, and floor mats, among other things. TPEs are ideal for automobiles due to their excellent wear, chemical, and electrical resistance characteristics. Additionally, environmental resilience and UV stability make TPE highly desirable for use in cars since it won’t degrade in direct sunlight.

2. Thermoplastic Elastomers is Used in Construction Materials

In construction, TPEs are used in the form of extruded weather seals for doors and windows as well as other seals such as glazing and pipe seals. TPEs are great for these applications due to their chemical and environmental resilience and their durability and flexibility.

3. Thermoplastic Elastomers is Used in Industrial Applications

TPEs are used in industrial applications, especially to create seals and reduce vibration. Uses include: vibration isolators, springs and shock absorbers, drum suspension bushes, and seals and O-rings. TPEs are ideal for these applications due to their excellent damping ability. 

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4. Thermoplastic Elastomers is Used in Consumer Products

In consumer products, TPEs are often co-injected with a separate plastic material or over-molded onto a substrate. They’re found in power tool grips, remote controls, mobile covers, magnetic seals in refrigerators, and shock-absorbing components for vacuum cleaners. TPEs can be used in various consumer products due to their durability, flexibility, ease of molding, and chemical resistance.

5. Thermoplastic Elastomers is Used in Medical Supplies

Supplies such as breathing tubes, syringe tips, catheters, and masks often contain TPEs. These materials see wide use in medical settings because of their excellent chemical resistance, biocompatibility, flexibility, and lightweight.

6. Thermoplastic Elastomers is Used in Electronic Devices

TPE materials often show up in condensers, casings for plugs and sockets, cables, and smartphone components. They are ideal for such applications because they’re not conductive and are easy to mold.

TPEs are used in shoe soles and various sporting goods including: ski equipment (pole handles, boots) and diving equipment (flippers, masks, and snorkels). The low density, flexibility, and abrasion resistance of TPEs make them great options for footwear and sporting goods.

When Do You Use Thermoplastic Elastomers?

TPEs are used in applications where flexibility is desirable. Many thermoplastics are far more rigid than TPEs and simply don’t fit the bill for soft or flexible components. This is where TPEs shine. Additionally, TPEs are used in applications where chemical, environmental, and abrasion resistance are important. 

For more information, see our guide on thermoplastic elastomer.

Where Can Thermoplastic Elastomers Be Used as an Alternative?

TPEs can be substituted in place of materials like silicone, latex, and PVC compounds. Comparatively, TPEs are cheaper to manufacture but exhibit similar characteristics - specifically flexibility and durometer rating. Silicone, latex, and PVC compounds are tedious to turn into products. These materials often require additives along with extra time to allow the material to cure in a mold. Additionally, since TPEs can be formed through automated processes such as injection molding or extrusion, they are easier to mass-produce.

What Is the Most Common Thermoplastic Elastomer Production Method?

Injection molding and extrusion are the most popular methods for processing TPEs. However, blow molding, thermoforming, and 3D printing are also viable options. Unlike silicone, latex, and PVC compounds, TPE doesn’t require additional stabilizers, reinforcing agents, or cure systems. Therefore, TPEs function well for large-volume injection molding or extrusion runs.

For more information see our guide on the Types of Thermoplastic Elastomers (TPEs).

How Is Thermoplastic Elastomer Processed Before Being Used?

Unlike silicone, latex, and PVC compounds, TPE processing doesn’t require additives to help it set and cure. However, some TPE materials must be sufficiently dried before processing. Drying TPE ensures that excess moisture doesn’t hinder manufacturing or affect the final material’s properties. Refer to the material data sheet for each individual resin to determine drying temperatures and times.

What Are the Advantages of Using Thermoplastic Elastomers?

Perhaps the greatest advantage of TPE is that it exhibits characteristics of thermosetting rubber but can be formed using the same processes used for thermoplastics. TPE is lightweight and exhibits excellent material properties that make it ideal for certain applications. It is also cheaper to process than the materials it typically replaces such as silicone, latex, and PVC compounds. TPE is easy to color or dye, making it attractive for customer-facing parts.

For more information see our guide on the Advantages of Using Thermoplastic Elastomers.

What Are the Disadvantages of Using Thermoplastic Elastomers?

Disadvantages of thermoplastic elastomers include sensitivity to shear forces, low resistance to odors, and, in some cases, price. TPEs can be more expensive than thermoset rubbers. Additionally, their low melting temperature makes TPE materials unusable in high-heat applications.