Minerals in plastic

Minerals in plastics are used both as a filler and to impart strength, anticorrosion and fire retardant properties, particularly in the packaging, construction, automotive and healthcare sectors.

There are a number of different polymeric resins filled or reinforced by industrial minerals, such as talc and calcium. Rigid polyvinyl chloride (PVC) and polypropylene (PP) are two resins that account for the bulk of mineral consumption by the industry.

Industrial minerals are also used in polyamide, unsaturated polyesters, high density poly ethelene (HDPE) and low density poly ethaline (LDPE), in addition to talc and silica used in the compounding and manufacture of rubber goods for anti-sticking or reinforcing. The most commonly used minerals in plastics are calcium carbonate, talc, wollastonite, kaolin and mica, in addition to lesser used minerals like silica, huntite and magnetite. 

Plastics in packaging

Historically, packaging has consumed a number of different materials including metal, glass and paper; however, plastic packaging has dominated the sector and is the largest market for plastic resins, according to the American Chemistry Council.

According to the US Plastics Industry Trade Association: "The ability to meet unique packaging needs – from antistatic protective packaging for electronic components to shelf-able containers for food products that once required costly cold storage – make plastics the hands down preference for just about every form of packaging."

With the world’s population expected to reach around nine billion by 2050, the size of the plastic packaging consumer base is projected to grow for at least the next 40 years. Reports agency Research and Markets figures indicate that the global plastic packaging industry grew by a compound annual growth rate (CAGR) of around 7.2% between 2001 and 2010, making it the fastest growing segment in packaging. Meanwhile, figures from research group Smithers Pira indicate that rigid and flexible plastics will experience the highest growth, at around 4% of all plastics materials in 2016. 

Bioplastics are a newcomer into the plastics sector, owing to increased focus on sustainability, according to the Plastics Industry Trade Association, and currently account for less than 1% of total global plastics use. The European Bioplastics Association estimates that global bioplastic production will increase from 1.7m tonnes in 2015 to 7.8m tonnes by 2019, but for now, conventional plastics remain an economical choice for packaging.

"Plastic containers, which generally require less energy to manufacture than other packaging, also require less fuel to transport than other packaging materials that are invariably heavier and more bulky," the Plastics Industry Trade Association noted in its latest Plastics Market Watch report, published at the end of 2015. 

The construction industry is the second largest consumer of plastics, second only to packaging. 

While wood and metal remain staples in construction, the properties imparted by plastic, such as strength and corrosion resistance, mean the materials are used in a number of different construction end markets. Aside from these positive attributes, plastics are also used in construction to make buildings more airtight, durable, water resistant and less expensive to build, maintain and operate.

Plastic’s applications in construction include roofing, insulation, wall coverings, windows, piping, composite planks and rails, and plastic house wrap. 

While the building sector has not yet fully recovered from the downturn, the construction sector in the US is on an upswing.

"Worldwide economic conditions, the prospect of an interest rate hike and an acute labour shortage appear to be the major clouds on an otherwise sunny horizon," the Plastics Industry Trade Association said in its construction report at the start of this year. 

The aeronautic and automotive sectors are also major consumers of minerals in plastics, with new developments and technologies in car production driving growth. Figures from the Plastics Industry Trade Association indicate that while automobile and light truck sales have not exceeded record highs seen in 2001, the increase of automobiles sold – from 10.4m units in 2009, to 16.8m units in 2015 – in the US reflects an uptick in the sector. Global automobile and truck manufacture in 2014 was just over 87m and was expected to end 2015 at 91.2m. This, coupled with China’s aim to produce over 100m vehicles annually, represents a large growth market for plastics. 

Talc is one of the most commonly used minerals in plastic production and major producers include Mondo Minerals, Minerals Technologies Inc. and Imerys Talc. Not limited to one industry, talc can be used in automotive plastics, household appliances, construction and in food packaging.

More than just a filler mineral, highly pure, laminar talc can enhance the performance of polyolefin compounds such as PP. In PP pipes, talc increases rigidity, creep strength and impact resistance, making it an environmentally friendly alternative to PVC.

Properties imparted by talc when used as a filler:

• Increased modulus of elasticity and stiffness of structures, the main function of talc in plastic.

• Fine talc increases impact resistance in polypropylene bumpers.

• Increased dimensional stability.

• Colour consistency in dyed PP compounds particularly with highly purified talc. 

• Increased scratch resistance by reducing mechanical scratch impact.

• Higher production rates as heating and cooling of compounds is accelerated. 

• Low abrasion due to mineral softness.

• Prevents deformation by increasing creep strength.

 Calcium carbonate 

Calcium carbonate is one of the most commonly used filler minerals in plastics. When its particle size is controlled, it can be used to increase strength and stiffness. Precipitated calcium carbonate (PCC) is a functional additive in plastics, which increases impact strength in rigid PVC resin systems. Its uses include window profiles, fencing, siding, thermoforming, calendared stock and foamed PVC. It is also used in unsaturated polyester for thickening and gloss production. Ground calcium carbonate (GCC) and ground dolomite are used for resin extension and economy. 

Calcium carbonate-containing PVC compounds are used in a myriad of products in a range of industries, including as tubing, wire and cable insulation, latex gloves, bin bags and compounds such as extruded pipes, conduits and window profiles.

Another common mineral used in plastics is wollastonite, which, due to its acicular structure, provides an increase in flexural modulus, scratch resistance and heat distortion temperature, while reducing negative attributes such as shrinkage.

Used also for its reinforcement properties, thermal stability and chemical purity, fine particle sized wollastonite imparts a balance of impact strength, high elongation and polymer structure rigidity.

According to major producer NYCO, new ultrafine high strength reinforcements offer compounders weight reduction to achieve lower density composites. Production of the mineral in North America is dominated by a handful of suppliers, particularly after the purchase of Rock Minerals Inc., NYCO’s parent company, by S&B, which was later bought by French industrial minerals producer, Imerys SA. Privately-owned Canadian Wollastonite also began production in 2012 and while the company does not currently supply to the plastics industry, it is working on the development of new end markets. 

Zeolite

Natural zeolite can be used as a filler in plastic, masterbatch or compounds for the reduction of smell and odour, reduction of volatile organic compounds (VOC) and increased breathability.  

Huntite and hydromagnesite

Huntite and hydromagnesite are used as flame retardant fillers in both plastics and rubber. Heat causes the material to break down and release carbon dioxide at temperatures above 220°C, which takes in heat and helps to cool the burning material, slowing the spread of a fire. Substitutes for huntite in plastics include aluminium hydroxide, which is more commonly used. According to LKAB, whose US locations are a significant supplier of the mineral to the plastics sector, the fine and platy crystal structure of huntite improves the stability and the strength of char which is formed by the burning of polymers or rubber, reducing the risk of the spread of fire from droplets of molten material. 

Owing to their unique rheology – the response of soft solids with plastic flow – huntite and hydromagnesite can also be used as rheological modifiers in polymer products like sealants, as their chemical composition makes both minerals efficient acid scavengers in pH-sensitive polymer systems

Magnetite

Currently, LKAB is proceeding with R&D into the use of magnetite in plastic equipment used in the food processing industry. When used as a filler in plastics, the mineral’s properties enable the detection of plastic parts contaminating food. The company has been working with partners to incorporate magnetite-based material into plastic parts used in food industry processing equipment, which allows for the tracing of plastic parts.

While contamination of food by metal is easily detected by x-ray, plastic contamination is more difficult to determine, according to LKAB. Magnetite’s high density and ferrimagnetism are properties that make it traceable using either x-ray or metal detectors such as high frequency coil.

As it is non-toxic, magnetite is ideal for use in food processing applications and passes both US Food and Drug Administration (FDA) and European Commission (EC) requirements. 

In more conventional applications, while magnetite has been used as a refractory mineral for the iron and steel industry for some time, more recently, the mineral has been adapted for use as a functional filler for a number of sectors. One of these is the automotive industry, where the mineral provides damping characteristics to automotive moulded parts and foams.

A growing future for minerals

While plastic consumption has not escaped the global downturn, plastic uptake across a number of end use sectors has been increasing and will likely continue to exhibit growth, at least in the near future. Applications in the building and construction sector are expected to continue to exhibit growth as the industry demands more functionality, efficiency and lower costs from its materials, which at the same time are becoming lighter and stronger.

The focus on environmentally-friendly solutions and carbon footprint reduction will also lead the charge in packaging, offering mineral producers and plastic manufacturers to become increasingly innovative to address growing demand.

At the end of 2015, William Carteaux, the CEO of the plastics industry trade association, SPI, said in a statement assessing the plastic packaging market that the plastic industry is ubiquitous, owing to its myriad of advantages over other materials. 

"Plastic products are lighter, use less energy to produce and transport, and have multiple recycling and recovery options. Through cutting-edge science that’s produced bioplastics and other innovative applications, the plastics industry has answered the call of consumers who are deeply committed to reducing their carbon footprint," he said.