Set for heavy loads

The use of minerals in plastics as functional fillers is one of the primary consuming market sectors for the industrial minerals business. A wide range of minerals perform specific functions to enhance the desired properties of the plastic end product.

While mineral filler use has been around since the advent of plastics, advances in plastic manufacturing technology and the increasing and changing demands from the plastic end user industries have dictated that mineral filler producers also keep pace with market requirements.

Electrolux’s total European demand for GCC
filled PP used in its washing machines and
dishwashers equates to about 55,000 tpa,
which is about 20% of the European market.
Electrolux Group


This has led to increased sophistication in mineral filler processing and surface treatment methods in order to produce higher performance mineral grades to satisfy the stringent demand requirements in manufacturing modern plastic components or products.

The accompanying table shows some of the key industrial minerals used and their main functions.

Mineral fillers are consumed in both thermoplastics, especially in polypropylene (PP) and polyvinyl chloride (PVC) products, and elastomers, mainly in rubber tyre formulations.

In Europe, the most recent estimates available reveal that elastomers consume 3-3.5m. tpa fillers, thermoplastics, 1.4-1.6m. tpa, and thermosets, 0.6m. tpa.


European plastic filler consumption 2007

Source: Roger Rothon (2009) “Filler and filler modifier markets and trends” at High Performance Fillers for Polymer Composites, Barcelona, 4-5 March 2009.


Compounding

The point where industrial minerals meet polymers is at the compounding stage of plastics manufacture (see flow chart). Here the chosen polymer or resin, the most expensive component of the plastic, is mixed with fillers and additives.

The majority of fillers are industrial minerals, although there are also some synthetic materials and organic materials, such as wood flour. They perform a range of functions (see table), but above all they help reduce costs by reducing the volume of polymer/resin used if at all possible.

Additives include pigments and dyes (also comprising industrial minerals and derived compounds), antioxidants, slip/release agents, coupling agents, and antibacterial agents.

Most compounding is now undertaken using a twin-screw extruder machine. This conveys, melts, mixes, injects additives, degases and pressurises to form a wide range of plastic compounds.

One of the main costs in plastics manufacture is at that of the compounding facility, ie. power, water, and machine wear and tear. So manufacturers strive to attain the optimum compounding facilities for their products.

For high mineral filler loadings in plastics, ie. >50%, a continuous mixer combined with a single screw extruder has been demonstrated to be a potential alternative. The result is excellent dispersion and energy savings when compared with a twin-screw extruder.

Tests carried out by US processing equipment supplier Farrel Corp. (acquired by HF Machinery Group division of L. Possehl & Co., mbH, Germany in 2009) and carbonate filler leader Omya AG, have shown that such a set-up can handle compounds with up to 84% filler loadings.


Industrial minerals used in plastics

From the accompanying table on European consumption of fillers, it can be seen that ground calcium carbonate (GCC) at 2m. tonnes is by far and away the dominant mineral filler, used at loading levels of 15-80% in a wide range of plastics, but particularly in PVC.

Talc, kaolin, precipitated silica, and the flame retardant minerals aluminium trihydrate (ATH) and magnesium hydroxide (MHD) come next by volume in the 200-300,000 tonne range.

At 100,000 tonnes and less are barium sulphate, crystalline silica, precipitated calcium carbonate (PCC), calcined kaolin, fumed silica, and wollastonite.

The market sectors using these mineral filled plastic are automotive (includes rubber in tyres), wire and cable, flooring, domestic appliances, and sealants.

Roger Rothon, of Rothon Consultants, UK, further categorises a “high performance” range of filler grades within the overall range of fillers consumed. These include fumed and precipitated silicas, PCC, flame retardants, calcined clays, and special grades of talc and wollastonite (see table).

Rothon estimates the European consumption of high performance fillers to be 3.3m. tonnes or about 60% of the total. Primary markets include automotive (especially in tyres), wire and cable (a key area for flame retardants), sealants, and in breathable films.

There has been increased use of surface coating of filler minerals in order to modify their characteristics and enhance their performance when compounded with the polymer and other additives.

The main surface treatments are fatty acids and organo-silanes, of which 6,500 tonnes and 13,500 tonnes, respectively, are consumed in Europe. Most high performance minerals, with the exception of talc, use these surface coatings.

Organo-silanes for coated precipitated silica in tyre tread formulations is the leading surface treatment market, while flame retardants (ATH, MHD) in wire and cable and GCC in breathable film are also important and growing applications.

Indeed, world speciality silica demand (for all grades) stood at 1.9m. tonnes in 2009, and is expected to grow 6.3% annually to 2.7m. tonnes in 2014, with precipitated silica in rubber looking to take 45% of the market by that time.

As a rule of thumb, when oil prices are high or rising, then filler loading levels tend to increase, as the price of polymers increase, and vice versa. However, it really depends on the end product performance criteria.

Other trends in the mineral filler industry include:

• Almost complete substitution of carbon black by silane coated precipitated silica in the move to green tyre manufacture
• Growth in breathable films, eg. for disposable nappies, has driven demand for fatty acid coated GCC
• Polyolefin films, eg. rubbish bags, using increased loadings, eg. typically 20-30% GCC, and up to 50%.
• Substitution of steel with lighter weight mineral filled plastics
• Increased use of recycled plastics using reinforcement mineral fillers
• Thermoplastic polyolefins requiring more reinforcement using platy minerals such as talc
• Increased use of talc replacing glass fibre in engineering resins eg. ABS, PC, PET, and PA.
• Continued development of speciality masterbatches based on higher loading levels of filler minerals, eg. 75-80% GCC or talc
• Development and emerging use of nanominerals, eg. nanotalcs
• Use of high aspect ratio kaolins for gas barrier applications to reduce permeability in polyolefins, PET, and other plastic films
• Development of surface treated diatomite fillers (already used in silicone rubber applications) for thermoplastics and elastomers

In 2008, Europe produced about 60m. tonnes of plastics, of which some 48m. tonnes were consumed by converters. Of this figure, PP accounted for the largest share, 18%, and PVC, 12%.

Just over a third of Europe’s PP compound consumption comprises mineral filled PP, followed by glass fibre filled PP (also using industrial minerals in glass fibre production), and impact modified PP (see pie chart).


PP compound consumption in Europe by product type 2009



Source: Applied Market Information Ltd


Simplified flow chart of plastic manufacturing process
showing the compounding stage where mineral fillers
are mixed to form the plastic compound.