PR 20 – High performance recycled content engineering compounds make the grade - Exclusive article for Industrial Technology October 2009

Plastics compounds with high levels of recycled plastics waste, tailored to meet demanding high performance specifications, are increasingly being used in engineering applications. Terry Burton, technical manager of integrated polymer solutions specialist Luxus Ltd who process over 18000 tonnes of recyclate per annum, explains.

Eco friendliness and sustainability are now firmly established as key design criteria in the minds of engineers. The use of recycled content compounds, especially engineering plastics, is now a focus area for many manufacturing companies. In the UK the recycled plastics market is driven by a combination of legislation and a market shift towards sustainability. EU rules suggest that 95% of cars must be recyclable by 2010 and many local authorities now insist that wheeled bins have to be manufactured from materials containing a minimum of 65% recyclate.

Manufacturing companies now stand alongside most other organisations in their desire to use recycled materials so they can enhance their green credentials and reduce their carbon footprints.

Central to the development of these compounds is an understanding of what is achievable, given the material supply chain and manufacturing processes used to convert waste plastic into usable products.

‘Cost down’ is often cited as a reason to use recycled materials but in practice this is not always achieved – particularly with the current volatility of raw material prices for virgin plastics. When you factor in prime material and energy costs of maybe £40 to £60 per tonne, at today’s rates, the end cost is likely to be similar to that of virgin. However, the benefits of meeting legislative requirements or targets for using recycled materials will still tick all the boxes on a manufacturers’ environmental policy document.

Materials
Virtually all engineering thermoplastics can be recycled. The most common types reused include ABS, HDPE, PA, PC, PC/ABS, PET, PMMA, POM, PP, TPE and PBT. Most are enhanced by compounding with mineral fillers or combinations of these materials including talc, calcium carbonate, mica, barium, glass fibres or beads. Typical formulations contain 40 – 50% prime, 20 – 40% filler and 30 – 40% recyclate polymer.

Meeting specifications
Correctly produced recycled engineering compounds will meet ISO or ASTM specifications. They may be slightly different to prime based materials but will still meet defined critical performance properties.

Developing a formula for an engineering compound based on recycled materials is as challenging as creating polymers from prime stocks. It is very much a partnership arrangement with the customer and calls for an appreciation of recycling processes. In effect, customer and technical compounder work together to develop a unique compound that is entirely fit for purpose and offers the best combination of physical properties, colour and finish possible. Key physical properties including melt flow, impact, tensile strength, modulus, HDT and Vicat can be engineered to meet performance criteria.

The first step is to work with the project or design engineer to gain an in-depth understanding of the final product, its application and method of processing. If we are looking at a new material a specification of critical factors is agreed at the earliest opportunity. If we are replacing an existing grade we test the material and compare our formulation on the same test equipment. This provides the customer with meaningful comparative data on which to evaluate our materials or develop new grades if required. Luxus’ laboratory is equipped to a very high standard and can undertake all the tests mentioned earlier plus FITR (Fourier Transform Infrared Spectroscopy).  The accurate and detailed data generated provides the building blocks for the formulation of the material.

To guarantee consistent quality and continuity of supply we formulate to allow for alternative sources of recyclate that might have to be used should the primary supply become unavailable. We use our technical ability to make adjustments to the formulation to ensure that our compounds remain within the specification parameters agreed with the customer. Recycled polymer is in finite supply and feedstocks and markets change so to minimise the impact we maintain a stock of raw material in excess of 2000 tonnes.

Technical compounding
A formulation could have 10 different feedstocks plus five or six different additives so precision handling at the early stages of a formulation is absolutely critical. When scaled up for production all the ingredients are brought together and fed into state-of-the-art compounding extruders via gravimetric feeders that measure the constituent parts four times every second. Screw configurations, in both feeders and compounding machines, also have to be changed to suit the processing and handling characteristics of the polymers and fillers. During production samples undergo stringent quality tests in our laboratory while skilled machine operators continually monitor pellet geometry.

Manufacturers’ processes
Injection moulding is by far the most popular destination process for recycled content engineering compounds produced by Luxus. Approximately 75% of our materials are used in this area. Extrusion accounts for 15% of output while blow and rotational moulding make up the balance.

Applications
 In the construction industry glass and mineral filled PP is being used for water attenuation systems. The lighting sector uses TPE seals and grommets and PC for internal and external housings. Blinds manufacturers are using PA gears, bearings and bushes as well as barium filled PP for weights. In industrial packaging glass filled PP spacers are employed to protect goods in transit. Hi-fi products such as speaker cases feature products moulded in mica filled PP, while PC is used for control equipment and ABS for housings. In the electrical industry flame retardant PP is specified for cable ducting.

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