Commercial carpet tiles
Part 1: Materials

Introduction

The commercial carpeting market is the scene for some of the fiercest competition in the construction products industry. In the search for an edge, the more agile manufacturers are reacting to prompts by specifiers and government agencies to produce carpet tiles that significantly reduce their environmental impact.

There are two main concerns – one is the potentially toxic emissions to air during the installed life of a tile, and the other is the quantity of used carpet treated as waste.

Toxins such as styrene, formaldehyde and xylene can be harmful at low levels, but improved detection technology, more stringent performance standards and new materials bring the prospect of a healthier working environment.

The amount of carpet waste we bury is staggering – it’s estimated that about 165,000 tonnes are sent to landfill in the UK annually, and worse still, much of it has not reached anywhere near the end of its working life.

The obvious solution is to re-use when possible – suitable tiles are collected from site, graded and sold back into the market. Sadly, progress in this sector has been disappointing - whilst feasible, in practice and without critical mass, choice is restricted and recovered quantities unpredictable. For refurbishment to work in the future, manufacturers need to become re-engaged and to commit greater resources.

In contrast, the recycling of carpet materials has been the subject of substantial capital investment. Ideally, at the end of its working life the tile can be returned to the manufacturer where its components can be disassembled and returned to the production stream to form new carpet – this ‘cradle to cradle’ concept is the most virtuous form of recycling.
 

Specification issues

Allegedly, flooring products account for around 40% of a building’s environmental impact and soft flooring will be changed between 6 and 12 times during the 60 years of a building’s life. Whatever the source of these figures, they are a useful prompt to consider the importance of specifying products such as carpeting with an eye to minimising environmental impact.

Perhaps the most important consideration is to reduce the frequency of carpet changes. Carpets are changed for two main reasons – fashion and wear. Not a lot can be done about fashion, though clearly linking carpets with the design ethos of ‘de jour’ is inviting instant obsolescence; but plenty can be done about wear. By specifying carpets that have durable qualities through their construction, their protection from soiling and their suitability to undergo cleaning regimes, the designer can go a long way in achieving the low impact goal.

Carpet tile construction varies greatly in materials and sustainability. Because of the high performance expectations, commercial wearing layers have traditionally been made using nylon, and only lately have alternatives begun to emerge. Though the most obvious, the wearing layer is usually surpassed by the backing layer in terms of environmental impact. Some manufacturers continue to use the earliest type bitumen formulas for backing materials, but most will use PVC which was developed to replace it – providing reduced weight, improved stability and ease of laying. PVC itself is becoming eclipsed by some manufacturers eager to reduce PVC’s impact – replacing it with arguably superior materials include PET and polyolefins.

Apart from selecting a durable carpet composed of materials with minimal environmental impact, the third most important aspect is considering what happens when the carpet reaches the end of its working life. The specifier should consider to what extent the carpet can be recycled. Some manufacturers build in a recycling programme (cradle to cradle), but most currently don’t.
 

Carpet tile construction

Commercial carpet tile construction generally comprise of a pile fibre wearing layer, usually nylon. The majority of carpets involve yarn pile tufted into the primary backing, typically a non-woven polyester material which is in turn bonded to a secondary backing. The secondary backing, particularly in carpet tiles, provides rigidity and dimensional stability.
 
Image courtesy of Desso Carpets
    

Construction materials: the wearing layer: pile fibres

Commercial carpet tile construction generally comprise of a pile fibre wearing layer, usually nylon. The majority of carpets involve yarn pile tufted into the primary backing, typically a non-woven polyester material which is in turn bonded to a secondary backing. The secondary backing, particularly in carpet tiles, provides rigidity and dimensional stability.

Nylon

Nylon accounts for around two-thirds of the fibre used in carpets - mainly because of its durability, making it ideal for areas of high traffic. Nylon fibre is produced in two forms: Nylon 6 is the cheaper of the two, but can now match its rival’s performance. The big advantage of Nylon 6 is that it is much easier to recycle; Nylon 6.6 has a higher performance rating than Nylon 6 but it may not be enough to make a difference in selection.It is worth noting that although all nylon is easy to dye, the preferred process in terms of longevity of colouring is ‘solution dyeing’ (see ‘dyeing’ below)

	Excellent wear performance
	Resistant to abrasion
	Easily dyed
	Some fibres include recycled contents
	Recyclable
	Petrochemical-based polymer
	Potential for toxic off-gassing
	Frequent cleaning required implying water and energy use
	Unable to dissipate static electricity
	Non-biodegradable in landfill

    

Wool

Though wool is used in the manufacture of commercial carpet tiles, its use is usually restricted, because of its relative lack of durability, to areas of low traffic. It is not unusual to find pile of 100% wool, but most manufacturers prefer to add nylon (20%) to enhance the wearing qualities.

Wool comes in different grades where quality is determined by the length of pile, and the density of the yarn and tufts. New Zealand wool tends to be softer than British wool.

Wool is distinguished because it is the most well-known ‘natural’ pile fibre used in carpet tiles – though other fibres such as goat hair are also used in a small number of cases.

	Natural fibre
	Good texture and colours
	Naturally fire-resistant
	Good dyeing properties
	Can be composted down if separated from its backing and not mixed with synthetics
	Some concern about methane from sheep
	Not suitable for commercial areas of high traffic
	Some concern about potential for trapping VOCs
	Easily stained - needs treating with stain-repellent
	Can shrink when saturated with water
	Expensive

 

Polypropylene (aka ‘Polylolefin’, ‘Olefin’)

After nylon, polypropylene is the most popular pile yarn. Though possessed of wearing qualities, it is not quite as robust as nylon – which tends to limit its use to some offices, but not for areas of heavy foot traffic such as airports or retail outlets.

	Reasonable wear performance in areas of lighter foot traffic
	Resistant to water based stains, mildew, pilling and electrostatic build-up
	Easy to dye
	Inexpensive
	Petrochemical-based
	Poorer texture and feel than wool or nylon
	Poor resistance to abrasion and easily crushed
	Can look dingy when soiled
	Its low melting point has been known to cause it to fuse to furniture
	Non-biodegradable in landfill

    

Recycled polyester (PET)

PET is polyethylene terephthalate, which is one of a number of fibres known commonly as polyester. High quality PET material is commonly sourced from the recycling of plastic bottles. Polyester are good for stains and bright and vibrant colours can be had, but they should not be used in areas of heavy foot traffic.
 

	Manufactured from recycled soft drinks bottles
	Reasonable wear performance in areas of lighter foot traffic
	It is a hydrophobic fibre - giving it a natural stain and mildew repellency
	Petrochemical-based
	Poor resistance to abrasion - unsuitable for some commercial installations
	A recent research paper presented evidence that PET may yield endocrine disruptors under conditions of common use, though the yield mechanism has not yet been established. The implication for carpeting is as yet unknown. (Environmental Health Perspectives, November 2009)
	No manufacturing process has yet been developed to recycle PET carpet fibre
	Non-biodegradable in landfill

 

Bio-based polymers

Bio-based polymer fibres are an important development because their sourcing from plant materials rather than petro-chemicals. It is early days yet, but several of the major carpet manufacturers are investing into research and development. The highest profile bio-based fibre is PLA (Poly Lactic Acid) which is derived from cornstarch, sugar beet or wheat starch. The resulting fibres resemble those of polyester, but, to date, there still appear to be durability issues in bringing PLA to the market as a pile fibre. Some think that it might prove to be better suited as a backing material.
 

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Backing

 
Backing construction

 
Primary backing

Yarn is tufted into the primary backing which is typically a non-woven polyester material, light in weight and of low environmental impact.
 

Binding layer

The binder that adheres the primary to the secondary backing is usually SBR (Styrene Butadiene Rubber), a synthetic latex compounded with chalk. The average tile contains around 1kg of binder and, in new carpets, the SBR is responsible for much of the characteristic ‘new carpet’ odour. Though there are no concerns of toxicity in use, the production of SBR was as long ago in 1976 associated with a higher incidence of leukaemia and other malignancies among workers. (Epidemiologic investigations of styrene-butadiene rubber production and reinforced plastics production; Scandinavian journal of work, environment & health, 01/02/1978) see also (www.cdc.gov/niosh/84105_41.html)
 

Secondary backing

The secondary backing provides the dimensional stability of the tile through weight and rigidity. The backing makes up the bulk of the weight of the carpet – averaging around 4 kg/m2 – and is responsible for the major environmental impact of the carpet. The material construction of the secondary backing affects the ease with which a tile is installed and removed.
 

Backing materials

 

Bitumen

 
Bitumen is the traditional form of commercial carpet backing. Natural bitumen derives from the oil sands of Alberta, Canada, which is often mixed in carpets with synthetic bitumen, a bi-product of crude oil distillation. Traditional problems associated with bitumen backings such as cracking and adhesion to sub-flooring have been addressed by the introduction of other materials such as fibreglass and polypropylene.

Bitumen tile waste has been estimated at 50 kilo tonnes – of which only a small amount is recovered and re-used. WRAP are working at ways of improving the figure including using recovered bitumen in road asphalt.
 

	Can be recycled
	Oil sand extraction highly damaging to the landscape
	Synthetic bitumen is petro-chemical based
	Most bitumen backing is still sent to landfill

 

PVC

PVC is the most common of carpet tile secondary backings. In the search for a material that could avoid the very visceral problems experienced with bitumen backing, PVC offered a lighter, more rigid and user-friendly alternative. However, with the continuing health concerns associated with PVC, some manufacturers have exited the PVC backing market and have adopted alternatives with what are hoped to be lesser impacts.

Some backings are using recycled PVC, but environmental campaigners maintain that dangerous phthalates (eg DHEP) are 'kept in system' and people continue to be exposed to the risks.
 

	Tried and tested technology
	Inexpensive
	Concerns expressed concerning additives and stabilisers ( though, mystifyingly, these are not shared by the BRE Green Guide).
	Petrochemical-based
	Pile materials attached to PVC backing cannot be reused eg in a a close-loop recycling scheme
	Non-biodegradable in landfill
	PVC tile waste accounts for around 15 kilo tonnes annually, most of which is sent to landfill

    

Polyolefins: Polyethylene / Polypropylene

 
Whilst common as a pile fibre material, polyolefin backing has only recently been developed – mainly as a result of the search for an alternative to PVC, but also because it offers less weight for the same or better performance.

Another attraction is the ease with which Polyolefin can be integrated into closed-loop recycling schemes – backings do no damage to nylon pile and the polyolefin can be ground down to be blended with new backings.

	Manufactured from food grade polymers (ie free from additives and stabilisers)
	Stronger than PVC
	Can be easily recycled
	Non-toxic
	Petrochemical-based
	Non-biodegradable in landfill

 

PVB (Polyvinyl butyral)

PVB is a non-chlorinated vinyl, one of vinyls now being used as a direct substitute for PVC (chlorine is the source of many of the environmental health concerns with PVC). Post-consumer PVB obtained as waste from car windscreens is now beginning to be incorporated in carpet backing.
 

	A robust replacement for PVC
	Uses post-consumer waste
	Unlike PVC, it does not need phthalates
	Non-toxic
	Like PVC, PVB retains pile fibres which prohibits recycling
	Petrochemical-based
	Non-biodegradable in landfill

See also: material safety data sheet http://fscimage.fishersci.com/msds/99649.htm
 

Urethane

Lacking the necessary rigidity, Urethane is little-used in the commercial carpet market. It is sometimes used as an extra backing layer to improve acoustic performance. Urethane is generally a petrochemical derivative, but recent developments have included polyols, such as soya beans, as a source
 

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Adhesives

 
Adhesives are capable of being more toxic than the carpet they are made to adhere. Most adhesives are still based on SBR synthetic latex (see ‘Binding layer’ above) which emits VOCs. However, newer products are water-based and contain less than 5% organic compounds. VOC emissions associated with newer products are listed as less than 0.05% after 72 hours. The designer is advised to check the adhesives safety data sheet before specifying.

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Recycling

 

Post industrial recycled content

• Production waste generally generated during manufacturing
 

Post consumer recovery

• Recovery of product and recycling of constituents requires significant capital investment by carpet manufacturers in plant, processes and logistics.
• The pile requires mechanical separation from the backing
• The materials resulting from the recovery process can reduce standards of new carpet components through dyeing and abrasion resistance.
• The 'gold standard' is the 'closed loop' recycling where materials can be used over and over.

Closed loop recycling - Image courtesy of Shaw Contract Group
 

Recycling v downcycling

 
Recycling

• Recycling needs supporting with suitable infrastructure to collect materials:

- Complex and intensive process, relatively few facilities in the world that can do it

- Check that infrastructure is already in place

- Ensure that the benefits of recycling are not outweighed by energy and reprocessing
 

Downcycling

• An alternative to recycling, downcycling into other products.

• Downcycling downgrades the material - eventually it has to be disposed of through landfill or incineration

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Go to Commercial carpet tiles, Part 2: Performance, standards & treatments  >>>>>>>>>>>>
 

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