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Last edited 05 Jan 2023

Plastic and recycling

[edit] Plastic and construction

'Plastic' is a general name given to a wide range of synthetic materials that are based on polymers. The construction industry uses plastic for a wide range of applications because of its versatility, strength-to-weight ratio, durability, corrosion resistance, and so on.

It can be manufactured into forms such as; pipes, cables, coverings, panels, films, sheets and so on; and can be formed or expanded to create low-density materials; and be dissolved in solvents or dispersed as emulsions. In terms of construction sites plastic is also used extensively for packaging and transportation.

Plastic has over recent years been increasingly highlighted as a material for concern because 98% of plastic produced is fossil fuel based, it has related carbon emissions, as well as sometimes issues relating to health and toxicity but increasingly because of issue surrounding pollution through the lack of recycling. Plastic used in packaging has been highlighted in many programmes because much of the plastic produced relates to packaging, with wider construction waste programmes such as WRAP 'Design out waste" programme tackled wider waste based issues covering all materials including plastics.

[edit] Background

The well known symbol that represents recycling, with three arrows following one another in a triangle was actually designed in 1970 resulting from a competition organised by the Container Corporation of America (CCA), who held a student contest to develop a new label for recycled and recyclable paper cardboard and raise awareness about recycling. The competition was won by Gary Anderson, 23 year old student at the University of Southern California, who later went into urban planning, he won $2,500 for his design inspired by M.C.Esher. Anderson said "The figure was designed as a Möbius strip to symbolise continuity within a finite entity,I used the arrows to give directionality to the symbol...I wanted to suggest both the dynamic (things are changing) and the static it’s a static equilibrium, a permanent kind of thing."

In 1988, the Society of the Plastics Industry introduced the Resin Identification Code (RIC) system dividing plastics into 7 different categories, and the symbol design from Anderson became associated with this. In 2008, the system transitioned to the standards body ASTM International and in 2010 ASTM D7611 – Standard Practice for Coding Plastic Manufacturers Articles for Resin Identification, was issued. In June 2013, the three arrows were replaced with a solid triangle because consumers associated the original design with recyclability, which was not always the case. The RIC system although being useful, is in someways more applicable to packaging and as the construction industry employs a wide range of plastics many fall outside of this system.

The study of plastics is complex because of the massive number of derivations, in mixtures, processes and similarity in naming, the characteristic of each plastic varies in use as does the manufacturing process, associated impacts, potential for reuse, reclaim and recycling. Here as a start, there are in general two primary ways to categorise plastics, either on the basic of their chemical composition or how they are processed, these two methods of classification will give very different lists of plastic types. Innovation is continual both in terms of dealing with issues surrounding recyclability, with new methods and approaches to recycle more difficult plastics but also in the development of new breeds of plastics or bio-plastics which although amount to a tiny part of overall plastic production are a significant innovation.

[edit] Resin Identification Code (RIC)

[edit] RIC 1 - Polyethylene Terephthalate (PET or PETE)

Polyethylene Terephthalate is a stable polyester with increasing uses. It has for sometime been used in bottles and food food containers but is also increasing used as an alternative to thermoset plastics (because of its recyclability) in casings of electrical and automotive industries, such as electrical encapsulation, solenoids, smart meters, photovoltaics and junction boxes.

[edit] RIC 2 - High Density Polyethylene (HDPE)

High density polyethylene chemically, has a very high molecular weight. Polyethylene is a whitish, semi-crystalline, and effectively opaque engineering thermoplastic. In households it is commonly found in containers for milk, motor oil, shampoos, soap bottles, detergents, and bleaches, and has been used for municipal and industrial water applications for over 50 years, as well as more recently ground source geothermal applications. It is also used for vapour barriers, air and moisture barrier membranes, carpet textiles, roofing, industrial adhesives and tapes. It may also be found is temporary use as packaging elements such as window films, counter top protection etc.

[edit] RIC 3 - Polyvinyl chloride (PVC)

Polyvinyl chloride (PVC) sometimes known as ‘vinyl’, is a plastic material that has widespread use in building, transport, electrical, healthcare and packaging. It has been produced widely since 1933 and now accounts for approximately 20% of all plastic manufactured around the world, second only to polyethylene (polyethene). Examples of PVC construction productsinclude, window and door profiles and conservatories (uPVC ad CPVC), pipes and fittings, power, data and telecoms wiring and cables, internal and external cladding, ducting, roofing membranes, flooring, wall coverings.

[edit] RIC 4 - Low Density Polyethylene (LDPE)

Low Density Polyethylene (LDPE) is a flexible, odourless, transparent, thermoplastic polymer it can be recycled and is used commonly in products like grocery and waste bags, juice containers, and cling film. In construction it is also commonly used as a cling wrap for materials transported with pallets as it conforms well to different surfaces. It is not strong or puncture resistant but is used widely in construction and agriculture as surface protection, covers, tarps etc.

[edit] RIC 5 - Polypropylene (PP)

Polypropylene (PP) also known as polypropene or polymerised propene) is a thermoplastic polymer with similar qualities to polyethylene (PE) but slightly harder and better resistance to heat and organic solvents. PP can be injection moulded and extruded into many shapes and products such as cups, cutlery, containers, housewares and car parts e.g batteries. It is also spun into fibres for inclusion in industrial and domestic textiles, including for clothing. PP fibres are added to concrete to increase strength and reduce cracking, for non-woven fabrics for ground stabilisation, in roofing membranes(waterproofing top-layer in single-ply systems), reinforcement in construction and road paving, electrical cable insulation(alternative to PVC), piping systems, carpets, rugs and upholstery, medical and laboratory equipment, plastic machine parts, industrial rope and cords.

[edit] RIC 6 - Polystyrene (PS)

Polystyrene, a hard, stiff, brilliantly transparent synthetic resin produced by the polymerisation of styrene. It has been widely employed in the food-service industry as rigid trays and containers, disposable eating utensils, and foamed cups, plates, and bowls. In terms of construction it can be found as a polystyrene plastic, film or foam, of which there are well known terms expanded polystyrene (EPS), extruded polystyrene (XPS), oriented polystyrene (OPS) and high impact polystyrene (HIPS). The EPA has previously published recognition that styrene (the primary building block of polystyrene) as a health threat to humans, considered a human carcinogen by the World Health Organizations International Agency for Research on Cancer. It is though used as often as an insulant as well as in housing for such things as fire alarms, casings and packaging of goods, though it is used increasingly less.

[edit] RIC 7 - Other

In general the other category usually includes a few plastic products such as acrylics, nylon, and fibreglass, in terms of the construction industry the number of materials that can be found in this category can be broad as it is most likely to also include composites such as Fibre-reinforced polymers (FRP), Carbon-fibre-reinforced polymers (CFRP), Glass-fibre-reinforced plastic (GFRP) plus many others.

[edit] Carbon-chain and hetero-chain plastics

Plastic is a synthetic or semi-synthetic organic polymer so will always include carbon and hydrogen, most industrial plastic is made from petrochemicals although, plastics may be made from almost any organic polymer, .

Carbon-chain plastics are made up of polymers having only aliphatic (linear) carbon atoms as their backbone chains such as for example polypropylene. Hetero-chain polymers contain others atoms in their backbone chain, such as oxygen, nitrogen, or sulphur as well as carbon.

The polymers used to make plastic are mixed with additives, such as colouring, plasticisers, stabilisers, fillers, or reinforcements., which impact the chemical composition as well as its chemical and mechanical properties.

[edit] Thermosetting polymers and thermoplastics

Both carbon chain and Hetero-chain polymers can be processed in two different ways, either as thermoplastics or as thermosetting polymers (or thermosets), and it is this processing and the end result that impacts the materials' potential to be recycled.

Thermosets, thermosetting plastic or thermosetting resins, create an infusible, insoluble network by a chemical reaction where the whole entire heated, finished object is in effect a single large molecule. These thermosets with their covalent intermolecular cross-links, consist of the major resin classes such as isocyanate, unsaturated polyester, formaldehyde, epoxies, and alkyds and because of the cross-links they are extremely strong, whilst also being lightweight. But it is the cross-links that also make these products so difficult to recycle.

Thermoplastics have the characteristic of being able to be moulded, remoulded or recycled repeatedly and therefore recyclable. However some plastics such as PVC (Polyvinyl Chloride) and PE (Polyethylene) can also be processed with cross-links, making them thermosets and therefore more difficult to recycle.

There are varying sources of data on global plastic production but statistics generally agree that the majority of plastic produced globally is of the thermoplastic type and as such potentially recyclable, somewhere around 75% of the total, whilst other sources (WE Forum) state that somewhere around only 11% of global plastic production is made up of non recyclable thermosets.

[edit] Recycling of plastics

Whilst up to 75% of global plastic production might be thermoplastic the reality in 2022 as was highlighted by OECD is that "only 9% of plastic waste is recycled (15% is collected for recycling but 40% of that is disposed of as residues). Another 19% is incinerated, 50% ends up in landfill and 22% evades waste management systems and goes into uncontrolled dump sites, is burned in open pits or ends up in terrestrial or aquatic environments, especially in poorer countries."

Whilst different sources often give different figures it is agreed in general that plastic production has continued to increase over the past 30 years dramatically. Again the OECD suggest it has quadrupled over the past 30 years, whilst it doubled from 2000 to 2019 to reach 460 million tonnes, accounting for 3.4% of global greenhouse gas emissions.

In turn global plastic waste generation more than doubled from 2000 to 2019 to 353 million tonnes, highlighting that nearly two-thirds of plastic waste comes from plastics with lifetimes of under five years, with 40% coming from packaging, 12% from consumer goods and 11% from clothing and textiles.

As such an increasing number of professionals in the construction industry push for a significant reduction in the amount of plastic being specified on construction projects, the potential to specify reused materials primarily, followed by materials with high recycled plastic content and circular economy to support this. Once specified this approach should include design consideration for end of life scenarios, towards dismantling, reuse and finally further recycling possibilities.

Because of the number, variety and slight variations of plastic products in the construction market, here is an extensive list of plastics by name, a brief description of their make-up, their use and the possibilities from reuse and recycling.

[edit] Bisphenol A (BPA)

Bisphenol A is a man-made industrial chemical which is used to harden polycarbonate plastics and make epoxy resin. The chemical is found in most household products made of hard plastics, such as water bottles, baby bottles, and food containers. BPA can also be found in epoxy resins that are used as linings of canned food and drinks.

Research has shown that BPA is an endocrine disrupter, which means that it interferes with your body's natural hormones. It is known to seep into food or beverages from containers with BPA and can pose serious health hazards.

There are now products that are labelled as being BPA free, but it is worthwhile being a ware that this is relatively recent and older products are likely to contain BPA. In general though it is accepted that plastics from categories 1, 2, 4 and 5 of the RIC system above are likely to contain lower levels of BPA.

BPA substitutes that have been reported as less harmful or seep out of the plastic at much slower rates. Bisguaiacol-F (BGF) is a natural alternative that can be produced from paper waste and may be less likely to induce endocrine disruption. Study s have found both promise and criticism of alternatives guidance is difficult.

[edit] Bio-plastics

Bio-plastics can be both made in a similar way to thermoplastics and also as thermoset but as a relatively new field understanding is often limited. Bio-plastics are not recyclable in the sense of the the general understanding of recycling of plastic, they are though seen as more degradable over time which is a sense is a form of recycling to return to their natural state.

The term ‘bioplastic’ is used increasingly and is often misunderstood. According to 'Bio-plastics for a circular economy' 'Bio-plastics are plastics that are either made from renewable resources (‘bio-based’), are biodegradable, are made through biological processes or a combination of these. Some biodegradable but fossil-based plastics are also referred to as bio-plastics, however, the use of this terminology is advised against, as it is misleading'

"Although most commercial plastics are made from fossil resources, these materials can also be made from renewable resources and are commonly referred to as bio-plastics. In this case, the monomers are extracted or synthesised from biomass compounds (such as sugars in plants) and then polymerised to either make a direct replacement for an existing plastic, such as polyethylene (PE), or novel polymers, such as polyhydroxyalkanoates (PHAs). Biomass extraction can also yield non-synthetic natural polymers, such as starch, natural rubber and proteins."

Bio-plastics are not recyclable in the sense of the the general understanding of recycling of plastic, they are though seen as more degradable over time. Fossil fuel based plastics are also degradable but never fully return a natural organic state, and thus remain a source of pollution, leaching of chemicals and micro fragments into the environment.

Some bio-plastics are compostable and can be broken down by microorganisms, and will decompose into nutrient-rich biomass in less than 6 months, leaving behind no toxins or residue. However most bio-plastics are biodegradable, meaning they can be broken down by microorganisms such as bacteria, fungi and algae into water, carbon dioxide, methane, biomass and inorganic compounds. In many cases bio-plastics that are biodegradable need to be treated in industrial composting plants or treatment centres, however the end result decomposes in the same way as compostable material.

In general there are currently perhaps 5 different types of base material that are used to create bio-plastics

[edit] Starch-based bioplastic

Starch-based bioplastic (often corn starch) Often mixed with biodegradable polyesters to create small hard cases and food packaging.

[edit] Cellulose-based bioplastic

Cellulose-based bioplastic (cellulose esters and cellulose derivatives) can be used for films, moulded frames, electronic devices.

[edit] Protein-based bioplastic

Protein-based bioplastic (wheat gluten, casein and milk) for food packaging and some development of films and coatings.

[edit] Bio-derived Polyethylene

Bio-derived Polyethylene (fermented raw agricultural materials such as sugarcane and corn) has been used to produce high density polyethylene for crates, trays, bottles and caps, as well industrial containers.

[edit] Aliphatic Polyesters

Aliphatic Polyesters, are mainly in development phase, sensitive to water, and can be mixed with other compounds. Bio-based polyesters such as polylactic acid (PLA), polyglycolic acid (PGA), poly-ε-caprolactone (PCL), polyhydroxybutyrate (PHB), and poly(3-hydroxy valerate).