POLYMERS, THERMAL INSULATION AND THE ENVIRONMENT
Published: 27/10/2021
Around 60 million tonnes of plastics are used in Europe every year (year 2018). Of these, about 20% is absorbed by the building construction sector.
A sector in which plastic raw materials participate in the form of numerous applications, such as: cables, pipes and electrical ducts, flooring, window profiles, paneling, sanitary water drainage pipes, Heat Venting and Air Conditioning (HVAC ).
Plastic polymers are present in the form of artifacts, powders, liquids, gels, with a variable incidence depending on the need and the type of the building.
The European Environmental Agency’s stand on plastics and the circular economy can be seen here.
Most widely used plastics
A historical material of this segment is certainly Polyvinyl Chloride (PVC) which is worth about 40% of the total consumption of the sector and present in both rigid and flexible applications.
We find it in hydraulic systems (drainage pipes and fittings), shutters and window frames, in surface and floor coverings, in rigid and corrugated pipes for guiding and protecting the electrical cables and elastic sheaths for the primary insulation of the electrical cables themselves.
In second place, in terms of consumption, we find two other no less important materials, Polystyrene (PS) and Polyurethane (PU), both of which are foams.
Polystyrene (amorphous material) has gained a respectable position both in the extruded and steam sintered version (XPS and EPS respectively), and is used in the thermal and acoustic insulation systems in roofs, facades (wall insulation), floors and interior walls.
The extruded version has a much more compact surface finishing and a better mechanical structure than the sintered one.
Polyurethane has an authoritative position in the thermal insulation of industrial buildings. It is generally incorporated in sandwich panels, protected by metal sheets of variable thickness with smooth or corrugated versions.
The panels are used in top roofing, or as an external protection for both thermal and acoustic purposes. It is also used in the form of structural spray foam, for the insulation of inaccessible areas, or for strengthening and / or sealing the foundations of buildings in the event of ground subsidence.
Another structural material, which plays an important role in both commercial and industrial constructions, is Polycarbonate (PC). It is an engineering amorphous polymer, used in the form of extruded compact or structural/honeycomb sheets.
Compact sheets are used in flat or curved canopies, while honeycomb sheets of various thickness and geometric shape (for instance, flat, corrugated or wave shape) are used for facades, industrial roofs, skylights, verandas, parking lots.
Engineered Panels are also produced with this material. They are equipped with an integrated quick in joint system (male-female) to compose large size walls. The width of these panels is usually limited (500mm – 600mm) but their length can be the one necessary, or rather, the transportable one.
These Polycarbonate panels have in addition to translucency, which allows the diffusion of the natural light inside the rooms, a good insulating capacity.
To increase the insulating performance of these honeycomb elements, the manufacturers create isolated “sectors” in the thickness of the product obtained by means of an increasing number of internal walls, partitions (from 3 to 13) connected to each other by ribs with different geometric shapes (from the simplest, parallel, to those with an X shape to a double X).
The search for the most performing geometric shape is to offer the sheet the best structural mechanical resistance (compression) with the lowest possible thickness, in order to preserve the product lightness (about 5 kg / m2) and a competitive cost.
The different solutions adopted give the sheets excellent resistance to crushing, even in the presence of high overall nominal thicknesses (≤60mm).
The number of walls allows to obtain the best thermal insulation (K value about 0.7 W/m2K), while preserving a good transmission of natural light in the building.
In addition, Polycarbonate offers natural resistance to shocks and UV, the latter being further improved thanks to extra specific surface protections co-extruded during the manufacturing process. The material has intrinsically a good degree of safety against flame which allows it to obtain class B-s1, d0 according to the EN 13501-1 fire reaction standard, without the need for additional flame-retardant agents.
In less structural applications, but no less important, we find Polyethylene (PE).
Polyethylene (semi-crystalline material) is used in the form of film for insulating-waterproofing membranes, in pipes for underfloor heating, in rigid pipes and fittings for the transport of drinking water.
More recently it has also begun to be appreciated in expanded form for the insulation of ventilation ducts, or hot water and refrigerant gas pipes.
It is found in tubular form with variable thicknesses or in the form of mats.
Thanks to its elasticity it is possible to easily cut it, shape it, fold it, creating insulative coatings with shapes able to fit the purpose.
All these interesting thermoplastic applications for the construction sector: pipes, profiles, cable sheaths, flat and structural sheets, flooring covers, insulating panels; are produced thanks to the extrusion process.
Find out more about it here: https://www.2milasrl.it/en/conversion-technologies-extrusion/.
Polymers and Environment – Towards the sector’s circular economy
Despite the fact that the prevalence of thermoplastic materials used are intrinsically recyclable, still today in this sector a high percentage of products (about 45% EU average) unfortunately end up in landfills (see graph 1 further on).
The percentage of course varies from country to country and is influenced by the different construction methods.
Of the remaining 55%, about 30% is sent to energy recovery, while only 20% is actually truly recycled. Although the incidence of plastic materials on the overall weight of a building rarely exceeds 1%, this recycling percentage must necessarily improve.
It should be remembered that since these are mainly extruded products, almost all are mono-material based (with the exception of electrical cables that are already born as composites), and the thermoplastic polymers used are potentially recyclable with modern recycling systems.
As indicated in the past in other documents, the recovery systems and technologies have taken great steps forward in the last five years both in terms of selection capacity and subdivision of the various polymers, deriving from post-consumer end-of-life waste.
Recycling techniques
The treatments available for the management/recovery of “waste” at the end of life are essentially three.
Mechanical recycling: this takes place through a process of shredding the artifacts at the end of their life, the washing of the shredded material, drying it and subsequently sending it to a melt process (through extrusion), which eventually will bring it to a final stage called granulation.
The manufacturing process allows some formulation interventions, directly in the production line, in the melt phase, during its recovery.
Pyrolysis (or chemical recycling) is used when the polymeric organic component, of an artifact coming from waste, is difficult to select and separate.
The process allows to break down the original polymers into pieces until monomers, dimers, trimers and distillates are obtained, separated, to redirect them as such into a new polymerization, or in mixture with an analogous monomer from a fossil source. By doing so, the original polymer chain is recomposed.
Energy recovery: being mainly materials deriving from fossil sources (hydrocarbons), these are subject to combustion and have a high intrinsic calorific value. A value close to that of the original source.
Their use (conversion) in this way is very useful for the production of steam to be introduced into power plants for the generation of electricity.
There is a fourth system, the landfill. But this option is rapidly running out and will certainly be increasingly not encouraged and abandoned.
According to the new directives of the European Community, by 2030 the level of recycling will necessarily be increased.
It is therefore clear that we will need to do much better than what has been done up to now in the choice of raw materials, in all their forms.
It means paying much more attention to the function but also to the “end of life” of any final product placed on the market, in particular those made with thermoplastic materials that are potentially easily recyclable.
It will be necessary to imagine new virtuous solutions in terms of circular economy, to reuse the product, to recover and/or recycle the raw material of which it is made.
For example, in the case of composite applications (such as, plastics + metal elements), the solutions must be designed to make the separation of the two raw materials simple.
This type of attention to separation is an exercise definitely in tune with the circularity model required by Europe.
It should also be remembered that, ideally, the recycled materials coming from specific fields should be able to re-enter the same market that has generated them.
Guidelines on polystyrene recycling can be found here.
Polyurethane recovery
It is known that expanded rigid polyurethane is a cross-linked material very popular in the B&C world and we know it is also the ideal candidate for landfill.
Its chemical structure (Polyol and Isocyanate) has never been easy to manage in recycle.
Being cross-linked (themo-set) it cannot be melted. In case of combustion, it releases hydrogen cyanide, a gas that is not easy to manage even in waste-to-energy conversion.
However, it should be noted that new solutions for the chemical recycling of expanded PU have also appeared. When available, they will represent a decisive step forward for reducing the environmental impact of this material.
At present we can mention a joint experimental research conducted by the University of Padua (I) in collaboration with some companies using PU. A first pilot plant is being activated at company LaPrima Plastics in Vicenza (I).
Other existing forms of PU still difficult to recover as for instance: paints, lacquers or sealants. However, it must be said that these versions, on average, represent less than 10% of the total polymers used in construction.
Guidelines on recycling polyurethanes can be found here.
Greenhouse gases, overall situation
For operators of the construction sector, designers and architects, this is therefore a phase of a new important all-round effort to obtain a substantial benefit in terms of reduction of CFP (environmental carbon footprint) to reach climate neutrality (Carbon Neutral) by 2050.
A great challenge that will certainly lead to the development of new construction solutions and new synergies between companies and the territory. But probably an additional opportunity, for an overall reinterpretation of some traditional construction models.
Globally, greenhouse gas emissions fell slightly in 2020 due to the Covid pandemic. Global CO2 production was 36Gt. (36 billion tons), compared to more than 40 calculated just three years ago, as reported by euronews.
In terms of greenhouse gas emissions (especially CO2), the construction sector is certainly penalized by the cement industry.
In the breakdown of emissions by industrial segment, the construction segment weighs about 6% (direct emissions), a value mainly supported by the production of cement products. The cement industry has been reported to contribute 5-8% of global CO2 emissions with of 850kg of CO2 per ton of clinker produced – source
Indirectly, however, it is calculated that the construction sector also participates in 21% of the emissions related to the industrial sector (for about 8%), due to the poor efficiency of the industrial structures and the consequent high consumption of fossil fuels.
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