Building with Plastic Blocks by Jon Evans
From the June 2011 issue of Plastics Engineering
If the three little pigs were around today, then the third little pig would probably be looking to construct his house from plastic rather than bricks. For various reasons, plastics are becoming an increasingly popular material for construction, with the demand for plastic resin for construction applications growing substantially over the past 10 years.
According to Arjen Sevenster, manager of technical and environmental affairs at the European Council of Vinyl Manufacturers, European demand for plastic resin for construction applications grew from 9.6 million tonnes in 2004 to 11 million tonnes in 2007. It then fell to 9.1 million tonnes in 2008 and 2009, reflecting the major downturn in the construction industry caused by the financial crisis, but it is now growing again.
‘We expect the demand to have increased to close to 10 million tonnes in 2010,’ says Sevenster. Indeed, because the downturn affected the whole of the construction sector, plastics continued to increase their share of the construction material market, currently at around 15%, even while demand was falling. As a consequence, construction is now the second largest user of plastics in both Western Europe and the US, after packaging.
The rise of plastics as a construction material is being driven by a number of different factors. Most obviously, plastics offer a number of inherent advantages over other construction materials: they are light weight, durable, and easy to install and maintain. In addition, chemical companies and plastic producers are developing new plastic resins and products with enhanced properties, especially in terms of strength, that are increasingly allowing them to replace conventional construction materials like metal and concrete.
Another major factor is the increasing emphasis in many countries on designing and constructing energy-efficient buildings. In Europe, the European Commission’s Energy Performance of Buildings Directive, which came into force in May 2010, calls for all new buildings to have ‘nearly zero energy’ demand from 2021, starting with all new public buildings in 2019. In the US, the Department of Energy runs several programs and initiatives to improve the energy efficiency of residential and commercial buildings, including BetterBuildings and the Commercial Building Initiative.
‘The use of plastics is [being] driven by new energy legislation, ‘ explains Ulla Biernat, a BASF spokesperson for performance polymers. ‘Plastics very often offer high energy efficiency and cost-efficiency.’
One of the most immediately effective ways to reduce a building’s energy demand is to surround it with some kind of insulation: within the internal and external walls, and under the floors and ceiling. Heating and cooling can account for up to 60% of a building’s energy demand. As insulation materials have a low heat conductivity, in part due to pockets of air that form within them, they prevent heat flowing either into or out of a building. This helps to keep the building at a constant, comfortable temperature and reduces the need for active heating or cooling.
A wide range of materials can be used for insulation, including cellulose, mineral wool and glass foam, but plastics, mainly in the form of polystyrene and polyurethane foams, are increasingly the insulation material of choice. For a start, plastic insulation is itself more energy efficient to manufacture than mineral wool and glass foam, requiring 16% less energy and producing 9% less greenhouse gas emissions, according to a study conducted for Plastics Europe, the European association of plastics manufacturers. It can also be much thinner and lighter than other forms of insulation.
‘You can make very good insulation with any material provided you make it thick enough,’ explains Sevenster. ‘Now the advantage of plastics is perhaps that you can achieve the same performance with less thickness.’ This is due to the closed-cell structure of polystyrene and polyurethane foams, menaing that the air-filled pockets are not connected to each other. This makes them particularly poor at conducting heat and therefore particularly effective insulators.
What is more, relatively small modifications can make these plastic foams even more effective. For instance, the German chemical giant BASF has developed versions of their polystyrene foams that contain finely-dispersed graphite particles. These particles soak up heat in the form of infra-red radiation and then reflect it back like a mirror, further reducing the thermal conductivity of the foam. As a result, it’s thickness can be reduced by 20% while still providing the same level of insulation.
Plastic insulation materials are impervious to moisture, do not rot and are naturally flame-resistant. They can also be applied as solid panels or as a liquid foam that subsequently hardens, allowing them to be injected into hard-to-reach nooks and crannies. This means they can be used both to insulate existing buildings and in the construction of new ones.
An example of what can be achieved even with older buildings is provided by a 210-year-old timer-frame house in Babenhausen, Germany, which as part of a refurbishment project was insulated with extruded polystyrene rigid foam (XPS) supplied by BASF. After XPS panels were fitted beneath the floor of the building, it went from using 25‒30L of heating oil per square metre per year to just 7L, and now loses 30% less heat than a newly-built house.
According to studies conducted by Plastics Europe, plastic insulation saves the amount of energy used in its production in just four months, while over its lifetime it saves more than 200 times the energy used in its manufacture. Plastics Europe has also estimated that the total net energy saving of all the plastic insulation sold in Europe in 2004 over its lifetime amounted to at least 9,500 million gigajoules. This equates to 20% of the yearly energy consumption of the entire European Union or the energy contained in 800 big oil tankers.
But the use of plastics in construction extends far beyond insulation, which is not even the largest user. That accolade goes to piping, which accounts for 35% of the plastics used in construction, mainly in the form of PVC (polyvinyl chloride) and polyethylene (see Box). Plastics are also commonly used to produce windows, doors and roofing, with energy efficiency again a prime consideration.
In a well-insulated building, windows present the main route by which heat can escape from and enter into buildings: windows are 10 times less energy efficient than walls and the average house loses 30% of its heating or cooling energy through its windows. Fitting multiple-glazed windows can help to reduce heat loss, while windows can also be coated with substances that allow the passage of visible wavelengths of light but reflect the longer, heat-giving infra-red wavelengths. That still leaves the window frames, however, which account for around 25% of the total area of a window.
The two most popular materials for constructing material frames are wood and PVC, which actually have a similarly low level of natural heat conductivity. But the thermal conductivity of PVC frames can be lowered further by incorporating plastic foam insulation into them. While the use of spacers made of thermoplastic rather than aluminium to separate the individual panes of glass in multiple-glazed windows can also greatly reduce heat loss.
PVC can also be used as a roofing material, where it’s great advantage is that it can produce light coloured roofs that reflect up to 80% of the sunlight falling on them, helping to keep the building beneath cool. In contrast, roofs made of dark materials such as asphalt, which the US Environment Protection Agency estimates account for 90% of roofs in the US, can reach temperatures as high as 85°C.
But plastics offer a lot more than just energy efficiency. For a start, engineers and architects are beginning to find that plastics can allow them to kill two birds with one stone, by using a single plastic material to perform numerous functions. Take Basotect, a novel plastic foam made from a nitrogen-rich compound known as melamine, developed by BASF.
Unlike polystyrene foam, Basotect has an open-celled structure, meaning that the pockets of air connect with each other to form a network, making it very lightweight. Despite this structure, Basotect’s nitrogen-rich nature means that it is also a very effective insulation material.
For example, it is now being used by Hanno, a German manufacturer of insulation system, to reduce energy losses in rooms housing banks of computers. Such rooms tend to get very hot, because of all the heat generated by the computers, and so are actively cooled by circulating cold air around the room. The rooms are also often equipped with false floors, underneath which all the computer cabling is unobtrusively run. But this can result in much of the cold air escaping, along with the cables, through the holes in the false floor. Hanno now fills the gaps around the cables with Basotect, blocking the holes with an almost airtight seal that reduces the loss of cold air by up to 99.9%.
In addition to its impressive insulating properties, however, Basotect’s open-celled structure means that it is also a very effective sound-absorber. It’s especially good at dampening sounds at medium and high frequencies, meaning that it can reduce the incidence of echo caused by sound waves reflecting from surfaces. As such, it has been used to reduce unwanted noise in theatres, hotels, restaurants, Olympic swimming stadiums and subway stations.
This combination of properties makes Basotect ideal for a whole range of applications, such as providing acoustic and thermal insulation in the Hefei Grand Theater in the Anhui Province, China, where the air conditioning is channeled through ducts under the theater seats. Here, Basotect both prevents the cold air escaping into the basement and also reduces the noise generated by the air conditioners.
Engineers and architects are also discovering that certain plastic materials are strong enough to do some of the heavy lifting in construction. One good example is fibre reinforced plastic (FRP) composites, in which a plastic material such as polyamide or polypropylene is reinforced with tiny fibres or particles. Most commonly, these are glass fibres, but carbon fibres and even nanoparticles can also be used.
Because these fibres and nanoparticles are tough and robust, and form a three-dimensional network, they confer additional strength to the plastic material. Such FRP composites are already replacing steel wall studs in steel-framed houses, reducing the risk of corrosion and the development of thermal bridges. These are regions in a thermally-insulated wall where heat can pass freely, greatly reducing the wall’s insulating properties. Obviously, this is much more of a concern if the wall studs are made of steel than FRP composites, which have low thermal conductivities.
But the potential of FRP composites goes well beyond wall studs: they are allowing architects and engineers to produce shapes that simply can’t be produced with other materials. For example, the new Sheraton Hotel at Milan airport in Italy possess a curvy outer skin made from glass fibre reinforced composite cladding.
Other plastic materials are also giving architects and engineers licence to experiment. ‘The design freedom with plastics materials is unique and enables the creation of some very interesting buildings and structures such as the Chanel mobile art pavilion which has a PVC-coated polyester roof and ETFE (ethylene tetrafluoroethylene) roof lights,’ a spokesperson for the British Plastics Federation told Plastics Engineering. ‘Another example of innovation in plastics construction is the Allianz Arena in Munich, which is constructed with 2874 inflated ETFE rhomboidal shells.’
Plastics are even changing the way in which structures can be built, allowing the production of modular houses. In this approach, sections of the house are manufactured from FRP composites at a factory somewhere and then transported to where the house is to be built. The house is then assembled from the separate sections, like a giant version of flat-pack furniture. For example, the Florida-based company InnoVida produces pre-fabricated panels of glass fibre reinforced plastic that can be assembled to form a house in less than three days.
Plastics are even allowing the construction industry to take advantage of some of the latest technologies. Already, insulating materials like Basotect are helping to improve the efficiency of solar heating systems, which use solar collectors on the roof of buildings to heat water. Coating plastic insulating materials on the back of the solar collectors, usually a sheet of metal with a dark coating, helps to ensure that as little of the captured heat is lost as possible.
That’s just the beginning though: some of the advanced plastic materials being developed, such as electrically conducting plastics, could take construction far into the future. Conducting plastics offer the possibility of developing flexible solar panels that can simply be unrolled onto roofs, rather than expensively installed as is the case with rigid solar panels. Electrically-conducting plastics could also be incorporated within walls, in the form of sensors that continually monitor the integrity of the building.
If the third little pig built his house from plastic, not only would it be strong enough to withstand the wolf’s huffing and puffing, but it would also be energy efficient, solar powered and able to tell the pig exactly how much damage the wolf was causing.