Which polycarbonate to choose for a greenhouse or canopy

Recommendation points

• Material properties, history and evolution
• The problem of quality raw materials
• Vacation form: monolithic, honeycomb and lock polycarbonate
• Purpose and operating conditions
• Specific differences between different brands and types

Polycarbonate – one of the best translucent plastics today – meets both approving and negative reviews. We propose to understand the reasons for such an ambivalent attitude, the rules for choosing polycarbonate, its properties and features of use in various outbuildings.

Material properties, history and evolution

A polymer such as polycarbonate has been known to the world since the middle of the last century. However, the use of thermoplastic translucent plastic has long been limited to optics and avionics, largely due to the high cost and difficulty of providing the required properties. The material became widespread after the development of such simple forms as Bisphenol A, on the basis of which the vast majority of polycarbonate products for household use are produced..

Quality polycarbonate of high chemical purity – the most durable of the existing translucent polymers for general industrial use. It has low thermal conductivity and high shock resistance, which allows it to be used as a filling material for fences that require high or artificially limited light transmission. With its low weight and easy processing, this plastic is highly resistant to chemicals and ultraviolet light, and tolerates high temperatures well.

For more than 60 years of its existence, the polymer has gone through a difficult path of development and improvement. Expensive in the early stages of production, it had a complex technology for obtaining and manufacturing products. However, today, although polycarbonate remains one of the most expensive materials, nevertheless, it is widely available and, when used for its intended purpose, fully justifies the costs. Modern polycarbonate has different forms of delivery, can differ significantly in chemical composition, is characterized by specific installation and operation rules. We will discuss each of these nuances separately..

The problem of quality raw materials

Most of the criticism of polycarbonate is based on the experience of observing the processes of its destruction under the influence of various environmental factors. With an eye on the high cost, this material is sometimes attributed to unusual qualities, while the characteristic properties, as a rule, are exaggerated. Not surprisingly, the effect of disappointment translates into a flurry of unflattering reviews..

First, let’s figure out what high-quality pure polycarbonate products are. According to GOST 56712-2015, 80% is considered a sufficient indicator of chemical purity, in practice, the polymer content in high-quality products can reach 87-90%, the rest falls on stabilizers and modifiers of plastics, as well as dissolved gases. Translucency of 1 cm thick polycarbonate reaches 90%, which is comparable to the optical properties of ordinary window glass, the material retains ultraviolet light and reflects heat radiation well. The ultimate bending strength of the panels is 90 MPa, the modulus of elasticity is not less than 2000 MPa. Polycarbonate in any form is very elastic and retains its shape well, and due to the absence of harmful chemical impurities and in the presence of a protective layer it is guaranteed not to lose its properties for 15 years.

If we are talking about cheap products of low quality, the certification of which according to the current GOST was either not carried out, or was falsified, the consumer is dealing with plastic containing from 50 to 70% polycarbonate. The rest of the mass falls on cheaper fillers – polyethylene or acrylates. As a result, the maximum translucency can be reduced to 80% in a new product and to 50–60% over several years of operation. The high content of impurities does not provide a sufficient density of molecular bonds of the plastic, and therefore the ultimate strength can be 1.5–2 times lower. Resistance to aggressive environments is also reduced in line with the vulnerabilities of third-party fillers. One of the most interesting nuances of the production technology is that the possibility of applying a durable protective layer by coextrusion is available only if the base is of high chemical purity, therefore, most materials in the low price segment are devoid of UV resistance..

Vacation form: monolithic, honeycomb and lock polycarbonate

The most famous type of polycarbonate is extrusion panels with a system of longitudinal cells. According to the previously mentioned GOST, there are four specific cell shapes: honeycomb hexagonal, rectangular, triangular and cruciform. The reference annex on the structural form of panels in this standard specifies the permissible mesh size, thickness of partitions, inner and outer layers, total panel thickness, which can reach 32 mm with five layers. Depending on the geometry parameters, the product can acquire various strength, noise insulation and heat-saving properties..

A separate type of cellular polycarbonate is panels with locks for technological joining. Such a material is less susceptible to errors when providing technological clearances in accordance with the degree of linear expansion. Conventional sheets without shaped ends require at least 6 mm per meter in each direction when covering. These tolerances are provided for by the dimensions and geometry of the locks; if available, the panels are guaranteed not to swell or crack from temperature fluctuations. The main disadvantages of locking panels are the limitation of the freedom of covering frames of complex shapes, for example, domed, hip and broken slopes, a large number of illiquid waste.

The third form of polycarbonate is a monolithic plastic sheet. Due to the uniform structure, it is easier to determine the strength properties of such a material; moreover, it is possible to provide resistance to increased loads without a significant increase in the sheet thickness. The main disadvantage of monolithic plastic is its low thermal conductivity, so it is practically not used for single-layer greenhouse coating. But for awnings and canopies, such polycarbonate is ideal..

Purpose and operating conditions

The grade, quality and type of polycarbonate must be selected in accordance with the conditions of the environment in which it will stay. You also need to know what types of exposure are permissible for this material and which are not..

For example, for all its qualities, polycarbonate is vulnerable to a number of chemical compounds. The main hazards are methanol and its compounds, organic solvents such as acetone and toluene, concentrated hydrochloric acid and alkaline liquids. If there is a potential for their contact with polycarbonate, for example, during the processing of soil and crops or when re-painting the supporting frame, it is better to abandon the use of translucent plastic in favor of glass.

We should not forget about resistance to physical stress. The thickness of all types of polycarbonate must correspond to the current wind loads and the density of the fastening. In general, the strength of polycarbonate is quite high: a monolithic sheet with a thickness of 6–8 mm can withstand the fall of an ice block weighing up to 10 kg without irreversible changes in shape. Cellular polycarbonate in this regard does not have outstanding characteristics, but the scope of its use is greenhouses and verandas, where the greatest danger is hail, and not ice.

Specific differences between different brands and types

There are more subtle difficulties when choosing polycarbonate. For example, the issue of light transmission is rarely considered, while this is one of the most important parameters. For greenhouses, where the amount of light is more important than in any other design, only high quality transparent polycarbonate should be purchased. At the same time, the presence of a UV filter in the protective coating is preferable, because most plants do not relate very well to the ultraviolet spectrum, however, for rare crops, its effect is critically necessary.

Polycarbonate for awnings and canopies, as a rule, get colored in the mass. This is required to limit the light flux and keep cool on a summer day, to protect the front door or objects under the canopy from heating by the Sun. Another way to limit the opacity is to use a mesh with a certain bandwidth that is stretched over the cover. The same technique can be used in greenhouses to limit light output in the final stages of plant growth..