Styropor. Properties of Styropor Foams

Transcription

1 Technical Information BASF Plastics key to your success August 2006 = Registered trademark of BASF Aktiengesellschaft Styropor 305 Properties of Styropor Foams The use of Styropor foams demands a knowledge of their properties, in order to use them optimally and to be able to obtain stable functionality. They are different from other conventional materials in that their properties are already sufficiently well known. Thus, one knows that steel can rust, wood can rot, glass can break, or that cardboard loses its rigidity when acted upon by moisture. However, people are often not so well informed about the properties of Styropor foam. This Technical Information Bulletin goes into the details of the properties that are important for this product s use. 1. Labelling 1.1 Labelling for Building Applications According to EN 13163, the labelling for thermal insulation materials made from expanded polystyrene (EPS) must display the following items: CE Mark of Conformity Name or designation and business address of the manufacturer the last two digits of the year in which the label was applied EN Product identity Fire behaviour-class Thermal resistivity thermal conductivity Thickness Identification markings for the characteristic properties Such characteristic properties will include water absorption, release of hazardous substances, dynamic stiffness, thickness, pressure resistance, water vapour diffusion, compressive strength at 10 % deformation, deformation under defined conditions of pressure and temperature, flexural strength, tensile strength perpendicular to the flat plane, dimensional stability, dimensional stability under defined conditions of temperature and moisture, freeze-thaw transition strain, creep properties and long-term thickness reduction. 1.2 Labelling for Packaging Uses Packaging made from EPS is labelled according to DIN , Part 1. An example of a compliant label is provided here: Foam DIN EPS 20 B F Breaking down this designation into detail: DIN EPS: Type of material: EPS foam, foam moulded 20: Gross density: 20 kg/m 3, tolerance: ± 2.5 kg/m 3 B: Degree of dryness: Residual moisture 0.1 % (based on volume) F: Fire behaviour: Meets the requirements for Class F 1 according to DIN 53438, Part 3. The moulded components are silicone-free.

2 2. Physical properties of foams 2.1 Mechanical properties Compressive strength Compressive strength is the most important mechanical property for Styropor foams. This characteristic depends predominantly upon the gross density: the lower the density, the lesser will be the compressive strength. The cell form, temperature and age of the foam also exert an influence. On the other hand, the particle size has essentially no effect on the compressive strength of cut foam samples. Since the measured values will depend on the sample shape, and the testing rate and temperature, the test conditions must be standardised. Testing according to EN 826 Pressure testing on hard foam materials is performed according to EN 826. For this measurement, the use of a test cube with an edge length of 50 mm is preferred. For foam materials from which a test sample having this edge length cannot be prepared, other dimensions can be specified. The pressure foot deforms the cube at a constant rate (5 mm/ min, or 10 %/min with respect to the original height of the test sample), and the applied force along with the consequent compression are recorded. Fig. 1 shows compressive strength vs. progressive deformation in the case of a compression test on Styropor foam cubes of 50 mm edge length with gross densities of 15, 20, 25 and 30 kg/m 3. At first, the force required for a given deformation increases proportionally (Hooke s region). The elastic limit is exceeded after % deformation, and the sample is irreversibly deformed. The initial steep increase in the curve then flattens out to a shallow incline. Styropor foams belong to the class of closed-shell hard foams (see DIN 7726 for a definition); there is no abrupt fracture above the elastic limit, but rather the cells are steadily (and to some extent irreversibly) deformed. In order to characterise the behaviour of Styropor foams under compressive stress, EN 826 specifies the Compressive Strength at 10 % Deformation test, which examines the resistance to deformation when a 50 mm cube is compressed to a thickness of 45 mm. Fig. 1 shows that heavier foams display a higher resistance to deformation, e. g. greater compressive strength, due to their thicker cell walls. At the same time, one can see that the spring characteristic also varies with the gross density. A foam test sample with a lower gross density is softer than a sample with higher gross density, and its curve will have a flatter slope. The quotient of the compressive strength (within the elastic region) with the corresponding deformation is the elastic modulus, which likewise increases with higher gross density. The relationship between Compressive Strength at 10 % Deformation and gross density in Styropor foams is displayed in Fig. 2. Testing according to ASTM and British Standard There are two ASTM standards for determining the compressive strength of foam materials. ASTM-C prescribes a preferred sample size of 6 in. x 6 in. (minimum 2 in. x 2 in.) for thermal insulation panels, and a sample thickness of at least 0.5 in. The testing rate is 5 % of the sample thickness per minute. ASTM D /79 recommends round or square test samples with a 4 36 sq. in. surface, thickness of 1 in. (max. thickness equal to the sample width), with a deformation rate of 10 % of the sample thickness per minute. The compressive strength is specified at 10 % deformation. Thus, the compressive strength values measured according to ASTM-C und D /79 cannot be compared with the values obtained according to EN 826. On the other hand, testing according to British Standard 4370/1988 is consistent with the testing according to EN 826. Factors influencing the measured values Shape of the test sample The test values obtained from cubes that have an edge length of 50 mm are ca % higher than those from measurements taken from a square-shaped sample (127 mm x 127 mm x 40 mm, such as prescribed in ASTM , based on the same level of deformation). While an increase in surface area leads to relatively poorer compressive strength values, the thickness of the test sample exerts hardly any effect. Compressive stress 600 kpa Fig. 1 Compressive stress versus deformation for expanded foams made from Styropor kg/m 3 60 Density Fig. 2 (above) Stress for compression of 10%, (0.1), vs density, 305/2

3

4

5

6

7 to 0.07 mm permeterin length and degree Kelvin. This means that a temperature change of ca. 17 K brings a reversible change in size of 0.1 % = 1 mm/m. For applications that involve thermal transition stresses, specific constructive countermeasures should be kept in mind. Another factor to consider is the low-temperature shrinkage of Styropor foams. If + 20 C is used as a reference temperature, and the material is cooled down to 20 C during use, a component 40 cm in length will lose ca. 1 mm in length under these extreme storage conditions. This must be kept in mind for applications in construction. 2.3 Other Physical Properties of Foams Water and Water Vapour A fundamental differentiation is made between water absorption and water vapour diffusion. Water absorption In contrast to other substances, Styropor foams are not hygroscopic. Even underwater, these foams will only absorb a small amount of moisture. Since the cell walls are waterimpermeable, the water can only penetrate through channels between the welded beads. This means that the amount of water absorption is very strongly dependent both on the EPS raw material used as well as on the processing conditions, especially those for the expansion. The water absorption is measured according to DIN EN The test samples are preferably squares with a footprint of 200 x 200 mm and the corresponding measured thickness. The water absorption is practically independent of the gross density. The water absorption during underwater storage has only slight importance for most applications, and is only of interest in special cases, such as for example earthworks and foundations, floating installations, buoyancy installations, and the like. Water vapour diffusion In contrast to water, given a suitable temperature gradient, water vapour that is present in the air as humidity will gradually penetrate (diffuse) into the foam, and cool down enough to be deposited as liquid water (condensation). This water vapour diffusion brings the contrasts between different substances due to more or less resistance. This resistance (µs) arises from the vapour diffusion resistance factor (µ) and the layer thickness (S). The diffusion resis tance factor (µ) is a dimensionless number that specifies how much larger is the resistance offered by a building material with respect to an equally thick air layer (air: µ = 1). Metals have extremely high diffusion resistance factors, which is why metal foil is used as a vapour barrier. The values for all common substances lie between the extremes of air and metal. Depending on the gross density, Styropor hard foams can have a variety of values for the water vapour diffusion resistance number, µ = (see Table 1, values calculated according to DIN 4108). Values that are respectively less favourable for building construction are used in the condensate calculation Electrical Properties Styropor foam is an electrical insulator. The dielectric constant measured in the frequency range of from MHz and at gross densities of from kg/m 3 lies between The loss factor tg up to 1 MHz is below , and up to 400 MHz is The specific dielectric strength reaches values of 2 kv/mm. The surface resistance at 23 C and 50 % relative humidity is Ω (IEC 60093). As a result of the high surface resistance, the surfaces of individual foam particles can attain an electrostatic charge especially in low humidity. The addition of a static inhibitor during the manufacturing process allows the surface resistance of the foam to be reduced. 3. Chemical Properties (see Table 2) The trademarked products Styropor P, F, Peripor and Neopor behave like polystyrene in the presence of other chemical substances. If the foam is attacked, it will undergo decomposition more rapidly than the compact parent substance because of the thin cell walls. This means that foams with lower gross densities will be attacked more intensively. Styropor foams are unreactive to water, most acids, and to alkali. The essential oils in citrus peels and juice will attack these foams. The foams are resistant toward animal and vegetable fats, and paraffincontaining corrosion inhibitors, as long as they do not contain any aggressive solvents. The sensitivity to organic solvents is of the most concern with adhesives and varnishes. The same is true for plastics with plasticisers (plasticiser migration with PVC). Prior to bringing foams from Styropor, Peripor and Neopor into contact with substances in unknown compositions, a test should be carried out to identify any potential reaction - this is best done through storage in the agent in question, or by use of some other meaningful method. The storage temperature can be raised to allow for a shorter reaction period. Action of UV-Light Long exposures to energetic radiation, e. g. short-wave UV radiation, X-rays and gamma radiation may cause embrittlement of the foam framework. This process depends on the type of radiation, the dose, and the exposure time. In practise, only UV radiation will be important. Over longer exposures to UV light, the foam surface will become yellowed and brittle, which can cause wind and rain erosion. Simple countermeasures can be taken to definitely prevent the action of UV light and erosion, such as finishes, coatings, lamination, and the like. Within rooms, the UV component of the light is so small that no damage to a Styropor foam will take place, as has been shown through decades of experience with ceiling tiles. In rooms used for packaging within normal use-cycle times, the action of UV light will play no role. 4. Fire Behaviour Styropor foams are flammable. In addition to material-specific factors, their fire performance will depend on the conditions of use. This is why one must differentiate between products without flame retardants, such as Styropor P products (hereafter referred to a P-products ), and products that do contain a flame retardant such as Styropor F products, Peripor and Neopor (hereafter referred to as F-Products ). A substantial effect on the fire behaviour is exerted by combining the foam with other protective and covering layers. F-products are products that contain a flame retardant, so that the ignitability of the foam and the spread of flames across the surface are significantly curtailed. 305/7

8 Table 2: Resistance of Styropor Foam Materials to Chemicals Agent used Styropor P, F Salt solution (seawater) + Soaps and surfactants + Bleaching lyes, such as hypochlorite, chlorine water, hydrogen peroxide solution + Dilute acid + Hydrochloric acid, 35 %; Nitric acid up to 50 % + Anhydrous acids, e. g. smoking sulphuric acid, 100 % formic acid Caustic soda, caustic potash, aqueous ammonia + Organic solvents, such as acetone, ethyl acetate, benzene, xylene, paint thinner, trichloroethylene Saturated aliphatic hydrocarbons, petroleum ether, solvent naphtha Paraffin oil, Vaseline +/ Diesel oil Gasoline (regular and high-octane) Alcohols, e. g. methanol, ethanol +/ Silicone oil + + Resistant: the foam is not decomposed even with long exposures +/ Partially resistant: with longer exposures, the foam can shrink or be superficially attacked Not resistant: the foam shrinks more or less rapidly or is dissolved Through trials according to DIN carried out on F-product foams, brominated dioxins have not been found, either in the gas phase or in the product residues, and only negligible quantities of brominated furans, none of which fall under the German Chemicals Prohibition Ordinance of A comprehensive treatment of the fire behaviour of Styropor foams with respect to their application in the construction trade can be found in the Technical Information Fire Protection Performance of Styropor Foams. 5. Biological effects Pentane is released during the storage and processing of Styropor. Especially when the foams are cut by using a heated wire, ventilation must be provided to draw away the vapours produced, since in addition to pentane they contain small amounts of styrene. The MAK values for styrene and for pentane must be observed (specified in the Technical Information Expanded Styropor and the Environment ). Styropor foam materials do not serve as food for animals. They do not rot, are not water soluble, and release no water-soluble substances that could lead to contamination of the groundwater. With attention to the corresponding instructions of local municipalities, these foams can be stored together with household waste. (See the Technical Information Recycling an recovery of used Styropor foams (EPS) ) Styropor foam materials have been manufactured and processed for a number of decades. To date, no health-damaging effects of any kind have been established. 6. Environmental Issues Questions related to the environment in connection with the manufacturing and processing of Styropor and the use of Styropor foams have been addressed comprehensively in the Technical Information Bulletin: Expanded Styropor and the Environment. Stipulations related to German Food Laws Details regarding stipulations related to German Food Laws are contained in the Technical Information Food regulation. Note The data contained in this publication are based on our current knowledge and experience. In view of the many factors that may affect processing and application of our product, these data do not relieve processors from carrying out their own investigations and tests; neither do these data imply any guarantee of certain properties, nor the suitability of the product for a specific purpose. Any descriptions, drawings, photographs, data, proportions, weights etc. given herein may change without prior information and do not constitute the agreed contractual quality of the product. It is the responsibility of the recipient of our products to ensure that any proprietary rights and existing laws and legislation are observed. 305/8