Organic heat-insulating materials

Gas-filled plastics are the most effective organic heat-insulation materials. Plastics, which consist of the system of isolated cells, are called foam plastics; system of connected pores – cellular plastics; system of repeating hollows - honeycomb plastics (Fig. 17.5).

Foam plastics based on polysterene, polyvinylchloride, polyurethanes and phenol-formaldehyde resins are the most widespread in construction. Basic properties of porous plastics change depending on the type of polymers and method of manufacture (Table. 17.2). Ratio between strength of heat-insulating plastics and their density is considerably higher than for other heat- insulating materials. Foam plastics have lower water absorption and higher sound insulating ability than cellular plastics.

Weight of foam plastics is less in 4-5 times in comparison with such traditional materials as mineral wool boards, glass-fiber boards and foam-glass at improvement of heat-insulation properties in 1.5-2.2 times. Foam urethanes are one of the most effective foam plastics. They are used mainly as heaters in three- and double-layer panels. High heat-insulating properties of foam urethanes, their closed cellular structure, which provide minimal water absorption, absence of corrosive influence on metals and good adhesion to the most of materials enable application of this type of foam plastics for spraying on different (especially metal) structures.

Sprayed layer can be used simultaneously as heat-insulation and protection of metal against corrosion. Sprayed polyurethanes can be used for coating of engineering structures, mainly oil storage tanks. Their application is possible for the thermal insulation coatings of houses, refrigerators, pipes, etc. Basic obstacle for application of foam plastics is their high combustibility, including sprayed ones. Therefore a plastic thermal insulation must be reliably protected from the action of fire.

In the last years foam plastics with decreased combustibility are developed. Their surface is coated with fireproof materials for this purpose.

Table 17.2

Basic properties of porous plastics

Phenolic foam plasticsare the least combustible. They are more economic than other, have a wide source of raw materials. However their strength is lower than foam urethane. Furthermore opened cellular structure of phenoplasts and, as a result, high water absorption requires more careful waterproofing of them.

For construction considerable interest is paid to by foam plastics on the basis of epoxy polymers - foam epoxy. This material is characterized by low thermal-conductivity and at the same time it has advantages of epoxy polymers: high adhesion to a number of materials, comparatively high mechanical properties, water and chemical resistance, etc.

Peat heat-insulating products can be manufactured as boards, panels, etc. Poorly decomposed peat which is fissioned at processing on separate fibres can be used as raw material for them. The products formed by pressing act are dried and resinous substances, which glue together fibers, are secreted from peat. Density of peat boards is 170-260 kg/m³, bending strength – 0.3 MPa, thermal-conductivity – 0.052-0.075 W/(m·K). Water absorption achieves 180-190% during 24 hours. In the moistened state, especially at storage in stacks, peat products can have ability to self-ignition. Limit temperature of their application is 100°C. Peat heat-insulating products can be applied for the insulation of refrigerators, industrial equipment, etc. It is required to protect these products from moistening.

Sawdust concrete can be used as heat-insulation material due to it comparatively low density (not more than 550 kg/m³). Sawdust concrete is a type of light-weight concrete. Ground wood or some phytogenous waste products can be used as the aggregate of this material. Compressive strength of sawdust concrete products, assigned for thermal insulation, is 0.5-1.5 MPa; water absorption 60-85%; thermal-conductivity 0.15-0.17 W/(m K) at humidity 15%. Sawdust concrete products, taking into account their high heat-insulating ability at the low values of strength and module of elasticity, are rationally applied for hangings and self-bearing external panels and large blocks at the proper protection from moistening.

Fibrolite is similar to properties of sawdust concrete, which includes wood wool with fibers length in the range of 200-500 mm as aggregate. Fibrolite can be manufactured as boards with density in the range of 300-500 kg/m³ and bending strength from 0.4 to 1.2 MPa. Water absorption of fibrolite is 35-60% and thermal-conductivity is in the range of 0.09-0.15 W/m°C. Fibrolite differs by high acoustic absorption due to connected structure of pores; easy processability and high adhesion to plaster.

Wood wool for providing the normal hardening is processed (mineralized) in solutions of calcium chloride or other salts.

Wide application of local heat-insulation materials is the most rational in conditions of farm construction. Effective raw materials for the manufacture of local heat-insulation materials are mainly wastes of woodworking industry and agriculture.

Acoustic materials

Materials which absorbing more than 40% of sound waves energy if frequency oscillations is in the range of 500-1000 Hz, i.e. coefficient of acoustic absorption is more than 0.4, are called sound-absorbing materials. These materials are widely applied in the modern construction practice. Mineral wool boards based on starch binder can be used as sound-absorbing material. Such boards (Fig. 17.6) have density 350-450 kg/m³, bending strength 1-1.8 MPa, coefficient of acoustic absorption 0.6-0.8. Also, carboxymethyl cellulose, polyvinyl acetate emulsion, phenol alcohols can be used as organic binders for sound-absorbing materials.

The acoustic boards based on mineral wool granules or mineral wool fibers are used for the acoustical ceiling construction public and office buildings with relative humidity of air not more than 70% at a temperature of 15-20°C. Surface of board can be painted by polyvinyl acetate emulsion.

Mineral wool boards with a gypsum facing and the gypsum perforated boards with the layer of fabric on which mineral wool is placed, are also applied as sound-absorbing materials. Perforated wood fiberboards, cement acoustic fiberboard with density of 400 – 500 kg/m³; porous concrete boards with the system of connected pores; polyurethane cellular plastic and asbestos cement perforated boards can be also used as sound-absorbing materials. Ceramic boards and blocks based on brick chips with liquid glass are applied for sound proofing of the technological equipment at operating temperature up to 500°C. Also concrete based on porous aggregates (perlite, vermiculite, slag pumice, etc.) are applied as acoustic ones.

Different acoustic facings are applied. They can be used not only for the improvement of premises acoustic but also for the decorative finishing of interior surfaces. Acoustic ceilings from the profiled aluminium sheets and other sound-absorbing materials are widely used.

Sound-insulating materials are manufactured as mates, boards, gaskets, etc, with density not exceeded 300 kg/m³, module elasticity – 15 MPa. For sound insulation porous rubber, elastic polymer materials, mineral wool, wood-fiber boards, asbestos and other materials are used.

Date: 2015-12-18; view: 819