Polyurethane Reinforcing fibre

Loos (2011) reported that investigators from Bayer Material Science LLC, USA and Moulded Fibre Glass, Cleveland, USA have developed a prototype wind turbine blade 0.74 m long manufactured from polyurethane reinforced with carbon nanotubes (CNT PU). The researchers claim that the advanced material has a specific tensile strength five times and 60 times that of carbon fibre composite and aluminium, respectively, and is tougher than carbon fibre-reinforced polymer (CFRP) but the excellent properties of these materials come with a price penalty. 

In the special case of pipelines operating at relatively high temperatures such as for the transmission of heavy fuel oil at up to 85°C, heat insulation and electrical insulation are provided by up to 50 mm of foam-expanded polyurethane. As a further insurance against penetration of water, and to prevent mechanical damage, outer coatings of polyethylene (5 mm), butyl laminate tape (0-8 mm) or coal-tar enamel reinforced with glass fibre (2-5 mm) have been used. 

Flexible plastics and rubbers can, as a matter of fact, only be treated with rubber-elastic lacquers, mainly on the basis of polyurethane, which, moreover, should be resistant to oxidation, oils, fuel and UV light. Besides, polyurethane lacquers are often used for several other plastics, such as PVC, polyamides, ABS and glass-fibre reinforced resins. 

Structural adhesives based on polyurethanes are used widely in the transport industry, especially for bonding plastics reinforced with glass or other fibres. They are used also as sealants in glazing for motor vehicles—most notably following the introduction in recent years of front and rear windows bonded as elements in the construction. 

The PFM films may also be backed with a glass fibre reinforced polyurethane foam. This technology is already being used in thermoplastic roof modules and gives rise to parts having low weight, high stiffness and excellent thermal insulation. 

Research on the pyrolysis of thermoset plastics is less common than thermoplastic pyrolysis research. Thermosets are most often used in composite materials which contain many different components, mainly fibre reinforcement, fillers and the thermoset or polymer, which is the matrix or continuous phase. There has been interest in the application of the technology of pyrolysis to recycle composite plastics [25, 26]. Product yields of gas, oil/wax and char are complicated and misleading because of the wide variety of formulations used in the production of the composite. For example, a high amount of filler and fibre reinforcement results in a high solid residue and inevitably a reduced gas and oiFwax yield. Similarly, in many cases, the polymeric resin is a mixture of different thermosets and thermoplastics and for real-world samples, the formulation is proprietary information. Table 11.4 shows the product yield for the pyrolysis of polyurethane, polyester, polyamide and polycarbonate in a fluidized-bed pyrolysis reactor [9]. 

Typical systems are two-part polyurethane systems that may produce rigid, rubbery, foamed or filled products. Typical fillers include chopped fibres and mineral fillers. Composite systems may also be produced by having pre-placed reinforcements in the mould, in which case the technique is known as reinforced reactive injection moulding (RRIM). 

A typical layered structure consists of two thin, glass-fibre-reinforced polymer skins bonded to a thick, lightweight honeycomb core (Fig. 4.5a). Such sandwich panels are used in railway carriages and aircraft there are similar structures inside many skins. Other examples are less obvious the space between the outer container and the toughened polystyrene liner of a refrigerator is filled with rigid polyurethane foam. 

Polyurethane foam is used with facings such as paper, glass fibre, plasterboard or glass fibre reinforced concrete. The facings and foam are layers connected in series, so the temperature drop across each layer is added for the steady-state heat flow. If layer i has thickness Lj and conductivity ki then the overall U-value of the product is given by... 

A reaction between the reinforced plastics material and the surrounding medium is defined here as an event which breaks and makes new covalent chemical bonds in the participating substances. One illustration is the hydrolysis reaction which breaks ester and amide groups in polyesters, polyamides and certain polyurethanes, when they are exposed to dilute acids or alkalis. Another example is the oxidation reaction that attacks carbon fibres whenever they are in contact with dilute nitric acid, acid/ dichromate, hypochlorite solutions, and so on. Such reactions can easily be foreseen and avoided by the use of more appropriate resins, fibres, and so on. The rate of chemical reactions involving resins is much more difficult to predict and they can sometimes be so slow that the effects are not necessarily unacceptable at ambient temperatures. One obvious illustration is the... 

Fibre reinforced polymers (FRPs) are composed of a reinforcement material (glass, aramid or carbon fibres) surrounded and retained by a (thermoplastic or thermosetting) polymer matrix (unsaturated polyester, epoxy, vinyl ester, or polyurethane). FRPs were first used in the rehahiUtation of reinforced or pre-stressed concrete, but they have also been widely used in the reinforcement of timber structures. 

Plastics and rubbers occur most frequently as conveyor belts and straps as well as in cables and pipes. Ventilating conduits and chutes are made of glass-fibre-reinforced polyester. In addition, in-situ expanded rigid polyurethanes have recently been gaining ground as thermal insulating materials. 

One of the significant classes of polyurethanes is resin, which is mainly used in the paint and coatings industry for binders, adhesives and fibre reinforced polymer (FRP) composite matrix. Polyurethane resins are highly functional polymers with a low molecular weight in their intermediate state and have been used for the above applications. Polyurethanes are preferred as binders... 

A study of glass fibre reinforced soybean oil-based polyurethane indicates that the mechanical properties such as tensile strength (259 c 270 MPa), flexural strength (418 cf. 444 MPa), tensile modulus (17 ct 18.6 GPa) and flexural modulus (18 cf. 27 GPa) of the soybean-based composites, were comparable with those of composites based on petrochemical (Jeffol) polyurethane. Since this soybean oil-based polyurethane composite offers better thermal, oxidative and hydrolytic stability than those based on petrochemicals, vegetable oil-based polyurethane composites could offer a viable alternative to petrochemical-based composites. 

Two types of environmentally friendly jute fibre reinforced green composites have been studied. These are based on Mesua ferrea L. seed oil-based poly(urethane ester) and poly(urethane amide) resin blends with commercially available partially butylated melamine-formaldehyde and epoxy resins by solution impregnation and hot-curing methods. The composites were cured at a temperature of about 130-140°C under a pressure of 35.5 kg cm for around 2 h.The physical, mechanical and chemical properties of the epoxy-modified polyurethane composites were better than those of the MF-modified composites. They also possessed excellent chemical resistance and hydrolytic stability in water, acid and salt solutions, making them useful for low load-bearing applications. 

Details of vegetable oil-based polymers conventional composites have been discussed in an earlier chapter. In this chapter, nanocomposites of vegetable oil-based polymers are discussed. Certain questions arise as to how much difference there is between these composites. The questions are significant when the same reinforcing agent is used in both cases. As an example, a vegetable oil-based polyurethane with alkali-treated chopped jute fibres in a conventional composite and cellulose nanofibres (obtained from jute fibres) in a vegetable oil-based polymer nanocomposite are discussed. The... 

Of late many of the major car manufacturers now use biocomposites in various applications, e.g., door trim panels made of polyurethane (PU)-flax/sisal mat in Audi A2 midrange car jute-based door panels in Mercedes E-class polyester-cotton fibres in Trabant car under floor protection trim of Mercedes A class made from banana fibre-reinforced composites and the Mercedes S class automotive components made from different bio-fibre-reinforced composites. All these so-called biocomposites use natural fibres but the resin matrix is always an oil-derived synthetic material. 

Temperature-dependent permeability to moisture could even be provided by polyurethane-based shape memory polymer (SMP). Better comfort is also provided by moving humidity and sweat away from the surface of the skin, either with hydrophilic linings or by the use of channelled cross-section fibres with reinforced wicking properties. 

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