Flexural modulus reinforced polymers

Effect of Glass Reinforcement on Flexural Modulus of Polymers... 

There are other proprietary systems such as polyacrylamate. It is Ashland Chemical s Airmax that is designed for use with preforms or glass mats. These reinforced plastics possess high flexural modulus, good impact resistance, and high temperature stability. Systems with similar performance from isocyanate-based polymers are also used. 

Increase in flexural modulus with reinforcement of thermoplastic polymers. U, unreinforced R, reinforced. 

Since it is silica-based, glass fiber for polymer reinforcement could be thought of as a cousin to mineral fillers. But glass fiber is more carefully produced in controlled, uniform, and symmetrical shapes with extremely high aspea ratios, with particle dimensions that are (usually) visible to the human eye. Glass-fiber reinforcement is probably the most cost-effective and most proven way of reinforcing polymers to inaease tensile and flexural modulus and strength. 

In a more recent work, MWNTs have been incorporated into surface-modified, reactive P(St-co-GMA) nanofibres by electrospinning. Then resulting nanofibres have been functionalised with epoxide groups and added to the epoxy matrix producing reinforced epoxy resins. The polymer composites have demonstrated over a 20% increase in flexural modulus, when compared with neat epoxy, despite a very low composite fibre weight fraction (at approximately 0.2% by a single-layer fibrous mat). The increase is attributed to the combined effect of the well-dispersed MWNTs and the surface chemistry of the electrospun fibres that enabled an effective cross-linking between the polymer matrix and the nanofibres. 

Inspection of the data in Table 6.7 reveals that in absolute terms the flexural moduli of the common structural metals aluminium and steel are respectively 7 and 20 times greater than their present glass-reinforced polymer competitors. When a comparison is made of the specific flexural modulus property, then the difference between the metals and structural plastic reduces to about 3 5 times. For example, steel is about three times stifler than polycarbonate. Exceptionally, however, glass-filled EPDM and RIM urethane still have specific modulus properties of approximately 20-65 times less than the reinforced hard plastic resins and metals. Therefore, as a simple material replacement comparison, for a RRIM urethane or glass-filled EPDM, to replace a metal component and maintain the same stiffness inevitably means using a much greater volume of polymer... 

Polypropylene is a very versatile polymer. It has many properties that make it the polymer of choice for various applications (e.g., excellent chemical resistance, good mechanical properties and low cost). There are many ways in which the mechanical properties of polypropylene can be modified to suit a wide variety of end-use applications. Various fillers and reinforcements, such as glass fiber, mica, talc, and calcium carbonate, are typical ingredients that are added to polypropylene resin to attain cost-effective composite mechanical properties. Fibrous materials tend to increase both mechanical and thermal properties, such as tensile strength, flexural strength, flexural modulus, heat deflection temperature, creep resistance, and sometimes impact strength. Fillers, such as talc and calcium carbonate, are often used as extenders to produce a less-costly material. However, some improvement in stiffness and impact can be obtained with these materials. 

Table 2.10 Comparison of flexural modulus of virgin reinforced and reinforced engineering polymers ...

Fibre-glass reinforced epoxy resins are used particularly in the power transmission, building products and pressure vessel markets. In the case of epoxy resins, tensile strengths fall from 600 in the virgin polymer to 68 MPa while the flexural modulus falls from 3 to 1.1 GPa. 

Talc s low cost qualifies it as a extender, for lowering the cost of the compound and extending the resin with minimal sacrifice in physical properties. Its aspect ratio qualifies it as a reinforcing fiUer, for enhancing performance properties of the compound. Polymers filled with platelike talc exhibit higher stiffness, tensile strength, and creep resistance at ambient as well as elevated temperatures. For example, when polypropylene homopolymer is filled with a 40 percent loading of talc, its flexural modulus is tripled from about 200,000 psi to about 600,000 psi. 

Figure 1 Cost-related (specific) flexural strength of major thermoplastics, versus cost-related (specific) thermal tolerance. The unit cost is the market price in US cents (1992) of 1 cm plastics. The thermal tolerance is the temperature difference (AT) over room temperature (AT — T - room T), by which temperature (7 ) the flexural modulus is equal to 1 GPa. Designations, abbreviations WFRP-S, wood fiber reinforced PP (S type) of AECL, Canada (See Table 1) PMMA, polymethylmethacrylate PVC, pol)winyl chloride PS, polystyrene PP, polypropylene UP, unsaturated polyesters PA-GF, glass fiber (35%) reinforced polyamide PHR, phenolic resin EP, epoxy resin ABS, acrylonitrile/butadiene/styrene copolymer UF, urea/formaldehyde LDPE, low density polyethylene PC, polycarbonate POM, polyoxymethylene CAB, cellulose acetate butyrate LCP, liquid crystal polymers PEEK, polyether-etherketone PTFE, polytetrafluorethylene.

In Table 2.4 are listed those polymers in their virgin (i.e., unreinforced) state that have a high tensile strength and those that have a high flexural modulus. Further improvements in these properties can be achieved by incorporation of reinforcing agents, which will be discussed later. 

Identification of Reinforced Polymers with Outstanding Tensile Strength and Flexural Modulus... 

The effect of fiberglass reinforcement on the mechanical properties of polymers is reviewed in Table 3.1. Generally speaking, glass fiber is incorporated in the 20%-50% range. This has an appreciated effect on tensile strength and flexural modulus. 

With the exception of epoxies and perfluoroalkoxy, the incorporation of 25%-50% glass fiber reinforcement leads to an improvement in flexural modulus. As shown in Table 3.2, the outstanding polymers are polyethylene terephthalate, where... 

Reinforced polymers that combine high tensile strength with high flexural modulus include polybutylene terephthalate, polyether ether ketone, polyamide-imide, and polyethylene terephthalate (see Table 3.3). 

The incorporation of 30% of glass fiber into polyphenylene oxide brings about a relatively small increase in tensile strength from between 50 and 65 MPa for the unreinforced polymer to 85 MPa in the reinforced polymer (Table 3.1). The addition of glass fiber is accompanied by an increase in flexural modulus from 2.5 to 17.2 GPa (Table 3.2) and a dramatic decrease in modulus of elasticity from between 20 and 60% down to 1% (Table 3.4). The incorporation of glass fibers into polyphenylene oxide produces a distinct improvement in the wear resistance of the reinforced polymer accompanied by small improvements in fatigue index [19] and the coefficient of friction [20]. 

With talc reinforcements, both crystallization kinetics and crystal microstructure of the polymer (PLA) are significantly altered, for example, the overall crystallinity is reached more quickly due to increase in crystallization kinetics. The degree of crystallinity obtained from DSC measurements increased from 3.6% in neat PLA to 15.4% in PLA-talc composites with a filler content of 7.0 wt% [68]. This in turn can lead to reduced cycle time in injection molding and stiffer materials than neat PLA, when molded under the same conditions. At similar loading level of talc (7.0 wt%), the tensile modulus increased by 15%, while flexural modulus increased by 22% [68]. 

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