Flexural modulus thermoplastics

Ho et al (1996) examined polyol or polysiloxane thermoplastic polyurethanes (TPUs) as modifiers in cresol-formaldehye novolac epoxy resins cured with phenolic novolac resin for computer-chip encapsulation. A stable sea-island dispersion of TPU particles was achieved by the epoxy ring-opening with isocyanate groups of the urethane prepolymer to form an oxazolidone. The flexural modulus was reduced by addition of TPU and also the Tg was increased due to the rigid oxazolidone structure. Mayadunne et al (1999) extended this work to a series of phenol- and naphthol-based aralkyl epoxy resins. 

As to Its other characteristics, styrene-butadlene-caprolactone (S-B-CL) trlblock terpolymer with high butadiene content behaves much like a thermoplastic elastomer, with raw tensile strength equal to and ozone resistance better than S-B-S type copolymer (3). The Impact-resistant resin by blending 25 parts of S-B-CL trlblock with 75 parts of styrene/acrylonltrlle (SAN) copolymer resembles ABS type material In such properties as tensile strength, flexural modulus, oil resistance, and transparency (4). 

Talc - Talc is a filler made by dry or wet grinding of mineral magnesium silicate. Talc improves stiffness, dimensional stability, flexural modulus, creep resistance, flow, surface smoothness, moisture resistance, tensile strength, and wear resistance of plastics. It also increases heat deflection temperature and decreases vapor permeability. Can be used as a film antiblock agent. Used mainly in polypropylene but also in thermoplastic and unsaturated polyesters and epoxy resins at low levels. Surface-modified grades are available. 

Because of the low pressure (0.3 MPa) in the mold as compared to those encountered in thermoplastic injection molding (150 MPa) this process is suitable for the production of thin part with large surface areas. A significant application for this is in panel formation in the automotive industry, including fascias, door panels, spoilers, grills, and bumpers. While a rigid foam part with a flexural strength of 700 MPa would require a thickness of 7 mm, a RRIM part, because of the reinforcement, would allow a much smaller thickness (< 3 mm) by virtue of the increase in flexural modulus. 

The applications of RIM have been widened by introducing 20% by weight of chopped glass fibres into the polyol component. Apart from changes in the pump type, to cope with the higher viscosity liquid and the abrasive wear, there is little modification in the process. The flexural modulus is increased by a factor of 3 or so, to be comparable with that of thermoplastics. 

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

This concept has been demonstrated by the work of Liu and Kontopoulou [45] and Bailly and Kontopoulou [27] on silica-reinforced thermoplastic olefins (TPOs). Their data have shown that when silica resides in the PP matrix, the improvements in Young s and flexural modulus are accompanied by unchanged or even slightly improved impact strength (Figure 2.12). The effects on impact properties were particularly beneficial when surface-modified silica (mSi02) was used. 

Figure 8.59 Flexural modulus vs. temperature for DuPont Hytrel thermoplastic polyester elastomer resins [7],...

In the quoted study, it was foimd that the polysulfone was initially miscible with the cyanate prepolymer and phase separates into spherical domains during the course of the cyanate polymerization process. The flexural modulus was not significantly modified by the thermoplastic/organoclay addition. On the other hand, the fracture toughness was slightly improved with the addition of polysulfone and clay to the cyanate. 

Figure 7.6 Comparison of flexural modulus of glass fiber reinforced engineering thermoplastics. Data on the unfilled resins are included for comparison. (To convert from psi to Pa multiply by 6895.)...

Figure 9.7 Flexural modulus versus filler concentration in a thermoplastic elastomer, TPO comparison of talc (CA53) with nanoclay (CA53-15A) in the presence of maleated PP (PB3200).

---