Unfilled polyurethane

Abrasion resistance has not been discussed here, but it is an important factor in performance. In limited field testing on another series of promising polyurethanes, the unfilled polyurethanes abrade at a rapid rate compared to compounded rubbers. The excellent abrasion resistance frequently shown by polyurethanes in conventional tests does not occur in field tests where the samples are track pads for tanks. 

Property Unfilled polyurethane 15% Surface-modified rubber particles 85% polyurethane ... 

The dynamic properties of polyurethane composites made with treated rubber particles can also be very similar to those of the unfilled polyurethane. Comparison of d5mamic mechanical analysis (DMA) curves for composites composed of surface-modified rubber particles in polyurethane and corresponding curves for the unfilled polyurethane show nearly identical hysteretic heating. End products, such as wheels and rollers, made in either unfilled pol5mrethane or in composites comprising treated rubber particles/pol)mrethane have essentially identical heat build-up in dynamic applications. 

The static moduli failure stresses and dynamic moduli of both filled and unfilled polyurethanes are measured over a range of equihbrium water contents and these results are compared with those obtained from dry controls. The degradation of mechanical properties in the presence of water, and the hydrolytic disruption of filler/matrix adhesion is assessed. A quantitative relationship between the water content and mechanical properties is established and the mechanics of the water/polymer/filler interaction are considered. 4 refs. 

Conventional machining operations are used preferably from the same plastic to be used in the product (Chapter 8, SECONDARY EQUIPMENT). Different casting techniques are used that provide low cost even though they are usually labor intensive. The casting of unfilled or filled/reinforced plastic used include TS polyurethane, epoxy, structural foam, and RTV silicone. Also used are die cast metals. 

One example is the use of rigid selfexpanding closed cell polyurethane foams as a method to inhibit corrosion of the interior surfaces of metal (steel, etc.) structural cavities exposed to seawater and moisture is one of many example of plastic providing corrosion protection. Unfilled metal cavities are a general feature of various structures or products used in the marine, building, electronics,... 

FIGURE 9.16 Resilience values for chlorobutyl rubber (CIIR), butadiene rubber (BR), unfilled natural rubber (NR), filled natural rubber (SRB), and polyurethane (PU) samples tested using a Shore rebound resibometer, an Instron compression tester and a scanning probe microscope (SPM). (From Huson, M.G. and Maxweb, J.M.,... 

In unfilled rubbers, which are not capable of strain-induced crystallization, the upturns on Mooney-Rivlin curves have shown to be absent 92 95). They disappear also in crystallizable rubbers at elevated temperatures and in the presence of solvents. On the other hand, the upturns do not appear for butadiene, nitrile and polyurethane rubbers if the limited chain extensibility function is introduced in the Mooney-Rivlin expression 97). Mark 92) has concluded that in the absence of selfreinforcement due to strain-induced crystallization or domains the rupture of the networks occurs long before the limited chain extensibility can be reached. 

It is important to recognize that these correlations only apply to a specific polymer and, as discussed above, will be sensitive to changes in the polymer crystallinity, the inclusion of filler, and the exact chemical composition. The sensitivity of solubility in polydimethylsiloxane to the filler content has been noted (14 15) and the correlation in Table III for PDMS applies ony to the unfilled fluid. The crystallinity of many polymers depends on their molecular weight, and may change if the polymer is subject to biodegradation. The solubility parameter, i.e. the polarity, of polyurethanes, is sensitive to the nature and ratio of the ether (or ester) and urethane segments. 

In general, plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics. The materials that will respond satisfactorily in the range of 1010 and 1011 erg per gram are glass and asbestos-filled phenolics, certain epoxies, polyurethane, polystyrene, mineral-filled polyesters, silicone, and furane. The next group of plastics in order of radiation resistance includes polyethylene, melamine, urea formaldehyde, unfilled phenolic, and silicone resins. Those materials that have poor radiation resistance include methyl methacrylate, unfilled polyesters, cellulosics, polyamides, and fluorocarbons. 

Formulations for producing polyurethanes (PUs) by reaction injection moulding (RIM) usually contain mixtures of polyols and diols in order to achieve the desired properties in the moulded part. The present work forms part (1) of a systematic investigation into the effects of polyol blends and glass fibres on the physical properties of unfilled and filled PUs formed by RIM. In the case of unfilled PUs, by using a multi-component polyol mixture, it is possible to investigate the effects on properties of (a) polyol structure, molar mass and functionality, (b) the relative proportions of diol-based hard blocks and triol-based soft blocks and (c) polyol blend compatibility. The... 

In interpenetrating polymer networks, chemical crosslinking and phase separation and their timing affect properties. Fumed silica, alumina, and carbon fiber were used in a network developed Ifom polyurethane and polycslcracrylalc. The presence of fillers affected many properties. Conversion rates were higher in the presence of fillers. Also, microphase separation was affected. As a result of these two changes the filled material was unrecognizable from the unfilled material. 

Figure 1. Stress vs. strain at 25° and 60°C for polyether polyurethanes filled symbols at 25°C unfilled symbols 60°C. Commercial polymer (, 0),unaged ( > A),aged wet. PU13 (9,0),unaged (, ) aged wet.

Simple chemoviscosity models have been used to examine the effects of shear rate on the chemoviscosity = T) as shown in Table 4.3. For example, Sundstrom and Burkett (1981) and Hartley and Williams (1981) found that polyesters and polyurethanes exhibit essentially Newtonian behaviour, whereas epoxies and phenolics show marked shear thinning. The power-law model is the most extensively used shear-rate model for thermosets and has been used for unfilled (Ryan and Kamal, 1976, Kascaval et al, 1993,... 

SF is characterized as a plastic structure with a nearly uniform density foam core and integral near-solid skins (facings). When these structures are used in load-bearing applications, the foam bulk density is typically 50 to 90% of the plastic s unfoamed bulk density. Most SF products (90wt%) are made from different TPs, principally PS, PE, PVC, and ABS. Polyurethane is the primary TS plastic. Unfilled and reinforced SFs represent about 70% of the products. The principal method of processing (75%) is modified low-pressure injection molding. Extrusion and RIM account for about 10% each. 

Figure 6.3 Dependence of tan S on temperature (T) of polyurethanes based on OPG, 2,4-TDI, and ODA at IkHz frequency (1) unfilled polymer (2) with 2wt% A-175 (3) with 2wt% AEG (4) with 2wt% ADEG.

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