PU composites

Fig. 13.10 Burning rate characteristics of an AP-PU composite propellant, showing plateau burning.

The PU compositions can be prepared by dispersing the mass ABS resin in the reactants used to prepare the PU and then contacting the resultant dispersion with the other urethane reactants under conditions sufficient to form the PU. The reaction can be accelerated by the addition of suitable urethane catalysts, for example by tertiary amines (33). When the PU is prepared by reactive extrusion, the ABS resin may be added already initially along with the urethane-forming reactants. This toughened PU is particularly useful in making structural automotive body parts and housings for electrical appliances. 

PPy/polyurethane (PU) composites with conductivities as high as 1 S cm-1 have also been prepared.71 The PU was initially cast on indium-tin oxide coated glass electrodes, whereupon electropolymerization was carried out. The condition employed... 

M.R. Williamson, R. Black, C. Kielty, PCL-PU composite vascular scaffold production for vascular tissue engineering attachment, proliferation and bioactivity of human vascular endothelial cells. Biomaterials 27 (19) (2006) 3608-3616. 

Chemical functionalization of CNT surfaces could improve their dispersion in the polymer matrix and enhance the nanotube-polymer interfacial interaction and the mechanical load transfer. The effects of nanotube functionalization on the properties of CNT-TPU composites have been investigated in details. Xia and Song have synthesized polycaprolactone polyurethane (PU)-grafted SWNTs (PU-g-SWNTs) and corresponding PU-g-SWNT-PU composites by in-situ polymerization. The results show that PU-g-SWNTs improve the dispersion of SWNTs in the PU matrix and strengthen the interfacial interaction between the PU and SWNTs. Compared with neat PU and pristine SWNT PU composites, PU-g-SWNT-PU composites demonstrate remarkable enhancement on Young s modulus. The Young s modulus of a 0.7 wt /o PU-g-SWNT-PU composite increases by 178% over the blank PU and 88% over the 0.7 wt% pristine SWNT-PU composite, respectively. 

The PE-based PU was prepared by reacting 90 g crude MDI with 90 g PE-based resin (prepared based on ingredients in Table 5). The mixture was agitated vigorously using a standard propeller with a speed of 2000 rpm until well-mixed ( 60 seconds) at room temperature. The reaction time cream time (CT), gel time (FT), tack-free-time (TFT), and rise time (RT) were noted. These reaction times were important in the preparation of PU composites in identifying the initial reaction time and demolding time. 

The molded PU was conditioned for 16 h at 23 2 C before further characterization following standard method BS 4370 Part 1 1988. The FR-filled PU composites were prepared by using the same procedure, but with the addition of FR (by weight percent of resin) as shown in Table 5. 

FIGURE 5 Shore D hardness index of the control PU and FR-filled PU composites. 

Figure 7 and Figme 8 show the flexural strength and modulus of the eontrol PU and the FR-filled PU composites respectively. As the content of FR increased, the flexural strength decreased. The reduction in strength is ascribed to the poor adhesion between FR and PU matrix due to agglomeration of FR particles as exhibited in the SEM micrographs. 

The same trend is observed for the specific heat capacity. The intensity of the change in specific heat capacity (A is associated with T. Specific heat capacity of control PU is 1392 J/kg-K. Specific heat capacity of the PU composite increased by 5.8 % when 2% FR is added. However, specific heat capacity of FR-filled PU composites decreased by 3.5% and 14% when 4% and 6% FR respectively are added. A significant drop in specific heat capacity (A C ) is observed when more flame retardant is introduced to PU composites, therefore gradual and Unear reduction ocoured according to addition of FR (Sarier Onder 2007). 

TABLES TheT and specific heat capacity of control PU and FR-fiUed PU composites... 

Figure 10 presents the enthalpy of control PU and the FR-filled PU composites. It decreased by increasing the amount of FR. This trend is in good agreement with results reported elsewhere (Toldy et al. 2006) where, they use OPCs and... 

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