Polyurethane nanocomposites thermal stability

Modesti, M. Lorenzetti, A. Besco, S. Hrelja, D. Semenzato, S. Bertani, R. Michelin, R.A.. Synergism between flame retardant and modified layered silicate on thermal stability and fire behaviour of polyurethane nanocomposite foams. Polym. Degrad. Stab. 2008, 93, 2166-2171. 

Nonwoven mats of cellulose microfibrils were also used to prepare polyurethane composite materials via film stacking method [160], Water-redispersible nanofibrillated cellulose in powder form was recently prepared from refined bleached beech pulp by carboxymethylation and mechanical disintegration [161], However, the carboxymethylated sample displayed a loss of crystallinity and strong decrease in thermal stability limiting its use for nanocomposite processing. 

Acid modified multi-walled carbon nanotubes and Mesua ferrea L. seed oil-based hyperbranched polyurethane-based nanocomposites have also been reported, exhibiting 300% improvement in tensile strength, enhancement of thermal stability up to 275°C, excellent shape recovery up to 98% (Fig. 11.7), enhanced biodegradabUity and cytocompatibility, confirmed by the inhibition of a RBC haemolysis test at a very low loading of CNT. ... 

Tetraethoxyorthosilane and linseed oil polyol silica embedded polyurethane nanocomposites were obtained by a sol-gel technique. The polyol/ silica nanoparticles network showed a strong interaction with uniform, spherical silica nanoparticles of 2-30 nm size embedded in the polymer matrix. The system was further reinforced by 2 wt% and 5 wt% fumed silica. The resultant systems showed improved thermal stability with mild to moderate antibacterial behaviour against E. coli and S. aureus. 

Barick et al. investigate the thermal stability of thermoplastic polyurethane (TPU) nanocomposite based on organically modified layered silicate (OMLS) prepared by intercalation process followed by compression molding, founding that... 

Jana RN, Cho JW. Thermal stability and molecular interaction of polyurethane nanocomposites prepared by in sim polymerization with functionalized multiwalled carbon nanotubes. J Appl Polym Sci June 2008 108 2857-64. 

Other polymers that have been subjected to thermal stability studies include cycloaliphatic diisocyanate based polyurethanes (DSC, TGA, ET-IR) [40-42], polyallyl azide [DSC, TGA, FT-IR, nuclear magnetic spectroscopy (NMR)] [43], ethylene vinyl acetate nanocomposites (TGA, XRD) [44], methyl methacrylate - N-phenylmaleimide... 

Keywords Polyurethanes, Nanocomposites, Nanoparticles, Thermal stability. Degradation mechanisms, TGA... 

Zhu et al. studied polyurethane foams from soy reinforced with cellulose microfibers. They found an increase on the onset degradation temperature of the thermal degradation of polyurethane with the addition of 2 wt % cellulose fibers. They attributed this fact to the insulator effect of cellulose fibers [52]. Navarro-Baena et al. studied shape memory PU based on PLA-PCL-PLA block copolymer and reinforced with both CNCs and PLA grafted CNCs [72]. Aside the increment on the shape memory behavior of the polyurethane-based nanocomposites, they reported an increase on the thermal stability of the PU matrix in particular, they reported that, although CNCs improved the thermal stability of both PCL and PLEA blocks, in particular the thermal stability of the PCL block was improved in the nanocomposites increasing the maximum degradation temperature of about 40 with respect to the PCL block of the neat PU-matrix [72]. 

The imphcation from the above work is that polymer present in the galleries of montmorillonite through intercalation and exfoliation has enhanced thermal stability provided by a different thermal degradation mechanism when compared to the pure polymer. Calculations of the activation energy of polyurethane-imide-clay nanocomposites [37] utilizing the Broido [38] and Coats-Redfern equations were consistent with a mechanism that increased the thermal stability of the polymer-clay nanocomposite in relation to the pure polymer. An optimization of melt-blending processing that improved the exfoliation efficiency of polymer-clay nanocomposites resulted in increased thermal stability by TGA when compared to polymer-clay nanocomposites with inferior exfoliation, and pure polymer [39]. 

Guo et al. synthesized a series of block-type amphiphilic copolymers via copolymerization of methacrylate end-capped oligo-urethane and MPS via the sol-gel process [167]. After hydrolysis and condensation of the copolymer precursors (self-assembled in the form of spherical micelles), polyurethane-silica hybrid materials with excellent thermal stability and mechanical properties were obtained. Etmimi et al. synthesized PS-GO nanocomposites via surface RAFT-mediated miniemulsion polymerization [155]. The molar mass and dispersity of PS in the nanocomposites were dependent on the amount of RAFT-grafted GO in the system. The PS-GO nanocomposites were of exfoliated morphology, and their thermal stability and mechanical properties were dependent on the modified GO content and better than those of neat PS polymer. Salami-Kalajahi et al. studied the effect of pristine nanoparticle loading on the properties of PMMA-silica nanocomposites prepared... 

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