The effects of preselected six different layered double hydroxides (LDHs) (Zn/Al 4:1 DDS, Mg/Al 2:1 DDS, Zn/Al 2:1 stearate, Mg/Fe 4:1 stearate, Zn/Al 2:1 laurate, and Mg/Fe 4:1 laurate) on the mechanical, thermal, and fire properties of poly(methyl methacrylate) (PMMA) nanocomposites, synthesized by intercalative in situ bulk polymerization, were evaluated. PMMA nanocomposites containing three different LDH concentrations (1, 3, and 5 wt%) were produced, and it was observed that all the nanocomposites with lower LDH
EFFECT OF DOUBLE HYDROXIDES ON PROPERTIES OF PMMA NANOCOMPOSITESconcentration (1 wt%) showed a higher elastic modulus than PMMA. However, as the LDH concentration increased, the elastic modulus decreased for all the nanocomposites. It was shown that PMMA/(Zn/Al 2:1 stearate) containing 5 wt% of LDH in its composition exhibited a decomposition temperature about 97• C higher than pure PMMA. According to this study, it was found that it is possible to enhance some mechanical and thermal properties of PMMA using very low LDH concentrations (mass fraction of LDH equal to 1%). LDHs are inexpensive materials based on abundant metals with a simple synthesis method that has a low environmental impact. C 2012 Wiley Periodicals, Inc. Adv Polym Techn 00: 1-15, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21309
The natural fiber market has been growing extraordinarily. Hereupon the current work presents the natural fiber of the periquiteira tree Cochlospermum orinocense of the Amazon forest. The chemical composition, physical aspects, morphology, thermal and mechanical properties of this fiber will be discussed. The thermal stability of the fiber samples was about 200 °C. The decomposition of cellulose and hemicelluloses in the fibers occurred at 300 ºC and above, while the degradation of the fibers happened above 400 °C. This fiber had good specific strength and good binding properties due to their low weight and presence of high cellulose (60.15wt.%), low lignin (12.03wt.%). More pronounced mass loss indicated the degradation of the amorphous regions of the cellulose, and finally reached a peak of approximately 390 °C.
This study evaluated the influence of cellulose nanocrystals (CNC) content on the properties of epoxy nanocomposites. The CNC were obtained from microcrystalline cellulose by acid hydrolysis. 4.0, 5.5 and 7.0% of untreated CNC were incorporated into epoxy resin. Sonication was used to disperse the CNC in the resin. The thermal stability, the glass transition temperature and the degree of conversion were reduced as observed by Thermogravimetry and Differential Scanning Calorimetry, respectively. The tensile and bending modulus showed no significant improvement and the impact resistance showed a slight reduction due to the non-uniform dispersion of the CNCs, as observed by Transmission Electron Microscopy. Analysis of Scanning Electron Microscopy showed a change of the fracture mechanism of the epoxy resin: the CNCs increased the elastic modulus by reinforcement, but accelerated the fracture by acting as defects. The Halpin-Tsai model was applied to predict the elastic modulus of the epoxy/CNC system.
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