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Constant Weight (constant + weight)

Distribution by Scientific Domains

Polymers and Materials Science	50%

Selected Abstracts

Processing of urea-formaldehyde-based particleboard from hazelnut shell and improvement of its fire and water resistance

FIRE AND MATERIALS, Issue 8 2009
M. Gürü
Abstract The purpose of this study was to manufacture urea-formaldehyde-based particleboard from hazelnut shell and eliminate its disadvantages such as flammability, water absorption, swelling thickness by using fly ash and phenol-formaldehyde. Synthesized urea-formaldehyde and grained hazelnut shells were blended at different ratios ranging from 0.8 to 3.2 hazelnut shell/urea-formaldehyde and dried at 70°C in an oven until constant weight was reached. In addition, other parameters affecting polymer composite particleboard from hazelnut shell and urea-formaldehyde were investigated to be the amount of fly ash, amount of phenol formaldehyde and the effects of these parameters on bending stress, limit oxygen index, water absorption capacity and swelling in the thickness. The optimization results showed that the maximum bending strength was 4.1N/mm2, at urea-formaldehyde ratio of 1.0, reaction temperature of 70°C, reaction time of 25,min, hazelnut shell/urea-formaldehyde resin of 2.4 and mean particle size of 0.1,mm. Although the limited oxygen index and smoke density of composite particleboard without fly ash has 22.3 and 1.62, with fly ash of 16% (w/w) according to the filler has 38.2 and 1.47, respectively. Water absorption and increase in the swelling thickness exponentially decreased with increasing phenol formaldehyde. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Thermal stability and ablation properties of silicone rubber composites

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008
Eung Soo Kim
Abstract Effects of incorporation of clay and carbon fiber (CF) into a high temperature vulcanized (HTV) silicone rubber, i.e., poly(dimethylsiloxane) (PDMS) containing vinyl groups, on its thermal stability and ablation properties were explored through thermogravimetric analyses (TGA) and oxy-acetylene torch tests. Natural clay, sodium montmorillonite (MMT), was modified with a silane compound bearing tetra sulfide (TS) groups to prepare MMTS4: the TS groups may react with the vinyl groups of HTV and enhance the interfacial interaction between the clay and HTV. MMTS4 layers were better dispersed than MMT layers in the respective composites with exfoliated/intercalated coexisting morphology. According to TGA results and to the insulation index, the HTV/MMTS4 composite was more thermally stable than HTV/MMT. However, addition of CF to the composites lowered their thermal stability, because of the high thermal conductivity of CF. The time elapsed for the composite specimen, loaded with a constant weight, to break off after the oxy-acetylene flame bursts onto the surface of the specimen was employed as an index for an integrated assessment of the ablation properties, simultaneously taking into consideration the mechanical strength of the char and the rate of decomposition. The elapsed time increased in the order of: HTV < HTV/CF , HTV/MMTS4 < HTV/CF/MMTS4 , HTV/MMT < HTV/CF/MMT. This order was different from the increasing order of the thermal stability determined by TGA results and the insulation index. The decreased degree of crosslinking of the composites with MMTS4 compared with that of the composite with MMT may be unfavorable for the formation of a mechanically strong char and could lead to early rupture of the HTV/MMTS4 specimen. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Preparation of extruded melt-mixed polypropylene/montmorillonite nanocomposites with inline monitoring

POLYMER ENGINEERING & SCIENCE, Issue 3 2010
Marcelo K. Bertolino
This article advances the use of an inline optical detector to monitor the disaggregation of the montmorillonite (MMT) clay tactoids during the preparation of polypropylene (PP)/MMT nanocomposites via polymer melt compounding. During the exfoliation of the tactoids their size are reduced below the minimum particle size to produce light extinction and so, the signal of the inline detector reduces as the nanosize composite is formed. The measurement is done at the transient state with the MMT clay added as a pulse with constant weight into the PP extrusion melt flow and followed by the optical detector. The data comes out as the common residence time distribution curves having its maximum intensity related to the tactoids average particle size, keeping all other variables constants. The light extinction was measured for composites with different clays (Cloisite® 15A, 30B, Na+, and Sintered 20A) using the same PP grafted with maleic anhydride compatibilizer. The dissaglomeration/exfoliation efficiency increases as: ,,Sintered 20A'' < ,,Na+ clay'' < ,,organo-modified clay'' < ,,organo-modified clay + compatibilizer''. The best result is obtained using Cloisite® 15A and Cloisite® 20A following the expected reduction of the particle size obtained during a nanocomposite melt processing. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source]

Weighted Wilcoxon-Type Smoothly Clipped Absolute Deviation Method

BIOMETRICS, Issue 2 2009
Lan Wang
Summary Shrinkage-type variable selection procedures have recently seen increasing applications in biomedical research. However, their performance can be adversely influenced by outliers in either the response or the covariate space. This article proposes a weighted Wilcoxon-type smoothly clipped absolute deviation (WW-SCAD) method, which deals with robust variable selection and robust estimation simultaneously. The new procedure can be conveniently implemented with the statistical software R. We establish that the WW-SCAD correctly identifies the set of zero coefficients with probability approaching one and estimates the nonzero coefficients with the rate n,1/2. Moreover, with appropriately chosen weights the WW-SCAD is robust with respect to outliers in both the x and y directions. The important special case with constant weights yields an oracle-type estimator with high efficiency in the presence of heavier-tailed random errors. The robustness of the WW-SCAD is partly justified by its asymptotic performance under local shrinking contamination. We propose a Bayesian information criterion type tuning parameter selector for the WW-SCAD. The performance of the WW-SCAD is demonstrated via simulations and by an application to a study that investigates the effects of personal characteristics and dietary factors on plasma beta-carotene level. [source]