Accelerated Compression Set at Elevated Temperature in Rigid Polymer Foams

A series of rigid polyurethane foams are synthesized via the reaction of isocyanate terminated polyimide prepolymers with polyether polyol. Deionized water and n-pentane are used for blowing agents. The prepolymers and polymers are characterized by conventional methods, and physical, mechanical and thermal properties are studied. The results show that in comparison to pure polyurethane foams, these rigid polymer foams exhibit improved thermal stability as well as good compressive property. SEM of the compressed body of rigid polyurethane-imide foams show that the destructive forms are open-type tear of the film and the breakdown of the cell body wall.

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An Analysis of Relations for Determining the Thermal Conductivity of Rigid Polymer Foams

International Journal of Applied Mechanics and Engineering ◽

10.2478/ijame-2018-0058 ◽

2018 ◽

Vol 23 (4) ◽

pp. 1015-1023 ◽

Cited By ~ 3

Author(s):

A. Alsabry ◽

V.I. Nikitsin ◽

V.A. Kofanov ◽

B. Backiel-Brzozowska

Keyword(s):

Experimental Data ◽

Thermal Conductivity ◽

Porous Media ◽

Thermal Conductivity Coefficient ◽

Geometrical Structure ◽

Polymer Foams ◽

Conductivity Method ◽

Thermal Exchange ◽

Rigid Polymer ◽

Structure Calculations

Abstract In the paper the authors present the effectiveness of the generalized thermal conductivity method for polymer foams, including modelling their geometrical structure. Calculations of the effective thermal conductivity coefficient λ are based on the generally accepted assumption of the additivity of different thermal exchange mechanisms in porous media and this coefficient is presented as a sum the coefficients of conductive λq, radiative λp, and convective λk thermal conductivity. However, in literature not enough attention is given to relations determined by means of the theory of generalized conductivity, including modelling the geometrical structure. This paper presents an analysis of these relations and verifies their ability to predict experimental data in comparison with the best formulae included in the paper [2].

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ENHANCING THE REVERSION RESISTANCE, CROSSLINKING DENSITY AND THERMO-MECHANICAL PROPERTIES OF ACCELERATED SULFUR CURED CHLOROBUTYL RUBBER USING 4,4′-BIS (MALEIMIDO) DIPHENYL METHANE

Rubber Chemistry and Technology ◽

10.5254/rct.18.82605 ◽

2019 ◽

Vol 92 (1) ◽

pp. 110-128 ◽

Cited By ~ 2

Author(s):

Shibulal Gopisathi ◽

Changsin Park ◽

Yang Il Huh ◽

Jinseok Jeon ◽

Chang Hyun Yun ◽

...

Keyword(s):

Mechanical Properties ◽

Elevated Temperature ◽

Crosslink Density ◽

Kinetic Studies ◽

Crosslinking Density ◽

Low Level ◽

Compression Set ◽

Higher Temperature ◽

Chlorobutyl Rubber

ABSTRACT Vulcanizates of chlorobutyl rubber (CIIR) with the accelerated sulfur generally exhibit poor crosslinking density owing to the low level of unsaturation in the backbone of CIIR. Therefore, the sulfur cured CIIR shows inferior thermo-mechanical properties at elevated temperature. In addition to this, the vulcanization of CIIR with accelerated sulfur is limited at higher temperature due to reversion. To solve these problems, 4,4′-bis (maleimido) diphenyl methane (BMDM) was applied as a crosslinking additive along with the accelerated sulfur. The detailed curing studies have proved that the presence of BMDM greatly enhanced the rheometric torque and the reversion resistance while curing CIIR with accelerated sulfur even at higher vulcanization temperature. Moreover, the crosslinking densities of the sulfur cured CIIR have increased by 109% with the use of 1 phr BMDM and further rose to 380% with 5 phr BMDM. The improved crosslink density could enable reduction of the compression set of the sulfur cured CIIR to around 40% at 100 °C when it was vulcanized in the presence of 5 phr BMDM. The kinetic studies revealed that incorporation of this additive does not adversely affect the original vulcanization behavior of CIIR with accelerated sulfur, instead it marginally improved the speed of the vulcanization.

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Improved compression properties of polypropylene extrusion foams by supramolecular additives

Journal of Cellular Plastics ◽

10.1177/0021955x17695096 ◽

2017 ◽

Vol 54 (3) ◽

pp. 483-498 ◽

Cited By ~ 8

Author(s):

M Mörl ◽

C Steinlein ◽

K Kreger ◽

H-W Schmidt ◽

V Altstädt

Keyword(s):

Lightweight Design ◽

Polymer Melt ◽

Compression Modulus ◽

Polymer Foams ◽

Rigid Polymer ◽

Compression Properties ◽

Foam Morphology ◽

Polypropylene Foam ◽

Extruded Foams

Owing to the high lightweight design potential polymer foams become increasingly important. For rigid polymer foams, requiring high dimensional stability under load, a high compression modulus is a key feature. Here, we demonstrate how supramolecular additives can be utilized to control the foam morphology and to significantly improve the compression behavior of extruded foams made of linear isotactic polypropylene. Three different 1,3,5-benzenetrisamides were selected as supramolecular additives. These additives are soluble in the polymer melt and form a supramolecular nanofiber network upon cooling, acting as nucleating sites for both, foam cells and polymer crystals. It is shown that the in situ formed nanofiber network is very effective in reducing the cell size of extruded foams. Depending on the molecular structure and the concentration of the supramolecular additives, the compression modulus of polypropylene-polymer foams can be significantly increased compared to a reference foam with talc. Unexpectedly, an improvement of 100% with a concentration of only 0.02 wt% of a supramolecular additive compared to the neat polypropylene foam featuring similar densities is achieved. This improvement cannot be correlated with the foam morphology and is most likely attributed to the presence of the supramolecular nanofiber network.

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Evidence for a shear mechanism for the precipitation of γ-zirconium hydride in zirconium

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010011043x ◽

1978 ◽

Vol 36 (1) ◽

pp. 658-659

Author(s):

G.J.C. Carpenter

Keyword(s):

Elevated Temperature ◽

Strain Field ◽

Zirconium Hydride ◽

Zirconium Atom ◽

Atom Diffusion ◽

Solvus Temperature ◽

Hexagonal Close Packed ◽

Partial Dislocations ◽

The Face

In zirconium-hydrogen alloys, rapid cooling from an elevated temperature causes precipitation of the face-centred tetragonal (fct) phase, γZrH, in the form of needles, parallel to the close-packed <1120>zr directions (1). With low hydrogen concentrations, the hydride solvus is sufficiently low that zirconium atom diffusion cannot occur. For example, with 6 μg/g hydrogen, the solvus temperature is approximately 370 K (2), at which only the hydrogen diffuses readily. Shears are therefore necessary to produce the crystallographic transformation from hexagonal close-packed (hep) zirconium to fct hydride.The simplest mechanism for the transformation is the passage of Shockley partial dislocations having Burgers vectors (b) of the type 1/3<0110> on every second (0001)Zr plane. If the partial dislocations are in the form of loops with the same b, the crosssection of a hydride precipitate will be as shown in fig.1. A consequence of this type of transformation is that a cumulative shear, S, is produced that leads to a strain field in the surrounding zirconium matrix, as illustrated in fig.2a.

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Microstructural characterization of a rapidly solidified Al-Fe-V-Si alloy for elevated temperature applications

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104819 ◽

1988 ◽

Vol 46 ◽

pp. 550-551

Author(s):

R. E. Franck ◽

J. A. Hawk ◽

G. J. Shiflet

Keyword(s):

High Temperature ◽

Elevated Temperature ◽

Grain Growth ◽

Volume Fraction ◽

Microstructural Characterization ◽

Second Phase ◽

Microstructural Stability ◽

Elevated Temperature Strength ◽

Temperature Applications

Rapid solidification processing (RSP) is one method of producing high strength aluminum alloys for elevated temperature applications. Allied-Signal, Inc. has produced an Al-12.4 Fe-1.2 V-2.3 Si (composition in wt pct) alloy which possesses good microstructural stability up to 425°C. This alloy contains a high volume fraction (37 v/o) of fine nearly spherical, α-Al12(Fe, V)3Si dispersoids. The improved elevated temperature strength and stability of this alloy is due to the slower dispersoid coarsening rate of the silicide particles. Additionally, the high v/o of second phase particles should inhibit recrystallization and grain growth, and thus reduce any loss in strength due to long term, high temperature annealing.The focus of this research is to investigate microstructural changes induced by long term, high temperature static annealing heat-treatments. Annealing treatments for up to 1000 hours were carried out on this alloy at 500°C, 550°C and 600°C. Particle coarsening and/or recrystallization and grain growth would be accelerated in these temperature regimes.

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