摘要:

AbstractIn the present study, the effect of atomic oxygen (AO) exposure, as a simulation of low earth orbit, on the flexural properties and prefailure damage mechanisms of a series of short glass fiber/mica/epoxy composites under three‐point bending were elucidated using acoustic emission (AE) techniques. The incorporation of mica in the composites was shown to increase the resistance to AO as measured by the weight loss, ashing rate, and reaction efficiency. Furthermore, as the mica content increased, the resistance increased such that the all‐mica composite had over one order of magnitude lower ashing rate and reaction efficiency than did the all‐glass‐fiber composite. This increased resistance was caused by the mica particles preferentially orienting parallel to the surface of the composites, creating an inorganic barrier to attack. The AO‐induced erosion was found to have an insignificant effect on both the flexural properties and prefailure damage mechanisms because the erosion was confined to the epoxy surface only and did not affect

ISSN:0021-8995    

DOI:10.1002/app.1991.070421001

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe interaction between combinations of sulfur, stearic acid, and ZnO were studied by differential scanning calorimetry in the absence of rubber. The only reaction observed was between ZnO and stearic acid. A small amount of zinc stearate formed as soon as the stearic acid melted, but the solid product blocked further reaction, which was only completed at 154°C. Water played a major role in the reaction, and in the presence of water, the reaction went to completion at lower temperatures. Sulfur, too, affected the temperature of the ZnO/stearic acid reaction. The preparation of zinc stearate by a number of routes was investigated

ISSN:0021-8995    

DOI:10.1002/app.1991.070421002

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe interaction of combinations of sulfur, 2,2′‐dibenzothiazole (MBTS), ZnO, and stearic acid were studied by differential scanning calorimetry. A MBTS/stearic acid interaction was indicated as evidenced by the effect the MBTS/stearic acid combination had on the melting of sulfur, the Sα→ Sβtransition being suppressed in favor of a Sα→ Sγtransition. The dissolution/interaction of MBTS in molten sulfur was also delayed by the MBTS/stearic acid interaction, which, it is proposed, involved protonation of the N atom in MBTS by stearic acid. MBTS did not affect the formation of zinc stearate from ZnO and stearic acid, but when sulfure was added to the mixture, the ZnO/stearic acid reaction did not go to completion. No direct evidence for the formation of 2,2′‐dibenzothiazole polysulphides was found, but the absence of the Sγ→ Sμtransition in sulfur/MBTS mixes was interpreted as indirect evidence of a reaction between these curatives. There was no evidence for the formation of a sulfur/MBTS/ZnO compound of the type generally attributed the role of an active sulfurating agent in accelerated s

ISSN:0021-8995    

DOI:10.1002/app.1991.070421003

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe interaction among various combinations of sulfur, tetramethylthiuram monosulphide (TMTM), ZnO, and stearic acid were studied by differential scanning calorimetry in the absence of rubber. Sulfur and TMTM reacted to form tetramethylthiuram disulphide, and the ternary eutectic mixture melted at about 80°C. The absence of the Sγ→ Sμtransition in sulfur/TMTM mixes was related to a sulfur/TMTM interaction, wherein the eightmembered sulfur rings were opened at temperatures well below 170°C. The interaction of stearic acid with TMTM led to the decomposition of TMTM, but the reaction was largely suppressed when both ZnO and sulfur were present in the mixture. No evidence was found for the formation of a zinc‐accelerator complex of the type normally attributed a role in the accelerated sulfur vulcan

ISSN:0021-8995    

DOI:10.1002/app.1991.070421004

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe interaction of combinations of sulfur, tetramethylthiuram disulfide (TMTD), ZnO, and stearic acid were investigated by differential scanning calorimetry in the absence of rubber. TMTD decomposed partially to tetramethylthiuram monosulphide on liquefaction. Sulfur and TMTD reacted at vulcanization temperatures, and although the exact composition of all the products was not established, several features involving DSC and HPLC analysis were interpreted in terms of the formation of tetramethylthiuram polysulfides (TMTP). TMTD decomposed much faster to volatile products such as Me2NH, CS2, and CS when heated in the presence of stearic acid. Contrary to literature reports on the facile reaction of TMTD and ZnO to yield zinc perthiomercaptides (or zinc dimethyldithiocarbamate), the TMTD/ZnO reaction was found to be extremely sluggish under a variety of conditions. In the presence of sulfur, too, the TMTD/ZnO reaction was of negligible importance. It was inferred that several reactions occurred concurrently on heating a TMTD/stearic acid/ZnO system. These reactions were not observed for the sulfur/TMTD/stearic acid/ZnO mixture per se, but, instead, the stearic acid/ZnO reaction was very prominent. The formation of zinc stearate occurred at temperatures as low as 77°C in the quadruple system. TMTD and zinc stearate were virtually unreactive at vulcanization temperatures. None of the reactions involving ZnO could be attributed to the formation of a zinc perthiomercaptide, generally accepted to be a precursor in thiuram vulcanization

ISSN:0021-8995    

DOI:10.1002/app.1991.070421005

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractAllyl ether resins with various chemical structures and degrees of functionality were used as promoters and cross‐linkers for polymerization of acrylic oligomers at room temperature in air. Thin films were prepared to allow monitoring of polymerization via disappearance of acrylate and allylic unsaturation by FTIR. The effect of air upon curing of films was investigated; excluding air from the surface of the film had a much greater effect than did addition of allyl ether. In air, the curing rate and extent of cure were found to be dependent upon molecular weightMnand degree of functionality of the allyl compounds. At high allyl monomer concentrations, homopolymerization of the allyl groups occurred. The mechanical properties (tensile strength, Young's modulus, and elongation at break) of films were evaluated on an Instron, whereas viscoelastic properties, transition temperatures, and cross‐link densities of polymer bars were studied by dynamic mechanical analysis and relaxation measurements. The study showed that addition of highly functional allyl ethers combines the advantages of an air‐curable system with those of highly cross‐linked materials, allowing ultimate properties to be t

ISSN:0021-8995    

DOI:10.1002/app.1991.070421006

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractBinary polymer films containing different percentages of corn starch and low‐density polyethylene (LDPE) were exposed to soils over a period of 8 months and monitored for starch removal and chemical changes of the matrix using FTIR spectroscopy. A standard curve using the area of the CO stretch band and an empirical second‐degree polynomial to fit the data made it possible to calculate starch concentration over a wide range (0–46% by mass). Starch removal was found to proceed rapidly during the first 40 days and to nearcompletion in very high starch blends (52% and 67% by weight). Starch removal was slower, consisting of mostly surface removal in 29% starch blends. Weight loss data supported spectroscopic data showing similar gross features. Weight loss and spectroscopic data were consistent with percolation theory and suggested that starch removal continues past 240 days. Degradation rates in different soils containing different amounts of organic matter were approximately the same after a period of a few weeks. IR analysis did not show significant chemical changes in the polyethylene matrix after 240 days. However, the matrix did show evidence of swelling, an increase in surface area, and removal of low molecular weight com

ISSN:0021-8995    

DOI:10.1002/app.1991.070421007

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractChanges brought about in the crystal morphology of drawn (oriented) PET fibers following both heat and liquid treatments were studied using wide angle X‐rays and critical dissolution time techniques. The results obtained showed that the two techniques were sensitive to different but closely related morphological properties of the polymer, the former being sensitive to the apparent degree of the crystalline content, and the latter, a measure of the size of such crystallites that were produce

ISSN:0021-8995    

DOI:10.1002/app.1991.070421008

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractSolid agar–agar was irradiated with60Co gamma‐rays, and effects of radiation on the cross‐links of agar–agar molecule were studied by measuring the melting and setting points of the agar–agar hydrogel at different radiation dose and elapsed time after ir

ISSN:0021-8995    

DOI:10.1002/app.1991.070421009

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractCold plasma treatment of polyester fabric in the presence of several volatile monomers containing expected flame retardant elements was made and some of the flammability characteristics of the plasma/monomer‐treated fabric were studied. The plasma treatment on the fabric caused a slight decrease in both oxygen index values and burning rates. It is believed that crosslinking outweighs the effect of grafted elements. The results of wettability and TGA tests as well as SEM data are include

ISSN:0021-8995    

DOI:10.1002/app.1991.070421010

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY