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1.
    
Currently, the application of composites in aerospace parts exposed to higher temperatures and in aggressive media is still severely limited. To replace metal alloys, alternative resins systems with suitable long-term heat resistance are needed. In this study, the effect of the aviation hydraulic fluid Skydrol on the thermal and mechanical properties of a high-Tg, anhydride-cured epoxy resin in the unmodified and toughened state at elevated temperature is investigated. An aliphatic polyester diol was selected as an intrinsic toughener and its impact on the thermal, mechanical, and aging properties was determined. Experimental characterization of the aging effects is carried out with dynamic-mechanical characterization, infrared spectroscopy, and electron dispersion x-ray spectroscopy. In addition, the fracture toughness and the fatigue crack propagation behavior are determined. Initially, the toughened system shows an improved fracture toughness. Since oxidation is blocked by the Skydrol fluid only thermal degradation takes place as determined by the decrease in glass transition temperature Tg and network density. The thermal degradation leads to a tougher behavior, which is observed in both systems in static and dynamic mode with toughness decreasing with aging time again.  相似文献   

2.
    
Colloidal particle formation followed by their clustering has been shown to be the normal way of ageing of aminoplastic resins, in particular melamine–urea–formaldehyde (MUF) resins. Ageing (or further advancement of the resin by other means such as longer condensation times) causes whitening of the resin. This is a macroscopic indication both of the formation of colloidal particles and of their clustering. Some clustering appears rather early in this process, even when the great majority of the resin does visually appear to be in colloidal state, being transparent. However, it eventually progresses to resins which are mostly in colloidal, clustered state, followed much later by a supercluster formation starting to involve the whole resin. There appears to be clear correspondence between molecular mass increases as obtained by gel permeation chromatography (GPC), low‐angle laser light scattering (LALLS) analysis, and observation by polarizing optical microscopy. LALLS, however, appears to indicate the dimensions of the colloidal particles themselves when the level of colloidal aggregation is rather low, but it indicates the dimensions of the clusters once these are mostly aggregated. The smaller visible colloidal particles, already aggregates, were found by polarizing optical microscopy to be of a mostly elongated, rodlike shape, the length of which was shown to grow much further than their width with resin advancement and ageing. As their dimensions indicate, these are already clusters; this implies that the mainly linear increase of the polycondensate chains influences also the simpler colloidal clusters' growth direction, possibly explaining the resins' lack of tridimensional hardening while still in storage. It also explains why molecules such as free urea and acetals, by disrupting these colloidal aggregation mechanisms, allow both a much longer shelf life of the resin and its better performance in hardening. These findings explained the considerable difference in the behavior and performance of different MUF resin formulations. The ageing of the MUF resins of different preparation procedures appeared then to proceed from (1) clear resin (molecular colloidal aggregation) to (2) superclusters of a whitened, heavily thixotropic resin, which is the beginning of physical gelation to (3) liquid/cluster separation, which is the terminal stage of physical gelation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2690–2699, 2004  相似文献   

3.
    
With unsubstituted phenol, formaldehyde, and primary aromatic amines as the starting materials, a series of monofunctional benzoxazine resins with low viscosities at room temperature were developed. The polymerization behavior of these resins into thermosetting materials was monitored by differential scanning calorimetry. Stress relaxation of the obtained polybenzoxazines revealed these polymers to be chemically crosslinked networks. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2953–2966, 2002  相似文献   

4.
    
Currently, epoxy resin (EP) is widely used in various fields, but its flammability greatly limits the wider application of EP. In recent years, additive flame retardants have been widely used to enhance the flame retardancy of EPs, but poor resistance to weather and aging is a prevalent issue encountered with additive flame retardants. To improve the weather fastness, researchers have successfully created and synthesized EP molecules that possess a combined effect of P, N, and B. The results demonstrate a significant enhancement in the mechanical properties of materials containing 20% BVN/10% VPD/EP compared with those of pure EP. 20% BVN/20% VPD/EP exhibited a vertical combustion rating of V-1 with a limiting oxygen index measuring at 29.8%. The flame retardant epoxy thermosets exhibited a notable decrease in both the maximum heat release rate and total heat release. The findings indicate that the inherent flame-retardant properties of the P-N-B coacting EP are not only characterized by exceptional curing and flame retardancy but also by superior resistance to weathering and aging compared with the additive flame retardant.  相似文献   

5.
    
Possessing excellent properties including good biocompatibility, high strength, and stiffness, polyether-ether-ketone (PEEK) has significant application values in medical and industrial fields. However, the relatively poor wettability and low adhesion limit its further applications. Atmospheric pressure plasma jet (APPJ) has been utilized for adjusting PEEK properties, but better hydrophilization effect and time stability after treatment are still urgently needed. In this paper, we employ a water-mixing nitrogen (N2 H2O) APPJ to process PEEK, and surface wettability can be effectively improved (contact angle ~18° within 2 min, distance between sample and nozzle outlet: 10 mm) without inducing obvious microstructure damages. Additionally, after storing for 40 days, the sample treated by N2 H2O APPJ also possessed better wettability (~54°) compared with that treated by N2 APPJ (~65°). On the basis of this low-damage and high-efficient modification method, we perform aging experiments under different conditions (different temperatures 25, −10°C; and low vacuum condition: 50 kPa) to determine a relatively optimum storing condition for this method. The experiment results indicate that low temperature and vacuum are conducive to retaining the plasma-induced wettability (~34°). The treatment method and storing conditions for PEEK presented here may facilitate the application of PEEK in various fields.  相似文献   

6.
    
The aging of a novolak resin solution used in iron‐making blast furnace taphole clays is reported. The novolak resin propylene glycol solution was aged at temperatures between 2 and 80°C for up to 56 days. The viscosity was measured to evaluate the change in the resin's behavior. A cure reaction was found to occur with the addition of hexamethylenetetramine (HMTA) at temperatures lower than had previously been reported. Methods for handling and storage of taphole clay to avoid excessive increases in viscosity due to aging are discussed. An approach for estimating the long term aging at temperatures of 30 to 50°C was considered using shorter term aging data obtained at 70 and 80°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 267–276, 2004  相似文献   

7.
    
The thermooxidative aging of ammonia‐catalyzed phenolic resin for 30 days at 60–170°C was investigated in this article. The aging mechanism and thermal properties of the phenolic resin during thermooxidative aging were described by thermogravimetry (TG)–Fourier transform infrared (FTIR) spectroscopy, attenuated total reflectance (ATR)–FTIR spectroscopy, and dynamic mechanical thermal analysis. The results show that the C? N bond decomposed into ammonia and the dehydration condensation between the residual hydroxyl groups occurred during the thermooxidative aging. Because of the presence of oxygen, the methylene bridges were oxidized into carbonyl groups. After aging for 30 days, the mass loss ratio reached 4.50%. The results of weight change at high temperatures coincided with the results of TG–FTIR spectroscopy and ATR–FTIR spectroscopy. The glass‐transition temperature (Tg) increased from 240 to 312°C after thermooxidative aging for 30 days, which revealed the postcuring of phenolic resins. In addition, an empirical equation between the weight change ratio and Tg was obtained. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

8.
    
The influence of temperature and pH on the ageing of piping made from polyamide 11 (PA‐11) was studied using water from an oilfield (pH = 5.5) and deionized water (pH = 7.0) with monitoring by corrected inherent viscosity (CIV) measurements. The hydrolytic degradation was more extensive at high temperatures in oilfield water. When the system reaches equilibrium, the pH affects mainly the CIV plateau values. Thermogravimetry, energy‐dispersive X‐ray spectroscopy, differential scanning calorimetry, X‐ray diffraction, and scanning electron microscopy measurements were also used to investigate aspects involved in the ageing PA‐11. The hydrolytic degradation of PA‐11 leads to formation of low molar mass compounds, such as oligomers dispersed in the polymeric matrix. This is a process that occurs preferentially in the amorphous domain of PA‐11, which leads to an increase in the degree of crystallinity and the formation of a new γ‐phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

9.
Tests of the strain sweep, frequency sweep, and stress relaxation for raw epoxidized natural rubber were carried out with a rubber processing analyzer. The results showed that the complex viscosity, η*, decreased with the prolongation of the aging time in the region of Newtonian flow, but in the region of non‐Newtonian flow, the decrement of η* with a rising shear rate decreased with the prolongation of the aging time. The torque (S′) response from the strain sweep indicated that aging brought about an obvious decrease in the increment of S′ with rising strain in the linear viscoelastic region and a small increase in the slope of the plateau on the curve of the S′ response in the nonlinear viscoelastic region. The stress relaxation rate constants k and b, calculated according to the equations St = S0e?kt and St = S1t?b (where St, S0, and S1 are the stresses at relaxation time t, t = 0, and t = 1, respectively), increased, and the stress relaxation time obtained directly from the rubber processing analyzer shortened with the prolongation of the aging time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1277–1281, 2006  相似文献   

10.
    
A multifunctional epoxy tetraglycidyl dibenzmethyldiamine and triglycidyl benzylamine were blended, respectively, into impregnation resin, which mainly consists of diglycidyl ether of bisphenol A (DGEBA) and acid anhydride hardener. This resin is expected to impregnate HT‐7U superconducting Tokamak toroidal field coils and improve the fracture toughness of DGEBA–acid anhydride resin at cryogenic temperature. However, the experimental results reveal that resin lap shear strengths decrease remarkably both at ambient and liquid nitrogen temperatures. After blending multifunctional epoxy for several hours, its viscosity increased quickly at room temperature. The usable potting life is too short to impregnate large coils such as those used in fusion reaction. By FTIR the possible reason was investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1385–1389, 2003  相似文献   

11.
    
The relaxation kinetic of the epoxy network diglycidyl ether of bisphenol A (BADGE n = 0) and m‐xylylenediamine (m‐XDA) was analyzed from DSC experimental data, using different theoretical models. Based on a Petrie model, which involved separate contributions of temperature and structure, three characteristic parameters were calculated: a preexponential factor A, an apparent activation energy EH, and a parameter C, which indicate the dependency of relaxation time on structure. This model allowed us to calculate the relaxation function at different ageing temperatures. Another method used to study a relaxation kinetic was the Kovacs–Hutchinson model, which takes into account the dependency of the relaxation time on temperature and structure. The last model used was a two‐parameter equation from Williams–Watts, where the relaxation time is independent of temperature. Using data of characteristic times a master curve for the relaxation function was obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1591–1595, 2005  相似文献   

12.
    
Colloidal particles formation followed by their clustering have been shown to be the normal way of ageing of aminoplastic resins, namely urea–formaldehyde (UF) resins, melamine–formaldehyde (MF) resins, and melamine–urea–formaldehyde (MUF) resins. Ageing or further advancement of the resin by other means such as longer condensation times causes whitening of the resin. This is a macroscopic indication of both the formation of colloidal particles and of their clustering. It eventually progresses to resins, which are mostly in colloidal, clustered state, followed much later on by a supercluster formation starting to involve the whole resin. The initial, filament‐like colloidal aggregates formed by UF resins have different appearance than the globular ones formed by MF resins. MUF resins present a short rod‐like appearance hybrid between the two. GPC has been shown to detect the existence of colloidal superaggregates in a UF resin, while smaller aggregates might not be detected at all. The star‐like structures visible in the colloidal globules of MF resins are likely to be light interference patterns of the early colloidal structures in the resins. These star‐like interference patterns become more complex with resin ageing or advancement due to the advancement of the resin to more complex aggregates, to eventually reach the stage in which filament‐like and rod‐like structures start to appear. The next step is formation of globular masses that are representative of the true start of physical gelation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1406–1412, 2006  相似文献   

13.
    
The viscosity and shear strength of pressure‐sensitive adhesives based on natural rubber (standard Malaysian rubber grade L) were studied with gum rosin and petroresin as the tackifying resins. Effects of the concentration of the tackifying resin and the molecular weight of rubber on the two properties were systematically investigated. Toluene was used as the solvent throughout the study to prepare the adhesives. The viscosity and shear strength of the adhesives were determined with a rotary viscometer and a texture analyzer, respectively. For the shear test, a hand coater was used to coat the adhesives on the release paper substrate to provide coating thicknesses of 60 and 120 μm. The results indicated that the viscosity increased with the resin loading and molecular weight of rubber increasing. The viscosity of the adhesive prepared from petroresin had a higher value than that of the gum‐rosin‐based adhesive. The shear strength of the adhesives decreased gradually with increasing resin content for both tackifying resins and coating thicknesses, and this observation was attributed to the decrease in the cohesive strength due to the dilution effect of the resins. However, the shear strength passed through a maximum at a molecular weight of rubber of 8.5 × 104 for both resins. The gum‐rosin‐based adhesive consistently showed higher shear strength than that of the petroresin/natural rubber adhesive because of the better cohesiveness and compatibility of the former system. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

14.
    
This study investigates creep and viscoelastic behavior of the diglycidyl ether of bisphenol A (DGEBA) epoxy resin and triethylenetetramine (TETA) system containing an imidazolium ionic liquid (IL), the 1-n-butyl-3-methylimidazolium chloride ( C 4 MImCl ). Different time-dependent analysis methods are studied using data from tensile creep, tensile creep/recovery, and three-point and four-point flexural creep tests of epoxy with 1.0 or 4.0 phr of IL. From the results, the composition containing 1.0 phr of C 4 MImCl , cured at 60°C, presented greater viscoelasticity and crosslink density compared to compositions cured at 30 and 40°C, which was attributed to higher free volume and higher molecular mobility induced by the presence of the IL. In tensile creep tests using the stepped isostress method (SSM), no important degrading effects were found after the addition of 1.0 phr of IL over long time periods. This composition also showed the best overall performance in flexural SSM creep tests.  相似文献   

15.
    
New epoxy resins, ER1–M(II) and ER2–M(II) (molar ratio of epichlorohydrin), bearing Schiff‐base metal complexes were prepared by the condensation of epichlorohydrin with Schiff‐base metal complexes (L2M, azomethine metal complexes) in 2 : 1 and 1.25 : 1 molar ratios, respectively, in an alkaline medium. The synthesized epoxy resins were characterized by various instrumental techniques, such as analytical, spectral, and thermal analysis. The epoxide equivalent weight (g/equiv) and epoxy value (equiv/100 g) of the synthesized epoxy resins were measured by standard procedures. The results of thermogravimetric analysis ascribed that ER2–M(II) showed better heat‐resistance properties than ER1–M(II) epoxy resin. The glass‐transition temperatures of all of the synthesized polymers were in the range 153–230°C. The antimicrobial activities of these resins were screened against some bacteria and against some yeast with an agar well diffusion method. All of the synthesized resins showed promising antimicrobial activities. Cu(II)‐chelated resin showed wider effective antibacterial and antifungal activities than the other resins because of a higher stability constant. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

16.
The proper viscosity of urea-formaldehyde (UF) resin adhesive for optimum adhesion depends on the type of a raw wood material for wood-based composite panels. This study investigated the practical relationship between apparent viscosity and molecular weight (MW) of UF resin adhesives during the control of their synthesis. The UF resins were synthesized at various formaldehyde/urea (F/U) mole ratios ranging from 0.8 to 1.5 with different apparent viscosities. In addition, low- and high-viscosity UF resins with 1.0 and 1.2 F/U mole ratios, respectively, were mixed at five different blending ratios of 100:0, 75:25, 50:50, 25:75, and 0:100 to obtain different viscosities. The MW of each resin was measured by gel permeation chromatography, and the relationship between apparent viscosity and MW was derived using the Mark-Houwink (M-H) equation. The results showed a good relationship between the two parameters, allowing the prediction of the MW of UF resins based on their apparent viscosity after synthesis. The weight average molecular weight (Mw) values fit well with the M-H equation, while the number average molecular weight (Mn) values did not. For the first time, this paper has reported that k and α, constants of the M-H equation based on Mw of the UF resin, ranged from 0.015 to 0.017 and 1.172 to 1.276, respectively. These suggest that the relationship between apparent viscosity and Mw should be considered for the synthesis of UF resin adhesives.  相似文献   

17.
    
Pressure‐sensitive adhesives (PSAs) used in disposable diaper construction have been formulated using blends of olefinic block copolymer (OBC) and an ethylene–propylene (PE‐PP) amorphous polyolefin (APO) polymer, with three different unsaturated hydrocarbon resins (with varying aromatic content), and also with two different saturated aliphatic hydrocarbon resin (with varying cycloaliphaticity). The viscoelastic properties of theses PSA formulations were studied using dynamic mechanical analysis (DMA). Viscosity profiles at five different temperatures were generated to better understand the application window for the resulting adhesive formulation. Rheology master curves were generated using time–temperature–superposition analysis and correlated with the processability characteristics. Adhesives used in disposable diaper construction were applied between a polyethylene backing and a nonwoven substrate with an air‐assisted spiral spray application technique on an Acumeter Spray Coater. After the adhesive was applied, peel adhesion testing on the samples was performed. It has been observed that the OBC/PE–PP‐based disposable diaper construction PSA has a lower application temperature along with wider tolerance for hydrocarbon resin chemistries, especially for the saturated aliphatic resin‐based PSA formulations. Based on the coating parameters used, it has been learned that the adhesive formulations seem to show a higher shear rate at the nozzle, but Reynolds number calculated indicated no major turbulence occurring at the nozzle during spraying. Very good spray patterns were obtained for the olefinic polymer‐based PSA formulations. Disposable diaper construction article showed good adhesive peel properties, especially for the adhesive formulations containing saturated aliphatic hydrocarbon resin, which were comparable to the SBS‐based control. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3311–3318, 2013  相似文献   

18.
    
As an important engineering material, polycarbonate (PC) has been used widely. When exposed to the environment, PC will have aging process, which will reduce its performance and efficiency. This article studies the changing regularities of PCs structure and properties of ageing in western areas of China by measuring the change of intrinsic viscosity (IV), thermal decomposition temperature, glass transition temperature, and the groups within PC. The analysis of its IV, DSC, and thermo gravimetric analysis exhibited the same changing regularity, i.e., the aged PC (in Lasa, Yuli, and Jiangjin) experienced degradation and crosslinking, while degradation occurred earlier in the process of ageing, crosslinking predominated in later period. In addition, the results of UV absorption spectra and infrared absorption spectra showed the evidence of decomposition of the ester groups, resulting in the production of alcohol and phenol. And the results of mechanical tests indicated that the ductility disappeared mainly in the first year of outdoor aging. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

19.
    
A series of low viscosity acrylate‐based epoxy resin (AE)/glycol diglycidyl ether (GDE) systems were prepared. The effect of GDE and low molecular weight polyamide (LPA) content on the rheological behavior, phase structure, damping, and mechanical properties were studied by differential scanning calorimeter (DSC), viscometer, scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA), and electro mechanical machine. The viscosity of the uncured AE systems decreased significantly after the incorporation of GDE. The damping properties were found to decrease slightly with the increasing GDE and LPA content. The tensile strength of the cured AE/GDE samples enhanced significantly after the incorporation of GDE with at least 150% improvement for all the samples while it decreased slightly with increasing LPA content. The AE/GDE cured systems were intended for future use as structural damping materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42959.  相似文献   

20.
    
A “green” vinyl ester resin (GVER) is investigated for use in structural applications. The GVER was formulated using a monodisperse vinyl ester created via a novel synthetic route capable of using bio‐waste material from paper and biodiesel industries. The GVER was used either as a neat resin or as blended with a commercial vinyl ester resin. The processing viscosity and gel times are investigated. The GVER reaches a similar viscosity as the commercial resin with only half the styrene monomer content, thereby reducing the volatile organic compounds associated with manufacturing. Composites of the GVER matrix reinforced by carbon fabric were tested for their tensile and flexural properties. The mechanical performance of the GVER compares favorably with commercial resin and provide a route for composites manufacturing from sustainably sourced vinyl ester matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44642.  相似文献   

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