摘要:

The changes in the crosslink density, elastically effective chains and entanglements in the network, and the molecular weights between crosslinks of three different commercially available structural silicone sealants used in glazing applications were monitored as a function of specific aging factors. The aging variables included simultaneous exposure to ozone and moisture in which the pH of the moisture was maintained at discrete levels in the acid and the alkaline range. The simultaneous effect of external loading on the performance of these sealants was also studied. Unexposed and unstressed test samples kept at ambient laboratory conditions were used as the control. Results of these weathering studies indicate that the crosslink density of the sealants will decrease during the initial period as a result of their exposure, and some surface cracking was observed. However, following this initial exposure period, the sealants showed an increase in the crosslinking activity. All three formulations of the silicone sealants appeared to crack at angles of 90° across the line of tension (loading). The acid and ozone combination especially appears to act synergistically in the deterioration of these sealants. However, the test coupons exposed to moisture at the higher, or caustic, pH level did not show similar behavior. The medium-modulus material exhibited good overall resistance to the synergetic effects which can cause surface cracking of the sealant. However, significant changes were observed in the elastically effective chains in the network and for the molecular weights between crosslinks. The effect of external loading on the sealants was significant only for the high-modulus formulation. Even though the attack of ozone and acid on these silicone sealants was not classified as aggressive, the slow progressive attack and surface cracking should still be of concern. It is hoped that these test results can lead to more informed decisions concerning silicone sealant life following their exposure to ozone and acid precipitation.

ISSN:0360-2559    

DOI:10.1080/03602559408010736

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new disk-type viscous pump, with radial pumping grooves on its stator, is described and its performance analyzed. Its flow rate and discharge pressure relationship is found to be linear. Two proposed viscous pumps of this new design having slightly different dimensions are considered and compared to the recently reported design utilizing multilobes. Analyses on these two proposed pumps show that this new design exhibits higher flow rate characteristics than the recent multilobe design for the same pump size and rotor–stator clearances.

ISSN:0360-2559    

DOI:10.1080/03602559408010737

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Transport characteristics of aliphatic esters into Du Pont's VITON fluoropolymers have been investigated. Diffusion coefficients are calculated from the dimensional change measurements and are compared with those obtained from the weight-gain measurements. Effects of fluorine content of the polymers on the transport properties are discussed.

ISSN:0360-2559    

DOI:10.1080/03602559408010738

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

By blending thermoplastics (TPs)—polycarbonate (PC) and polyethersulfone (PES)—with thermotropic liquid crystalline polymers (TLCPs)—KU9221 and KU9231—and then extruding the blends to form fibers, thein situreinforcing characteristics were studied. The injection experiment of blends was compared with the extrusion experiment. According to the experimental results,in situreinforcing characteristics of these processes were analyzed theoretically. These researches have come to some important conclusions. TLCP domains can be transformed to form fibers that are oriented in the direction of flow during processing; these TLCP microfibers result in improved mechanical properties of the TP/TLCP blends. The extruding flow is more effective in orienting TLCP domains and results in betterin situreinforcement than that of injection molding, and the extruded fibers have better mechanical properties. The mechanical properties of the blend fibers are improved greatly with increasing tensile ratio of melt drawing and the content of TLCPs.

ISSN:0360-2559    

DOI:10.1080/03602559408010739

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Pretreatment of wood chips with some microorganisms including white-rot fungi and streptomyces improves the strength properties of mechanical pulps. We studied the effect of these white-rot fungi and streptomyces on the mechanical properties of handsheets. Strength and optical properties were compared in handsheets prepared from mechanical pulp of treated and untreated wood chips. The fungal pretreatments resulted in handsheet strength properties better than the control and also better than streptomyces when compared at an equivalent freeness. Fungal pretreatments decreased brightness and light-scattering coefficients but did not adversely affect opacity. Lignin content of the chips was reduced by fungal pretreatments.

ISSN:0360-2559    

DOI:10.1080/03602559408010740

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Nylon 6,6 cord is used as reinforcement in rubber products (e.g., tires, hoses, and belts). The problem of bonding rubber to textile cords is due to the big difference between the surface properties. To obtain a durable reinforced rubber product, it is necessary to produce a bond strong enough to resist the different conditions, for example, high temperature, cyclic tension, compression loads, and shock, depending on the applied rubber product. Choosing a suitable adhesive system and addition of an adhesion promoter into the rubber compound are factors which play a very important role. Many other factors are known to affect the bond strength obtained with resorcinol formaldehyde latex (RFL) adhesives. For example, method of RFL preparation, its composition, amount of adhesive applied to cords, its distribution on the cord, heat treatment conditions after dipping, method of storing dipped cord, composition of rubber compound, and vulcanization conditions are factors affecting the cord-to-rubber bonding. The scope of this research is to study the effect of the heat treatment conditions (temperature and time) after dipping and the effect of the presence of an adhesion promoter in the rubber compound on the adhesion between nylon 6,6 cord and chloroprene rubber. On studying the static adhesion (H-pull-out test) for this system, the test results showed that RFL dipping solution increases adhesion by about a factor of 2, while the heat treatment conditions have only a moderate effect. The resorcinol/hexamethylene tetramine based adhesion promoting material in the rubber compound gave a significant improvement, with both undipped and dipped cords.

ISSN:0360-2559    

DOI:10.1080/03602559408010741

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Wood–plastic composites (WPC) were prepared with kadom and mango wood of Bangladesh under Co-60 gamma irradiation using methylmethacrylate (MMA) as the bulk monomer mixed with methanol (swelling solvent) at different proportions in presence of a number of additives such asN-vinyl pyrrolidone, tripropylene glycol diacrylate, trimethylol propane triacrylate, copper sulfate, sulfuric acid, and urea. Composites prepared with urea, NVP, and CuSO4possess better tensile and protective properties.

ISSN:0360-2559    

DOI:10.1080/03602559408010742

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The problem of helical flow of a Sutterby model fluid has been analyzed numerically using a finite difference technique. Sutterby model fluid is one of the most important non-Newtonian fluids representing constitutive equations for high polymer aqueous solutions of CMC, HEC, and MC, and hence the problem is of practical significance. Computations have been made for the case when the inner cylinder rotates about the common axis with constant angular velocity and the outer cylinder is at rest, while a constant pressure gradient is acting on the axis of rotation. The dimensionless velocity profiles, volumetric flow rate, torque, and pressure distribution have been calculated for various values of the model parameters and the radius ratio.

ISSN:0360-2559    

DOI:10.1080/03602559408010743

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Photoactive polymer has been prepared by the reaction of VOQ2OH (Q: 8-quinolyloxo ligand) with secondary cellulose acetate in dry benzene solution. The photoactive polymer produced, red-violet in color, was characterized by IR and UV-visible spectroscopy. Irradiation of this type of polymer in styrene monomer, both in bulk and in benzene solutions, produces a graft and cross-linked copolymer. This indicates that a radical is produced on the backbone of the secondary cellulose acetate molecule by the so-called intraphotoredox reaction. UV-visible spectral changes during irradiation in styrene solution suggest that the photoreaction is relatively uncomplicated with production of vanadium(IV) species. The grafted polymer was characterized by IR spectroscopy, and the percent grafting and grafting efficiency were determined and monitored as a function of the photoactive cellulose acetate concentration.

ISSN:0360-2559    

DOI:10.1080/03602559408010744

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Cresol–lignin liquors produced as waste from bagasse pulping, at different temperatures (160°–190°C) for 1.5 h and at 170°C for different times (0.75–3 h) were tested to evaluate their reactivity in both alkaline and acidic media toward preparation of cresol–lignin formaldehyde resins. The effects of different polymerization parameters—e.g., time, temperature, ratio of polyphenols to formaldehyde, and reaction medium (acidic or alkaline)—on the yield and properties of produced resins were detected. The yields of the resins produced in alkaline medium are higher than those produced in acidic medium.

ISSN:0360-2559    

DOI:10.1080/03602559408010745

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor