The instantaneous elastic moduli for a nylon-6 monofilament were derived on strain recoveries right after creep, stress relaxation, and rapid elongation,Ec,Es andEe, respectively. It was found that during strain recoveryEs(>Ee) andEe increase monotonically with increasing load,m1, on the sample. The extrapolated value of Es atm1=0 g is almost equal to Young's modulus, 4.06 GPa. The value ofEc also increased with increasingm1, and atm1=600 g (1.93 t cm–2) reached about 14 GPa. The endothermic heat change right after creep, stress relaxation or rapid elongation,Q, was negligibly small. For comparison,Es,Ec andQ were also investigated for silicone rubber. It was found thatEs (53.8 M Pa at the draw ratioD=1.2) decreased abruptly atD=1.3. In the range ofD=1.4–1.9,Es was only 22.6 MPa. In the case of stress relaxation,Q increased with increasingD from 4 J mol–1 (atD=1.2) to 56 J mol–1 (atD=1.9). FurthermoreEc (5.58 MPa atm1=133.8 g (429.4 kg cm–2)) increased gradually with increasing m1 and attained 16.6 MPa atm1=548.4 g (1.76 t cm–2). In the case of creep,Q was in the range of 0–11.5 J mol–1 and larger when larger loads,m2 were removed during the later stages of creep.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe author wishes to thank Mr. Keizi Igarashi and Mr. Tetsuya Yasui for helping in the experiments. 相似文献
The correlation between the mechanical strength and the crystallization behavior of natural rubber (NR)/halloysite nanotubes (HNT) composites is discussed. The tensile strength of NR is improved with the addition of HNT. This improvement is attributed to the unique structure of HNT, which facilitates good dispersion and strong interfacial interaction. HNT also play an important role in assisting the strain-induced crystallization of NR. Crystallization under strain is observed using synchrotron wide-angle X-ray scattering. The stress–strain curves and the corresponding degree of crystallinity after straining provide further evidence. Based on these analyses, a mechanistic model for strain-induced crystallization and the evolution of the orientation of the network structure is proposed. 相似文献
To improve the quality of industrial nitrile rubbers, the copolymer chemical composition, pA(t), should ideally be kept constant along the reaction. This work proposes a closed‐loop control strategy for the semibatch operation of the reactor with the aim of regulating pA(t) within a reduced range of variability. The proposed strategy is evaluated by simulating a mathematical model of the process. To this effect, a simplified mathematical model of the reaction is first derived and then utilized to obtain a suboptimal control law and a soft‐sensor that estimates the polymerization rates. The suboptimal control law is compensated by adding a term proportional to errors in pA(t). The simulated example considers the production of the low‐composition AJLT grade, with the copolymerization reaction represented by a detailed mathematical model adjusted to an industrial plant. Due to the high performance of the soft‐sensor, the simulation results suggest that the proposed closed‐loop strategy is efficient to adequately regulate pA(t) in spite of structural and parametric uncertainties, while other quality variables remained practically unaffected. 相似文献
Rubber magnetic composites were prepared by incorporation of strontium ferrite into rubber compounds based on acrylonitrile butadiene rubber and ethylene propylene diene monomer rubber. The sulfur, peroxide, and mixed sulfur/peroxide curing systems were introduced as cross‐linking agents for rubber matrices. The aim was to investigate the influence of curing system composition on curing process and cross‐link density of composite materials. Then, static and dynamic mechanical properties and thermal and magnetic characteristics were investigated in relation to the cross‐link density of rubber magnetic composites and structure of the formed cross‐links. The changes of dynamical and physicomechanical properties were in close correlation with the change of cross‐link density, whereas the tensile strength of magnetic composites showed increasing trend with increasing amount of peroxide in mixed curing systems. On the other hand, thermal conductivity and magnetic characteristics were found not to be dependent on the curing system composition. 相似文献
Water‐induced mechanically adaptive rubber nanocomposites were prepared by mixing bacterial cellulose whiskers (BCWs) suspension with styrene‐butadiene rubber (SBR) latex, followed by evaporation method. The structure, morphology, dynamic mechanical properties, water stimuli‐responsive behavior, and biodegradability of SBR/BCWs nanocomposite films were investigated. The results showed that the hydrophilic whiskers had a significant reinforcement effect on the storage modulus of SBR matrix, which originated from the formation of a rigid three‐dimensional filler network within matrix by strong hydrogen bonding between whiskers. The SBR/BCWs nanocomposites showed pronounced water stimuli‐responsive behavior compared with neat SBR. The storage modulus of SBR/BCWs nanocomposite could be decreased by 99.2% after equilibrium water swelling. This remarkable water‐triggered modulus change is attributed to the disentanglement of BCWs network via competitive hydrogen bonding with water. 相似文献
The effects of high-temperature curing and overcuring on the cure characteristics, crosslink structure, physical properties and dynamic mechanical properties (DMPs) of gum and carbon black (N330) filled natural rubber (NR) vulcanizates cured with conventional (CV), semi-efficient (SEV) and efficient (EV) cure systems, which have about the same total crosslink densities under a moderate curing temperature of 150°C, were investigated. The gum NR vulcanizates cured with CV, SEV and EV curing systems have about the same glass transition temperature (Tg) and tan δ values below the temperature of about 0°C, but showed some apparent differences in the tan δ values increasing in the order CVG′ and tan δ values above Tg higher than those of the gum NR vulcanizates.
High-temperature curing and overcuring cause decreases to various extents in the cure plateau torque, Shore A hardness, 300% modulus and tensile strength, and lead to apparent changes in the DMPs. Typically, there is an increase in Tg of all three kinds of gum and N330-filled NR vulcanizates because of changes in the total crosslink densities and crosslink types. The CV vulcanizates show the most significant change in cure characteristics, physical properties and DMPs since the highest content of polysulfidic crosslinks appears in the CV vulcanizate, causing the highest level of reversion and having a dominant effect on the properties. 相似文献
Bubble size is a key variable for predicting the ability to separate and concentrate proteins in a foam fraction ation process.
It is used to characterize not only the bubble-specific interfacial a rea but also coalescence of bubbles in the foam phase.
This article describes the development of a photoelectric method for measuring the bubble size distribution in both bubble
and foam columns for concentrating proteins. The method uses a vacuum to withdraw a stream of gas-liquid dispersion from the
bubble or foam column through a capillary tube with a funnel-shaped inlet. The resulting sample bubble cylinders are detected,
and their lengths are calculated by using two pairs of infrared photoelectric sensors that are connected with a high-speed
data acquisition system controlled by a microcomputer. The bubble size distributions in the bubble column 12 and 1 cm below
the interface and in the foam phase 1 cm above the interface are obtained in a continuous foam fractionation process for concentrating
ovalbumin. The effects of certain operating conditions such as the feed protein concentration, superficial gas velocity, liquid
flow rate, and solution pH are investigated. The results may prove to be helpful in understanding the mechanisms controlling
the foam fractionation of proteins. 相似文献