Poly (p-phenylene terephthalamide) fibers prepared by wet or dry-jet wet spinning processes have a notable response to very brief heat treatment (seconds) under tension. The modulus of the as-spun fiber can be greatly affected by the heat treatment conditions (temperature, tension and duration). The crystallite orientation and the fiber modulus will increase by this short-term heating under tension. Poly (p-phenylene terephthalamide) fibers have a very high molecular orientation (orientation angle 12-20°). Kevlar and Twaron fibers are poly (p-phenylene terephthalamide) fibers. This review reports for PPTA fibers the heat treatment techniques, devices and its process conditions. It reports in details the structural relationships between the fiber properties which are influenced by the heat treatment process. In particular, focused deeply on the effect of the crystal structure and the morphology of the fibers on the mechanical properties of PPTA fibers.
A reversible confinement of ionic liquid (IL) among the amide segments has been carried out for the preparation of high-modulus and highstrength aliphatic semicrystalline nylon 6 fibers. In this research work, the suppression or the weakening of the hydrogen bonds during the conventional low-speed melt spinning process is followed by a hot-drawing stage and a subsequent IL extraction of the IL out of the 2% wt IL-confined fibers and an immediate thermal stabilization process for the improvement of the properties of the pristine nylon 6 fibers. The resulted crystal structural developments of the IL-confined fibers are attributed to ultimate molecular orientations, which have contributed to the developments of the overall fiber properties. Here, the influences of the IL on the γ and the α crystal phases, the γ-α transition, the morphological properties, and the tensile properties are investigated. The FTIR reported, experimentally, additional peaks at 1237 cm −1 for the γ crystal phase and at 1417 and 1476 cm −1 for the α crystal phase, in conformity with the theoretical computations. The XRD demonstrated that the conventional low-speed melt spinning can successfully be used to prepare as-spun IL-confined fibers having highly improved properties. The so prepared asspun IL-confined fibers are found to have a γ phase structure that has a small crystal size and high crystal perfections. Fortunately, the γ-to-α crystal phase transition for the IL-confined nylon 6 fibers can be acquired during the hot-drawing stage (stress-induced phase transformation). Furthermore, the IL extraction process followed by a thermal stabilization process, interestingly, has led to significant increases in both of the tensile strengths and the tensile moduli of the reverted nylon 6 fibers. The values that are found are 8.46 cN/dtex for the tensile strength and 39.09 cN/dtex for the tensile modulus. The structure−property relationships between the IL-confined and the reverted nylon 6 fibers have also been discussed.
The present paper
provides a solution to enhance the reliability
of bonding. The effect of the nonwoven carbon tissue (NWCT) composite
adhesive layer on the bonding strength and reliability of aluminum
alloy of single lap joints (SLJ) was investigated by embedding NWCT
into the epoxy adhesive layer. The bonding strength, Weibull distribution,
metallography of cross section, and fracture surface morphology of
NWCT specimens were investigated. The results showed that the average
bonding strength and Weibull characteristic strength (WCS) of NWCT-reinforced
specimen were 16.78 and 17.17 MPa, which increased by 70.2 and 66.7%,
respectively, compared with the neat specimen, and the Weibull modulus
increased from 11.46 to 22.83, which indicated that NWCT specimens
had higher bonding reliability. The mechanism of microcrack formation
was obtained by analyzing the cross section of specimen loaded 95%
WCS without macroscopic damage. The metallographic section showed
that the microcrack of the neat specimen originated from the adhesive–aluminum
interface, while the microcracks of the NWCT specimen originated from
the interface between short carbon fibers (SCF) and adhesive. Typical
failure modes were gained from visual observation and SEM. The failure
mode of the neat specimen included more Al–adhesive interface
failure, while the NWCT specimen included more internal failure of
adhesive–SCFs with the fracture, pullout, peeling, and slippage
of SCFs improving the toughness and bonding strength of the adhesive
layer. The bridging effect of SCFs in the adhesive layer reinforced
by NWCT can even the load and release the stress to improve the bonding
reliability.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.