The crystallization degree in semi-crystalline thermoplastics plays an important role in determining the final properties of structural composite material (e.g. toughness, stiffness and solvent resistance). The main purpose of this work is to study different induced degrees of crystallinity in carbon fiber (CF) reinforced polyphenylene sulfide (PPS) composites, by using three different cooling rates during hot compression molding processing (51%, 58% and 62% of crystallinity). In this study, the morphology, thermal and mechanical properties of the produced laminates were investigated and compared. The results showed an increase in the storage modulus (9.8%), Young's modulus (9.2%) and ILSS (14.2%) for the lower cooling rates. Evidences of fiber/interface improvement and crystallites nucleation on the fiber reinforcement surface were also identified.

Economically viable high‐density polyethylene (HDPE)/graphene nanocomposites were produced using mass produced graphene powder and an industrial twin‐screw melt‐compounding machine. Rheological and electrical properties were investigated and scanning electron microscopy was carried out to investigate graphene dispersion and its network formation in the matrix. Mechanical properties of the nanocomposites were evaluated using tensile, flexural and impact tests. Differential scanning calorimetry analysis indicated that the crystalline structure of the polymer might be affected by high loadings of graphene. SEM evaluation revealed reasonable graphene dispersion in the matrix. In addition, the amount of graphene required to form a percolated network was similar for both rheological and electrical networks. The nanocomposites exhibited a significant increase in Young's and flexural moduli without a notable reduction in impact strength up to 14 wt% graphene loading. In these experiments, compounding graphene powder with HDPE produced a clear and distinct improvement in mechanical properties at an industrially suitable low cost. POLYM. ENG. SCI., 59:675–682, 2019. © 2018 Society of Plastics Engineers

In order to investigate the combined action of temperature, humidity, and ultraviolet (UV) radiation, polyphenylene sulfide (PPS)-carbon fiber composite specimens were exposed to environmental degradation through two different techniques: water immersion and UV climatic chamber. The moisture weight gain curves of the composites were compared with those of the neat matrix in order to determine the interface effect on moisture absorption. Fourier-transform infrared spectroscopy of UV-weathered samples presented oxidation formation. Compressive tests and dynamic mechanical thermal analysis (DMA) revealed that the weathered materials gained in stiffness, nevertheless a small deterioration in strength was found after long periods of UV radiation exposure.

The thermal decomposition behavior of poly(ether imide) (PEI)/carbon fiber composites used in aeronautical field was studied using thermogravimetric analysis in an inert atmosphere, at several heating rates between 2 and 10 C min À1 . The activation energies (E a ) were determined by Flynn-Wall-Ozawa (FWO) and Kissinger methods, and the preexponential factor (A) was calculated by the FWO method. The obtained data were used in order to predict the thermal lifetime of the material under the established temperature range and 5% mass loss criterion. Overall, the results represented PEI's good thermal stability. Furthermore, it was concluded that the material can be safely applied for aeronautical use.

Dynamic mechanical properties of a polyurethane (PU) elastomer and a mortar processed with the same elastomer (modified polytetramethylene ether glycol (PTMEG)) were studied. The results obtained showed that the liquid aromatic amine ETHACURE® 300, used as cure agent, can be used to substitute the aromatic amine MOCA®, which is usually used as cure agent in high performance elastomers. The resulting mortar produced with ETHACURE® 300 presents similar dynamic‐mechanical thermal properties when compared with MOCA ®. However, dynamic‐mechanical thermal analysis studies showed that the mortar developed with ETHACURE® 300 presents some advantages such as the low values of tan δ, indicating a good capacity of recovery of the strain after retreating an applied force. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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In order to investigate how environmental degradation affects the mechanical and thermal performance of polyetherimide/carbon fiber laminates, in this work different weathering were conducted. Additionally, dynamic mechanical analysis, interlaminar shear strength tests and non-destructive inspections were performed on this composite before and after being submitted to hygrothermal, UV radiation and thermal shock weathering. According to our results, hygrothermally aged samples had their glass transition temperature and elastic and storage moduli reduced by plasticization effect. Photooxidation, due to UV radiation exposure, occurred only on the surface of the laminates. Thermal shock induced a reversible stress on the composite’s interface region. The results revealed that the mechanical behavior can vary during weather exposure but since this variation is only subtle, this thermoplastic laminate can be considered for high-performance applications, such as aerospace.

The crystalline content of a composite can affect its performance under environmental conditions. The objective of this study is to evaluate the influence of the crystallinity degree of CF/PPS composites to hygrothermal, salt fog and ultraviolet/condensation conditioning. DSC and DMA results, and Young's modulus and ILSS values were used to evaluate the changes in the thermal and mechanical properties of CF/PPS composites after conditioning. The crystallinity degree showed to affect the water uptake and the severity of degradation. Differences up to 40% were found among the mechanical properties values depending on the crystallinity. In the hygrothermal and salt fog conditioning the least crystalline laminates were mostly degraded. In contrast, in the ultraviolet/condensation conditioning the composites with the highest crystalline contents were more affected.