Journal of Thermoplastic Composite Materials

First, some groups of C=O and C–O were introduced onto high-density polyethylene (HDPE) chains by ultraviolet irradiation for short time in ozone atmosphere. The content of the groups was increased with increasing the irradiation time. The irradiated HDPE was blended with calcium carbonate (CaCO₃) to prepare the composites. The melting temperature and crystallinity of HDPE in irradiated HDPE/CaCO₃ composites were lower than the HDPE in HDPE/CaCO₃ composites. Compared with the HDPE/CaCO₃ composites, the dispersion of CaCO₃ and the interfacial interaction between CaCO₃ and HDPE in the irradiated HDPE/CaCO₃ composites increased respectively. With increasing the irradiation time, the mechanical properties (especially impact strength) of the irradiated HDPE/CaCO₃ composites were markedly enhanced, while their thermal stability decreased slightly. For example, the tensile strength and impact strength of the irradiated (20 min) HDPE/CaCO₃ composites increased from 25.7 MPa and 72 J m⁻¹ to 30.3 MPa and 416 J m⁻¹, respectively, compared with those of the HDPE/CaCO₃ composites, and stiffened and toughened HDPE composites were obtained.

The C–O, C=O, and C(=O)O groups were introduced onto high-density polyethylene (HDPE) chains by ultraviolet irradiation in air and the groups’ content increased with increase in the irradiation time. When they irradiated for 16 h, gels were formed in the irradiated HDPE, and the content of the gels increased with increase in the irradiation time. Compared with HDPE, the crystal form of the irradiated HDPE did not change and still retained the orthorhombic structure, and its melting temperature decreased, while its crystallinity increased. The irradiated HDPE was added in HDPE/CaCO₃ composites as a compatibilizer, and HDPE/irradiated HDPE/CaCO₃ composites were obtained. Compared with those in HDPE/CaCO₃ composites, the dispersion of the CaCO₃ and interfacial interaction between CaCO₃ and HDPE matrix in HDPE/irradiated HDPE/CaCO₃ composites improved due to compatibilization of the irradiated HDPE, and its mechanical properties (especially impact strength), thus, showed remarkable enhancement. With increase in irradiation time, the tensile strength of HDPE/irradiated HDPE/CaCO₃ composites enhanced and its impact strength increased during irradiation time of 16 h and then decreased slightly. In the same irradiation time, the tensile strength and impact strength of HDPE/irradiated HDPE/CaCO₃ composites increased with increase in the content of the irradiated HDPE.

In this article, an attempt is made to improve the filler-loading capacity of fly ash (FA) by its surface modification with zinc hydroxide and calcium hydroxide. In the modification reaction, FA to calcium hydroxide weight ratio was maintained constant at 5:1, while that of FA to zinc hydroxide was varied as 5:0.4, 5:0.6, and 5:0.8 and the optimized composition was utilized as filler in nylon 6. Modified FA was found to have formed hemimorphite on to its surface, giving rise to spine-structured surface morphology. FA surface modified with 5:0.6 weight ratio of FA to zinc hydroxide (FaZn6Ca) provided FA with the highest level of spine-structured surface morphology and thus was determined to the optimized composition to be utilized as filler in nylon 6. Concentration of FaZn6Ca was varied up to 40 phr in nylon 6. Prepared composites were characterized for mechanical, thermal, rheological, crystallinity, and morphological properties. Melting and crystallization temperatures remained approximately constant; tensile strength, flexural strength, crystallinity, tensile modulus, flexural modulus, enthalpy of melting (H_m), and enthalpy of crystallization increased, whereas elongation at break and impact strength decreased with increase in FaZn6Ca concentration in nylon 6. Spine-structured surface morphology formed on the surface of FA increased the filler-loading capacity of FaZn6Ca in nylon 6; while the improvement in the properties were caused due to better interactions happening between nylon 6 and FaZn6Ca due to the hydrophilic nature of both the materials. Since FA is obtained as waste from thermal power plant, the use of this material as a filler in nylon 6 would help ease the solid waste disposal problem which will benefit the environment.

Recycled carbon fiber (RCF) was employed as a reinforcing material to prepare polyoxymethylene (POM)-based composites through a simple melting extrusion. An effective approach was developed to clean and modify the surface of the as-received RCF with nitric acid and then with a silane coupling agent. The mechanical evaluation demonstrated that a significant reinforcement was achieved for POM/RCF composites due to the improved interfacial adhesion between the fibers and the matrix. The thermal stabilities of the composites were also improved in the presence of RCF. The morphological observation of impact fracture surfaces indicated that the RCF gained a homogeneous dispersion in POM matrix due to good interfacial boding between fibers and matrix. The studies on nonisothermal and isothermal crystallization behaviors showed that RCF acted as a nucleation agent for the crystallization of POM domain in composites; therefore, the crystallization rate and nucleation density increased remarkably due to the heterogeneous nucleating effect of RCF. These crystallization features may be advantageous for the enhancement of mechanical performance and processability of POM-based composites.

This article is concerned with the effects of the silane surface treatment of silicon dioxide (SiO₂) on the tribological properties of the SiO₂-reinforced polymethyl methacrylate (PMMA) (SiO₂/PMMA) composites filled with carbon fiber (CF). Silane treatment and CF bring positive effect to improve friction reduction and antiwear properties of SiO₂/PMMA composites. Fourier transform infrared analysis shows that SiO₂ has been oxidized and etched by silane treatment. The presence of active groups increases the polarity of SiO₂, and so the bonding property between the particle and the matrix improves. The scanning electron microscopy (SEM) observation revealed that this hybrid reinforcement could be interpreted in terms of a positive rolling effect of the particles between the two sliding surfaces, which protected the short CFs from being pulled out of the PMMA matrix.

In this study, the preparation of nylon 6/talc nanocomposites was studied by melt blending in a co-rotating twin-screw extruder having length/diameter ratio of 32:1 at a screw rotation speed of 100 r min⁻¹. Concentration of nanotalc was varied from 1 phr to 5 phr in nylon 6. The composite samples were subjected to a series of three extrusion cycles, and the effect of reprocessing on the structural properties of materials was investigated. Properties such as mechanical (tensile flexural and impact), thermal (differential scanning calorimetry), morphological (scanning electron microscopy), rheological (viscosity vs. shear rate), and colour spectrophotometry were investigated. This study would enrich the knowledge about the recycling of nylon 6, with the additional aspect of the use of collected data from more complex system, that is, composite materials, where the nanotalc particles play a role in the interactions initiated by repeated extrusion processing. Mechanical, thermal, rheological and colour properties improved with the increase in nanotalc in nylon 6 and remained nearly unchanged up to second extrusion processing. However, all the properties decreased on third extrusion processing due to the degradation of nylon 6 matrix.

In this article, the different chemical modifications of natural fiber on the physical and mechanical properties of polypropylene (PP)/wood flour (WF)/nanoclay hybrid composites were studied. To meet this objective, the chemical treatments on WF, namely alkali, acetylation, and benzoylation, were carried out. Then, the composites were prepared through the melt mixing of WF and PP at 50% weight ratios, with various amounts of nanoclay (0, 3, and 6 per hundred compounds (phc)) in Haake internal mixer and the test specimens were prepared by injection molding. The amount of coupling agent was fixed at 2 phc for all formulations. The tensile strength, impact strength, and water uptake of these composites were analyzed and the reinforcing properties of the chemically treated composites were compared with those of untreated composites. The chemical modification efficiency was verified by Fourier transform infrared (FTIR) analysis, and the dispersion state of nanoclay in the composites was examined using X-ray diffractometer and transmission electron microscopy. The results showed that the tensile modulus, tensile strength, and impact strength of the composites increased by applying chemical treatments. Modified composites had lower water absorption (WA) and thickness swelling than unmodified ones. Furthermore, the highest mechanical properties and the lowest water uptake were observed in the composite modified with acetic anhydride. FTIR spectra show that the intensity of O–H bond at 3444.2 cm^–1 and formation of ester bond at 1741.4 cm^–1 were indications of changes in the chemical structure of the fibers. The tensile modulus and strength increased with increase of nanoclay up to 3 phc and then decreased. However, the impact strength and WA decreased with increase of nanoclay loading. The morphological findings showed that the samples containing 3 phc of nanoclay had higher order of intercalation and better dispersion.

Mechanical strength of phenylenebenzobisoxazole (PBO) fibers and cross-linked polyethylene (XLPE) matrix composites were studied with particular interest on the effects of oxygen cold plasma-treated fibers. PBO fibers were treated in a radio frequency plasma reactor using oxygen for different treatment times to increase the interface adhesion. Tensile tests on PBO fibers showed that plasma treatment caused an increase in average tensile strength compared with untreated fibers. Fracture analysis confirmed the increase in interfacial adhesion due to oxygen plasma treatment.

Montmorillonite (MMT)/rice husk (RH) hybrid filler-filled low-density polyethylene (LDPE) nanocomposite films, containing 0, 2, 3, 4, 5, and 6 wt% MMT (based on the total weight) were prepared by extrusion blown film. The films were characterized by morphological, mechanical, oxygen (O₂) barrier, and thermal properties. The delamination of MMT layers evidenced from X-ray diffraction results suggests an increase in the interlayer distance and shows intercalated structure of the nanocomposites. Adding MMT did not adversely affect the interfacial morphology, as confirmed by scanning electron microscopy. Addition of MMT into the LDPE/RH system improved the mechanical and O₂ barrier properties. For instance, tensile strength, tensile modulus, and tear strength increased by 8, 10, and 5%, respectively, with the addition of 3 wt% MMT. Further, the O₂ barrier of the composite films improved more than twofold by adding 4 wt% MMT. Initial degradation temperature of LDPE/RH composites increased with the incorporation of MMT suggesting that the nanocomposites are more thermally stable than LDPE/RH composites.

Silaned nano-silicon dioxide (SiO₂) was used to improve the adhesion properties of carbon fiber/polyoxymethylene (CF/POM) composites. The CF and nano-SiO₂ were treated and the changes on the surface properties of the treated and untreated composites were studied by impact, three-point bending tests, and scanning electron microscopic analysis. The measurement showed that the fracture toughness increases with the increase of CF content, while very high content of CF did not further cause the increase of the toughness of CF/POM composite. The impact strength of treated specimens is still higher than those of the untreated ones. The modified composite with the good matrix/fiber adhesion possessed 20% higher interlaminar shear strengths compared to the composite having weak interface.