Qipeng Guo

Bamboo fiber‐reinforced polypropylene composites: A study of the mechanical properties

A new type of bamboo fiber-reinforced polypropylene (PP) composite was prepared and its mechanical properties were tested. To enhance the adhesion between the bamboo fiber and the polypropylene matrix, maleic anhydride-grafted polypropylene (MAPP) was prepared and used as a compatibilizer for the composite. The maleic anhydride content of the MAPP was 0.5 wt %. It was found that with 24 wt % of such MAPP being used in the composite formulation, the mechanical properties of the composite such as the tensile modulus, the tensile strength, and the impact strength all increased significantly. The new composite has a tensile strength of 32–36 MPa and a tensile modulus of 5–6 GPa. Compared to the commercially available wood pulp board, the new material is lighter, water-resistant, cheaper, and more importantly has a tensile strength that is more than three times higher than that of the commercial product.

Bamboo fiber-reinforced polypropylene composites: Crystallization and interfacial morphology

Bamboo fiber-reinforced polypropylene (PP) composites were prepared. PP and two maleated polypropylenes (s-MAPP and m-MAPP) were used as matrices. Crystallization and interfacial morphology were studied by using differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and optical microscopy. It has been shown that the addition of bamboo fiber to any of the three polymers causes an increase in the overall crystallization rate. A considerable amount of β-form crystallinity was produced in the PP, s-MAPP, and m-MAPP by mixing with bamboo fiber; and all the bamboo fiber-filled samples contain both the α- and the β-forms. The relative amount of the β-form in the samples was calculated from WAXD data by the K value. There is no β-form observed in the pure PP, s-MAPP, and m-MAPP. Bamboo fiber acted as both a reinforcement and a β-nucleator. The nucleation density of both s-MAPP and m-MAPP at the fiber surface is remarkably higher than that of PP because an improved interfacial adhesion is reached in the case of s-MAPP and m-MAPP as matrices. The transcrystalline growth of s-MAPP and m-MAPP on the bamboo fiber surface was observed under optical microscope with crossed polars.

Miscibility and mechanical properties of epoxy resin/polysulfone blends

Abstract Bispehnol A-based polysulfone (PSF) was found to be miscible with uncured bisphenol A-type epoxy resin, i.e. diglycidyl ether of bisphenol A (DGEBA), as shown by the existence of a single glass transition temperature ( T g ) within the whole composition range. Miscibility between PSF and DGEBA is considered to be due mainly to entropy contribution. Furthermore, PSF was judged to be miscible with the 4,4′-diaminodiphenylmethane (DDM)-cured epoxy resin (ER) as revealed by the means of differential scanning calorimetry (d.s.c.), dynamic mechanical analysis (d.m.a.) and scanning electron microscopy (SEM). D.s.c. and d.m.a. studies showed that the DDM-cured ER/PSF blends had only one T g . SEM observation revealed that the DDM-cured ER/PSF blends was homogeneous. Both tensile and flexural properties of the DDM-cured ER/PSF blends slightly improved compared to those of the pure DDM-cured ER. Both fracture toughness ( K IC ) and fracture energy ( G IC ) increased by ca . 20% with the addition of PSF to the system. Morphological investigation of the K IC fracture surface suggests typical characteristics of brittle fracture.

Miscibility, morphology and fracture toughness of epoxy resin/poly(styrene-co-acrylonitrile) blends

Abstract Poly(styrene-co-acrylonitrile) (SAN) with 25 wt% acrylonitrile (AN) content was found to be miscible with uncured bisphenol-A-type resin, i.e. diglycidylether of bisphenol A (DGEBA), as shown by the existence of a single glass transition temperature within the whole composition range. Miscibility between SAN and DGEBA is considered to be due mainly to entropy contribution. However, SAN was judged to be immiscible with the 4,4′-diaminodiphenylmethane-cured epoxy resin (DDM-cured ER) as revealed by the means of differential scanning calorimetry (d.s.c.), dynamic mechanical analysis (d.m.a.) and scanning electron microscopy (SEM). It was observed that the DDM-cured ER/SAN blends have two Tgs, which remain almost invariant with composition and are close to those of the pure components, respectively. SEM study revealed that all the DDM-cured ER/SAN blends have a two-phase structure. The fracture mechanics studies indicate that the DDM-cured ER/SAN blends containing 10 wt% give a substantial improvement of fracture toughness KIC. The fracture toughness KIC increases with SAN content and shows a maximum at 10 wt% SAN content, followed by a dramatic decrease in KIC for the cured blends containing 15 wt% SAN or more. SEM investigation of the KIC fracture surfaces indicates that the toughening effect of the SAN-modified epoxy resin is greatly dependent on the morphological structures.

Carbon nanotube based elastomer composites – an approach towards multifunctional materials

The current study focuses on giving a basic understanding of tubular graphene sheets or carbon nanotubes (CNTs) and points towards their role in fabricating elastomer composites. Since the properties and the performance of CNT reinforced elastomer composites predominantly depend on the rate of dispersion of fillers in the matrix, the physical and chemical interaction of polymer chains with the nanotubes, crosslinking chemistry of rubbers and the orientation of the tubes within the matrix, here, a thorough study of these topics is carried out. For this, various techniques of composite manufacturing such as pulverization, heterocoagulation, freeze drying, etc. are discussed by emphasizing the dispersion and alignment of CNTs in elastomers. The importance of the functionalization technique as well as the confinement effect of nanotubes in elastomer media is derived. In a word, this article is aimed exclusively at addressing the prevailing problems related to the CNT dispersion in various rubber matrices, the solutions to produce advanced high-performance elastomeric composites and various fields of applications of such composites, especially electronics. Special attention has also been given to the non-linear viscoelasticity effects of elastomers such as the Payne effect, Mullins effect and hysteresis in regulating the composite properties. Moreover, the current challenges and opportunities for efficiently translating the extraordinary electrical properties of CNTs to rubbery matrices are also dealt with.

Synergistic effect of multi walled carbon nanotubes and reduced graphene oxides in natural rubber for sensing application

Utilizing the electrical properties of polymer nanocomposites is an important strategy to develop high performance solvent sensors. Here we report the synergistic effect of multi walled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) in regulating the sensitivity of the naturally occurring elastomer, natural rubber (NR). Composites were fabricated by dispersing CNTs alone and together with exfoliated RGO sheets (thermally reduced at temperatures of 200 and 600 °C ) in NR by a solution blending method. RGO exfoliation and the uniform distribution of fillers in the composites were studied by atomic force microscopy, Fourier transformation infrared spectroscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. The solvent sensitivity of the composite samples was noted from the sudden variation in electrical conductivity which was due to the breakdown of the filler networks during swelling in different solvents. It was found that the synergy between CNTs and RGO exfoliated at 200 °C imparts maximum sensitivity to NR in recognizing the usually used aromatic laboratory solvents. Mechanical and dynamic mechanical studies reveal efficient filler reinforcement, depending strongly on the nature of filler–elastomer interactions and supports the sensing mechanism. Such interactions were quantitatively determined using the Maier and Goritz model from Payne effect experiments. It is concluded that the polarity induced by RGO addition reduces the interactions between CNTs and ultimately results in the solvent sensitivity.

Miscibility and mechanical properties of tetrafunctional epoxy resin/phenolphthalein poly(ether ether ketone) blends

Phenolphthalein poly(ether ether ketone) (PEK-C) was found to be miscible with uncured tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM), which is a type of tetrafunctional epoxy resin (ER), as shown by the existence of a single glass transition temperature (Tg) within the whole composition range. The miscibility between PEK-C and TGDDM is considered to be due mainly to entropy contribution. Furthermore, blends of PEK-C and TGDDM cured with 4,4′-diaminodiphenylmethane (DDM) were studied using dynamic mechanical analysis (DMA), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). DMA studies show that the DDM-cured TGDDM/PEK-C blends have only one Tg. SEM observation also confirmed that the blends were homogeneous. FTIR studies showed that the curing reaction is incomplete due to the high viscosity of PEK-C. As the PEK-C content increased, the tensile properties of the blends decreased slightly and the fracture toughness factor also showed a slight decreasing tendency, presumably due to the reduced crosslink density of the epoxy network. SEM observation of the fracture surfaces of fracture toughness test specimens showed the brittle nature of the fracture for the pure ER and its blends with PEK-C.

Phase behaviour and mechanical properties of epoxy resin containing phenolphthalein poly(ether ether ketone)

Abstract Blends of bisphenol-A-type epoxy resin(ER) and phenolphthalein poly(ether ether ketone) (PEK-C) cured with 4,4′-diaminodiphenylmethane (DDM) were studied using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The phase behaviour of the DDM-cured ER/PEK-C blends was greatly dependent on the curing condition and was affected by both the thermodynamic and kinetic factors. The homogeneous DDM-cured ER/PEK-C blends were obtained. The studies of DSC and Fourier-transform infrared (FTi.r.) spectroscopy indicate that there existed some unreacted oxirane rings of ER in the blends, and the curing reaction was incomplete even though the samples of the blends were further post-cured at 250°C. Mechanical measurements show that incorporation of PEK-C slightly decreased both the fracture toughness (KIC and GIC) and the flexural properties, presumably due to the reduced cross-link density of the epoxy network. SEM observation of the surfaces of fracture mechanical measurement specimens indicates the nature of brittle fracture for the plain ER and the blends.

Miscibility and morphology of thermosetting polymer blends of novolac resin with poly(ethylene oxide)

Abstract Polymer blends of novolac resin and poly(ethylene oxide) (PEO) were prepared by solution casting from N, N -dimethylformamide (DNIF). The miscibility and morphology of the blends before and after curing were investigated by optical microscopy differential scanning calorimetry (d.s.c.) and Fourier transform infrared ( FT i.r.) spectroscopy. It was found that PEO is miscible with uncured novolac over the entire composition range, as shown by the existence of a single composition-dependence glass transition temperature (T g ). FT i.r. studies revealed that hydrogen bonding interactions exist between the hydroxyl groups of novolac and the ether oxygens of PEO. The relative amount and the average strength of the hydrogen bonds in the blends were higher than those in the pure novolac resin. The curing with 15 wt% hexamine (HMTA) (relative to novolac content) resulted in the disappearance of a detectable T g in both the neat novolac and the novolac-rich blends, due to the reduced mobility of the novolac chain segments. An analysis of the reduction in T m and crystallization rate with increasing novolac content revealed that the HMTA-cured blends remained completely miscible. After curing with HMTA, considerable hydrogen bonding interaction between the components still existed, which is the driving force for the miscibility of the HMTA-cured blends. The relative amount and the average strength of hydrogen bonds in the cured blends were lower than those in the uncured blends.

Thermosetting polymer blends of unsaturated polyester resin and poly(ethylene oxide). II. Hydrogen-bonding interaction, crystallization kinetics, and morphology

Hydrogen-bonding interaction between the two components of the poly(ethylene oxide) (PEO)/oligoester (OER) blends and the PEO/crosslinked unsaturated polyester resin (PER) blends was found to be an important driving force to the miscibility of these polymer blends. Its strength is approximately as strong as the self-association of hydroxyl groups in either the pure OER or the pure PER. The crystallization kinetics and morphology of PEO in PEO/PER blends was remarkably affected by crosslinking. It was found that the overall crystallization rate of PEO in PEO/PER blends is larger than that in PEO/OER blends at the crystallization temperature investigated, which was considered to be the result of nucleation controlling mechanism. With decreasing PEO content, the regular shape of PEO spherulites turns irregular in PEO/ OER blends, whereas in PEO/PER blends, the birefrigent spherulites turns into dendritic structures. Raising the crystallization temperature favors the formation of dendritic textures in PEO/PER blends.