Computer simulation of the damage evolution of fiber-reinforced polypropylene-matrix composites with matrix defects

The damage evolution of fiber-reinforced polypropylene-matrix composites with matrix defects was studied via a Monte Carlo technique combined with a finite element method. A finite element model was constructed to predict the effects of various matrix defect shapes on the stress distributions. The results indicated that a small matrix defect had almost no effect on fiber stress distributions other than interfacial shear stress distributions. Then, a finite element model with a statistical distribution of the fiber strength was constructed to investigate the influences of the spatial distribution and the volume fraction of matrix defects on composite failure. The results showed that it was accurate to use the shear-lag models and Green's function methods to predict the tensile strength of composites even though the axial stresses in the matrix were neglected.

Online study of the formation of PA6 droplets in PP matrix under shear flow

Breakup process of polyamide 6 (PA6) in polypropylene (PP) matrix under shear flow was online studied by using a Linkam CSS 450 stage equipped with optical microscopy. Both tip streaming and fracture breakup modes of PA6 droplets were observed in this study. It was reported that the droplet would break up by tip streaming model when the radio of the droplet phase viscosity to the matrix phase viscosity (n(r) = n(d)/n(m)) is smaller than 0.1 (Taylor, Proc R Soc London A 1934, 146, 501; Grace, Chem Eng Commun 1982, 14, 225; Bartok and Mason, J Colloid Sci 1959, 14, 13; Rumscheidt and Mason, J Colloid Sci 1961, 16, 238; de Bruijn, Chem Eng Sci 1993, 48, 277). However, the tip streaming model was observed even when the viscosity ratio was much greater than 0.1 (n(r) = 1.9). In this study for the tip streaming mode, small droplets were ruptured from the tip of the mother droplet. On the other hand, the mother droplet was broken into two or more daughter droplets with one or several satellite droplets between them for the fracture mode. It was found that PA6 droplet was much elongated at first, and then broke up via tip streaming or fracture to form daughter droplets or small satellite droplets with the shape of fiber or ellipse.

An investigation on the dispersion of montmorillonite (MMT) primary particles in PP matrix

A novel path of preparing PP/o-MMT nanocomposites, which pay attention to the breaking up of MMT original agglomerates and dispersing of its primary particles, rather than the intercalation or exfoliation degree of o-MMT, was reported. The method of predispersing the o-MMT particles into a polar poly(vinyl alcohol) (PVA) matrix and then melt blending the pre-treated PVA/o-MMT hybrids with PP was studied. 3-isopropenyl-alpha,alpha-dimethylbenzene-isocyanate (TMI) was used as a modifier of PVA to improve the compatibility between PVA and PP matrix. Pre-disperse o-MMT with TMI modified PVA was proved to be an effective way to get a composite with fine o-MMT particles dispersion. But the method, which is pre-dispersing o-MMT with non modified PVA and then using TMI to modify such PVA/o-MMT hybrid, would largely reduce the reaction degree between TMI and PVA because of the relatively lower reaction temperature. Although the latter method also can obtain finer dispersion composites than that with using PP-g-MAH as compatibilizer, the relatively higher degradation degree of PP matrix in this method will limit the use of this nanocomposite.

Effect of Y for enhanced age hardening response and mechanical properties of Mg-Gd-Y-Zr alloys

In this study, compositional dependence of age hardening response and tensile properties were investigated for Mg-10G(d-x)Y-0.4Zr (x = 1, 3, 5 wt.%) alloys. With increasing Y content, the age hardening response of the alloys enhanced and tensile properties increased. The Mg-10Gd-5Y-0.4Zr alloy exhibited maximum tensile strength and yield strength at aged-peak hardness, and the values were 302 MPa and 289 MPa at room temperature, and 340 MPa and 267 MPa at 250 degrees C, respectively. The strong peak age hardening was attributed to the precipitation of prismatic beta' plates in a triangular arrangement. The cubic shaped beta phase was also observed at grain boundaries. The remarkable improvement in strength is associated with a uniform and high dense distribution of beta' and cubic shaped beta precipitate phases in Mg matrix. Elongation of Mg-10Gd-0.4Zr alloys decreased with increasing Y content, and the elongation of Mg-10Gd-5Y-0.4Zr alloy was less than 3% below 250 degrees C, whereas the alloys containing I wt.% and 3 wt.% Y exhibited higher elongation than 5% at room temperature.

The mechanical properties of magnesium matrix composites reinforced with 10 wt.% W14Al86 alloy particles

The Mg-based metal matrix composite reinforced by 10 wt.% W14Al86 alloy particles has been prepared by mechanical alloying and press-forming process. X-ray diffraction studies confirm the formation of the composite. Microstructure characterization of the samples reveals the uniform distribution of fine W14Al86 alloy. Mechanical properties characterization revealed that the reinforcement of W14Al86 alloy lead to a significant increase in hardness and tensile strength of Mg and AZ91.

Thermal and dynamic mechanical properties of PES/PPS blends

Blends of poly(ether-sulfone) (PES) and poly(phenylene sulfide) (PPS) with various compositions were prepared using an internal mixer at 290degreesC and 50 rpm for 10 min. The thermal and dynamic mechanical properties of PES/PPS blends have been investigated by means of DSC and DMA. The blends showed two glass transition temperatures corresponding to PPS-rich and PES-rich phases. Both of them decreased obviously for the blends with PES matrix. On the other hand, T-g of PPS and PES phase decreased a little when PPS is the continuous phase. In the blends quenched from molten state the cold crystallization temperature of PPS was detected in the blends of PES/PPS with mass ratio 50/50 and 60/40. The melting point, crystallization temperature and the crystallinity of blended PPS were nearly unaffected when the mass ratio of PES was less than 60%, however, when the amount of PES is over 60% in the blends, the crystallization of PPS chains was hindered. The thermal and the dynamic mechanical properties of the PPS/PES blends were mainly controlled by the continued phase.

Brittle-ductile transition of particle toughened polymers: influence of the matrix properties

It was theoretically pointed out that the product of the yield stress and yield strain of matrix polymer that determined the brittle-ductile transition (BDT) of particle toughened polymers. For given particle and test condition, the higher the product of the yield stress and the yield strain of the matrix polymer, the smaller the critical interparticle distance (IDc) of the blends was. This was why the IDc (0.15 mum) of the polypropylene (PP)/rubber blends was smaller than that (0.30 mum) of the nylon 66/rubber blends, and the IDc of the nylon 66/rubber blends was smaller than that (0.60 mum) of the high density polyethylene (HDPE)/rubber blends.

Facile preparation of amperometric laccase biosensor with multifunction based on the matrix of carbon nanotubes-chitosan composite

The carbon nanotubes-chitosan (CNTs-CS) composite provides a suitable biosensing matrix due to its good conductivity, high stability, and good biocompatibility. Enzymes can be firmly incorporated into the matrix without the aid of other cross-linking reagents. The composite is easy to form insoluble film in solution above pH 6.3. Based on this, a facilely fabricated amperometric biosensor by entrapping laccase into the CNTs-CS composite film has been developed. At pH 6.0, the fungi laccase incorporated into the composite film remains better catalytic activity than that dissolved in solution. The system is in favor of the accessibility of substrate to the active site of laccase, thus the affinity to substrates is improved greatly, such as 2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS), catechol, and 0, with K. values of 19.86 mu M, 9.43 mu M, and 3.22 mM, respectively. The major advantages of the as-prepared biosensor are: detecting different substrates (ABTS, catechol, and 02), possessing high affinity and sensitivity, durable long-term stability, and facile preparation procedure. On the other hand, the system can be applied in fabrication of biofuel cells as the cathodic catalysts based on its good electrocatalysis for oxygen reduction.

Poly(L-lactide)/starch blends compatibilized with poly(L-lactide)-g-starch copolymer

The poly(L-lactide) (PLLA)/starch blends were prepared by the PLLA grafting starch (PLLA-g-St) copolymers as a compatibilizer, and their thermal, mechanical and morphological characterizations were performed to show the better performance of these blends compared to the virgin PLLA/starch blend without the compatibilizer, including PLLA crystallinity, interfacial adhesion between the PLLA matrix and starch dispersive phases, mechanical test, medium resistance, and contact angle. The 50/50 composite of PLLA/starch compatibilized by 10% PLLA-g-St gave a tensile strength of 24.7 MPa and an elongation at break of 8.7%, respectively, vs. 11.3 MPa and 1.5%, respectively, for the simple 50/50 blend of PLLA/starch.

Numerical simulation of mesoscopic mechanical behaviors of gradual multi-fiber-reinforced polymer matrix composites

To simulate the deformation and the fracture of gradual multi-fiber-reinforced matrix composites, a numerical simulation method for the mesoscopic mechanical behaviors was developed on the basis of the finite element and the Monte Carlo methods. The results indicate that the strength of a composite increases if the variability of statistical fiber strengths is decreased.