A. Moet

Classification of homogeneous ethylene‐octene copolymers based on comonomer content

Ethylene-octene copolymers prepared by Dows INSITE™ constrained geometry catalyst technology present a broad range of solid-state structures from highly crystalline, lamellar morphologies to the granular morphology of low crystallinity copolymers. As the comonomer content increases, the accompanying tensile behavior changes from necking and cold drawing typical of a semicrystalline thermoplastic to uniform drawing and high recovery characteristic of an elastomer. Although changes in morphological features and tensile properties occur gradually with increasing comonomer content, the combined body of observations from melting behavior, morphology, dynamic mechanical response, yielding, and large-scale deformation suggest a classification scheme with four distinct categories. Materials with densities higher than 0.93 g/cc, type IV, exhibit a lamellar morphology with well-developed spherulitic superstructure. Type III polymers with densities between 0.93 and 0.91 g/cc have thinner lamellae and smaller spherulites. Type II materials with densities between 0.91 and 0.89 g/cc have a mixed morphology of small lamellae and bundled crystals. These materials can form very small spherulites. Type I copolymers with densities less than 0.89 g/cc have no lamellae or spherulites. Fringed micellar or bundled crystals are inferred from the low degree of crystallinity, the low melting temperature, and the granular, nonlamellar morphology.

Polymer-clay nanocomposites: Free-radical grafting of polystyrene on to organophilic montmorillonite interlayers

Vinyl monomer-montmorillonite intercalates, which are able to swell and disperse in organic solvents, have been prepared by a cation exchange process by the interaction between the Na+ or Ca2+ cations of montmorillonite and vinylbenzyltrimethylammonium chloride. The resulting vinyl monomer-montmorillonite materials have been identified by X-ray diffraction (XRD), elemental analysis and infrared absorption spectra. Free-radical solution polymerizations of the penetrated styrene between the interlayers of 5, 10, 25 and 50 wt% vinyl monomer-montmorillonite have resulted in grafted polystyrenemontmorillonite materials. The effect of montmorillonite amounts on the formed polystyrene was determined by extraction with organic solvents, which showed an increase in the grafted polymer formed (0.84–2.94 g/g MMT), and a decrease in the external polystyrene with increasing amounts of montmorillonite. The molecular weight of the external polystyrenes was found to be in the range of 22000. The vinyl monomer-montmorillonite and polymer-montmorillonite intercalates have been identified by XRD, elemental analysis and infrared spectroscopy. Examination of the polystyrene-montmorillonite materials by SEM, TEM and XRD showed spherical particles of nanosize about 150–400 nm, and basal spacings of 1.72–2.45 nm.

Reduction of residual stress in montmorillonite/epoxy compounds

An epoxy resin was cured while in intimate contact with small amounts of epoxyphilic montmorillonites. It was determined that cured epoxy exists within the montmorillonite interlayer by the observation of very high interlayer spacings, even greater than 8 nm, Generally, epoxy compounds containing montmorillonites that had been swollen in the curing agent prior to curing exhibited larger interlayer spacings, especially among the non-dispersed montmorillonite layers. The maximum observed residual stress was reduced by greater than 50% in the epoxyphilic montmorillonite/epoxy compounds over that of the pure epoxy. The epoxyphilic montmorillonite/epoxy compounds generally exhibited higher values of glass transition temperature, flexural modulus, and ultimate flexural strength than the pure epoxy. The tyramine-montmorillonite compounds typically had the highest values overall.

Effect of damage dissemination on crack propagation in polypropylene

Kinematic measurements of Fatigue Crack Propagation (FCP) in thick compact tension polypropylene specimens shows that the rate of FCP does not increase monotonically as predicted by conventional laws of fracture mechanics. Specifically, crack deceleration occurs with increasing crack length. Microscopic examination indicates that crazes (damage) disseminate around and ahead of the main crack, thus controlling its rate of propagation. Accounting for damage dissemination, in terms of the crack layer theory, shows that the rate of FCP is controlled by the shape of the active zone and by its size, in addition to the crack length. Abrupt changes in the first two parameters are directly related to the observed crack deceleration.

Characterization of short-fibre reinforced thermoplastics for fracture fixation devices.

This study focuses on determining the effects of clinically relevant procedures on the flexural and fracture toughness properties of three short-fibre thermoplastic composites for potential application as fracture fixation devices. The procedures included sterilization, heat contouring and saline soaking. The three materials tested were polysulphone, polybutylene terephthalate and polyetheretherketone, all reinforced with 30% short carbon fibres. The polysulphone composite showed significant degradation in mechanical properties due to saline soaking. The polybutylene terephthalate exhibited significant degradation of mechanical properties following both contouring and saline soaking. The polyetheretherketone composite, however, exhibited no degradation in mechanical properties. The results demonstrated that flexion and fracture toughness testing were effective for determining the response of the composites to different applied conditions and demonstrated the stability of polyetheretherketone subjected to these treatments. Scanning electron microscopy demonstrated the most effective fibre-matrix bonding to be in the polyetheretherketone.

Thermodynamics of translational crack layer propagation

AbstractRecognizing that fracture in many materials propagates as a crack preceded by intensive damage, a theory is presented to model the crack and the preceding damage as a single thermodynamic entity, i.e., a crack layer (CL). The active zone of the CL may propagate by translational, rotational, expansional and/or distortional movements. Concepts of irreversible thermodynamics are employed to derive the law of CL propagation by translational mode as:

Morphology of HDPE/LDPE blends with different thermal histories

\dot l = \frac{{\beta J_1 \left\langle d \right\rangle }}{{\gamma ^ * R_1 - J_1 }}

The constrained blister test for the energy of interfacial adhesion

wherei is the rate of CL translation,β is a dissipative coefficient,J1 is the energy release rate, 〈d〉 is a characteristic size of the active zone, γ* is the specific enthalpy of damage andR1 is the translational resistance moment. This expression describes the entire history of CL propagation. Experimental results on fatigue crack propagation in polystryrene are in good agreement with the proposed formalism.