All issues / Volume 3 (2009) / Issue 10 (October)
This is an editorial article. It has no abstract.
It has been investigated how methylene diphenyl diisocyanate (MDI) influences the morphology, rheological, mechanical and relaxation properties, as well as PET crystallizability, of PET/PC/(PP/EPDM) ternary blends produced by the reactive extrusion process. It appears that irrespective of phase structure of the blends, MDI causes a rise in melt viscosity (decreased MFI-values) of the material which is the result of an increased molecular weight of the macromolecules; PET crystallization becomes retarded. MDI improves compatibility between PET and PC in PET/PC/(PP/EPDM) ternary blends. Addition of MDI leads to higher values of the dynamic shear modulus for PET high elastic state (in the temperature range between Tg PET and cool crystallization temperature of PET); the PET cool crystallization and melt crystallization processes become retarded; the PET and PC glass transition temperatures approach one another. MDI has been shown not to influence significantly the blend morphology or the character of interaction between the PP/EPDM disperse phase and PET/PC blend matrix.
While mineral concretes belong to the oldest composites used by mankind, in an increasing number of applications their compression strength σc and compressive strain at yield point εY are insufficient. Better results can be achieved with polymer concretes (PCs). We use a polymer concrete (PC): an unsaturated polyester resin as the matrix, CaCO3 and silica sand. Moreover, we have applied two further methods to improve its mechanical properties: reinforcement with polyester fibers and gamma irradiation with a 60Co source. A non-irradiated PC with 5 wt% CaCO3 has σc = 74 MPa, an irradiated sample with optimized CaCO3 contents 122 MPa. Scanning electron micrographs show that irradiation increases the interface areas between the fibers and the matrix. Improvements from 47 to 176% in εY values are achieved with respect to the conventional PC without fibers, non-irradiated and containing only one mineral component.
A polycarbonate-based nanohybrid has been created containing 1 wt% of Bentone 2010, an organically modified montmorillonite. A micro-section on the nanohybrid obtained using focused ion beam (FIB) and field emission scanning electron microscopy (FESEM) was employed to observe the orientation of the nanoclay inside a polycarbonate (PC) matrix in the cross-section FIB-milled face. A micro-scratch tester was used to measure the scratch resistance in terms of residual (healing) depth Rh under progressive load and in sliding wear. Effects of the number of scratches, normal load and scratch velocity have been evaluated as a function of nanoclay orientation. In sliding wear (multiple scratching along the same groove), our nanohybrid reaches residual depth values that remain constant after a certain number of scratches, a manifestation of strain hardening. The number of scratches to induce strain hardening decreases as the normal applied load increases. SEM was used to characterize deformation and wear mechanisms that operate on contacts and the results related to the wear data.
This paper focuses on the effect of multi-walled carbon nanotube (MWNT) addition on shrinkage and warpage properties of polypropylene (PP) injection mouldings before and after annealing. A Taguchi design of experiments has been implemented to highlight the influence and optimise processing conditions such as injection flow rate, holding pressure, back pressure and screw speed. The addition of 2 wt% of carbon nanotubes into PP significantly reduces the shrinkage and warpage of injection-moulded parts as compared to the neat PP. Skrinkage reduction up to 48% (respectively 33%) is noticed in the flow direction before (respectively after) annealing, whereas warpage reduction exceeds 55%. The sensitivity of the injection-mouldings dimensional properties to processing parameters remains roughly the same in case of neat PP and PP/MWNT nanocomposites when shrinkage is considered. It is even significantly reduced by carbon nanotubes addition when warpage is considered. Furthermore, the Taguchi method provides an efficient and effective tool to study the effects of process parameters on the warpage and shrinkage of injection moulded parts. The additive model used works well for predicting the warpage and shrinkage behaviour of PP and PP/MWNT composites.
Polyethylene (LDPE, LLDPE and HDPE) composites with different copper (micro- and nano-sized particles) contents were prepared by melt mixing and compression moulding. The melting and crystallization behaviour of the different composites was analysed using a differential scanning calorimeter (DSC), and the thermal stability in a thermogravimetric analyser (TGA). The thermal conductivities of the samples were also determined. The DSC results show that the Cu micro- and nano-particles influence the crystallization behaviour of the polyethylenes in different ways. The extent to which the copper particles influence the crystallization behaviour of the polyethylenes also depends on the respective morphologies of the different polyethylenes. The TGA results show an observable influence of both the presence of copper and the sizes of the copper particles on the thermal stabilities of the polymers. Thermal conductivities increased with increasing Cu content, but there was little difference between the thermal conductivities of the samples containing Cu micro- and nano-particles.
The falling weight impact properties of composites obtained by introducing 16 wt% of phormium tenax fibres extracted with two different methods i.e., either manually or by paddocking and scutching and in both cases chemically treated with a 1% solution of sodium hydroxide, have been investigated. The effect of the two extraction methods on fibre characteristics is compared by the tensile properties of the fibres and the flexural properties, fracture modes and hysteresis cycles parameters (impact energy partition, linear stiffness and normalised penetration energy) of final laminates. Laminates obtained using paddocked and scutched fibres are clearly superior to those manufactured using the manually extracted fibres: this is due to the more effective fibre impregnation in the former case than in the latter, which results in an improved dissipation of energy during the damping phase of the impact event. It is noteworthy, however, that the low volume of fibres introduced in the laminate with the manufacturing method adopted does not allow obtaining properties comparable with other semi-structural plant fibre composites, such as e.g., hemp fibre reinforced laminates.
In order to improve the poor interfacial adhesion of the kenaf fiber and polystyrene (PS) in their composite material, the surface of the kenaf fiber was modified using a synthesized polymeric coupling agent to promote adhesion with PS matrix. The dynamic thermo-mechanical properties of the composite composed of modified kenaf fiber and PS were also investigated. The polymeric coupling agent treatment of the kenaf fiber increased the fiber-matrix interaction through a condensation reaction between alkoxysilane and hydroxyl groups of kenaf cellulose. DMA (Dynamic Mechanical Thermal Analysis) results showed that the modified fiber composites have higher E′ and lower tanδ than those with untreated fiber indicating that a greater interfacial interaction between the matrix resin and the fiber. It was also found that the storage modulus increases in proportion with the Si/C ratio on the fiber surface.
It is an abnormal phenomenon that glass transition temperature (Tg) of isomeric polyimide (PI) is higher than its corresponding symmetrical PI. To illustrate this phenomenon at the molecular scale, we applied molecular dynamics method to predict the Tg of PI, which were prepared based on 4,4’-oxydianiline (ODA) and 3,3’,4,4’-biphenyltetracarboxylic dianhydride (3,3’,4,4’-BPDA), and its isomeric system (2,2’,3,3’-BPDA-ODA). Simulation result is consistent with experimental value. Non-bond energy plays an important role in glass transition process, for it has an abrupt change near Tg. The higher free volume fraction of isomeric PI can provide the polymer with more space to obtain segmental motion. However, from the torsion angle distribution calculations, it is shown that the torsion angle of its biphenyl group is constrained. Furthermore, from mean square displacement and vector autocorrelation functions calculations, this group is observed to rotate against other groups in the glassy state, and increases the chain rigidity to a great extent. So the isomeric PI needs much more relaxation time for the segment motion. Therefore, the higher Tg of isomeric PI is mainly attributed to the chain rigidity for the time scale, not the free volume for the space scale.