The principal toughening mechanism of a substantially toughened, rubber-modified epoxy has again been shown to involve internal cavitation of the rubber particles and the subsequent formation of shear bands. Additional evidence supporting this sequence of events which provides a significant amount of toughness enhancement, is presented. However, in addition to this well-known mechanism, more subtle toughening mechanisms have been found in this work. Evidence for such mechanisms as crack deflection and particle bridging is shown under certain circumstances in rubber-modified epoxies. The occurrence of these toughening mechanisms appears to have a particle size dependence. Relatively large particles provide only a modest increase in fracture toughness by a particle bridging/crack deflection mechanism. In contrast, smaller particles provide a significant increase in toughness by cavitation-induced shear banding. A critical, minimum diameter for particles which act as bridging particles exists and this critical diameter appears to scale with the properties of the neat epoxy. Bimodal mixtures of epoxies containing small and large particles are also examined and no synergistic effects are observed.

/pdf/influence-of-particle-size-and-particle-size-distribution-on-2othozgvms.pdf

Influence of particle size and particle size distribution on toughening mechanisms in rubber-modified epoxies

https://ris.utwente.nl/ws/files/6436071/Borggreve89impact.pdf

Impact behaviour of nylon-rubber blends: 6. Influence of structure on voiding processes; toughening mechanism

Characterization of volume strain at large deformation under uniaxial tension in high-density polyethylene

In theories of the minor phase (domain) formation in polyblends rendered as emulsions it is usually assumed that the size and shape of the domains are the result of melt viscosity effects (Taylor, Wu) or viscoelasticity effects (VanOene, Elmendorp) being balanced by interfacial tension. This assumption would predict a monotonic decrease of the domain size to a final limiting size with increasing energy of mixing. However, a systematic study of the dependence of domain morphology on industrial mixing processes which was carried out on a “model” LDPE/PS (2/1) mixture and the related polyalloy (i.e., the same mixture with a corresponding block copolymer as compatibilizer) does not support this expectation. Doirain size was found to go through a minimum as mixing energy was increased. A similar minimum was seen in data on specific volume of the melt vs. mixing energy, which indicates a correlation between melt specific volume and domain size. Calculation of the approximate surface area of the domains using a simple model of domain shape indicated that total interfacial energy in the polyblend and/or polyalloy is a trivial part of the mixing energy introduced. These calculations also indicated that if compatibilizer was located entirely at the interface, the surface layer would have a thickness of about 90 nm. Some micrographs seem to show such a surface layer. We propose that an abrasion mechanism is responsible for the early stage of the dispersion process, and that the final domain size may be controlled by a dispersion-coalescence equilibrium. This is compared with the theories of final particle size proposed by VanOene and Wu.

The interface in binary mixtures of polymers containing a corresponding block copolymer: Effects of industrial mixing processes and of coalescence

Plastic deformation behaviour of thermoplastic/clay nanocomposites

A model is presented for the volume strain of a two-phase blend which elongates homogeneously in a tensile test apparatus. In the case when only elastic deformation and crazing take place the volume strain against elongation curve can be constructed and calculated from the data of the stress-strain curve alone. When, as well as crazing and elastic deformation, shearing takes place, the data of the stress against elongation curve and the volume strain against elongation curve can be used to calculate the separate contributions of the three deformation mechanisms at any elongation. In principle, the model can be also used for any homogeneous system which deforms without necking and where one or more deformation mechanism is present.

/pdf/a-mathematical-relation-between-volume-strain-elongational-2flfxsinko.pdf

A mathematical relation between volume strain, elongational strain and stress in homogeneous deformation

https://pure.tue.nl/ws/files/2246523/621147.pdf

Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends: correlation between Poisson ratio and adhesion

S. Dirk Sjoerdsma

Papers

A mathematical relation between volume strain, elongational strain and stress in homogeneous deformation

Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends: correlation between Poisson ratio and adhesion