Sharp Brittle-ductile Transition Research Articles

Toward morphology development and impact strength of Co-continuous supertough dynamically vulcanized rubber toughened PLA blends: Effect of sulfur content

In this study, supertough dynamically vulcanized blends (DV) of polylactide (PLA) and acrylonitrile butadiene rubber (NBR) are prepared. Effects of sulfur content on the compatibility, interfacial adhesion, morphology and impact resistance are investigated. NBR presents in spherical droplets dispersed in the PLA phase in absence of sulfur. With addition of sulfur, however, NBR tends to present in a continuous phase formed by numerous microfibril-like elongated vulcanized rubber, whereas the DV with 3 phr sulfur demonstrates a more uniform co-continuous structure. Correspondingly, the DV exhibits a sharp brittle-ductile transition occurs as the sulfur content increases from 1.5 to 2.5 phr, and the DV with 3 phr achieves an impact strength of almost 30 times that of neat PLA. This work aims to illustrate the development of network-like dispersion of vulcanized rubber in PLA-based DVs, and the findings provide a useful guideline in future exploration of PLA-based DVs.

Preparation and characterization of super-toughened PA6/r-PVB blends with “transplanted” multicore morphology by reactive compatibilization

Super-toughened polyamide 6 (PA6) material was fabricated by applying a feasible and effective method involving reactive melt blending of PA6 and residue of plasticized poly(vinyl butyral) (r-PVB)/maleated poly(ethylene-1-octene) (POE-g-MA) masterbatch, in which the multicore structure could be formed in-situ in PA6 matrix. Interfacial, rheological and morphology measurements confirmed that the POE-g-MA was encapsulated by r-PVB in PA6 matrix. The sharp brittle-ductile transition was observed at a critical interparticle distance (τc) about 0.30 μm for PA6/r-PVB/POE-g-MA blends, and the impact strength was 22–24 times higher than that of neat PA6. The flexibility of r-PVB/POE-g-MA and the strong interfacial adhesion among the three blending composition were responsible for the super toughness of PA6/r-PVB/POE-g-MA ternary blends. The DSC results suggested that the improvement of toughness was also related to the decrease in glass transition temperature (Tg) and degree of crystallinity (Xc) of PA6 matrix.

Fluorinated polyimide with polyhedral oligomeric silsesquioxane aggregates: Toward low dielectric constant and high toughness

An amphiphilic alternating copolymer with hydrophobic polyhedral oligomeric silsesquioxane (POSS) segments and hydrophilic anhydride segments, which is able to self-assemble into nanoscale POSS aggregates, is introduced into fluorinated polyimide (FPI) films to polish up their toughness while lowering their dielectric constant. The dielectric constant of POSS/FPI composite films with 2.8 wt% amphiphilic alternating copolymer significantly decreases to 2.09 from 3.14 for pure FPI. Furthermore, a sharp brittle-ductile transition is observed in the tensile energy to break versus interparticle distance curve. When the interparticle distance is reduced to 215 nm, the elongation at break and tensile energy to break of POSS/FPI composite films increase to 27.5% and 23.5 MJ/m3 from 8.3% to 6.8 MJ/m3 respectively. The tensile-fractured surfaces of POSS/FPI composite films reveal that the toughening mechanism is mainly attributed to the prevention of crack propagation and the debonding of POSS aggregates with a plastic void growth.

Effect of core–shell structures of acrylonitrile–styrene–acrylate (ASA) terpolymer on the properties of poly(vinyl chloride) (PVC)/ASA blends: Miscibility, toughness, and heat resistance

ABSTRACTIn this work, acrylonitrile–styrene–acrylate (ASA) terpolymer was used to toughen rigid poly(vinyl chloride) (PVC). ASA has a core–shell structure, where the poly(butyl acrylate) (PBA) serves as the soft core while styrene‐acrylonitrile (SAN) copolymer works as the rigid shell. Herein, The PBA core content in ASA was varied from 0 to 80 wt %, and its effect on the physiochemical properties was investigated. It was found that the hard shell of ASA was miscible with PVC matrix, providing good interfacial adhesion between ASA and PVC. Increasing the soft PBA content considerably improved the room‐temperature impact toughness, and a sharp brittle–ductile transition (BDT) as a function of PBA content was observed. However, as the testing temperature decreased to 0 and −30 °C, the toughening effect became limited, and the BDT first shifted to high PBA content region and finally disappeared. It was suggested that whether the toughening effect can be achieved depended on the thickness of hard shell and the relaxation behavior of PBA core. Albeit the loss in rigidity was accompanied, the accomplished toughening effect was not on the sacrifice of heat distortion temperature. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46839.

Crosslinked bicontinuous biobased polylactide/natural rubber materials: Super toughness, “net-like”-structure of NR phase and excellent interfacial adhesion

Polylactide (PLA) and natural rubber (NR) are two major renewable resources in the polymer materials field. However, their blend has not yet met engineering needs, largely because of a lack of interfacial adhesion between the continuous PLA phase and dispersed NR droplets. To address this issue, we have designed a novel super toughened biobased PLA/NR blend prepared by peroxide-induced dynamic vulcanization, in which the cross-linked NR phase has a specific continuous “net-like” structure. A sharp brittle-ductile transition occurred in the blend with 35 wt% NR, showing impact strength of 58.3 kJ/m2, approximately 21 times that of the neat PLA. The peroxide initiated reactive compatibilization at the interface between PLA and NR. The toughening mechanism and deformation of the crosslinked “net-like” NR phase during stretching are discussed. Our results provide evidence of a continuous “net-like” NR located in the PLA matrix with good interfacial adhesion, which potentially enhances the mechanical properties of the material.

Effects of reactive blending temperature on impact toughness of poly(lactic acid) ternary blends

Reactive blending of poly(lactic acid) (PLA) with an ethylene/n-butyl acrylate/glycidyl methacrylate terpolymer elastomer (EBA-GMA) and a zinc ionomer of ethylene/methacrylic acid copolymer (EMAA-Zn) was performed at various temperatures using a twin screw extruder. Notched Izod impact strength, dynamic mechanical properties and morphological structure of the resulting blends were studied. A sharp brittle–ductile transition (BDT) of the resulting blends occurred when the blending temperature increased to 195∼210 °C and the EBA-GMA/EMAA-Zn ratio was equal to or large than 1. The influences of blending temperature on interfacial compatibilization and croslinking of the elastomer were also studied. Supertough PLA ternary blends were achieved by this reactive approach.

Synergistic toughening effect of chlorinated polyethylene and ethylene-vinyl acetate copolymer on the poly (vinyl chloride)/poly (α-methylstyrene-acrylonitrile) blends via compatibilization

Poly (vinyl chloride) (PVC)/poly (α-methylstyrene-acrylonitrile) (α-MSAN) (70/30) blends was toughened by blending with chlorinated polyethylene (CPE) and ethylene-vinyl acetate copolymer (EVA). EVA did not improve the impact strength appreciably. A prominent synergistic toughening effect was observed when EVA and 15 phr CPE were used in combination in PVC/α-MSAN (70/30) matrix. A sharp brittle–ductile transition in impact strength was observed in the range of 1–5 phr EVA. With the addition of 5 phr EVA, the impact strength increased almost 24 times compared with that of PVC/α-MSAN (70/30) blends. Morphology was used to investigate the toughening mechanism, and the synergistic effect can be attributed to better compatibility between phases, and to the formation of a network structure of the dispersed-phases. The improved compatibility was also supported by differential scanning calorimetry results. Heat distortion temperature remained almost unchanged over all the compositions, indicating that the improvement in toughness did not sacrifice heat resistance.

On compatibilization and toughening of a copolyester with a maleated thermoplastic elastomer

A maleated thermoplastic elastomer (TPEg) was prepared from maleic anhydride, grafting a mixture of polyethylene–octene elastomer and semi-crystalline polyolefin plastic (60/40 by weight) in a twin screw extruder. The non-grafted version (TPE) of the mixture was also prepared under the same processing conditions. The TPEg was employed to compatibilize and toughen amorphous copolyester PETG/TPE blends. The addition of the TPEg improves the compatibility between PETG and the TPE and results in fine dispersion of the TPE in the PETG matrix. At a fixed dispersed phase content of 15 wt%, a sharp brittle–ductile transition takes place, when the TPEg content in the dispersed phase increases from 20 to 30 wt%, namely, the TPEg content in the blends increases just from 3 to 4.5 wt%. After the brittle–ductile transition, the blends are maintained at super-tough level with notched impact strength more than twenty-fold higher than that of pure PETG plastic. The influence of the TPEg content on fractography of the PETG/TPE blends was also investigated. When the TPEg content in dispersed phase is below 20 wt%, the impact fracture surface shows a small area of slow crack growth region and numerous feather-like markings in fast crack growth region, indicating a brittle failure mode. While the TPEg content in the dispersed phase is above 30 wt%, the impact fracture surface exhibits drastically enlarged slow crack growth region and some parabolic markings in the fast crack growth region. Massive cavitation and extensive matrix shear yielding are predominant mechanisms of the impact energy dissipation upon impact testing.

Brittle–ductile transition in high‐density polyethylene/glass‐bead blends: Effects of interparticle distance and temperature

AbstractThe toughness of high‐density polyethylene (HDPE)/glass‐bead blends containing various glass‐bead contents as a function of temperature was studied. The toughness of the blends was determined from the notch Izod impact test. A sharp brittle–ductile transition was observed in impact strength–interparticle distance (ID) curves at various temperatures. The brittle–ductile transition of HDPE/glass‐bead blends occurred either with reduced ID or with increased temperature. The results indicated that the brittle–ductile‐transition temperature dropped markedly with increasing glass‐bead content. Moreover, the correlation between the critical interparticle distance (IDc) and temperature was obtained. Similar to the IDc of polymer blends with elastomers, the IDc nonlinearly increased with increasing temperature. However, this was the first observation of the variation of the IDc with temperature for polymer blends with rigid particles. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1855–1859, 2001

Toughened polypropylene with balanced rigidity. III. Compositions and mechanical properties

Toughened polypropylene with balanced rigidity (TRPP) was prepared by thermal mechanical blending of PP resin with a toughening master batch (TMB) in a twin screw extruder. The dependence of the mechanical properties of TRPPs on the ratio of ethylene-propylene to styrene-butadiene elastomers, the total elastomer content in the TRPP, and the amount of elastomers in the TMB were investigated. The TRPP with a total elastomer content of 14 wt %, which was made from a TMB with 32 wt % elastomer and a 80/20 (w/w) ratio of ethylene-propylene to styrene-butadiene elastomers, was found to have excellent balanced mechanical properties. The notched Izod impact strength at 23°C was 762 J/m (23 times that of PP), the flexural modulus was 1078 MPa (92% of that of PP), and the tensile strength at yield was 34.8 MPa (88% of that of PP). Moreover, its mechanical properties were much better than the simply blended sample with the same composition, demonstrating that dynamic vulcanization and polymer-bridge conjunction are excellent techniques to produce a high-impact, high-modulus PP. A sharp brittle–ductile transition was found at 14 wt % total elastomer content, which was assumed to be a percolation phenomenon. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1345–1350, 2001

Toughened polypropylene with balanced rigidity. III. Compositions and mechanical properties

Toughened polypropylene with balanced rigidity (TRPP) was prepared by thermal mechanical blending of PP resin with a toughening master batch (TMB) in a twin screw extruder. The dependence of the mechanical properties of TRPPs on the ratio of ethylene-propylene to styrene-butadiene elastomers, the total elastomer content in the TRPP, and the amount of elastomers in the TMB were investigated. The TRPP with a total elastomer content of 14 wt %, which was made from a TMB with 32 wt % elastomer and a 80/20 (w/w) ratio of ethylene-propylene to styrene-butadiene elastomers, was found to have excellent balanced mechanical properties. The notched Izod impact strength at 23°C was 762 J/m (23 times that of PP), the flexural modulus was 1078 MPa (92% of that of PP), and the tensile strength at yield was 34.8 MPa (88% of that of PP). Moreover, its mechanical properties were much better than the simply blended sample with the same composition, demonstrating that dynamic vulcanization and polymer-bridge conjunction are excellent techniques to produce a high-impact, high-modulus PP. A sharp brittle–ductile transition was found at 14 wt % total elastomer content, which was assumed to be a percolation phenomenon. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1345–1350, 2001

Influence of grain boundary composition on the moisture-induced embrittlement of Ni 3(Si,Ti) alloys

Ni 3(Si,Ti) alloys containing different levels of boron were tensile tested in air at room temperature at two different strain rates. The grain boundary compositions and fracture modes of these alloys were determined by Auger spectroscopy and scanning electron microscopy, respectively. Tensile elongation and fracture mode depend upon the fabrication procedure, heat treatment, and strain rate. Widely different boron concentrations were observed at the grain boundaries, depending on the fabrication procedure and heat treatment. In addition, silicon and titanium were depleted while nickel was enriched at the grain boundaries in all specimens examined. Tensile elongations correlated well with the grain boundary concentration of boron and also with an embrittlement parameter defined as (Si+Ti−B)/Ti. A sharp brittle-ductile transition was found to occur with increasing grain boundary concentration of boron and with decreasing values of the embrittlement parameter (Si+Ti−B)/Ti. The critical grain boundary concentrations corresponding to this transition were found to be sensitive to the strain rate. All the results can be explained in terms of the effect of grain-boundary composition on moisture-induced environmental embrittlement.

Polypropylene–rubber blends: 1. The effect of the matrix properties on the impact behaviour

The effect of matrix properties, i.e. crystallinity and molecular weight, on the impact behaviour of polypropylene–EPDM blends was studied. The blends were made on a twin-screw extruder. The impact strength was determined as a function of temperature, using a notched Izod impact test. The matrix crystallinity was varied by varying the matrix isotacticity, and ranged from 33 to 50 wt%. With increasing temperature the polymers show a sharp brittle–ductile transition. This brittle–ductile transition temperature ( T bd) shifts to higher temperatures with increasing crystallinity of the polypropylene. However, the balance of properties and the modulus– T bd relationship were better with blends made with higher crystalline PP. The matrix molecular weight was decreased by treating a high molecular weight PP–EPDM (85/15 vol%) master blend with peroxide. In this way blends were obtained with a high MFI and a small rubber particle size. The matrix MFI of the blends thus obtained ranged from 2 to 30 dg min −1. With decreasing matrix molecular weight the T bd increased. The peroxide treated blends exhibited a considerably lower T bd than comparable blends made in the standard way with a similarly small particle size. Peroxide treatment of a master blend is an effective method of preparing blends with a high MFI, small particle size and good ductility.

Ribbon Terrain Formation, Southwestern Fortuna Tessera, Venus: Implications for Lithosphere Evolution

The term tessera has been used to describe regions of deformed venusian crust exhibiting two or more intersecting sets of structural elements; however, tessera includes terrains formed by a variety of spatially and temporally discrete tectonic processes. Tessera fabric characterizes highland plateau structure, and thus understanding the nature of this deformation is critical to understanding the mode of highland plateau formation. Many tessera fabrics include ribbons, folds, and late graben. In this paper, we refine the geometry of ribbons through geologic mapping and radargrammetric analysis of type ribbon structures at southwestern Fortuna Tessera; we extend our findings to ribbon fabrics at Thetis Regio. Any model of ribbon formation must account for the following constraints on ribbon geometry. (a) Ribbon-forming lineaments exhibit sharp contrasts relative to adjacent materials. (b) Ribbon-bounding lineaments form a distinct pattern alternating between radar-dark and radar-bright, which represent trough walls oriented away from and toward the satellite, respectively. (c) Ribbons form long, narrow troughs that alternate with parallel, narrow ridges; ridges and troughs display extreme length:width aspect ratios. (d) Trough walls are near vertical. (e) Troughs are shallow with consistent shallow depth along individual troughs and in adjacent troughs. (f) In some cases (e.g., southwest Fortuna Tessera) trough walls are parallel and matched and would exhibit a close fit if the trough was closed; in these cases trough walls merge laterally forming V-shaped terminations. Trough floors are smooth and flat, lacking small-scale interior lineaments. (g) In other cases (e.g., Thetis Regio) ribbons display (a)–(d), but trough walls are defined by a series of subparallel lineaments including local interior lineaments, and trough floors ramp up to join trough walls displaying parallel rather than V-shaped terminations. Trough walls would not display a close fit if closed.We propose two member types of ribbons, tensile-fracture ribbons and shear-fracture ribbons. Tensile-fracture ribbons display features (a)–(f) and formed by the opening of tensile fractures of a thin brittle layer above a ductile substrate. They require a near fracture-free shallow crust and very shallow depth to the brittle–ductile transition (BDT) (<1 km). Shear-fracture ribbons display features (a)–(d) and (g) formed under near-surface transitional-tensile failure conditions or due to reactivation of steeply oriented preexisting fractures resulting in steep-sided graben. Formation of tensile-fracture ribbons would be favored with a sharp BDT at very shallow depth, whereas a broader and somewhat deeper BDT would favor formation of shear-fracture ribbons. In both cases, the thickness of the strong upper layer is quite thin (<1–2 km), and ribbon structures likely formed prior to long-wavelength folds, which require a greater effective elastic thickness and a deeper depth of support (∼6 km).The presence of ribbon structures within highland plateaus favors an upwelling model for highland plateau formation, in which crustal thickening results from magmatic underplating related to a mantle upwelling or mantle plume. In order for the plume to be able to anneal mechanically the crust as required by ribbon formation, the lithosphere would likely have to be quite thin. These implications are consistent with highland plateaus as an ancient signature of mantle plumes on thin lithosphere, whereas volcanic rises, which are presently thermally supported, reflect thick lithosphere. Phoebe Regio represents a transitional lithospheric thickness.

Sudy on the Polypropylene/High Density Polyethylene/Styrene-Butadiene-Styrene Block Copolymer Ternary Blends II. The Effect of Processing on the Properties and Morphology of Polypropylene/High Density Polyethylene/ StyreneButadiene-Styrene Ternary Blends

It has been shown that the impact strength of non-compatible polymer blends is closely related to the number, shape and morphology of the dispersed phase particles. The general condition for toughening is that the inter-particle distance must be smaller than a critical value T. (Critical Inter-Particle Distance). Thus a sharp brittleductile transition mould occur as T becomes smaller than T. This has been applied to interpret the relationships of the impact strength of the blends with their respective phase morphology, particle diameter and elastomer volume fraction. The objective of this study is to examine the effect of various blending processes on the morphology of the rubber particles in the PP/HDPE/SBS ternary blends. The relation of the impact strength of PP ternary blends with the SBS particle diameter has been investigated. It is found that the morphology of the SBS dispersed phase particles is closely related to the mechanical properties of the PP ternary blends and it is very much depen dent upon the processing parameters of the blends.

The effect of matrix toughness and dispersed elastomer phase on the brittle-ductile transition in PP/HDPE/SBS blends

In this paper the sbrittle-ductile transition of polypropylene, high density polyethylene, and a styrene-butadiene-styrene triblock copolymer (PP/HDPE/SBS) ternary blends is investigated for fixed compositions and prepared under various conditions. The morphology of the SBS dispersed phase particles and impact strength of the PP ternary blends is closely related to the processing conditions. There is a sharp Brittle-Ductile transition for the ternary blends when interparticle distance T becomes less than the critical interparticle distance Tc. Both the impact strength in general and more specifically, Tc depend upon the toughness of the PP/HDPE composite matrix.

The brittle–ductile transition in silicon. I. Experiments

The experiments described in this paper investigate the fundamental processes involved in the brittle–ductile transition (BDT) in silicon, and form the basis of a new theoretical model (see following paper). The fracture (or bending) stresses of four-point bend specimens of silicon containing semicircular surface cracks, introduced by surface indentation, were determined over a range of temperatures and strain rates. A sharp transition, characterized by a rapid increase in fracture stress with temperature, occurs at a temperature (Tc) that depends on the strain rate and the doping of the material used; these data are used to derive activation energies, which are found to be equal to those for dislocation glide. At temperatures above the sharp transition region, the specimens deform by macroscopic plastic yielding. Etch pitting experiments show that belowTcno significant dislocation activity occurs; the sharp brittle–ductile transition is associated with a sudden growth of well-defined dislocation arrays from certain points on the precursor flaw, before fracture occurs. These only appear in a dynamic test atT≽Tc; atT=Tc, they form only when the applied stress intensity factorKis of the same order as that for brittle failure (KIc) atT&lt;Tc. These experiments suggest that atT≈Tc, a 'nucleation' event precedes the generation of avalanches of dislocations whenK≈KIc. Static tests show that dislocations can be made to move from crack tips ofKvalue as low asca. 0.3KIc. Above the transition region general plasticity occurs, with slip being concentrated particularly around and spreading from the precursor flow. A 'warm-prestressing' effect is observed, whereby the low-temperature fracture stress is increased by prestressing aboveTc.