The fracture toughness of blends
of polypropylene terephthalate (PPT) with polyethylene terephthalate (PET)
and polybutylene terephthalate (PBT) were investigated. Binary blends were
prepared comprising 10:90, 30:70, 50:50, 70:30 and 90:10 mass/mass%. The fracture
toughness was determined for each blend using the essential work of fracture
(EWF) method and thin film double edge notched tension (DENT) specimens. The
specific essential work of fracture, we,
values obtained for blends of PET/PPT ranged from 27.33 to 37.38 kJ m–2
whilst PBT/PPT blends yielded values ranging from 41.78 to 64.23 kJ m–2.
Differential scanning calorimetry (DSC) was employed to assess whether or
not crystallinity levels influence the mechanical properties evaluated. The
fracture toughness of PPT deteriorated with PET incorporation. However, high
we values exceeding that of pure PPT were obtained for PBT/PPT blends across
the composition range studied. 相似文献
Characterization of Mode-I fracture toughness of ductile polymeric thin films is nontrivial. Proper specimen preparation and experimental procedures are required to ensure in-plane tensile loading. In this study, a custom-built double-edge notched tensile test fixture was employed to characterize the Mode-I essential work of fracture (EWF) toughness of metallocene linear low-density polyethylene (m-LLDPE) films. Effects of specimen geometry, strain rate and film orientation on the specific essential work of fracture, we, and the specific non-essential work of fracture, wp, were investigated. Results indicate both EWF parameters are independent of the crosshead speed, gauge length (distance between upper and lower clamps) and specimen width within the ranges tested. we is significantly higher for thinner films and for crack propagation perpendicular to the blown film machine direction (MD). The usefulness of EWF for evaluating m-LLDPE fracture toughness is discussed. 相似文献
In recent years, the essential work of fracture (EWF) method has been extensively employed for assessing a material's toughness by specific essential fracture work, especially for polymers showing ductile failure. However, most research has studied either the in-plane stress mode or the out-of-plane stress mode. To obtain a more in-depth understanding of the EWF theory, the specific essential and non-essential fracture work of polypropylene random copolymer (PP-R) was investigated in both in-plane stress mode and out-of-plane stress mode. The effects of ligament length, amount of pre-cracking and pre-cracking method on the specific essential and non-essential fracture work were explored. The specific essential fracture work obtained in both stress modes is compared and discussed. 相似文献
Phase behavior in domains of immiscible blends of poly(pentamethylene terephthalate)/poly(ether imide) (PPT/PEI) and poly(hexamethylene terephthalate)/poly(ether imide) (PHT/PEI) were investigated using differential scanning calorimetry (DSC). The measured glass transition temperature (Tg) reveals that aryl polyesters dissolve more in the PEI-rich phase than the PEI does in the aryl polyester-rich phase, for both PPT/PEI and PHT/PEI systems. Additionally, optical microscopy supports the conclusion that PPT (or PHT) dissolves more in the PEI-rich phase than PEI does in the PPT-rich (or PHT-rich) phase in the aryl polyester/PEI blends. Furthermore, the Flory–Huggins interaction parameters (χ12) for the PPT/PEI and the PHT/PEI blends were calculated to be 0.12 and 0.17, respectively. For the blend systems comprising of PEI and homologous aryl polyesters, the value of χ12 exhibits a trend of variation with respect to structure of aryl polyesters. For the PPT/PEI and PHT/PEI blends, investigated in this study, value of the polymer–polymer interaction parameter (χ12) between the aryl polyester and the PEI was found to be positive, which increases with the number of methylene moieties in the repeating unit of the aryl polyester, ultimately resulting in phase separation observed. 相似文献
The toughness of amorphous copolyester sheets was assessed by the essential work of fracture (EWF) concept. While the yielding-related
work of fracture terms did not change significantly, the necking-related parameters strongly decreased with decreasing entanglement
density of the copolyesters having different amounts of cyclohexylenedimethylene (CHDM) units in their backbones. Furthermore, copolyesters with high CHDM content and thus less entanglement density showed full recovery of the necked region beyond the glass transition temperature,
i.e. the ‘plastic’ zone in the related specimens formed by cold drawing and not by true plastic deformation. By contrast,
the copolyester with negligible amount of CHDM did not show this shape recovery. Modulated differential scanning calorimetry (MDSC) revealed that the necking in the latter
system was accompanied by strain-induced crystallization. The superior work hardening in the necking stage of the respective
poly(ethylene terephthalate) (PET) specimens can thus be ascribed to stretching of the entanglement network with superimposed crystallization.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
The effect of β phase polypropylene (PP), induced by β-nucleating agent (β-NA), on the fracture behavior in dynamically vulcanized thermoplastic elastomers (TPVs) based on dynamically vulcanized PP/ethylene-propylene-diene rubber (EPDM) blend was studied. Differential Scanning Calorimetry (DSC) and Wide-angle X-ray diffraction (WAXD) were employed to study the melting behavior and crystalline structures, and the results indicated that the β-NA induced β phase of PP effectively in TPVs. With the increasing dosage of the β-NA incorporated in, the content of β phase increased while the total crystallinity of the blend kept constant. The fracture behavior of the TPVs with different β phase content was studied with double edge notched tensile loaded specimens (DENT) using the essential work of fracture (EWF) approach. The specific essential work of fracture (we) increased with the increasing of β phase content, indicating that the presence of β phase could effectively enhance the fracture toughness of TPVs. 相似文献
The effect of Al2O3 content on microstructure, hardness, fracture toughness and electrical conductivity behaviours of c-ZrO2 ceramics was investigated using high-purity commercial powder of 8 mol% yttria-stabilised c-ZrO2 doped with up to 10 wt.% Al2O3. XRD results showed that the c-ZrO2 specimens doped up to 0.3 wt.% Al2O3 revealed no Al2O3 peaks, indicating that Al2O3 was completely solubilised in the c-ZrO2 matrix. However, when >0.3 wt.% Al2O3 was added, Al2O3 peaks started to appear, showing that overdoped Al2O3 was not solubilised in the c-ZrO2 matrix. The introduction of Al2O3 significantly enhanced the hardness and fracture toughness of c-ZrO2. The hardness and fracture toughness increased with increasing Al2O3 content. The maximum hardness and fracture toughness values reached 1,459?±?8 kg/mm2 and 2.41?±?0.02 MPa/m1/2, respectively, with the addition of 10 wt.% Al2O3, while these values were 1,314?±?11 kg/mm2 and 1.5 ?±?0.03 MPa/m1/2 for undoped c-ZrO2. The increase of hardness and fracture toughness can be attributed to smaller grain size, the increment of Young’s modulus of Al2O3-doped c-ZrO2 and different expansion coefficients of c-ZrO2 and Al2O3 grains. The electrical conductivity of the specimens was measured using a frequency response analyzer in the frequency range of 5–13 MHz and in the temperature range of 300–800 °C. It was seen that electrical conductivity slightly increased with increasing Al2O3 content up to 1 wt.%, and further increase in Al2O3 led to a decreased in the conductivity. 相似文献
Polycarbonate (PC), a ductile polymer, has been found by both linear elastic fracture mechanics and impact tests to present a ductile-brittle transition, which depends on notched specimen thickness, test speed and gamma irradiation. Owing to large amounts of plastic deformation, fracture toughness measurements by these test methods are not precise. In the present communication, a better method, the Essential Work of Fracture (EWF), to assess the fracture characteristics in plane state of stress was for the first time used to evaluate the fracture toughness of PC sheets subjected to gamma irradiation dose. Three-points bend tests of sharp pre-cracked specimens with different ligament lengths were 340 kGy gamma irradiated. EWF results showed that the total fracture work increased linearly with length for both non-irradiated and gamma irradiated conditions. A significant decrease in EWF fracture toughness was associated with brittleness promoted by gamma irradiation. This brittleness was also confirmed by macro and microscopy (SEM) evidence. 相似文献
The Essential Work of Fracture approach (EWF) was used to determine how UV-C irradiation alters the fracture behaviour of LDPE/EVA films. Complementary characterization was performed by FTIR, DSC, TOM, and uniaxial tensile testing. The crosslinking reactions that govern photo-oxidation process at initial stage of exposure stiffened the amorphous phase of the polymer, leading to films with enhanced elastic modulus, yield stress and ultimate strength, but impaired strain at break. In the fracture experiments carried out on films irradiated within 0 and 5 days, EWF methodology requirements were met and the corresponding fracture toughness parameters (we and βwp ) turned out to be sensitive to UV-C irradiation. Longer irradiation time triggered the development of microcracks, which not allowed further stable crack growth and invalidated the application of EWF approach. 相似文献
Fracture behaviour of polyethylene (PE)/Mg-Al layered double hydroxide (LDH) based nanocomposites has been studied by essential work of fracture (EWF) approach. Transmission electron microscopy (TEM and X-ray diffraction (XRD) analysis have been used to investigate the morphological features of these nanocomposites. A maximum in the non-essential work of fracture was observed at 5 wt.% LDH demonstrating enhanced resistance to crack propagation compared to pure PE. Morphological analyses of the nanocomposites show that the dispersed LDH platelets are partially exfoliated and also forms clusters with polymer chains remaining entrapped within. Rheological analyses show that the typical low-frequency Newtonian flow behaviour, as observed in unfilled polymer, shifts to shear-thinning behaviour with increasing LDH concentration. At 5 wt.% LDH a ductile-to-brittle transition has been observed. Fracture surface investigation by SEM reveals the arresting of the plastic crack growth by the LDH particle clusters, which is more significant at 5 wt.% LDH content. At higher LDH concentrations, the number of such particle clusters increases causing decrease in the average distance between them. As a result large-scale plastic deformation of the matrix at higher LDH concentration is effectively arrested favouring small strain failure and this in turn reaffirms the possible existence of a ductile-to-brittle transition. The study in general reveals that the resistance against crack initiation (essential work of fracture: EWF) and crack propagation (non-essential work of fracture: βwp) in these nanocomposites are structurally correlated with the matrix behaviour and the morphology (state of LDH particle dispersion) respectively. 相似文献
Polytyramine (PT) has been electro‐deposited onto multi‐walled carbon nanotube (MWCNT) modified glassy carbon (GC) electrodes via oxidation of tyramine in 0.1 M H3PO4 by cycling the potential over the range of −400 mV to 1300 mV (versus Ag/AgCl). The reactivity of the resulting chemically‐modified electrodes was characterized using cyclic voltammetry in the presence and absence of reduced nicotinamide adenine dinucleotide (NADH). The modified electrodes displayed electrochemical activity due to the formation of quinone species and were catalytically active towards NADH oxidation by lowering the oxidation peak potential by 170 mV compared to the value of the MWCNT modified electrode with a peak potential of 180±10 mV (versus Ag/AgCl). The MWCNT/PT surface was further characterized using SEM and XPS methods, which indicated that a thin polymeric film had been formed on the electrode surface. The present work demonstrates the advantage of using PT as a platform that combines both the immobilization of alcohol dehydrogenase (ADH) and the mediation of NADH oxidation at a low overpotential essential to the design of high performance ethanol biosensors, all within an easily electropolymerizable film. The resulting biosensor displayed an ethanol sensitivity of 4.28±0.06 μA mM−1 cm−2, a linear range between 0.1 mM and 0.5 mM and a detection limit of 10 μM. 相似文献
The crystal growth kinetics of germanium disulfide in undercooled melts has been studied by optical microscopy under isothermal conditions. The linear growth kinetics of GeS2 has been observed in the temperature range 672 ≤ T ≤ 711 K in thin film samples. The activation energy of crystal growth assuming Arrhenius behavior has been determined as EG = 166 ± 8 kJ mol?1 for thin film samples. From the dependence of reduced growth rate on undercooling, the interface driven 2-D surface nucleated model was estimated. 相似文献
Summary: The crack toughness behaviour of binary styrene‐butadiene (SB) triblock copolymer blends of a thermoplastic block copolymer (LN3) and a thermoplastic elastomer (LN4) with different molecular architecture was studied using essential work of fracture (EWF) concept and was correlated to the morphological features from transmission electron microscopy (TEM). An increase in the crack toughness behaviour between 60 and 80 wt.‐% LN3 has been observed and is attributed to a change from cylindrical to lamellar morphology. The time‐resolved crack propagation studies have offered new dimensions to understand the kinetic aspects of fracture behaviour while the strain field analysis has explained the time‐dependent deformation behaviour to characterise the time dependence of the strain energy dissipation modes.
Load‐displacement diagrams of non essential work of fracture values of LN3/LN4 blends. 相似文献