This is an editorial article. It has no abstract.
Novel biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [PHBV]/graphene nanocomposites were prepared by solution casting. The thermal properties, crystallization behavior, microstructure, and fracture morphology of the composites were investigated. Scanning electron microscope (SEM) results show that graphene layers are homogeneously dispersed in the polymer matrix. X-ray diffraction (XRD) and dynamic scanning calorimetry (DSC) studies show that the well dispersed graphene sheets act as nucleating agent for crystallization. Consequently, the mechanical properties of the composites have been substantially improved as evident from dynamic mechanical and static tensile tests. Differential thermal analysis (DTA) showed an increase in temperature of maximum degradation. Soil degradation tests of PHBV/graphene nanocomposites showed that presence of graphene doesn’t interfere in its biodegradability.
Epoxy/multiwall carbon nanotubes (MWCNT) composites were prepared using sodium salt of 6-aminohexanoic acid (SAHA) modified MWCNT and its effect properties of related composites were investigated. The composite prepared using a polar solvent, tetrahydrofuran exhibits better mechanical properties compared to those prepared using less polar solvent and without using solvent. The tensile properties and dynamic storage modulus was found to be increased as a result of modification of MWCNT with SAHA. This improvement in the tensile properties and dynamic mechanical properties of epoxy/MWCNT composite is a combined effect of cation-π interaction and chemical bonding. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to explain cation-π interaction between SAHA with MWCNT and chemical bonding of SAHA with epoxy resin. The effect of modification of MWCNT on morphology of a nanocomposite was confirmed by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The present approach does not disturb the ! electron clouds of MWCNT as opposed to chemical functionalization strategy.
In this study, maleic anhydride-grafted poly(butylene succinate) (PBS-g-MA) was synthesized via reactive meltgrafting process using different initiator contents. The grafting efficiency was increased with the initiator content, manifested by the higher degree of grafting in PBS-g-MA. The grafting reaction was confirmed through Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Then, PBS-g-MA was incorporated into organo-montmorillonite (OMMT) filled poly(butylene succinate) (PBS) nanocomposites as compatibilizer. Mechanical properties of PBS nanocomposites were enhanced after compatibilized with PBS-g-MA, due to the better dispersion of OMMT in PBS matrix and the improved filler-matrix interfacial interactions. This was verifiable through X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Differential scanning calorimetry (DSC) showed that the degree of crystallinity and melting temperature increased after addition of PBS-g-MA. However, the presence of PBS-g-MA did not favor the thermal stability of the nanocomposites, as reported in the thermogravimetry (TGA).
The crystallization of polymers, caused by flow fields in the melt, has been the subject of extensive studies for many years. In this study, we use periodical shear to induce polypropylene to form multi-layer structure, which is usually observed in plants. Two interesting points were found: firstly, the quest of mimicking natural structures was achieved by controlled periodical shear field; secondly, the evolution from nano to shish-kebab-like cylindrite structure was obtained in the multi-layer structure, which can be clarified by nuclei competition model. This study can be used to better understand the shear-induced crystallization of polymer. Here our intention is to place this new observation on the map, leaving a fuller presentation and discussion of the work to a future publication.
This study focuses on the effect of crosslinking density on the mechanical response of polystyrene-co-divinylbenzene (PS-DVB) particles under compression by means of nanoindentation-based flat punch method combined with SEM observation of particle morphologies. The monodisperse PS-DVB particles with about 5 µm in diameter are produced by the Ugelstad activated swelling method and the crosslinking density defined as the weight percentage of activated crosslinker DVB during the preparation process varies from 2.0 to 55.3%. Results show that the particle stress–strain behaviour is independent of the crosslinking density if the strain is less than 10%. With increasing strain level over 10%, a higher crosslinking leads to a stiffer behaviour of the particles. While slightly crosslinked (2.0 and 5.0 wt%) particles undergo plastic deformation with crazing and residual strain, highly crosslinked (21.3, 32.0 and 55.3 wt%) counterparts experience perfectly viscoelastic deformation. The crosslinking density significantly influences the fracture property as well as the failure morphology. Slightly crosslinked particles become permanently deformed after compression, while highly crosslinked ones are entirely fragmented once a critical strain is reached.
The electrical responses of conductive graphite/epoxy composites subjected to an applied electric field were investigated. The results showed that reversible dielectric breakdown can easily occur inside the composites even under low macroscopic field strengths. This is attributed to the Zener effect induced by an intense internal electric field. The dielectric breakdown can yield new conducting paths in the graphite/epoxy composites, thereby contributing to overall electrical conduction process.
This paper presents a finite element model to predict the progressive damage mechanisms in open-hole PEEK (Poly-Ether-Ether-Ketone) laminates. The stochastic laminate’s properties with non-uniform stress distribution are considered from element to element using the Gaussian distribution function. The failure modes considered are: fiber tension/compression, matrix tension/compression, fiber/matrix shear, and delamination damage. The onset of damage initiation and propagation are predicted and compared with three different failure criteria: strain-based damage criterion, Hashin-based degradation approach and stress-based damage criterion which is proposed by the authors of the present work. The interlaminar damage modes associated with fiber/matrix shearing and delamination are modeled using the cohesive elements technique in ABAQUS™ with fracture energy evolution law. Mesh sensitivity and the effect of various viscous regularization factors are investigated. Damage propagation and failure path are examined by re-running the program for several times.
Micro-lamellar patterns and orientation-induced micro-voids (cracks) in spherulites are probed in step-crystallized blends of two crystalline polymers: poly(ethylene oxide) (PEO) and low-molecular-weight poly(L-lactic acid) (PLLA) in different weight fractions, using polarizing light optical microscopy (POM), and scanning electron microscopy (SEM) with water-etching technique. It is revealed that blend composition led to entirely different PLLA lamellar regularities and void patterns. Water-etching into interiors of PEO/PLLA blends show 3D assembly of PLLA lamellae patterns. It is an important datum for structure modeling of banded polymer spherulites in bulk state. The mechanisms for the void/crack patterns and lamellar orientation are exemplified via dissecting into interior spherulites of bulk-form samples.