The influence of coupling agents on the melt rheological properties of natural fiber composites has been investigated in this work using capillary and rotational rheometers. Scanning electron microscopy was also employed to supplement the rheological data. It was found that molecular weight and molecular weight distribution of the polymer matrix and coupling agent characteristics influence the filler wetting and the melt flow properties of the filled composites. Generally, low molecular weight and narrow molecular weight distribution polyethylene matrix provides relatively larger increase of the viscosity of the composites. Coupling agents tend to increase the resistance to shearing, but wall slip effects may interfere with the measured values, especially at very high filler loadings. Entrance pressure loss in capillaries is also influenced by polymer matrix and coupling agent used.
Composites containing 50 wt.‐% fly ash in a PP homopolymer were prepared via batch mixing and compression moulding. The following coupling agents were evaluated: Lubrizol Solplus C800, N,N′‐(1,3‐phenylene)dimaleimide, γ‐methacryloxypropyltrimethoxysilane and maleic‐anhydride‐grafted PP. At the filler level investigated, C800 gave the best balance of composite strength and toughness. In the latter case filler‐matrix adhesion appeared weaker relative to γ‐MPS, BMI and m‐PP, all of which gave excessively strong filler‐matrix adhesion leading to a reduction in composite toughness. The unexpected weakness of the C800/fly ash interaction may be related to removal of surface calcium ions from the fly ash via reaction of a single calcium ion with two C800 molecules.
Polyimides function under high‐temperature sliding. The available literature explains transitions in friction and wear mainly by mechanical effects, such as influences of normal load, sliding velocity and humidity on polymer transfer to steel counterfaces. Theoretical models are evaluated for sintered and thermoplastic polyimides. Tribologists have been interested in tribochemical and tribophysical reactions in the sliding interface for about 25 years. Reactions such as hydrolysis, imidisation and/or degradation occur as a function of sliding temperature and are reviewed in this paper. An overview of polyimide synthesis and degradation is presented, while new insights in sliding mechanisms are obtained from a detailed study of Raman spectroscopy on worn polymer surfaces.
A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.
Both α‐cyclodextrin and linear dextrin are used to prepare biocomposites with poly(3,4‐ethylenedioxythiophene). Materials are prepared electrochemically in aqueous solution. Comparison with the pure polymer indicates that the electroactivity and electrostability decrease with the incorporation of the dextrins while the electrical conductivity is retained. The different properties of the two biocomposites suggest that the linear dextrin is mainly located at the surface, whereas the cyclodextrin is homogeneously distributed in the polymeric matrix. Cell adhesion and proliferation assays indicate that the cellular activity is significantly higher in the dextrin‐containing biocomposites.
It is demonstrated that SNN‐assisted melt dispersion can lead to a significant improvement of the thermal conductivity of PC/MWCNT composites accompanied by a dramatic reduction in their linear CTE. The thermal conductivity of the SNN‐containing composites after the 2‐step process was about 95% higher than that of neat PC and 25% higher than that from 1‐step processing at same loading. The CTE below the glass‐transition temperature of composites with a 1.0 wt.‐% MWCNT loading is substantially reduced compared to the neat polymer. A reduction in the CTE of up to 60.8% is observed for composites from the 2‐step process. Simultaneous achievement of high thermal conductivity and low CTE is required for electronic packaging in microelectronics for device protection.
A procedure for the production of carbon nanotube (CNT) reinforced poly(vinylidine difluoride) (PVDF) powders has been developed. These powders are versatile precursors for a range of nanocomposite materials. The morphology of the CNT/PVDF powder can be related to the interaction between filler and matrix, which depends on the degree of modification of the polymer with grafted maleic anhydride (MAH‐graft‐PVDF). The mechanical performance of the nanocomposite containing 2.5 wt.‐% CNT and 1.25 ppm of MAH increased in tensile modulus, tensile strength, and strain to failure by 34, 30, and 22%, respectively, as compared to PVDF.
Nowadays, silicon represents the most important material used for microelectronic applications. In this paper, both H–Si (111) surfaces and H–Si powders are used to initiate a multifunctional acrylate photopolymerization. The polymers formed are characterized by IR spectroscopy. This should be the way to create either an acrylate polymer coating on a Si wafer or a polymer film containing covalently linked silicon particles.
Recycling of thermoplastic wastes consisting of PE/PP/PS/HIPS blends was investigated by using SEBS/EPR and SBR/EPR as compatibilizers. The effect of the binary compatibilizer systems and processing conditions on the mechanical properties and morphology of the blends are discussed. The SEBS/EPR system allowed blends with better mechanical properties to be obtained than the SBR/EPR system; this was attributed to the chemical structure similarity between compatibilizers and recycled materials. The optimal conditions for processing of the recycled thermoplastics (blends) were found to be 190 °C, 14 min of processing time and 3.5 wt.‐% of compatibilizer. The morphology and mechanical properties of the blends were discussed using theoretical phase diagrams and models proposed in the literature, and good agreements between these properties were found.
The effects of MWNT content and aspect ratio on the properties of epoxy‐based nanocomposites are investigated using nanoindentation and nanoscratch methods. The Halpin‐Tsai model for predicting the elastic modulus and hardness is modified to include the effective aspect ratio factor. The modified model predicts the experimental results more accurately. The frictional behavior is investigated and a new equation is proposed that correlates the ploughing friction with the plasticity index. The dispersion state of MWNTs and the surface features of residual grooves are investigated using scanning electron micrographs and AFM profiles. The mechanisms of improvements in the properties are also discussed.
A novel electrospinning set‐up has been developed to successfully electrospin multiple jets with controlled fiber repulsion using a plastic filter. This set‐up shows reduced fiber repulsion as compared to a multineedle set‐up, along with increased throughput. The effect of processing parameters on the fiber repulsion in a multineedle set‐up was also studied. It was found that fiber repulsion could be reduced by controlling emitter voltage and emitter/collector distance. Other important parameters studied included fiber distribution and throughput. It was found that the plastic filter set‐up produced fibers with lower mean diameters and better uniformity. This novel plastic filter design for electrospinning provides increased electrospinning rates with better fiber uniformity.
A series of hydrogels based on poly(ethylenglycol) methyl ether methacrylate (PEGMEMA) is synthesized using macromonomers of three different molecular weights, in combination with varied degrees of chemical crosslinking. The effects of PEGMEMA, initiator, and crosslinker concentrations on gel yield and swelling properties are studied. In addition, the chemical structure of the gels is characterized by FTIR and solid‐state NMR spectra. The swelling and rheological behaviors of hydrogels as well as protein partitioning into the gels are discussed in terms of the network mesh size. Low protein sorption and bacteria deposition tendencies indicate that PEGMEMA‐based hydrogels could be highly beneficial for uses as fouling‐resistant materials, for instance, as protective coatings for desalination membranes.
Polyurethanes with narrow‐disperse (ND) and polydisperse (PD) hard segment (HS) distributions were prepared in a two‐step process. First, a poly(propylene oxide) end‐capped with MDI (4,4′methylenebis(phenyl isocyanate) was synthesized. To this prepolymer either a diamine–diamide was added to form ND HSs or a mixture of a diamine–diamide and additional MDI to form PD HSs in the copolymers. The polyurethanes displayed a ribbon‐like crystalline morphology, and it was found that the copolymers with ND HSs were more crystalline, had a higher modulus, a less temperature‐dependant modulus, and a higher melting temperature than their PD counterparts. Overall, the polyurethanes with the narrow‐dispersed HSs displayed superior properties.
Bio‐stereo nanocomposite polylactides are prepared by polymerization followed by stereocomplexation in scCO2/dichloromethane through in situ polymerization and master batch processes. The bio‐stereo nanocomposite polylactides show intercalated‐exfoliated and fully exfoliated nanoscale clay distribution in a perfect stereocomplex polylactide matrix. In situ polymerization proves better strategy to produce well‐exfoliated silicate layers in the stereocomplex matrix compared to the MB route that increases the melting temperature by up to ≈64 °C. The thermal properties of these materials maintain both stereocomplex and nanocomposite features simultaneously. The results open a new and versatile way to develop polylactide‐based materials.
The most widespread application of polymers in structural applications is their use as pipe material for e.g., gas distribution systems. Pipes have a design lifetime of typically 50 years, which rules out real‐time lifetime assessment methods. Here, an engineering approach is presented, which makes it possible to predict long‐term ductile failure of loaded glassy polymers based on short‐term tests. The approach is based upon the hypothesis that failure is governed by accumulation of plastic deformation up to a critical strain. A pressure‐modified Eyring relation is employed to calculate the accumulation of plastic strain for any simple loading geometry. It is demonstrated that the approach can produce accurate quantitative time‐to‐failure predictions for loaded PC specimens and uPVC pipe segments.
The effects of process engineering in the fabrication of PHBV, PLA and their blends prepared by melt blending are studied. The elongation of an optimized blend can be improved by 148 and 250% over the virgin PHBV and PLA polymers, respectively. DSC shows that the two polymers are immiscible in blends of any composition. The crystallinity of PHBV is hindered by the presence of PLA. UV‐Vis demonstrates the opacity of the blend with incorporation of PHBV to the PLA phase. The observed tensile modulus of the optimized sample is compared with theoretical values from the rule of mixtures. Gordon‐Taylor's equation is applied on the glass transition temperatures for theoretical modeling to explain the miscibility of the polymers.
Low temperature plasma (LTP) improves the shrink‐resistance of wool fabrics but impairs their softness, so different polysiloxane coatings were applied. Modifications in surface hydrophilicity and topography of fabrics and fibres have been recorded through drop test, contact angle and SEM, respectively. LTP improves the deposition of the polysiloxanes which, depending on their functionalities alter the original hydrophilicity of the wool surface. Softness and shrink‐resist results of the fabrics point out to a possible relationship between hydrophilicity of the wool fibre surface and the shrinkage behaviour of the fabrics. A possible mechanism of interaction between the different polysiloxane groups and the surface of untreated (UT) and LTP‐treated wool is proposed.
To improve the physical properties of poly(trimethylene terephthalate) (PTT), a series of nanocomposites based on PTT and exfoliated graphite (EG) are prepared via melt compounding and their structures, thermal stabilities, mechanical, and electrical properties are studied. XRD and SEM show that graphene nanosheets are well dispersed in the PTT matrix without forming crystalline aggregates even at high EG content. Thermal stability and dynamic mechanical moduli of the nanocomposites are substantially improved by EG addition, and a pronounced increase in electrical volume resistivity from an insulator to almost a semiconductor is observed with increasing EG content. The electrical percolation threshold of the nanocomposites is found to be formed at the EG concentration between 3.0 and 5.0 wt.‐%.
A novel multi‐compound electrospinning method is described, using high‐conductivity aqueous solutions for the inner fluid and low‐conductivity polymeric solutions for the outer fluids. The driving fluid among inner fluids at the equivalent conductivity is switched at a certain frequency. The switching of the Taylor cone results in the alternative embedding of inner components. Also, the number of inner capillaries is proportional to the encapsulation components. Therefore, our method might be useful to alternatively encapsulate a variety of water‐soluble materials in fibers.
Novel silver/polymer composites based on thiol‐ene chemistry are prepared by an in situ bottom‐up approach. The in situ synthesis of silver particles inside the polymer matrix is achieved in one pot by photoreduction reaction in presence of a silver precursor and the concurrent crosslinking reaction. XPS analysis confirms the formation of silver particles; TEM morphological investigation shows a very good dispersion and distribution of the nanometric silver particles within the thiol‐ene network. Antimicrobial properties of the photocured hybrids are also evaluated.
