The viscosity functions of long‐chain branched metallocene‐catalyzed ethene homopolymers and copolymers (LCB‐mPE) were described by an extended Carreau‐Yasuda model. The two characteristic relaxation times, λ1 and λ2, and the slope of the viscosity function between these two characteristic relaxation times can be correlated to the zero shear‐rate viscosity, η0, and the molar mass . The characteristic relaxation times, λ1 and λ2 (describing the main curvatures of the viscosity function) exhibit a power law dependency on the molar mass, . The parameterization of the viscosity function can be used for a molecular characterization and flow simulations of various kinds.
Unfilled and MWCNT‐filled PA fibers are prepared and the effect of the extensional flow on their mechanical performance and morphological variations is investigated. Morphological analyses using SEM, TEM, and SAXS suggest a stronger orientation of the MWCNTs along the fiber direction with increasing extensional flow. A particular MWCNT bundle formation in the PA drawn nanocomposite fibers is observed for the first time, and a pull‐out of the central nanotube in some bundles is noted. The maintenance of the “shish‐kebab” structure upon extensional flow is responsible for the mechanical improvements and dimensional stability in MWCNT‐filled PA fibers.
The first reported use of two‐dimensional mesh thermoplastic fibers in an epoxy matrix for mendable composites is presented, yielding 100% restoration of GIC, failure energy, and peak loads over repeated damage‐healing cycles. SEM imaging and EDS mapping showed different surface structures between CFRPp and CFRPf and confirmed strength recoveries were attained by delivery of EMAA to the fracture plane which enabled the fractured surfaces to rebind after heating to 150 °C for 30 min.
Cellulose acetate butyrate biocomposites, plasticized with tributyl citrate at volume fraction Vf = 0.1–0.3, were prepared with modified hemp. Inclusion of modified hemp fibres at Vf = 0.4 enhanced the modulus and strength of the flexible plasticized cellulose acetate butyrate. Composites containing pectate lyase enzyme treated fibres showed a modulus greater than untreated or alkali treated fibres, when compared at a similar fibre length of 100 µm. Composites containing the shortest alkali treated fibres of 45 µm gave the greatest property improvement, while 500 µm fibres showed worsened properties. Ball‐milled fibres provided reduced values of properties due to cellulose structural disruption, while compression moulding gave better compaction by removing voids.
Hybrid nanocomposite coatings were prepared by the UV‐curing technique with a methacrylic oligomer and multifunctional methacrylic polyhedral oligomeric silsesquioxane blocks (POSS®). The results obtained from the polyhedral compounds were compared with those of a disordered framework obtained by the condensation of a silica precursor (MEMO). The inorganic domains generated during synthesis created constraints in movement of polymer segments, which reflected in an increase in Tg of the hybrid nanocomposite coatings. The films were transparent. The random structure obtained by the condensation of the MEMO showed a stronger effect on Tg than that observed by introducing POSS®. The effect of inorganic domains reflected on thermal stability, surface hardness and mechanical properties of the hybrid nano‐composite coatings.
Novel PEAs derived from 1,4‐butanediol, dimethyl adipate and a preformed α,ω‐amino alcohol were synthesised and successfully electrospun from solution. The effects of increasing the ratio of amide/ester groups in the copolymer, polymer concentration, solvent mixtures and applied voltage on fibre morphology and diameter were investigated. The obtained fibres (diameter 180–450 nm) were randomly oriented. The fibre quality and homogeneity increased with increasing amide concentration. The solvent mixture CHCl3/HCOOH gave the best electrospinning results. The ultra‐fine fibres were characterised using SEM, DSC and FT‐IR, showing that the electrospun fibres are amorphous as compared to the pristine samples. These fibres are potential candidates for use as scaffolds in tissue engineering.
This paper reports the properties of highly oriented nanocomposite tapes based on isotactic PP and needle‐like sepiolite nanoclay, obtained by a solid state drawing process. The intrinsic 1D character of sepiolite allows its exploitation in 1D objects, such as oriented polymer fibres and tapes, where it can be uniaxially oriented upon drawing. A synergistic increase in mechanical properties is presented for highly drawn tapes (λ ≤ 20) and low filler loadings (≤2.5 wt.‐%), which can not be simply explained by micromechanical composite models. Instead, mechanical properties are intimately related to the dispersion state of the nanoclays in PP, the rheological properties of the nanocomposites and the polymer morphology.
Epoxy/BaTiO3 hybrid materials are prepared as good candidates for organic capacitors. The hybrid system is cured by using camphorquinone and a iodonium salt through a free‐radical promoted cationic polymerization using a long‐wavelength tungsten halogen lamp. The cured films are fully characterized. Morphological characterization shows a well‐dispersed inorganic phase within the organic matrix. Electrical characterization demonstrates a linear increase of the dielectric constant with increasing filler content, while low dielectric loss values are obtained.
The morphology of PE/CL nanocomposite samples subjected to convergent flows is studied. Elongational flow – the typical flow involved in spinning and film‐blowing processing operations – significantly increases with the reduction of the capillary diameter. The values of the convergent extensional stress (calculated by Cogswell's formula) for the PE/CL systems, for all the adopted capillary geometries, are greater than the calculated values for pure polyethylene. The applied convergent flow, at the entrance of the capillary, is able to change the clay morphology and consequently the final material properties on the PE/CL system with limited affinity between the matrix and organo‐modified clay particles.
Xylan sulfates have been prepared under homogeneous reaction conditions in DMF/LiCl applying SO3/pyridine and SO3/DMF. The degree of substitution (DSSulfate) of the products obtained was determined by elemental analysis. DSSulfate reached values of up to 1.90 applying a molar ratio of 3 mol sulfating agent per anhydroxylose unit. The structure of the xylans and of the xylan sulfates was studied in detail by one‐ and two‐dimensional NMR spectroscopy and MALDI‐TOF mass spectrometry.
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.
Iron‐oxide nanoparticles were functionalized with epoxy groups and were dispersed into a dicyclo‐aliphatic epoxy resin to obtain organic‐inorganic hybrid coatings via cationic ring‐opening photopolymerization. TEM investigations confirmed that the filler has a size‐distribution range between 5 to 20 nm, without the formation of aggregates. The influence of the presence of Fe2O3 on the rate of polymerization was investigated by real time FT‐IR spectroscopy. Increasing the iron‐oxide nanofiller in the photocurable resin induced an increase in the Tg values. By controlling the phase separation it was possible to obtain transparent iron‐oxide nanostructured coatings, characterized by improved hardness.
Organic/inorganic hybrid materials comprising an amine‐epoxide network and siloxane domains are produced by the sol/gel method. The presence of both plasticizing flexible linear siloxane sequences and reinforcing nanosized silica particles and branched silsesquioxanes (SSQO) structures is confirmed by 29Si NMR and SAXS analysis. The hybrids display simultaneously a monotonical reduction in Tg and an increase in rubbery plateau modulus with increasing siloxane content. At the same time, nanoindentation tests reveal an improved resistance to plastic deformation. The effect of siloxane content on the values of the rubbery plateau modulus is evaluated through the EBM model for blends and composites exhibiting the characteristic co‐continuity of the two constituent phases.
Epoxy‐networked materials containing N,N'‐dioctadecylimidazolium iodide are prepared by curing a mixture of DGEBA and different ratios of the ionic liquid with MCDEA at high temperature. The presence of ionic liquid results in an increase of the storage modulus and a decrease of the glass transition temperature, as indicated by DMA. Also, the onset curing temperature decreases as the amount of IL increase indicating that IL also takes part on the curing process. DSC and FTIR analyses confirm that the imidazolium‐based ionic liquid is able to promote the crosslink of the epoxy pre‐polymer without the presence of external curing agent.
This work reports a facile route to synthesize homochiral and stereocomplexed polylactide by reactive extrusion. The effect of the polymerization catalyst (combination of tin(II)octanoate and triphenylphosphine) before and after its deactivation is discussed. Poly‐L ‐lactide (PLLA) exhibits homochiral crystallinity and diblock poly‐L ,D ‐lactide (PDLLA) exhibits stereocomplex crystallinity. The presence of residual monomer leads to a plasticizing effect, reducing glass transition temperature (Tg). Changes of the tacticity (L ,D ‐tacticity) of the stereocomplex are due to the transesterification reactions between L and D units. Deactivation of the catalyst reduces transesterification reactions and preserves the polylactide stereocomplex upon heating.
Ordered nanowells with diameters of ca. 40 nm and depth of 1–2 nm were prepared on a poly(methyl methacrylate) (PMMA) spherical domain, which was exposed on the polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) copolymer thin film. The PS‐b‐PMMA film formed spherical PMMA domains after the film was annealed above the order–disorder transition temperature. CO2 was dissolved into the PS‐b‐PMMA thin film at 8.6 MPa and at a temperature of 20 °C. The release of CO2‐pressure at the same temperature created the nanowell on the PMMA domain. The temperature and pressure to create nanowells in the PMMA domain affected the possibility of nanowell's formation.
New talc/PBAT hybrid materials were prepared through reactive extrusion. First, PBAT was free‐radically grafted with MA to improve the interfacial adhesion between PBAT and talc. Then, the resulting MA‐g‐PBAT was reactively melt‐blended with talc through esterification reactions of MA moieties with the silanol functions from talc. Sn(Oct)2 and DMAP were used as catalysts. Interestingly, the tensile properties for these compatibilized composites were improved due to a better interfacial adhesion between both partners. XPS showed the formation of covalent ester bonds between the silanol functions from talc particles, and the MA moieties grafted onto the polyester backbones.
PVA nanofibers have been successfully prepared via an electrospinning process by optimizing the electrospinning operational parameters including applied voltage, polymer concentration, feed rate, and working distance. Inexpensive NaCl and Fe(NO3)3 are found to reduce the fiber size drastically (minimum of 157 and 169 nm, respectively) even at a low loading. The thermal stability is investigated by both thermogravimetric analysis and differential scanning calorimetry. Fourier transform infrared spectroscopy is utilized to characterize the functionality of the fibers and to investigate the interaction between PVA and inorganic additions. Glass transition and melting temperatures of the PVA fibers have slight change with the increase of the salt loading.
The degradation of cellulose to lmw samples with $\overline {DP} _{{\rm w}} $ varying from 15 to 130 is investigated. Cellulose samples prepared from the hydrolysis of regenerated cellulose fibers in dilute HCl possess $\overline {DP} _{{\rm w}} $ = 50. Applying homogenous degradation of microcrystalline cellulose in H3PO4 at RT for 3 weeks, samples with $\overline {DP} _{{\rm w}} $ = 35 and a PDI of 1.58 are obtained. Decreasing the hydrolysis temperature to 8 °C results in lmw cellulose with $\overline {DP} _{{\rm w}} $ > 70. Fractionation in DMA/LiCl provides samples with $\overline {DP} _{{\rm w}} $ = 12 to 130, together with a narrow molecular weight distribution. Detailed structural analysis by 2D NMR spectroscopy reveals that the prepared lmw celluloses are suitable as mimics for cellulose.
Organic/inorganic hybrid nanocomposite coatings were prepared through a dual‐cure process involving the cationic photopolymerization of a vinyl ether based system and the condensation of an alkoxysilane inorganic precursor. All formulations produced transparent cured films characterized by high gel contents. An increase in glass transition temperature and an increase in storage modulus above Tg in the rubbery plateau were observed with increasing TEOS content in the photocurable formulation. TEM micrographs showed that the organic and inorganic phases were strictly interconnected with no macroscopic phase separation; the sizes of the silica domains in the polymeric matrix were 3–5 nm.
