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Novel poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)(PHBH)/fibrillated nanocellulose biodegradable composites for additive manufacturing were produced and characterized. Fibrillated nanocellulose (NCF) was isolated with high energy ultrasonication and dispersed via solution mixing in the polymer matrix. Composite filaments having a nanofiller concentration of 0.5 wt%, 1 wt% and 3 wt% were then extruded, characterized and used in fused deposition modeling (FDM). Neat PHBH powder was then manually added to prepare a solid mixture at different fibrillated nanocellulose concentrations (from 0.5 to 3 wt%), to be then used to feed an extruder. SEM observations on filaments and 3D printed samples evidenced the good dispersion of fibrillated nanocellulose inside the matrix with the presence of agglomerates at higher NCF contents. The beneficial effects of the fibrillated nanocellulose in terms of stress at break and of elongation at break showed a maximum at a fibrillated nanocellulose content of 0.5 wt%. Moreover, the presence of fibrillated nanocellulose did not affect the thermal degradation behaviour of the materials, and also the glass transition and the melting temperatures were not influenced by NCF addition. [ABSTRACT FROM AUTHOR]

Composite films based on sodium carboxymethyl cellulose (Na‐CMC) loaded with a ZnAl(OH)2CO3·yH2O hydrotalcite (ZnAl‐HTlc), were developed and characterized. The composites were mechanically more stable than the matrix alone: the noticeable enhancement of elastic modulus, creep resistance and failure properties, all proportional to the filler content, came at the expenses of a certain embrittlement. The filler tended to aggregate in the composites and the size of the aggregates increased with ZnAl‐HTlc amount. Contact angle measurements highlighted how ZnAl‐HTlc introduction in the polymeric matrix could strongly modify the wettability conditions of the films increasing their hydrophilicity. Bioadhesion tests showed that the adhesion behavior of the composites decreased as ZnAl‐HTlc amount increases, testifying the influence of the filler on the ability of the film to bind skin surface. Therefore, the developed films may find application as active wound dressings since ZnAl‐HTlc can be easily intercalated with an active pharmaceutical ingredient to be progressively released on the wound. POLYM. ENG. SCI., 59:E112–E119, 2019. © 2018 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Mechanical properties of starch‐grafted‐polypropylene/kenaf fibers (KF) composites were investigated and compared to different theoretical models. In this work, the composites were prepared via melt compounding and compression molding processes at different KF loadings, that is, 10, 20, and 30 wt%. Tensile, fracture toughness and fatigue tests were performed. Generally, the mechanical properties increased with increasing kenaf fiber loadings. This is attributed to the good filler‐matrix interactions between KF and starch‐grafted‐polypropylene, as observed by scanning electron microscopy. Tensile properties were modeled using the rule of mixture, the Kelly‐Tyson and the Halpin‐Tsai models. Fatigue data were also modeled using different theoretical models to fit both S–N and normalized S–N curves with simple linear model and Boltzmann sigmoidal function. POLYM. COMPOS., 39:3289–3299, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

ABSTRACT: This work evaluates the influence of two types of carbonaceous fillers, carbon black (CB) and carbon nanotubes (CNTs), on the electrical, electromagnetic, and rheological properties of composites based on poly(acrylonitrile‐co‐butadiene‐co‐styrene) (ABS) prepared by the melt mixing. Electrical conductivity, electromagnetic shielding efficiency (EMI SE) in the X‐band frequency range (8–12.4 GHz), and melt flow index (MFI) results showed that ABS/CNT composites exhibit higher electrical conductivity and EMI SE, but lower MFI when compared to ABS/CB composites. The electrical conductivity of the binary composites showed an increase of around 16 orders of magnitude, when compared to neat ABS, for both fillers. Binary composites with 5 and 15 wt % of filler showed an EMI SE of, respectively, −44 and −83 dB for ABS/CNT, and −9 and −34 dB for ABS/CB. MFI for binary composites with 5 wt % were 15.45 and 0.55 g/10 min for CB and CNT, respectively. Hybrid composites ABS/CNT.CB with 3 wt % total filler and fraction 50:50 and 75:25 showed good correlation between EMI SE and MFI. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46546. [ABSTRACT FROM AUTHOR]

The main focus of this study is to characterize the interfacial interactions between silica nanoparticles and polypropylene and to investigate how the surface properties and morphology of the silica nanoparticles affect the elastic response of the silica-polypropylene composites. The composites were prepared by melt compounding and injection molding. Both non-functionalized and dimethyldichlorosilane-functionalized silica nanoparticles were used. Three-component composites were also prepared by including selected formulations of both poly(propylene- g-maleic anhydride) copolymer (PPgMA) and different types of silica. It was found that both silica types are nucleating agents for PP and significantly alter its crystallization behavior. A strong correlation between the glass transition temperature ( Tg) and the tensile modulus in silica-PP nanocomposites indicated the presence of a secondary reinforcing mechanism that is the pinning of the polymer chains on the silica surface. The presence of a complex constrained phase, represented by immobilized amorphous and transcrystalline phases, forming at the filler surface, was assessed by modulated differential scanning calorimetry and dynamic mechanical analysis. Finally, the interfacial interactions were correlated to the tensile and viscoelastic properties using the theoretical models proposed by Pukanszky and Sumita et al., respectively, and comparing the predictions of the models to experimental results. POLYM. COMPOS., 37:2018-2026, 2016. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, polypropylene (PP) composites reinforced with short glass fibers (GF) and exfoliated graphite nanoplatelets were obtained by melt compounding followed by injection molding. Morphological observations and quasi-static tensile tests were carried out in order to investigate how the morphology and the mechanical properties of the composites were affected by the combined effect of two fillers of rather different size scales (i.e., micro- and nanoscale). The results indicate that the dispersion of the nanofiller in the PP matrix promoted the formation of a stronger interface between the matrix and GF, as indicated by the increase of the interfacial shear strength determined by the single-fiber microdebonding test. Concurrently, a significant improvement of the tensile modulus and impact strength of the composites was observed, with small changes in the processability of hybrid composites compared to that of GF composites, as confirmed by rheological measurements. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41682. [ABSTRACT FROM AUTHOR]

The effects of various types and amounts of fumed silica and graphite nanoplatelets on the microstructure and thermomechanical properties of polypropylene composites containing 5, 10, and 20 wt% of short glass fibers have been analyzed. Hybrid composites were produced by melt compounding and compression molding. The aspect ratio of the short glass fiber decreased with the fiber loading and the nanofiller amount. The tensile strength and elastic modulus increased, while the elongation at break decreased as the content of both short glass fiber and nanofiller increased. A two-population model, based on the Halpin–Tsai and Tsai–Pagano composite theories, was used to predict the elastic modulus of the nano-micro hybrid composites. Experimental values appear to be reasonably consistent with model predictions. Tensile energy to break under impact conditions increased with the short glass fiber content but decreased with nanofiller amount. Moreover, storage modulus and creep stability were remarkably enhanced in short glass fiber composites by the presence of both nanofillers. [ABSTRACT FROM AUTHOR]

ABSTRACT Thermoplastic composites based on a commercial acrylic matrix widely used in the field of art protection and restoration (Paraloid B72) and various concentrations (up to 30 wt %) of microcrystalline cellulose powder (MCC) were prepared by melt-compounding and compression molding. The mechanical behavior of the resulting materials conditioned at a temperature of 23°C and a relative humidity level of 55% was compared to that of the corresponding dried materials. Even though the moisture absorption of the filler was lower than the neat matrix, the maximum moisture content increased with the MCC amount, probably due to the preferential water diffusion path through the microvoids and/or the filler-matrix interface. Although the increase of moisture content for filled samples, DMTA analysis evidenced a stabilization upon MCC introduction, with an increase of the storage modulus and a decrease of the thermal expansion coefficient proportional to the filler loading. A similar trend was displayed by the corresponding dried materials. The tensile elastic modulus and the ultimate properties such as the stress at break and the tensile energy to break (TEB) of conditioned samples increased proportionally to the filler amount. On the contrary, the failure properties of dried composites were negatively affected by the presence of the microcellulose. It is worthwhile to report that a significant improvement of the creep stability was induced by MCC introduction both for dried and conditioned samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40741. [ABSTRACT FROM AUTHOR]

We describe a new single polymer composite (SPC) prepared from two liquid crystalline vectran fibers. Vectran M is the as‐spun fiber while vectran HS is the high‐strength version. A study of the morphology of the pristine materials shows that the two fibers have different crystal structures. The wide‐angle X‐ray diffraction (WAXD) data confirm the presence of the so‐called pseudo‐hexagonal (PH) unit cell in vectran M, while an orthorhombic structure is revealed in the vectran HS fibers. A transition to the nematic phase is observed by in situ X‐ray diffraction at ∼277°C for the M fibers and at ∼315°C for the HS fibers. During the compaction process, the orientation of the reinforcing fibers is well maintained and the transition to a nematic phase seems to be delayed by processing at high applied pressure. Concomitantly, vectran M loses its orientation and the transition to the nematic phase disappears. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: A DGEBA-based epoxy matrix was loaded with 10, 20 and 30phr of fumed silica particles. Single edge notched bend (SENB) specimens were prepared and deformed to failure in three-point bending configuration. Their fracture surfaces were examined by atomic force acoustic microscopy (AFaM) in order to obtain information about the local elastic modulus of the surface at high spatial resolution. The collected information was correlated to the bulk thermo-mechanical properties of the composites. In particular, the decrease in thermo-mechanical properties like tensile modulus, yield strength, stress at break and glass transition temperature, observed for samples filled with 10 and 20phr with respect to the unfilled matrix was found to correspond to highly heterogeneous fracture surfaces presenting a broad distribution of elastic modulus values. The AFaM data were interpreted as representative of different degrees of filler exposure on fracture surfaces and also of localized cavitation effects involved in crack propagation, both phenomena accounting for the effective plasticizing effect macroscopically observed at silica amounts of 10 and 20phr. A substantial reduction in the exposure probability of silica particles on fracture surfaces was found for the sample filled with 30phr of silica, which also displayed an improvement of the mechanical and thermal properties. This latter evidence was tentatively explained by supposing a physical immobilization of polymer chains at the polymer-matrix interface. [Copyright &y& Elsevier]

Abstract: DGEBA-based epoxy nanocomposites filled with various amounts of fumed silica nanopowders (10, 20 and 30phr corresponding to 3.3, 6.4 and 9.2% by volume) were prepared by a solvent assisted dispersion procedure. The obtained nanocomposites were analyzed by means of differential scanning calorimetry, dynamic-mechanical thermal analysis, uniaxial tensile tests on un-notched samples and three-point bending tests on notched samples. All the thermal and mechanical properties showed non-monotonic trends with relative minima as the silica content increased. A trend inversion in the physical properties was detected at the highest filler level tested, which was not previously observed for epoxy systems filled with comparable amounts of unmodified silica. The behavior could be explained by considering a reduction of cross-linking degree of the epoxy matrix due to the huge viscosity increase induced by the silica nanoparticles during composites preparation. On the other hand, the physical immobilization of the cross-linked matrix can be supposed to be responsible for the inversion of the properties trend at the highest filler level, which is presumably very close to the percolation threshold. [Copyright &y& Elsevier]

In this work the mechanical response to external applied loads of a new glass fibre reinforced endodontic post is simulated by finite element (FE) analysis of a bidimensional model. The new post has a cylindrical shape with a smooth conical end in order to adequately fit the root cavity, and to avoid edges that could act as undesired stress concentrators. Mechanical data obtained by three-point bending tests on some prototypes fabricated in the laboratory are presented and used in the FE model. Under various loading conditions, the resulting stress component fields are hence compared with those obtained in the case of two commercial endodontic posts (i.e. a cast metal post and a carbon fibre post) and with the response of a natural tooth. The gold cast post-and-core produces the greatest stress concentration at the post-dentin interface. On the other hand, fibre-reinforced composite posts do present quite high stresses in the cervical region due to their flexibility and also to the presence of a less stiff core material. The glass fibre composite shows the lowest peak stresses inside the root because its stiffness is much similar to dentin. Except for the force concentration at the cervical margin, the glass fibre composite post induces a stress field quite similar to that of the natural tooth. [Copyright &y& Elsevier]

In this paper the creep crack propagation in a short glass fibre reinforced polypropylene composite has been investigated at various temperatures in the range from 32 to 60°C. Creep crack speed ( da/ dt) resulted initially decreasing till a minimum value, and then gradually increasing up to instability and fracture. Both initial and minimum crack speed values were found to strongly increase as test temperature increased. Moreover, isothermal curves of the applied stress intensity factor Kappl as a function of the crack speed ( da/ dt) were obtained at various temperatures. Portions of these curves in the stable crack acceleration region were hence shifted along the da/ dt, axis according to a time-temperature reduction scheme, thus allowing the construction of a creep crack propagation master curve. The shift factor values, aT for the creep crack propagation master curve appeared to be higher than those obtained, in the same temperature range, from dynamic mechanical measurements in a linear viscoelastic regime. [ABSTRACT FROM AUTHOR]

This work focuses on the development of multifunctional thermoplastic composites with thermal energy storage capability. A polyamide 12 (PA12) matrix was filled with a phase change material (PCM), constituted by paraffin microcapsules (Tmelt = 43 °C), and reinforced with carbon fibers (CFs) of two different lengths (chopped/CF "long"[CFL] and milled/CF "short" [CFS]). DSC tests showed that the melting/crystallization enthalpy values increase with the PCM weight fraction up to 60 J/g. The enthalpy was 41–94% of the expected value and decreased with an increase in the fiber content, because the capsules were damaged by the increasing viscosity and shear stresses during compounding. Long CFs increased the elastic modulus (+316%), tensile strength (+26%), and thermal conductivity (+54%) with respect to neat PA12. Thermal imaging tests evidenced a slower cooling for the samples containing PCM, and once again the CFS‐containing samples outperformed those with CFL, due to the higher effective PCM content. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47408. [ABSTRACT FROM AUTHOR]

The authors discuss the adoption of interphase engineering in polymer nanocomposites. They highlight the important role of interphase in providing the necessary stress transfer from the weak matrix to the strong reinforcement as well as considered the key factor of composite performance. They also discuss other topics related to nanofillers and nanocomposites.

Magnetostrictive polymer composites (MPCs) are a class of materials having the ability to simultaneously change dimensions, elastic and/or electromagnetic properties under the presence of a magnetic field. Their advantages over bulk magnetostrictive metals are high resistivity, extended frequency response, low weight, ease of formability and improved mechanical properties. In this review, advances in MPCs and their applications since the year 2000 are presented. A wide range of reinforcements and morphologies used to generate magnetostrictive response in polymers are considered, including carbonyl iron, nickel and rare-earth metal based reinforcements. A critical analysis of the various polymeric systems from stiff thermosets to soft elastomers is provided, focusing on how the material selection influences the magnetorheological and magnetoelectric properties. Multiscale approaches, such as continuum micromechanics based theories and multi-physics finite element approaches, for modeling the coupled magneto-elastic responses are also reviewed. Recognizing their unique properties, recent applications of MPCs in electric current and stress sensing, vibration damping, actuation, health monitoring and biomedical fields are also presented. The survey allows us to shed light on new directions for fundamental research, interface studies and modeling improvements for advancing the application of MPCs. [ABSTRACT FROM AUTHOR]

Two types of historical wood (18th century) (Juglans regia and Abies alba) presenting different degradation conditions were consolidated through acetone solutions of microcomposites consisting of a commercial polymer (Paraloid® B72) often used for wood consolidation and two different amounts (5 and 30 wt%) of microcrystalline cellulose (MCC). As a comparison, the same tests were also performed on modern samples of the same types of wood in a well preserved state. Rheological and mass variation measurements evidenced that the introduction of microfiller did not affect the viscosity and the water sorption of the neat resin to a significant extent. Moreover, mercury intrusion porosimetry highlighted how MCC filled composites were able to decrease the pore radius of treated wood samples, reaching values close to those of modern intact wood. Remarkably, the presence of MCC within Paraloid led to a positive enhancement of the stiffness and the flexural strength of treated damaged wood in both quasi-static and impact conditions, with the increase of the flexural modulus, the maximum stress and the rise of both initial and total impact absorbed energies. Additionally, an increase of the radial and tangential surface hardness due to the treatment with MCC filled composites was observed. [ABSTRACT FROM AUTHOR]

This review summarizes the recent (from year 2000) advancements in the interphase tailoring of fiber-reinforced polymer composites. The scientific and technological achievements are classified on the basis of the selected strategies distinguishing between (i) interphase tailoring via sizing/coating on fibers, (ii) creation of hierarchical fibers by nanostructures, (iii) fiber surface modifications by polymer deposition and (iv) potential effects of matrix modifications on the interphase formation. Special attention was paid to report on efforts dedicated to the creation of (multi)functional interphase in polymer composites. This review is round up by listing current trends in the characterization and modelling of the interphase. In the final outlook, future opportunities and challenges in the engineering of fiber/matrix interphase are summarized. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the results of an experimental study concerning the effect of different surface treatments on NiTi shape memory alloy wires are presented. These treatments were conducted in order to improve the adhesion properties between the NiTi wires and an epoxy resin, acting as the matrix of a composite material. Mechanical and chemical surface treatments (immersion in acid and alkaline solutions), and different combinations of the above surface preparation procedures were studied. For the characterisation of the resulting alloy surface conditions electrochemical impedance spectroscopy, polarisation curves and potential versus time measurements were carried out. The alloy wire/epoxy matrix adhesion was characterised through pull out tests. The results proved that all adopted treatments can remarkably influence the electrochemical properties of the wires. The acid treatments favour the formation of a surface passivation layer, while the alkaline treatments are effective in producing a rougher surface morphology. Moreover, these basic treatments significantly reduce corrosion resistance of the alloys, another material property that has been incidentally investigated in the present context. The main effect of the mechanical surface treatment, consisting in abrading the alloy wires using an emery paper, was to increase the homogeneity of surface roughness. From the experimental results clear indications on the most promising surface treatments can be inferred. [Copyright &y& Elsevier]

Heavy-metal contamination in children's toys is a widespread problem, and the international community has issued a series of safety standards to restrict and control the use of toxic metals in toys. In this work, a colored filler (CBF) was prepared using pearl oyster shell (POS) as the green raw material and azo dye as the colorant. Its surface properties were subsequently studied in comparison to those of POS powder using the inverse gas chromatography method. The dispersion surface free energy profiles for both CBF and POS showed that this component contributed the major part (>70%) to the total surface free energy. The CBF possessed lower polar surface free energy and was relatively more hydrophobic. It also showed a lower thermodynamic work of cohesion, allowing its better dispersion in a low density polyethylene (LDPE) matrix. Mechanical performance studies showed that adding CBF could significantly increase the tensile strength, elastic modulus, flexural strength and flexural modulus of LDPE composites. The absence of toxic metals coupled with excellent mechanical performance makes the CBF an ideal candidate as a filler for children's toys fabrication. [ABSTRACT FROM AUTHOR]

Photocurable composites based on a UV-light curable methacrylic-siloxane resin formulation and various concentrations (5 ÷ 20 wt%) of microcrystalline cellulose powder (MCC) were prepared and characterized to assess their suitability as protective coatings for wooden artworks. Dynamic mechanical thermal analysis highlighted that MCC promoted an enhancement of both storage and loss moduli and a decrease of the thermal expansion coefficient. Interestingly, the flexure elastic modulus and the flexure maximum stress of the neat photoresin increased upon the filler addition without any embrittling effect. An increment of hydrophobicity (contact angle), surface hardness (Shore D and pencil scratch tests) of the neat UV-light cured matrix even at the lowest filler loading was observed. These promising results suggest that the photo-curable microcomposites could be able to recover the mechanical and physical properties of damaged wood and replace the traditional resins soluble in toxic solvents utilized in this kind of restoration works. [ABSTRACT FROM AUTHOR]

In this work, a novel colored talc filler (CTF) was prepared, and its surface properties were subsequently studied and compared to those of talc filler (TF) using inverse gas chromatography (IGC) and contact angle measurement. The mechanical properties of acrylonitrile-butadiene-styrene (ABS) composites filled with CTF and TF were investigated as well. The results indicated that the dispersive component ( γ S D ) for both samples contributed the major part of the total surface energy ( γ S T ). The values determined by the contact angle methods were consistent, although lower than those using IGC analysis. Compared to γ S D , the polar component ( γ S S P ) contributed less to γ S T , implying a lower polarity for both samples. The γ S S P values calculated by the contact angle methods were also consistent and lower than those calculated using IGC. The lower γ S T value for CTF could reduce filler particle-particle interactions, allowing a better dispersion in ABS matrix, and thus leading to an increase in ABS/CTF composite performance. [ABSTRACT FROM AUTHOR]

Abstract: In this study a nanocomposite monofilament composed of a nematic thermotropic liquid crystalline polymer (TLCP) mixed with 1.5wt.% of carbon nanoparticles (CNP) was prepared by melt extrusion. The nanoparticles had either a fibrous (VGCF) or layered (GNP) geometry. The tensile strength and modulus of the fibers increased with the draw down ratio of the filament; a positive effect on the tensile modulus is displayed by fibrous CNP, achieving values higher than those of high property organic fibers utilized as reinforcement for composite materials. Thermotropic transitions were characterized by DSC and in situ synchrotron WAXD. In particular, it was shown that the breadth of the temperature span of the crystalline–nematic transition correlated inversely with the draw down ratio. At high draw down ratio, addition of CNP also increased the relative amount of oriented polymer chains and contributed to sharpening of the mesomorphic transition. [Copyright &y& Elsevier]