A major societal issue of disposal and environmental pollution is raised by the enormous and fast-growing production of single-use polyethylene terephthalate (PET) bottles, especially in developing countries. To contribute to the problem solution, an original route to recycle PET in the form of value-added environmentally friendly thermoplastic composites with banana fibres (Musa acuminata) has been developed at the laboratory scale. Banana fibres are a so far undervalued by-product of banana crops with great potential as polymer reinforcement. The melt-processing constraints of commercial PET, including used bottles, being incompatible with the thermal stability limits use of natural fibres; PET has been modified with bio-sourced reactants to produce co-polymers with moderate processing temperatures below 200 °C. First, commercial PET were partially glycolyzed with 1.3-propanediol to produce co-oligomers of about 20 repeating units, which were next chain extended with succinic anhydride and post-treated in a very unusual "soft solid state" process at temperatures in the vicinity of the melting point to generate co-polymers with excellent ductility. The molar mass build-up reaction is dominated by esterification of the chain ends and benefits from the addition of succinic anhydride to rebalance the acid-to-hydroxyl end-group ratio. Infra-red spectroscopy and intrinsic viscosity were extensively used to quantify the concentration of chain ends and the average molar mass of the co-polymers at all stages of the process. The best co-polymers are crystallisable, though at slow kinetics, with a Tg of 48 °C and a melting point strongly dependent upon thermal history. The composites show high stiffness (4.8 GPa at 20% fibres), consistent with the excellent dispersion of the fibres and a very high interfacial cohesion. The strong adhesion can be tentatively explained by covalent bonding involving unreacted succinic anhydride in excess during solid stating. A first approach to quantify the sustainable benefits of this PET recycling route, based on a rational eco-selection method, gives promising results since the composites come close to low-end wood materials in terms of the stiffness/embodied energy balance. Moreover, this approach can easily be extended to many other natural fibres. The present study is limited to a proof of concept at the laboratory scale but is encouraging enough to warrant a follow-up study toward scale-up and application development.

Polystyrene-like coatings are synthesized by plasma near atmospheric pressure. Elucidating their chemical structure after exposure to ambient air could be very challenging because of the interference of surface-related phenomena, mainly post-polymerization oxidation and contamination. In this paper, we propose secondary ion mass spectrometry (SIMS) in molecular depth-profiling mode, combined to multivariate analysis, as a more reliable tool for their investigation as a function of the injected power. Indeed, the information provided by the inner layers is more representative of the film in growth. The SIMS approach is validated by complementary, surface-sensitive and bulk techniques: X-rays photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The SIMS results suggest that the high concentration of -CH3 groups in the polymer matrix, pointed out by IR, is due to branching and/or grafting of CH3· radicals to active sites (prevalently in position α, β, γ) along the aliphatic backbone, in addition to a significant fraction of trapped oligomers. The oligomer contribution is supported by an original study based on the molecular weight dependence of the sputtering efficiency. The overall experimental evidences indicate a milder fragmentation of the precursor at lower powers, leading to a higher conservation of the aromaticity and a lesser branched and/or cross-linked content.

In this study, polypropylene/silica (PP/SiO2) composites containing 5 wt% of untreated precipitated silica were compatibilized with different coupling agents like maleic anhydride-grafted polypropylene, glycerol monostearate (GMS), ethylene acrylic acid zinc ionomer and a second polymer phase of polyamide 6 (PA6). The composites were melt-compounded by two different processes: either by direct melt mixing or by dilution of a masterbatch (two-step mixing) in a twin screw extruder using both injected water and high shear stress as a new processing method. The various samples were characterized by Fourier transform infrared spectroscopy (FTIR), thermal analysis, morphological and rheological measurements in order to determine the compatibilizers effects between the matrix and the untreated filler. Hence, atomic force microscopy observations revealed that the untreated silica was dispersed more homogeneously in the presence of PA6 and GMS compatibilizers when water injection is used as one. However, the roughness values are lower in this case. FTIR analysis confirmed the existence of interfacial interactions between OH groups of SiO2 and polar groups of compatibilizers. The storage (G′), loss moduli (G″) and the dynamic viscosity of PP/SiO2 composites increased with the incorporation of PA6. Furthermore, the thermal stability of the compatibilized PP/SiO2 compounds enhanced significantly in the presence of water. An improvement in decomposition temperature of about 50 °C was obtained compared to uncoupled composites.

The effect of simultaneous thermal and gamma irradiation ageing on the mechanical and physicochemical properties of industrial EPDM was investigated. Accelerated ageing, covering a wide range of dose rates, doses and temperatures, was preformed in stagnant air on EPDM polymer samples extracted from the cables in use in the Belgian nuclear power plants. The mechanical properties, ultimate tensile stress and elongation at break, are found to exhibit the strong dependence on the dose, ageing temperature and dose rate. The thermal decomposition of aged polymer is observed to be the dose dependent when thermogravimetry test is performed under air atmosphere. No dose dependence is observed when thermal decomposition is performed under nitrogen atmosphere. The thermal decomposition rates are found to fully mimic the reduction of elongation at break for all dose rates and ageing temperatures. This effect is argued to be the result of thermal and radiation mediated oxidation degradation process.

This work investigates the Volatile Organic Compounds (VOCs) emissions during the processing of composite of polyamide 6 (PA) bio-filled with technical lignin. This is of prime interest as volatile phenolic structural monomers issued from lignin could penetrate the human organism and cause undesirable health damages. A special attention is given to the measurement of formaldehyde as it is known to be a human carcinogen. Lignin main identified emission consists of a high level of formaldehyde and a large amount of complex substituted phenol and benzene, all representative and constitutive of its structure. Regarding the PA alone, it has been found that the predominant VOC product is ε-caprolactam. When filling PA6 with lignin, the emitted VOCs associated to this filler are mainly produced during the extrusion while, only traces are detected during the injection process. Formaldehyde emission level is three times higher during the injection than during the extrusion. Phenols and some remaining reactants used during industrial cellulosic extraction process are identified. Regarding the value of the Short-Term Exposure Limit (STEL), suitable industrial process, safety and hygiene rules must be adopted.

ABSTRACTEnvironmentally friendly bio‐filled composites of various proportions of polyamide 6 (PA6) and technical lignin have been prepared using a twin‐screw extruder. Transmission electron microscopy has been used to investigate the morphology of the composites. It reveals homogeneous single phase system, indicating the miscibility of PA6 and lignin. The glass transition temperature of the blends, determined by DMA, was shifted systematically to higher temperature with increasing concentration of lignin which highlights the miscibility of both components. In addition, Fourier Transform Infrared analyses have shown that new specific hydrogen‐bonding interactions are formed between hydroxyl groups of lignin and amine groups of the PA6. The presence of these intermolecular interactions between PA6 and lignin strongly influenced the thermal stability of the blends by lowering the onset of the blend's degradation process. However, the blends exhibit good mechanical properties whatever the lignin content. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42963.

The use of phenoxy nanocomposite films as carriers of nanofillers involving multiwalled carbon nanotubes and nanoclays is successfully demonstrated for application in epoxy carbon fibers reinforced composites (CFRC) processed by RTM. Model studies on individual nanocomposite filaments embedded in epoxy precursors show that the nanofillers are passively transported by the interdiffusion gradient during heating over distance around 800μm. A morphology gradient is generated after reaction induced phase separation and the nanofillers end up in the epoxy, despite their initial dispersion in the phenoxy. The proof of concept is extended to CFRC panels where nanocomposite phenoxy films are prepositioned between every odd carbon layer of the preform. Carbon nanotubes are filtered by the carbon fabrics, which limits their full diffusion and that of phenoxy through the preform. This has negative consequences on fracture toughness (GIc). For nanoclay, GIc is rather slightly improved although the origin is not fully clear.

Objectives, to complement our previous work by testing the null hypotheses that with short curing times and high DC, TPO-based resin composites would exhibit (1) higher polymerization stresses and consequently display (2) higher temperature rise and (3) higher flexural modulus, flexural strength and hardness, compared to a conventional CQ-based experimental composite.Methods. Two experimental resin composites using either Lucirin-TPO or camphorquinone/DMAEMA as photoinitiators were prepared. Light curing was carried out using spectral outputs adapted to the absorption properties of each initiator. Different irradiation protocols were selected (0.5, 1, 3, 9s at 500, 1000 and 2000 mW/cm2 for Lucirin-TPO based composites and 20 or 40s at 1000 mW/cm2 for Lucirin-TPO and camphorquinonebased composites). Degree of conversion (DC) was measured in real time by means of FT-NIR spectroscopy. Pulpal temperature rise (Delta T) was studied in a tooth model. Polymerization stress was monitored using the Bioman instrument. For cured specimens, flexural modulus and flexural strength were determined using a three point bending platform and Vickers hardness was determined with a microhardness indentor on samples prior to and after 24h incubation in 75/25 ethanol/H2O. Premolars were restored with both materials and microleakage at the teeth/composite interfaces following restoration was assessed.Results. Lucirin-TPO-based composites irradiated at radiant exposures of 3 J/cm(2) and more exhibited significantly higher DCs, associated with increased flexural moduli and hardness compared to CQ-based composites. For an ultra-short irradiation time of 40s at 1000 mW/cm2, TPO-composites displayed similar polymerization stresses compared to CQ-controls with yet a 25% increase for flexural modulus and 40% increase for hardness measured after EtOH/H2O sorption. Higher stress rates were however observed in all curing protocols compared to CQ-composites. Microleakage was similar between TPO and CQ-composites irradiated at 1000 mW/cm(2) for 3 and 20 s respectively, while a significant increase was observed for TPO-composites irradiated for 1 s. Delta T measured through a 0.6 mm thick dentin layer were all below 5.5 degrees C; TPO-composites exhibited similar or lower values compared to controls.Signcance. The use of Lucirin-TPO in resin composites along with appropriate curing conditions may allow for a major reduction of irradiation time while improving mechanical properties. The amount of stress observed during polymerization in TPO-based composites can be similar to those using CQ and the cohesion at the restoration-tooth interface was not affected by short curing times. Contrary to other studies, we found that the temperatures increases measured during polymerization were all well below the 5.5 C threshold for the pulp. (C) 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Objectives. New commercial tricalcium silicate based cements were elaborated to improve handling properties and setting time. The goals of the present work were: (i) to determine the composition of the new injectable and/or fast setting calcium silicate based cements, and (ii) to investigate the impact of the differences in composition on their setting kinetics. Methods. The materials considered were Angelus MTA (TM), Biodentine (TM), MM-MTA (TM), MTA-Caps (TM), and ProRoot MTA (TM) as control.Elemental composition of materials was studied by Inductively Coupled Plasma-Atomic Emission Spectroscopy and X-ray Energy Dispersive analysis, whereas phases in presence were analyzed by Micro-Raman spectroscopy and X-ray Diffraction analysis and cement surface by Scanning Electron Microscope. Setting kinetics was evaluated using rheometry. Results. Elemental analysis revealed, for all cements, the presence of three major components: calcium, silicon and oxygen. Chlorine was detected in MM-MTA, MTA-Caps and Biodentine. Different radio-opacifiers were identified: bismuth oxide in ProRoot MTA, Angelus MTA and MM-MTA, zirconium oxide in Biodentine and calcium tungstate (CaWO4) in MTA-Caps. All cements were composed of di-and tri-calcium silicate, except Biodentine for which only the latter was detected. Major differences in setting kinetics were observed: a modulus of 8 x 10(8) Pa is reached after 12 min for Biodentine, 150 min for MM-MTA, 230 min for Angelus MTA and 320 mm for ProRoot MTA. The maximum modulus reached by MTACaps was 7 x 10(8) Pa after 150 min.Signcance. Even if these cements possess some common compounds, major differences in their composition were observed between them, which directly influence their setting kinetics. (C) 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

This chapter is focused on polymer/clay nanocomposites prepared from untreated clay and processed by an original water-assisted extrusion. Polymer/clay nanocomposites are a huge scientific challenge and have a great industrial interest mainly due to their unique combination of properties. Indeed, with adding only few percent of clay, the final properties of nanocomposites are usually improved compared with the neat polymer. Nowadays, the related research is mostly fueled by two aspects: the replacement of organophilic layered silicates by pristine ones and the development of harmless, environmentally friendly production methods for especially the temperature-dependent reinforcement materials such as natural fibres. An alternative way to prepare nanocomposites is the water-mediated melt-compounding method, where water is used in order to avoid the need of classical alkylammonium intercalating/exfoliating agents. The structure, preparation, and properties of these polymer/clay nanocomposites are discussed.

This study shows the interest of elaborating polylactide/halloysite nanocomposites by means of water assisted extrusion (WAE). Besides, WAE gives access to materials with improved fire properties and prevents molecular degradation.

Objectives Bulk-fill composites have emerged, arguably, as a new “class” of resin-based composites, which are claimed to enable restoration in thick layers, up to 4mm. The objective of this work was to compare, under optimal curing conditions, the physico-mechanical properties of most currently available bulk-fill composites to those of two conventional composite materials chosen as references, one highly filled and one flowable “nano-hybrid” composite. Methods Tetric EvoCeram Bulk Fill (Ivoclar-Vivadent), Venus Bulk Fill (Heraeus-Kulzer), SDR (Dentsply), X-tra Fil (VOCO), X-tra Base (VOCO), Sonic Fill (Kerr), Filtek Bulk Fill (3M-Espe), Xenius (GC) were compared to the two reference materials. The materials were light-cured for 40s in a 2mm×2mm×25mm Teflon mould. Degree of conversion was measured by Raman spectroscopy, Elastic modulus and flexural strength were evaluated by three point bending, surface hardness using Vickers microindentation before and after 24h ethanol storage, and filler weight content by thermogravimetric analysis. The ratio of surface hardness before and after ethanol storage was considered as an evaluation of polymer softening. Data were analyzed by one-way ANOVA and post hoc Tukey's test (p=0.05). Results The mechanical properties of the bulk-fill composites were mostly lower compared with the conventional high viscosity material, and, at best, comparable to the conventional flowable composite. Linear correlations of the mechanical properties investigated were poor with degree of conversion (0.090.8). Softening in ethanol revealed differences in polymer network density between material types. Conclusion The reduction of time and improvement of convenience associated with bulk-fill materials is a clear advantage of this particular material class. However, a compromise with mechanical properties compared with more conventional commercially-available nano-hybrid materials was demonstrated by the present work. Significance Given the lower mechanical properties of most bulk-fill materials compared to a highly filled nano-hybrid composite, their use for restorations under high occlusal load is subject to caution. Further, the swelling behaviour of some of the bulk-fill materials may be a reason for concern, which highlights the critical requirement for a veneering material, not only to improve aesthetic quality of the translucent material, but to reduce the impact of degradation.

OBJECTIVES:To test the null hypotheses that photoactive resin composites containing a Type I photoinitiator would exhibit reduced DC or increased monomer elution at substantially short curing times compared with materials based on a Type 2 ketone/amine system. METHODS:Two experimental resin composites were prepared, using either Lucirin-TPO or camphorquinone/DMAEMA. Specimens were light-cured using appropriate spectral emission that coincided with the absorption properties of each initiator using different irradiation protocols (0.5, 1, 3, 9s at 500, 1000 and 2000mW/cm(2) for Lucirin-TPO based composites and 20 or 40s at 1000mW/cm(2) for Lucirin-TPO and camphorquinone-based composites). Degree of conversion (DC) was measured by Raman spectroscopy, propagating radical concentrations were collected by means of electron paramagnetic resonance (EPR) and monomer leaching was characterized using high-performance liquid chromatography (HPLC). RESULTS:The null hypotheses were rejected, except for a single irradiation protocol (0.5s @ 500mW/cm(2)). Lucirin-TPO-based composites could cure 20 times faster and release at least 4 times less monomers in comparison to camphorquinone-based composites. At 1000mW/cm(2), and 1s irradiation time for curing times of 1s, Lucirin-TPO based composites displayed 10% higher DC. The difference in polymerization efficiency of Lucirin-TPO compared with camphorquinone-based resin composites were explained using EPR; the former showing a significantly greater yield of radicals which varied logarithmically with radiant exposure. SIGNIFICANCE:Lucirin-TPO is substantially more efficient at absorbing and converting photon energy when using a curing-light with an appropriate spectral emission and otherwise a limitation noted in several previous publications. At concentrations of 0.0134mol/L, Lucirin-TPO-based composites require a minimum light intensity of 1000mW/cm(2) and an exposure time of 1s to provide significantly improved DC and minimal elution compared with a conventional photoinitiator system. The use of a wide range of curing protocols in the current experiment has realized the significant potential of Lucirin-TPO and its impact for clinical applications, in replacement to materials using camphorquinone.

Three pectic oligosaccharides (POS) obtained by enzymatic hydrolysis of sugar beet pectin by combining endopolygalacturonase and pectinmethylesterase, were characterized using high performance liquid chromatography, thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry and X-ray diffraction. According to chromatographic analyses, POS are composed of mixture of polymers with different molecular weights and different galacturonic acid contents. The thermal analysis showed no major variation in thermal behavior regarding POS composition but showed that POS were more sensitive to thermal degradation than the parent pectin as well as the deesterified pectin. No change in composition of the gaseous products was obtained through TGA-FTIR analysis. The X-ray pattern of POS clearly indicated a considerable decrease in crystallinity when compared to the native pectin. Thus, thermal characterization of POS may have practical repercussions if the formulation in which POS is incorporated is submitted to a high temperature treatment.

Objectives. This work aims to review the key factors affecting the polymerization efficiency of light-activated resin-based composites. The different properties and methods used to evaluate polymerization efficiency will also be critically appraised with focus on the developments in dental photopolymer technology and how recent advances have attempted to improve the shortcomings of contemporary resin composites.Methods. Apart from the classical literature on the subject, the review focused in particular on papers published since 2009. The literature research was performed in Scopus with the terms "dental resin OR dimethacrylate". The list was screened and all papers relevant to the objectives of this work were included.Results. Though new monomer technologies have been developed and some of them already introduced to the dental market, dimethacrylate-based composites still currently represent the vast majority of commercially available materials for direct restoration. The photopolymerization of resin-based composites has been the subject of numerous publications, which have highlighted the major impact of the setting process on material properties and quality of the final restoration. Many factors affect the polymerization efficiency, be they intrinsic; photoinitiator type and concentration, viscosity (co-monomer composition and ratio, filler content) and optical properties, or extrinsic; light type and spectrum, irradiation parameters (radiant energy, time and irradiance), curing modes, temperature and light guide tip positioning.Significance. : This review further highlights the apparent need for a more informative approach by manufacturers to relay appropriate information in order for dentists to optimize material properties of resin composites used in daily practice. (c) 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Bio-based polymers and polymer nanocomposites have known an increasing interest during the past few years. This work is focused on the elaboration and the characterization of bio-based nanocomposites made from polyamide 11 (PA11) and nonorganomodified montmorillonite. To elaborate these materials an original elaboration process, consisting in injecting water during the extrusion, was used. Results show that thanks to this process, a well exfoliated morphology is obtained for clay contents as high as 10% wt. This was explained on the one hand by the fact that the clay is soluble in water and on the other hand by the fact that water and PA11 are miscible at high pressure and high temperature. Moreover, the morphology analyses have revealed that from 10% wt of clay, the platelets were not totally randomly distributed but they were rather organized at a mesoscopic scale. The obtaining of such clay's dispersion involves an enhancement of thermomechanical properties. For example, for a clay content of 10% wt, the Young's modulus of the material can be doubled and its degradation temperature increased. The role of the elaboration conditions on the morphology and subsequent properties of the nanocomposites are also carefully analyzed. Finally, it has been evidenced that the presence of the filler infers on both the crystalline form induced and the crystallization kinetics. In summary, this study demonstrates that, in the case of PA11 nanocomposites, the water-assisted injection process leads to the achievement of an exfoliated morphology for clay contents as high as 10% wt that allows to obtain high performance materials and to be free from using organomodified clays. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013