Dielectric Analysis of Blended Polysulfone/Polyethylenimine Membrane Contactors for CO2 Capture.

Polysulfone membranes, used as contactors for CO2 capture, are blended with two different hyperbranched polyethyleneimines modified with benzoyl chloride (Additive 1) and phenyl isocyanate (Additive 2) in different percentages. Fourier-transformed infrared spectra evidence the presence of urea and amide groups, whereas the field emission scanning electron microscopy images show differences in the microstructure of the blended membranes. Dielectric spectra determine the motions of the side and backbone chains, which can facilitate the diffusion of CO2 . The spectra consist of six dielectric processes; three of them are due to the polysulfone (γPSf , ßPSf , and αPSf ), whereas the rest are characteristic of the additive (γHPEI , ßHPEI , and αHPEI ). The benzoyl chloride and phenyl isocyanate functional groups introduce variations in molecular mobility and modify the relaxations associated with the hyperbranched polyethyleneimine (HPEI). The additives also increase the conductivity of the blended membranes, which can compromise the performance of the membranes, specifically in the case of Additive 1. Ion hopping is found to be the prevailing charge transport mechanism while both relaxations, αHPEI and αPSf , are actives. These results, together with the final morphology of the membranes, may explain the greater absorption capacity of the membranes prepared with the hyperbranched polyethyleneimine modified with Additive 2.

The Role of Eucalyptus Species on the Structural and Thermal Performance of Cellulose Nanocrystals (CNCs) Isolated by Acid Hydrolysis.

Cellulose nanocrystals (CNCs) are attractive materials due to their renewable nature, high surface-to-volume ratio, crystallinity, biodegradability, anisotropic performance, or available hydroxyl groups. However, their source and obtaining pathway determine their subsequent performance. This work evaluates cellulose nanocrystals (CNCs) obtained from four different eucalyptus species by acid hydrolysis, i.e., E. benthamii, E. globulus, E. smithii, and the hybrid En × Eg. During preparation, CNCs incorporated sulphate groups to their structures, which highlighted dissimilar reactivities, as given by the calculated sulphate index (0.21, 0.97, 0.73 and 0.85, respectively). Although the impact of the incorporation of sulphate groups on the crystalline structure was committed, changes in the hydrophilicity and water retention ability or thermal stability were observed. These effects were also corroborated by the apparent activation energy during thermal decomposition obtained through kinetic analysis. Low-sulphated CNCs (E. benthamii) involved hints of a more crystalline structure along with less water retention ability, higher thermal stability, and greater average apparent activation energy (233 kJ·mol-1) during decomposition. Conversely, the high-sulphated species (E. globulus) involved higher reactivity during preparation that endorsed a little greater water retention ability and lower thermal stability, with subsequently less average apparent activation energy (185 kJ·mol-1). The E. smithii (212 kJ·mol-1) and En × Eg (196 kJ·mol-1) showed an intermediate behavior according to their sulphate index.

Membranes for Cation Transport Based on Dendronized Poly(epichlorohydrin-co-ethylene oxide). Part 1: The Effect of Dendron Amount and Column Orientation on Copolymer Mobility.

Dendronized polyethers give rise to columnar LC structures which can successfully act as cation transport materials. Therefore, we prepared two different materials, based on Poly(epichlorohydrin-co-ethylene oxide) (PECH-co-EO) grafted with methyl 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy] benzoate, containing 20% or 40% modified units, respectively. The obtained polymers were characterized by differential scanning calorimetry (DSC), X-ray diffraction and optical microscopy between crossed polars (POM) and compared to the unmodified PECH-co-EO. In order to reach efficient transport properties, homeotropically oriented membranes were prepared by a fine-tuned thermal annealing treatment and were subsequently investigated by dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA). We found that the presence of the dendrons induces a main chain partial crystallization of the polyether chain and coherently increases the polymer Tg. This effect is more evident in the oriented membranes. As for copolymer orientation upon annealing, the cooling rate and the annealing temperature were the most crucial factors. DMTA and DETA confirmed that grafting with the dendron strongly hinders copolymer motions, but did not show great differences between unoriented and oriented membranes, regardless of the amount of dendrons.

Molecular Mobility in Oriented and Unoriented Membranes Based on Poly[2-(Aziridin-1-yl)ethanol].

Unoriented and oriented membranes based on dendronized polymers and copolymers obtained by chemical modification of poly[2-(aziridin-1-yl) ethanol] (PAZE) with the dendron 3,4,5-tris[4-(n-dodecan-1-yloxy)benzyloxy]benzoate were considered. DSC, XRD, CP-MAS NMR and DETA, contribute to characterize the tendency to crystallize, the molecular mobility of the benzyloxy substituent, the dendritic liquid crystalline group and the clearing transition. The orientation of the mesogenic chain somewhat hindered this molecular motion, especially in the full substituted PAZE. The fragility, free volume and thermal expansion coefficients of these membranes near the glass transition are related to the orientation and the addition of the dendritic groups. PAZE-based membranes combine both order and mobility on a supramolecular and macroscopic level, controlled by the dendritic group and the thermal orientation, and open the possibility of preparing membranes with proper channel mobility that promotes selective ionic transport.

Study of the Degree of Cure through Thermal Analysis and Raman Spectroscopy in Composite-Forming Processes.

The curing of composite materials is one of the parameters that most affects their mechanical behavior. The inspection methods used do not always allow a correct characterization of the curing state of the thermosetting resins. In this work, Raman spectroscopy technology is used for measuring the degree of cure. The results are compared with conventional thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscope (SEM). Carbon fiber specimens manufactured with technologies out of autoclave (OoA) have been used, with an epoxy system Prepreg System, SE 84LV. The results obtained with Raman technology show that it is possible to verify the degree of polymerization, and the information is complementary from classical thermal characterization techniques such as TGA and DSC; thus, it is possible to have greater control in curing and improving the quality of the manufactured parts.

Spray-Drying Performance and Thermal Stability of L-Ascorbic Acid Microencapsulated with Sodium Alginate and Gum Arabic.

The potential of sodium alginate (ALG) and gum arabic (GA) as wall polymers for L-ascorbic acid (AA) encapsulation as a tool for their preservation against the thermo-oxidative degradation was investigated. The influence of such polymers used as wall material on the AA-content, size, encapsulation efficiency, encapsulation yield and thermo-oxidative stability were evaluated. The AA-microparticles were obtained using the spray-drying technique. An experimental Taguchi design was employed to assess the influence of the variables in the encapsulation process. The microparticles morphology and size distribution were characterized by scanning electron microscopy and laser diffraction. The thermal stability of AA microparticles was studied by differential scanning calorimetry and thermogravimetry analysis. This work points out the viability to encapsulate AA using GA and ALG through a spray-drying process. In general, a product yield ranging from 35.1% to 83.2% and an encapsulation efficiency above 90% were reached. Spherical microparticles with a smooth surface were obtained with a mean diameter around 6 µm and 9 µm for the those prepared with GA and ALG, respectively. The thermo-oxidative analysis showed that both polymers allow maintaining AA stable up to 188 °C, which is higher than the traditional processing temperature used in the fish feed industry.

Performance of Polyester-Based Electrospun Scaffolds under In Vitro Hydrolytic Conditions: From Short-Term to Long-Term Applications.

The evaluation of the performance of polyesters under in vitro physiologic conditions is essential to design scaffolds with an adequate lifespan for a given application. In this line, the degradation-durability patterns of poly(lactide-co-glycolide) (PLGA), polydioxanone (PDO), polycaprolactone (PCL) and polyhydroxybutyrate (PHB) scaffolds were monitored and compared giving, as a result, a basis for the specific design of scaffolds from short-term to long-term applications. For this purpose, they were immersed in ultra-pure water and phosphate buffer solution (PBS) at 37 °C. The scaffolds for short-time applications were PLGA and PDO, in which the molar mass diminished down to 20% in a 20-30 days lifespan. While PDO developed crystallinity that prevented the geometry of the fibres, those of PLGA coalesced and collapsed. The scaffolds for long-term applications were PCL and PHB, in which the molar mass followed a progressive decrease, reaching values of 10% for PCL and almost 50% for PHB after 650 days of immersion. This resistant pattern was mainly ascribed to the stability of the crystalline domains of the fibres, in which the diameters remained almost unaffected. From the perspective of an adequate balance between the durability and degradation, this study may serve technologists as a reference point to design polyester-based scaffolds for biomedical applications.

Crosslinked Sulfonated Poly(vinyl alcohol)/Graphene Oxide Electrospun Nanofibers as Polyelectrolytes.

Taking advantage of the high functionalization capacity of poly(vinyl alcohol) (PVA), bead-free homogeneous nanofibrous mats were produced. The addition of functional groups by means of grafting strategies such as the sulfonation and the addition of nanoparticles such as graphene oxide (GO) were considered to bring new features to PVA. Two series of sulfonated and nonsulfonated composite nanofibers, with different compositions of GO, were prepared by electrospinning. The use of sulfosuccinic acid (SSA) allowed crosslinked and functionalized mats with controlled size and morphology to be obtained. The functionalization of the main chain of the PVA and the determination of the optimum composition of GO were analyzed in terms of the nanofibrous morphology, the chemical structure, the thermal properties, and conductivity. The crosslinking and the sulfonation treatment decreased the average fiber diameter of the nanofibers, which were electrical insulators regardless of the composition. The addition of small amounts of GO contributed to the retention of humidity, which significantly increased the proton conductivity. Although the single sulfonation of the polymer matrix produced a decrease in the proton conductivity, the combination of the sulfonation, the crosslinking, and the addition of GO enhanced the proton conductivity. The proposed nanofibers can be considered as good candidates for being exploited as valuable components for ionic polyelectrolyte membranes.

Electrospun Poly(ethylene-co-vinyl alcohol)/Graphene Nanoplatelets Composites of Interest in Intelligent Food Packaging Applications.

Graphene nanoplatelets (GNPs) were synthetized from graphite powder and, thereafter, embedded in poly(ethylene-co-vinyl alcohol) (EVOH) fibers by electrospinning in the 0.1⁻2 wt.-% range. The morphological, chemical, and thermal characterization performed on the electrospun nanocomposite fibers mats revealed that the GNPs were efficiently dispersed and rolled along the EVOH fibrilar matrix up to contents of 0.5 wt.-%. Additionally, the dielectric behavior of the nanocomposite fibers was evaluated as a function of the frequency range and GNPs content. The obtained results indicated that their dielectric constant rapidly decreased with the frequency increase and only increased at low GNPs loadings while the nanocomposite fiber mats became electrically conductive, with the maximum at 0.5 wt.-% GNPs content. Finally, the electrospun mats were subjected to a thermal post-treatment and dark films with a high contact transparency were obtained, suggesting that the nanocomposites can be used either in a nonwoven fibers form or in a continuous film form. This study demonstrates the potential of electrospinning as a promising technology to produce GNPs-containing materials with high electrical conductivity that can be of potential interest in intelligent packaging applications as "smart" labels or tags.

Emission pattern of semi-volatile organic compounds from recycled styrenic polymers using headspace solid-phase microextraction gas chromatography-mass spectrometry.

The emission of low molecular weight compounds from recycled high-impact polystyrene (HIPS) has been investigated using headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS). Four released target analytes (styrene, benzaldehyde, acetophenone, and 2-phenylpropanal) were selected for the optimisation of the HS-SPME sampling procedure, by analysing operating parameters such as type of SPME fibre (polarity and operating mechanism), particle size, extraction temperature and time. 26 different compounds were identified to be released at different temperatures from recycled HIPS, including residues of polymerisation, oxidated derivates of styrene, and additives. The type of SPME fibre employed in the sampling procedure affected the detection of emitted components. An adsorptive fibre such as carbowax/polydimethylsiloxane (CAR/PDMS fibre) offered good selectivity for both non-polar and polar volatile compounds at lower temperatures; higher temperatures result in interferences from less-volatile released compounds. An absorptive fibre as polydimethylsiloxane (PDMS) fibre is suitable for the detection of less-volatile non-polar molecules at higher temperatures. The nature and relative amount of the emitted compounds increased with higher exposure temperature and smaller polymeric particle size. HS-SPME proves to be a suitable technique for screening the emission of semi-volatile organic compounds (SVOCs) from polymeric materials; reliable quantification of the content of target analytes in recycled HIPS is however difficult due to the complex mass-transfer processes involved, matrix effects, and the difficulties in equilibrating the analytical system.

Microwave-assisted extraction for qualitative and quantitative determination of brominated flame retardants in styrenic plastic fractions from waste electrical and electronic equipment (WEEE).

A fast method for the determination of brominated flame retardants (BFRs) in styrenic polymers using microwave-assisted extraction (MAE) and liquid chromatography with UV detection (HPLC-UV) was developed. Different extraction parameters (extraction temperature and time, type of solvent, particle size) were first optimised for standard high-impact polystyrene (HIPS) samples containing known amounts of tetrabromobisphenol A (TBBPA) and decabromodiphenyl ether (Deca-BDE). Complete extraction of TBBPA was achieved using a combination of polar/non-polar solvent system (isopropanol/n-hexane) and high extraction temperatures (130 degrees C). Lower extraction yields were, however, obtained for Deca-BDE, due to its high molecular weight and its non-polar nature. The developed method was successfully applied to the screening of BFRs in standard plastic samples from waste electrical and electronic equipment (WEEE); TBBPA could be fully recovered, and Deca-BDE could be identified, together with minor order polybrominated diphenyl ether (PBDE) congeners.

Analysis of brominated flame retardants in styrenic polymers. Comparison of the extraction efficiency of ultrasonication, microwave-assisted extraction and pressurised liquid extraction.

The extraction efficiency of pressurised liquid extraction (PLE), microwave-assisted extraction (MAE), and ultrasonic-assisted extraction (UAE) under different conditions has been compared for the recovery of the most commonly employed brominated flame retardants (BFRs) from styrenic polymeric matrixes. A HPLC-MS/MS method has been proposed for the simultaneous separation and quantification of tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD) diastereomers, and decabromodiphenyl ether (deca-BDE) in the polymeric extracts. PLE results in complete extraction of TBBPA and HBCD (95-100% recovery), and intermediate recovery rates for deca-BDE (50%). MAE, on the other hand, gives comparable performance to PLE for HBCD, but lower extraction yields for TBBPA and mainly deca-BDE. Ultrasonication, finally, offers relatively low extraction recoveries (10-50%). The proposed analytical procedures could be used for the effective identification and quantification of BFRs in styrenic plastics and for quality purposes in recycling facilities that deal with styrenic fractions from waste electrical and electronic equipment (WEEE).

Analytical strategies for the quality assessment of recycled high-impact polystyrene: a combination of thermal analysis, vibrational spectroscopy, and chromatography.

Various analytical techniques (thermal analysis, vibrational spectroscopy, and chromatographic analysis) were used in order to monitor the changes in polymeric properties of recycled high-impact polystyrene (HIPS) throughout mechanical recycling processes. Three key quality properties were defined and analysed; these were the degree of mixing (composition), the degree of degradation, and the presence of low molecular weight compounds. Polymeric contaminations of polyethylene (PE) and polypropylene (PP) were detected in some samples using differential scanning calorimetry (DSC). Vibrational spectroscopy showed the presence of oxidised parts of the polymeric chain and gave also an assessment of the microstructure of the polybutadiene phase in HIPS. The presence of low molecular weight compounds in the HIPS samples was demonstrated using microwave-assisted extraction followed by gas chromatography-mass spectrometry (GC-MS). Several volatile organic compounds (VOCs), residues from the polymerisation, additives, and contaminations were detected in the polymeric materials. Styrene was identified already in virgin HIPS; in addition, benzaldehyde, alpha-methylbenzenaldehyde, and acetophenone were detected in recycled HIPS. The presence of oxygenated derivates of styrene may be attributed to the oxidation of polystyrene (PS). Several styrene dimers were found in virgin and recycled HIPS; these are produced during polymerisation of styrene and retained in the polymeric matrix as polymerisation residues. The amount of these dimers was highest in virgin HIPS, which indicated that emission of these compounds may have occurred during the first life-time of the products. This paper demonstrates that a combination of different analytical strategies is necessary to obtain a detailed understanding of the quality of recycled HIPS.