1,721,028 research outputs found
Enhanced crystallization kinetics in poly(ethylene terephthalate) thin films evidenced by infrared spectroscopy
No full textThe cold crystallization process in poly(ethylene terephthalate) (PET) spin-coated ultrathin films was studied by infrared spectroscopy. The conformational change associated to the formation of crystal phase during annealing at 107 °C was measured in real time, by monitoring both intensity and frequency shift of trans and gauche conformer bands of the PET glycol segment. Enhancement of crystallization kinetics was observed in thin films deposited on amorphous silicon, with respect to a 20 μm thick free standing film used as reference, where the fastest kinetics was observed for the thinnest (35. nm) film. Experimental findings were interpreted in terms of scarce interaction between PET films and silicon substrate, which does not provide slowing down of crystallization kinetics as observed on different substrates. This results in a dominant effect of the polymer/air interface, where faster kinetics is observed, as also confirmed by atomic force microscopy imaging, particularly on the thinnest film. Additionally, Avrami and Avramov analyses evidence a decrease of both the Avrami exponent, related to growth dimensionality, and induction time, related to delay of nucleation start, when decreasing film thickness. Therefore, the reported results enrich the description of confinement and substrate interaction effects on the cold crystallization process taking place in PET ultrathin film
Polymerization Kinetics and Characterization of Dual Cured Polyurethane‐Acrylate Nanocomposites for Laminates
No full textFour different types of montmorillonites have been dispersed by sonication at 50 degrees C into a propoxylated aromatic epoxy diacrylate oligomer to achieve interlayered or exfoliated nanocomposites. A thermally-induced cross-linking reaction, forming a polyurethane network in the presence of 7 wt.-% of a montmorillonite, has been promoted by addition of an allophanate modified polyisocyanurate based on hexamethylene diisocyanate. The kinetic behavior of the network formation has been studied at 25, 40 and 60 degrees C by following the disappearance of the isocyanate vibrational band found at 2 270 cm(-1). A tight crosslinked polyurethane acrylate network has been achieved by a subsequent dual UV curing promoted by a photoinitiator mixture (0.6 wt,-%) added to the reactive mixture because of further reactions occur to the acrylate double bonds. The photopolymerization kinetic has been investigated on the different thermally treated polyurethane nanocomposite networks by Real Time FTIR spectroscopy monitoring the changes of the IR band at 810 cm(-1) assigned to the acrylate double bond vibrations. The influence of the different montmorillonite clays on the final nanocomposite morphology has been investigated by using XRD and SEM. Finally, the use of these mixtures as internal layer between two modified surface PET films has been also studied for the laminate production. The based-PET laminate films have been characterized by determining the bending resistance and optical properties as a function of different nanofillers
Polymers from Fossil and Renewable Resources. Scientific and Technological Comparison of Plastic Properties
No full textThe book describes the development and commercialization of materials with viscoelastic properties, placing particular emphasis on the scientific and technological differences between plastics and bioplastics. The authors explain how to handle each of the two types of materials and determine the comparative environmental impact of the material life-cycle. The practical values of the overlapping aspects of the two types of materials from technical properties to eco-compatibility are also discusse
Preparazione di film a base di gelatina/PBSA per miscelazione in emulsione
No full textL’obiettivo del lavoro è la preparazione di film ad alto contenuto di gelatina per applicazioni nell’ambito dell’imballaggio flessibile. Saranno quindi studiate le condizioni ottimali per la preparazione delle miscele con il nuovo metodo e si caratterizzeranno poi i materiali ottenuti
Keratin–PNIPAM Hybrid Microgels: Preparation, Morphology and Swelling Properties
No full textCombinations of synthetic polymers, such as poly(N-isopropylacrylamide) (PNIPAM), with natural biomolecules, such as keratin, show potential in the field of biomedicine, since these hybrids merge the thermoresponsive properties of PNIPAM with the bioactive characteristics of keratin. This synergy aims to produce hybrids that can respond to environmental stimuli while maintaining biocompatibility and functionality, making them suitable for various medical and biotechnological uses. In this study, we exploit keratin derived from wool waste in the textile industry, extracted via sulfitolysis, to synthesize hybrids with PNIPAM microgel. Utilizing two distinct methods—polymerization of NIPAM with keratin (HYB-P) and mixing preformed PNIPAM microgels with keratin (HYB-M)—resulted in hybrids with 20% and 25% keratin content, respectively. Dynamic light scattering (DLS) and transmission electron microscopic (TEM) analyses indicated the formation of colloidal systems with particle sizes of around 110 nm for HYB-P and 518 nm for HYB-M. The presence of keratin in both systems, 20% and 25%, respectively, was confirmed by spectroscopic (FTIR and NMR) and elemental analyses. Distinct structural differences were observed between HYB-P and HYB-M, suggesting a graft copolymer configuration for the former hybrid and a complexation for the latter one. Furthermore, these hybrids demonstrated temperature responsiveness akin to PNIPAM microgels and pH responsiveness, underscoring their potential for diverse biomedical applications
Rheological response of polylactic acid dispersions in water with xanthan gum
Full text linkIn this work, the rheological behaviour of stable PLA dispersions in water, intended for coating applications, was investigated. The newly prepared dispersions consist of PLA particles with average diameter of 221.9 ± 2.0 nm based on DLS and SEM analyses, at concentrations varying in the 5-22 wt % range. Xanthan gum (XG), a bacterial polysaccharide, was used as a thickening agent to modulate the viscosity of the formulations. The rheological properties of the PLA dispersions with different XG and PLA contents were studied in steady shear, amplitude sweep and frequency sweep experiments. Under steady shear conditions, the viscosity of all the formulations showed a shear-thinning behaviour similar to XG solutions in the whole investigated 1-1000 s-1 range, with values dependent on both PLA particles and XG concentrations.
Amplitude and frequency sweep data revealed a weak-gel behaviour except in the case of the most diluted sample, with moduli dependent on both PLA and XG content. A unified scaling parameter was identified in the volume fraction (Φ) of the PLA particles, calculated by considering the dependence of the continuous phase density on the XG concentration. Accordingly, a mastercurve at different volume fractions was built through the Time-Concentration Superposition (TCS) approach. The mastercurve describes the rheological response of the system over a wider frequency window than the experimentally accessible one, and reveals the presence of a superimposed relaxation process in the high-frequency region
Glycolysis of semi-interpenetrated polymer network foam based on poly(vinyl chloride) for recovery and reuse of the individual components
No full textRigid semi-Interpenetrated Polymer Network (semi-IPN) foam based on poly(vinyl chloride) (PVC) and crosslinked polyurea/isocyanurate are complex materials that at present are not recyclable. They are used in many fields, including wind blade cores. In this work we studied the depolymerization of the crosslinked portion of the foam under glycolysis conditions for the separation and reuse of the individual components. Reaction products were characterized by FT-IR, NMR, solvent solubility, DSC, elemental analysis, titration of amine and hydroxyl groups and rheology measurements. Triisocyanurates and urea moieties were synthesized and used as model compounds. Glycolysis conditions were optimized to maximize depolymerization while minimizing PVC degradation. The parameters studied were reaction time (8 min to 3 h), temperature (155 to 200 °C), catalyst (potassium acetate or dibutyl tin dilaurate (DBTL)), glycol (ethylene glycol, 1,4 butanediol, diethylene glycol, dipropylene glycol, polyethylene glycol), as well as the effect of PVC thermal stabilizers such as hindered phenols and organo-phosphites. The results showed that the optimal reaction condition for foam glycolysis is 165-175 °C for 20-30 min, using DBTL as catalyst and including thermal stabilizers. No drastic difference was noticed by the kind of glycol used, except for PEG that led to greater PVC degradation. The greatest part of the crosslinked portion (≥90 %) was depolymerized and the result were mainly hydroxyl- and in minor amount amine- terminated oligomers. The recovered PVC (purity roughly 90 %) had a low degree of degradation and a viscosity suitable for its processing as thermoplastic material, i.e. by injection moulding
New Functional and Smart Materials through Molecular Modification and Blending of Biorelated Polymers
No full textThe unique optical behaviour of bio-related materials with organic chromophores
No full textMolecularly designed materials based on macromolecules and organic dyes offer unique opportunities in connection with the possibility of preparing optically responsive 'smart' materials. Indeed macromolecules are able to transmit and amplify small signals reaching sites at interacting distance through the involvement of the whole chain. The corresponding materials can then acquire stimuli-responsive properties in relation to specific features connected to primary structure and conformation. As a first approach to benefit from the above features for preparing eco-compatible smartmaterials, bio-related polypeptides, polysaccharides and polyesters can be used as the macromolecular partner in combination with a selected dye following different interaction methodologies. Two distinct routes were used to prepare optically responsive products from the above bio-related polymers, respectively based either on the covalent bonding to the original macromolecules of photochromic molecular species, such as azobenzene and spiropyran, or on the morphology-modulated dispersion of highly conjugated dyes in the polymer bulk. Examples related to the two different routes have been investigated in our laboratory and are presented and discussed also with reference to selected recent cases from the literature
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