Ventura, H.; Claramunt, J.; Rodríguez-Pérez , M.; Ardanuy, M. Polymer degradation and stability Vol. 142, p. 129-138 DOI: 10.1016/j.polymdegradstab.2017.06.003 Data de publicació: 2017-06-12 Article en revista
This research analyses the effect of hydrothermal aging on the water uptake and mechanical performance of biocomposites based on a polyhydroxyalkanoate matrix and flax fibre reinforcement in the form of nonwoven (NW) fabrics. The effectiveness of various surface treatments—wet/dry cycling (C), argon plasma (Ar), ethylene plasma and combinations—of these NW in the improvement of the mechanical properties of the composites is also evaluated. The water uptake during aging is analysed at both room temperature and 65 °C. Moreover, the composites are characterised before and after the aging to determine its effects on the morphology, thermal behaviour and tensile properties. It is found that the water diffusion is mainly influenced by the fibre content, and no significant differences are found in the effects of the NW treatments. Although the highest tensile stiffness and strength was found for the composites prepared with the Ar-treated NW, the C treatment is the most effective to prevent the loss of tensile performance after aging.
Heidarzadeh, N.; Mehdi Rafizadeh, M.; Faramarz Afshar Taromi, F.; del Valle, LJ.; Franco, M.; Puiggali, J. Polymer degradation and stability Vol. 135, p. 18-30 DOI: 10.1016/j.polymdegradstab.2016.11.013 Data de publicació: 2017-01-01 Article en revista
In the present study poly (butylene sebacate-co-terephthalate)s having different compositions were synthesized with a high yield and a random distribution by thermal transesterification of poly (butylene sebacate) and poly (butylene terephthalate) homopolymers. The copolymer with the highest comonomer ratio was the least crystalline sample, although the melting peaks corresponding to both, sebacate and terephthalate-rich phases were still observable in calorimetric heating runs. This copolymer was associated with interesting thermal and mechanical properties, as the maximum melting point was higher than 100 °C and the storage modulus was also high (i.e. 1.1 × 109 N/m2 and 1.7 108 N/m2 were determined just before and after the main glass transition temperature of -12 °C).
As all studied samples were thermally stable up to temperatures clearly higher than the fusion temperature, they could be easily processed. Increasing the terephthalate content of the copolymers resulted in higher hydrophobicity, which had a minor influence on cell adhesion and proliferation of both fibroblast-like and epithelial-like cells. Hydrolytic and enzymatic degradability were assessed and the effect of composition and crystallinity on the degradation rate was investigated. Molecular weight measurements during exposure to a hydrolytic media indicated a first order kinetic mechanism during the initial stages of degradation before reaching a limiting molecular size, which was indicative of solubilization. The most amorphous sample appears as a highly promising biodegradable material since it showed a significant weight loss during exposure to all selected degradation media, but also exhibited good performance and properties that were comparable to those characteristic of polyethylene
The present work deals with the preparation and characterization of improved fire-retardant ethylene-acrylate foams. A commercial formulation, usually employed in the cable industry sector, Casico, was modified using two different synergistic flame retardant (FR) systems: silica/zinc borate micro-sized particles (M) and montmorillonite/graphene nanoplatelets (N). The different composites were prepared by melt-blending and the foams by a compression-molding chemical foaming process (Casico-based foams). All Casico-based foams presented a mainly closed-cell structure. The presence of the nanoparticles system (N) promoted the formation of microcellular foams, with cell sizes lower than 100 µm, and narrow cell distributions. Nevertheless, when both flame retardant systems were added a higher cell collapse was noticed. Due to the foam's Casico-N structure and the presence of the stiff layered nanoparticles an increase of the temperature of ß and a relaxations and specific loss modulus was registered for that foam respect to the Casico foam. In a general way, the Casico-based foams presented a thermal decomposition behavior similar to that of unfoamed Casico. Only a slight increase of the thermal stability of the step associated to the ionomer decomposition was observed respect to the Casico. Significant fire behavior improvements were observed for Casico-M-N foam. Specifically, this foam showed the lowest value of PHRR (peak of heat release rate), EHC (effective heat of combustion) and FIGRA (fire index growth rate), having therefore the lowest flammability, even lower than Casico unfoamed material.
In the present work, ground tire rubber (GTR) was mechano-chemically reclaimed at ambient temperature using two-roll mills. Road bitumen and styrene-butadiene-styrene (SBS)-modified bitumen at variable content (in range: 2.5-20 phr) were applied as reactive plasticizers to enhance reclaiming of GTR. For better understanding the plasticizing effect of bitumen on the quality of obtained reclaimed rubber, mechano-chemically reclaimed GTR has been compared with GTR after thermo-mechanical reclaiming via low temperature extrusion (120 °C), which allows generation of high shear forces on GTR. Reclaiming process was evaluated by oscillating disc rheometer measurements, followed by mechanical, physical, thermal, and morphological properties analyses performed on vulcanized reclaimed rubber. The obtained results showed that application of bitumen during mechano-chemical reclaiming of GTR improves processing and prevents oxidation of reclaimed GTR through enhancement of physical and chemical interactions between GTR and bitumen. On the other hand, high shear forces acting on GTR during thermo-mechanical reclaiming caused effective scission of cross-linking bonds, while at the same time an adverse oxidative degradation of GTR occurs. Noticeably, the type of bitumen strongly affected the nature of the interfacial interactions between GTR and bitumen. Plasticization/partial reclaiming of GTR (road bitumen, SBS-modified bitumen) and encapsulation of GTR (SBS modified bitumen) were confirmed by mechanical properties, FTIR, TGA and SEM measurements
Murase, S. K.; del Valle, LJ.; Kobauri, S.; Katsarava, R.; Puiggali, J. Polymer degradation and stability Vol. 119, p. 275-287 DOI: 10.1016/j.polymdegradstab.2015.05.018 Data de publicació: 2015-09-01 Article en revista
Fibrous mats from an alpha-amino acid based poly(ester amide) have been prepared due to the potential applications of this kind of polymers in the biomedical field thanks to the expected non-toxicity of their degradation products. Specifically, the electrospinning technique has been applied and both solution properties and operational parameters have been optimized to get continuous fibers in the micrometer range. Furthermore, fibrous mats have been loaded with biguanide compounds differing on molecular size but having a well-proved bactericide activity (i.e., chlorhexidine, CHX and poly-hexamethylenebiguanide, PHMB). The high solubility of the poly(ester amide) constituted by L-phenylalanine, adipic acid and 1,4-butanediol also allowed getting appropriate electrospinning conditions to incorporate degrading enzymes like alpha-chymotrypsin without significant denaturation.; Degradability of fibrous mats has been evaluated in distinct enzymatic media (lipase, proteinase K and alpha-chymotrypsin) being found a similar behavior that contrasts with the significant differences detected when film samples were employed. An accelerated degradation was clearly found for fibrous mats loaded with alpha-chymotrypsin even when they were exposed to a non-enzymatic aqueous medium.; Release of bactericide agents was evaluated and a specific delay was determined when the polymeric biguanide was employed. Nevertheless, PHMB showed a clearly enhanced activity. Biocompatibility of the new fibrous mats was verified being also determined an increase on the cell adhesion with respect to film samples as a consequence of the increased porosity. (C) 2015 Elsevier Ltd. All rights reserved.
Carrasco, F.; Cailloux, J.; Sanchez-Jimenez, P.E.; Maspoch, M. Polymer degradation and stability Vol. 104, p. 40-49 DOI: 10.1016/j.polymdegradstab.2014.03.026 Data de publicació: 2014-06-01 Article en revista
One-step reactive extrusion-calendering process (REX-calendering) has been used in order to obtain sheets of 1 mm from poly(lactic acid) modified with a styrene-acrylic multifunctional oligomeric agent. In a preliminary internal mixer study, torque versus time has been monitored in order to ascertain chain extender ratios and reaction time. Once all the parameters were optimized, reactive extrusion experiments have been performed. An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of PLA sheets manufactured by reactive extrusion. This improvement has consisted of replacing the n-order conversion function by a modified form of the Sestak-Berggren equation f(alpha) = c (1 - alpha)(n) alpha(m) that led to a better adjustment of experimental data and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential methods and n-order reaction kinetics. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function f(alpha) = 2 (alpha(1/2) - alpha), corresponding to a random scission mechanism for L = 2 (as well as other functions for L values up to 8), has been tested. Once optimized the kinetic model, the thermal degradation kinetics of sheets obtained by REX-calendering process was compared to that of conventional sheets and polymer matrix. (C) 2014 Elsevier Ltd. All rights reserved.
Carrasco, F.; Perez-Maqueda, L.A.; Santana, O.; Maspoch, M. Polymer degradation and stability Vol. 101, num. 1, p. 52-59 DOI: 10.1016/j.polymdegradstab.2014.01.014 Data de publicació: 2014-03 Article en revista
An enhanced general analytical equation has been developed in order to evaluate the kinetic parameters of the thermal degradation of nanocomposites, composed of poly(lactic acid) (PLA) and organo-modified montmorillonite (OMMT) nanoparticles. This improvement has consisted of replacing the n-order conversion function by a modified form of the Sestak-Berggren equation f(a) = c (1 - a)nam that led to a better adjustment of experimental data and also adequately represented the conventional mechanisms for solid-state processes. The kinetic parameters so obtained have been compared to those determined by conventional differential and isoconversional methods. Given that the thermal degradation of PLA has been argued to be caused by random chain scission reactions of ester groups, the conversion function f(a) = L (L - 1)x(1 - x)L-1, corresponding to a random scission mechanism, has been tested. Once optimized the kinetic model, the thermal degradation kinetics of nanocomposites (0.5 and 2.5% of OMMT) was compared to that of the polymer matrix. Moreover, the thermal stability of nanocomposites was tested and compared to that of the polymer matrix.
Diaz, A.; Franco, M.; Estrany, F.; del Valle, LJ.; Puiggali, J. Polymer degradation and stability Vol. 99, num. 1, p. 80-91 DOI: 10.1016/j.polymdegradstab.2013.11.022 Data de publicació: 2014-01 Article en revista
Random copolymers derived from 1,4-butanediol and two dicarboxylic units differing in the parity of the number of methylene groups and length of the polymethylene sequence (i.e. succinic and azelaic acids) were studied in terms of thermal properties, crystalline structure and morphology, crystallization kinetics and biodegradability.
All samples were semicrystalline and their thermal properties varied in a wide temperature range. Copolymers crystallized according to the monoclinic α-form of polybutylene succinate and the orthorhombic structure postulated for polybutylene azelate depending on the predominant dicarboxylate unit. The behavior of the copolymer with an intermediate composition was complex due to strong dependence of the predominant crystalline form on crystallization and processing conditions. Interestingly, crystallization into the azelate structure was favored when samples were rapidly cooled from the melt, resulting in an unexpected increase in the degree of crystallinity. Spherulitic morphologies were clearly different (i.e. ringed spherulites and axialites) depending on the preferential crystalline structure.
Enzymatic degradability of the two homopolyesters was highly different and could be enhanced by incorporation of comonomer units. Preferential enzymatic attack on amorphous regions highlighted the spherulitic morphologies of copolymers having well developed, distinctive ringed structures.
Marquez, Y.; Franco, M.; Turon, P.; Rodriguez, R.; Puiggali, J. Polymer degradation and stability Vol. 98, num. 12, p. 2709-2721 DOI: 10.1016/j.polymdegradstab.2013.10.002 Data de publicació: 2013-12 Article en revista
Diaz, E.; Franco, M.; Rodriguez, R.; Puiggali, J. Polymer degradation and stability Vol. 98, num. 1, p. 133-143 DOI: 10.1016/j.polymdegradstab.2012.10.019 Data de publicació: 2013-01 Article en revista
Hydrolytic degradation of a series of copolymers synthesized by ring opening polymerization of trimethylene carbonate and glycolide was studied by following the weight loss and changes in molecular weight, polydispersity index and mechanical properties. Analyses of H-1 NMR and FTIR spectra taken during exposure to a pH 7.4 phosphate buffered solution were also performed. Copolymers with different microstructures (i.e. random, triblock and segmented copolymers) were synthesized. Most segmented copolymers studied had identical trimethylene carbonate content but differed in the hard segment content. Composition was also varied to demonstrate the influence of the soft segment composition.
Results were consistent with a model where degradation started in the amorphous phases and affected the glycolide units of the less compact soft segments and the regions within lamellar stacks. This degradation step led to a clear decrease of GGG triads (NMR data) and amorphous glycolide content (FTIR data), as well as an increase in Young's modulus. Degradation subsequently proceeded through the crystalline glycolide units belonging to lamellar stacks. The molecular weight of the degraded samples reached always an asymptotic value that corresponded to a solubility limit for fragments with high TMC content and for highly crystalline entities constituted by glycolide rich fragments.
Results pointed to the importance of the hard segment content and the composition of the soft segment, which logically influenced the distribution between amorphous and crystalline phases.
Polyesters such as poly(3-hydroxybutyrate) (PHB) have attracted commercial and academic interest as new biotechnological materials. In previous studies it was confirmed that two commercial lipases hydrolyzed the ester bonds from the 3HB fractions of P(3HB-co-4HB) copolymer. In this study, one of the previously used commercial lipases has been used for the enzymatic degradation of PHB homopolymer obtained via fermentation with Cupriavidus necator in order to obtain low molecular mass polymer. The results confirmed the enzymatic reaction of the used lipase with this PHB and show a controlled decrease of the molecular mass from 300,000 Da–4000 Da.
Gedler, G.; De Sousa Pais, M.; De Redondo, V.; Velasco J.I. Polymer degradation and stability Vol. 97, num. 8, p. 1297-1304 DOI: 10.1016/j.polymdegradstab.2012.05.027 Data de publicació: 2012 Article en revista
A thermogravimetric study in both nitrogen and air atmospheres has been carried out on unfilled and
graphene-reinforced solid and foamed polycarbonate. Polycarbonate foams were prepared using
a supercritical CO2 dissolution one-step batch foaming process. Results showed that polycarbonate
displayed a characteristic one-step decomposition under nitrogen, while three-step degradation was
observed in air. In addition, as-received pristine graphene nanoplatelets displayed a three-step degradation
in air, compared to a mild degradation under nitrogen. It was found that the thermal stability
remarkably improved for the foamed composites, related to a combination of a heat transfer reduction
promoted by the insulating cellular structure and the presence of the platelet-like graphene, which
helped create a physical barrier effect, delaying the escape of volatile products generated during
Carrasco, F.; Pages, P.; Gamez, J.; Santana, O.; Maspoch, M. Polymer degradation and stability Vol. 95, num. 12, p. 2508-2514 DOI: 10.1016/j.polymdegradstab.2010.07.039 Data de publicació: 2010-12 Article en revista
The kinetics of the thermal decomposition of processed poly(lactic acid) has been studied and compared to that of raw material. Processing consisted of two different industrial processes: 1) Injection (with or without further annealing); 2) Extrusion followed by injection (with or without further annealing). For this study, an integral method (based on the general analytical solution), differential methods (based on the first conversion derivative and on the 2nd derivative) and special methods have been used. On the other hand, a method based on the maximum decomposition rate has been considered. By doing that, the kinetic parameters (reaction order, frequency factor and activation energy) have been determined. It has been demonstrated that there was only one first-order reaction for the entire conversion range. A new equation (based on the second conversion derivative plot as a function of temperature) was developed allowing the calculation of the reaction order. This method quantifies peak areas (and not peak heights, as reported by Kissinger). It is very useful because it considers both peak shape and width. Activation energy, as determined by using the general analytical solution, was 318 kJ/mol for unprocessed poly(lactic acid) whereas it was 280 ± 5 kJ/mol for processed materials. All the processed materials had approximately the same thermal stability (T5 = 333.0–335.8 °C, at 95% confidence level), which was slightly lower than that of unprocessed materials (T5 = 337.5 °C). PLA melting (during extrusion and injection) was responsible for depolymerization reactions (the small molecules formed during melting processes can volatilize readily).
The influence of degradation on non-isothermal crystallization from the melt of a segmented copolymer
constituted of glycolide and trimethylene carbonate units and used as a bioabsorbable surgical suture
was studied by optical microscopy, differential scanning calorimetry and time-resolved X-ray diffraction.
Fibrillar positive spherulites were obtained with slightly degraded samples but new axialitic morphologies
were detected when samples had a molecular weight, Mw, lower than 29,000 g/mol and the
crystallization started at a high temperature.
Crystal growth kinetics of samples degraded under different conditions was evaluated over a wide
temperature range by a non-isothermal method. Two crystallization regimes (I and II) were determined
for the more degraded samples (i.e., those able to crystallize according to axialitic and spherulitic
morphologies), whereas only regime II was found for samples of higher molecular weights. Primary
nucleation density decreased with the extent of degradation provided no morphological changes
occurred, and so did the regularity of lamellar stacking, as shown by synchrotron measurements,
although the morphological parameters remained practically constant.
Foix, D.; Erber, M.; Voit, B.; Lederer, A.; Ramis, X.; Mantecón, A.; Serra, À. Polymer degradation and stability Vol. 95, num. 4, p. 445-452 DOI: 10.1016/j.polymdegradstab.2010.01.011 Data de publicació: 2010-03 Article en revista
Carrasco, F.; Pages, P.; Gamez, J.; Santana, O.; Maspoch, M. Polymer degradation and stability Vol. 95, num. 2, p. 116-125 DOI: 10.1016/j.polymdegradstab.2009.11.045 Data de publicació: 2010-02 Article en revista
The processing of poly(lactic acid) (injection and extrusion/injection) as well as annealing of processed
materials were studied in order to analyze the variation of its chemical structure, thermal degradation
and mechanical properties. Processing of PLA was responsible for a decrease in molecular weight, as
determined by GPC, due to chain scission. The degree of crystallinity was evaluated by means of
differential scanning calorimetry and X-ray diffraction. It was found that mechanical processing led to
the quasi disappearance of crystal structure whereas it was recovered after annealing. These findings
were qualitatively corroborated by means of FTIR. By analyzing 1H NMR and 13C NMR chemical shifts and
peak areas, it was possible to affirm that the chemical composition of PLA did not change after processing,
but the proportion of methyl groups increased, thus indicating the presence of a different
molecular environment. The thermal stability of the various materials was established by calculating
various characteristic temperatures from thermograms as well as conversion and conversion derivative
curves. Finally, the mechanical behaviour was determined by means of tensile testing (Young modulus,
yield strength and elongation at break).
Fernández , A.I.; Haurie, L.; Formosa, J.; Chimenos, J. M.; De Sousa Pais, M.; Velasco J.I. Polymer degradation and stability Vol. 94, p. 57-60 DOI: 10.1016/j.polymdegradstab.2008.10.008 Data de publicació: 2008 Article en revista
Low-grade magnesium hydroxide (LG-MH) is a solid by-product that undergoes an endothermic
decomposition in the temperature range of 300–750 C. Due to its thermal behaviour and its lower cost
relative to pure Mg(OH)2, it was studied as a non-halogenated flame retardant filler in a 28% vinyl acetate
(VA) content poly(ethylene-co-vinyl acetate) matrix. The solid was characterized by XRF and the crystalline
phases determined by XRD, composed predominantly of Mg(OH)2 and calcium and magnesium
carbonates. Particle size reduction was performed by both mechanical as well as air jet milling in order to
optimize the particle size distribution.
Composites with different filler concentrations were prepared to evaluate the mechanical properties and
flame retardancy by means of limiting oxygen index tests. LOI was also determined in specimens filled
with commercial flame-retardants to analyse the effectiveness of this solid
Haurie, L.; Fernández , A.I.; Velasco J.I.; Chimenos, J. M.; Lopez, J.; Espiell, F. Polymer degradation and stability Vol. 91, num. 5, p. 989-994 DOI: 10.1016/j.polymdegradstab.2005.08.009 Data de publicació: 2006-05 Article en revista
Synthetic hydromagnesite obtained from an industrial by-product was evaluated as a non-halogenated flame retardant. It was used in combination with aluminium hydroxide (ATH) and compared with commercial flame retardants like magnesium hydroxide (MH) and natural hydromagnesite–huntite (U) in a polyolefin system of low-density polyethylene/poly(ethylene-co-vinyl acetate) (LDPE/EVA).
The thermal stability and flame behaviour of the halogen free flame retarded composites were studied by thermogravimetric and differential thermal analysis (TG-DTA), limiting oxygen index (LOI), epiradiateur and cone calorimeter. It has been shown that synthetic hydromagnesite could be an alternative solution to the use of MH in non-halogenated flame retardant systems in EVA.
Morancho, J.; Ramis, X.; Fernández, X.; Cadenato, A.; Salla, J.; Vallés, A.; Contat, L.; Ribes, A. Polymer degradation and stability Vol. 91, num. 1, p. 44-51 Data de publicació: 2006-01 Article en revista