[Show abstract][Hide abstract] ABSTRACT: In this research work, biocomposites based on a ternary system containing softwood Kraft lignin (Indulin AT), poly-L-lac-tic acid (PLLA) and polyethylene glycol (PEG) have been developed. Two binary systems based on PLLA/PEG and PLLA/lignin have also been studied to understand the role of plasticizer (i.e., PEG) and filler (i.e., lignin) on the overall physicomechanical behavior of PLLA. All samples have been prepared by melt-blending. A novel approach has also been introduced to improve the compatibility between PLLA and PEG by using a transesterification catalyst under reactive-mixing conditions. In PEG plasticized PLLA flexibility increases with increasing content of PEG and no significant effect of the molecular weight of PEG on the flexibility of PLLA has been observed. Differential scanning calorimetry and size-exclusion chromatography along with FTIR analysis show the formation of PLLA-b-PEG copolymer for high temperature processed PLLA/PEG systems. On the other hand, binary systems containing lignin show higher stiffness than PLLA/PEG system and good adhesion between the particles and the matrix has been observed by scanning electron microscopy. However, a concomitant good balance in stiffness introduced by the lignin particles and flexibility introduced by PEG has been observed in the ternary systems. This study also showed that high temperature reactive melt-blending of PLLA/PEG leads to the formation of a segmented PLLA-b-PEG block copolymer. V C 2012 Wiley Periodicals, Inc.
[Show abstract][Hide abstract] ABSTRACT: The development of autonomous healing material has an enormous scientific and technological interest. In this context, this research work deals with the investigation of autonomous healing behavior of epoxidized natural rubber (ENR) and its blends with ethylene methacrylic acid ionomers. The autonomous healing behavior of ENR and its blends containing two different ionomers [poly(ethylene-co-methacrylic acid sodium salt) (EMNa) and poly(ethylene-co-methacrylic acid zinc salt) (EMZn)] has been studied by ballistic puncture tests. Interestingly, EMNa/ENR blends exhibit complete healing just after the ballistic test but EMZn/ENR blends do not show full self-repairing. The healing efficiency has been evaluated by optical microscopy and a depressurized air-flow test. The healing mechanism has been investigated by characterizing thermal and mechanical properties of the blends. The chemical structure studied by FTIR and thermal analysis show that the ion content of ionomers and functionality of ENR has a significant influence on the self-healing behavior.
Smart Materials and Structures 02/2012; 21(3):035014. · 2.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of blending of ionomeric ethylene methacrylic acid copolymers with different polymers in relation to the self-healing behaviour was investigated. Different blends compositions based on ethylene-vinyl alcohol and epoxidized natural rubber, were studied by ballistic puncture tests and characterized with thermal and mechanical analyses. The healing of each blend composition after ballistic puncture tests was checked by applying a pressure gradient and by observations at optical and electron microscope. In the composition range explored, the self-healing response decreases with the increasing amount of ethylene-vinyl alcohol but it is maintained in all composition range for ionomer/rubber blends.
[Show abstract][Hide abstract] ABSTRACT: In-situ characterization of free-volume holes in polymer thin films under controlled humidity conditions with an atmospheric positron probe microanalyzer Appl. Phys. Lett. 101, 014102 (2012) Superior thermal conductivity and extremely high mechanical strength in polyethylene chains from ab initio calculation J. Appl. Phys. 111, 124304 (2012) Molecular weight distribution effects on the structure of strongly adsorbed polymers by Monte Carlo simulation J. Chem. Phys. 136, 214902 (2012) Adsorption-driven translocation of polymer chain into nanopores J. Chem. Phys. 136, 214901 (2012) Crystalline order of polymer nanoparticles over large areas at solid/liquid interfaces
[Show abstract][Hide abstract] ABSTRACT: The development of materials with the ability of intrinsic self-repairing after damage in a fashion resembling that of living tissues has important scientific and technological implications, particularly in relation to cost-effective approaches toward damage management of materials. Natural rubbers with epoxy functional groups in the macromolecular chain (ENR) and ethylene-methacrylic acid ionomers having acid groups partially neutralized with metal ions possess self-repairing behavior following high energy impacts. This research investigates the self-repairing behavior of both ENR and ionomers during ballistic puncture test on the basis of their thermal and mechanical properties. Heterogeneous blending of ionomers and ENR have also been used here as a strategy to tune the thermal and mechanical properties of the materials. Interestingly, blends of sodium ion containing ionomer exhibit complete self-repairing behavior, whereas blends of zinc ion containing ionomer show limited mending. The chemical structure studied by FTIR and thermal analysis shows that both ion content of ionomer and functionality of ENR have significant influence on the self-repairing behavior of blends. The mobility of rubbery phases along with its interaction to ionomer phase in the blends significantly changes the mending capability of materials. The healing behavior of the materials has been discussed on the basis of their thermal, mechanical, and rheological tests for each materials.
[Show abstract][Hide abstract] ABSTRACT: In this work, the effect of the processing conditions on the thermal behavior of a commercial poly(L-lactic acid) (PLLA) was investigated. In particular, PLLA having a very high molecular weight was proc-essed by a discontinuous mixer at different mixing condi-tions. The molar mass variation was investigated by size exclusion chromatography–multiangle laser light scatter-ing chromatography, and the thermal characteristics were detected by the conventional differential scanning calo-rimetry and dynamic mechanical thermal analysis. Tensile tests were performed at room temperature and at 60 C. Our attention was essentially focused on the crystalliza-tion behavior of the various samples obtained. A modest decline in the molar mass was obtained with two mixing temperatures of 210 and 250 C, but a significant increase in the crystalline phase content was noticed, with a con-comitant tremendous increment in the crystallization rate. A correlation was also made between the molar mass dis-tribution and crystallization rate in isothermal conditions, where clearly visible were the effects of the processing temperature on both the molar mass distribution and how the nucleating agents affected the crystallinity of PLLA. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3528–3536, 2011
Journal of Applied Polymer Science 09/2011; · 1.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Automotive W ith environmentally-friendly products becoming the norm, research and development of biopoly-mers, in addition to their versatile applications in durables -particularly automotives, invoke high expectations from the industry as well as consumers. However, we are yet to witness a scenario where the production of biopolymers is appropriate to the demand and their prices are competitive with the petrochemical-based polymers. For instance, the application of Poly(lactic acid) PLA and other biopolymers in the automotive sector (especially interiors) requires the products to meet the high quality standards of mechanical strength, a low degree of degradation by sunlight, resistance to abrasion, a high durability and a high thermal resistance. Although PLA has certain limitations new materials and modifying agents are expanding both its reach and applica-tions. Efforts are focused on boosting mechanical and ther-mal properties so biopolymers can be effective alternatives to less costly commodity materials. Especially for automotive application a new biodegradable copolymer has recently been patented: The copolymer is based on Poly(lactic acid) and Polycarbonate (PC) and has been developed within the Forbioplast project (No. KBBE-212239), funded by the 7th Framework Programme of the European Commission. The objective of the development was to find a material for automotive applications that has not only high thermal stability and high durability but is also biodegradable. PLA is a well-known biodegradable polymer that can be produced from renewable resources such as corn. The other component, PC, is a lightweight, high-performance material that possesses a unique balance of toughness, dimensional stability, optical clarity, high heat resistance and excellent electrical resistance. The new material, having a segmented copolymer structure (PLA-b-PC) has been prepared by reactive melt mixing in the presence of a specific catalyst. The presence of a segmented copolymer structure has been observed by analysing the molar mass distribution in size-exclusion chromatography (Fig. 1).
[Show abstract][Hide abstract] ABSTRACT: This research work deals with the investigation of autonomous healing behaviour of blends composed of an ethylene-methacrylic acid sodium salt ionomer (EMNa) with epoxidized natural rubber (ENR) or with poly(vinyl alcohol-coethylene) (EVA). Several important researches investigated the instantaneous and autonomous self-healing of ionomers in response to high energy impact such as projectile puncturing. Ionomers are thermoplastic ionic polymers, in which the maximum ion group content is approximately 15 mol% . The presence of ionic clusters  and the order-to-disorder transition phenomenon  of the clusters have been related to healing effects in ionomeric materials. Initial studies by Fall  and Kalista et al. [5,6] reported a two stage healing mechanism for ionomers under projectile puncture tests. In a first stage, elastic/viscoelastic recovery is supposed to close the damage, while in a second stage, welding by some local melting/solidification process allows full closure of the puncture. This self-healing mechanism was also supported by Varley and Van der Zwaag, who also showed that the ultimate healing level depends on the elastic response during the impact and post-failure viscous flow [7, 8]. The occurrence of consecutive healing events during high impact penetration of ionomers was also reported. The physical-crosslinking between acid functional groups and salt ions is thought to have influence on the healing mechanism and efficiency. However, Kalista et al.  and Fall  reported that the presence of ionic clusters seems to have limited significant influence on the self-healing of ionomers. This behaviour is however usually presented within a limited range of ambient conditions, where the mechanical characteristics are subjected to little variations. On the other hand, the availability of materials with controlled properties can greatly extend possible applications. Polymer blending is a common route to obtain mechanical performances spanning over wide limits. In this work, the effect of blending of an ethylene methacrylic acid copolymer ionomer with different polymers on the self-healing behaviour was investigated. In particular binary blends of different compositions based on EMNa/EVA and ENR, were studied by ballistic puncture tests and characterized with thermal and mechanical tests. The healing of each blend composition after ballistic puncture tests was checked applying a pressure gradient and was observed at optical and electron microscope. In the composition range explored (15-50% weight of EVA and ENR), the self-healing response decreases with the increasing amount of EVA but is maintained in all range for ENR/EMNa blends. Projectile puncture tests were performed in a ballistic laboratory by shooting 4.65x19.2 mm bullets through 100x100x2 mm square plates at 23 °C at a speed range of 703/730 m/s. To check for the healing efficiency, a pressure difference of 0.8 bar was applied in the puncture zone by a vacuum pump. All specimens were observed by optical stereo-microscope both in the bullet entrance and exit sides at 10 to 100x magnifications. Scanning electron microscopic (SEM) analyses were performed on the damaged surfaces of the specimens. Complete self-repairing behaviour was evident for all the blend compositions of ENR/EMNa blends. Also EVA/EMNa blends up to 30% EVA show that
[Show abstract][Hide abstract] ABSTRACT: Poly(ethylene-co-methacrylic acid sodium salt) Poly(vinyl alcohol-co-ethylene) Epoxidized natural rubber Ballistic puncture Blend Self-healing behavior of ionomer blends containing both rapidly crystallizing phase and with higher amount of amorphous phase has not yet been studied. This work gives a new insight to understand the development of materials with intrinsic self-healing property. In particular, binary blends based on poly(ethylene-co-methacrylic acid sodium salt) (EMNa)/Poly(vinyl alcohol-co-ethylene) (EVA) and epoxidized natural rubber (ENR), were studied by ballistic puncture tests. In the composition range explored (15–50 wt.% of EVA and ENR), the self-healing characteristics decrease with the increasing amount of EVA but are maintained in all ranges for ENR/EMNa blends. The ballistic damage initiated autonomous healing was observed by optical microscopy and the healing was further analyzed by thermal and mechanical behaviors of the blend materials.
[Show abstract][Hide abstract] ABSTRACT: A flow type quartz crystal microbalance (QCM) (bio)chemical sensor was developed for the real time determination of heavy metal ions that is suitable for environmental monitoring. A new process has been developed which enables to obtain surface-modified gold electrodes with high heavy metal ions complexing ability. The sensing performances of the piezoelectric sensor used in a flow-through setup were investigated by monitoring the frequency variation induced by the presence of heavy metal ions, such as copper and lead, as model ions, in aqueous media. X-Ray Reflectivity (XRR) and Atomic Force Microscopy (AFM) were carried out to characterize the unmodified and modified gold surfaces.
Journal of Nanoscience and Nanotechnology 03/2009; 9(2):1164-8. · 1.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The structural relaxation of PMMA copolymers with different chain flexibility has been studied by DSC with two classical procedures, namely: the rate of cooling and the isothermal approaches. The apparent activation energy of enthalpy relaxation was evaluated from the dependence of the glass transition temperature on the cooling rate while a comparison of the apparent relaxation rates was appraised from the enthalpy loss by annealing the different samples at the same level of undercooling (Ta = Tg-18 °C).