This is an editorial article. It has no abstract.
Composition dependence of the synergistic effect of nucleating agent and plasticizer in poly(lactic acid): A Mixture Design study
M. K. Fehri, C. Mugoni, P. Cinelli, I. Anguillesi, M. B. Coltelli, S. Fiori, M. Montorsi, A. Lazzeri
Vol. 10., No.4., Pages 274-288, 2016
Vol. 10., No.4., Pages 274-288, 2016
Blends consisting of commercial poly(lactic acid) (PLA), poly(lactic acid) oligomer (OLA8) as plasticizer and a sulfonic salt of a phthalic ester and poly(D-lactic acid) as nucleating agents were prepared by melt extrusion, following a Mixture Design approach, in order to systematically study mechanical and thermal properties as a function of composition. The full investigation was carried out by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and tensile tests. The crystallization half-time was also studied at 105 °C as a function of the blends composition. A range of compositions in which the plasticizer and the nucleation agent minimized the crystallization half-time in a synergistic way was clearly identified thanks to the application of the Mixture Design approach. The results allowed also the identification of a composition range to maximize the crystallinity developed during the rapid cooling below glass transition temperature in injection moulding, thus allowing an easier processing of PLA based materials. Moreover the mechanical properties were discussed by correlating them to the chemical structural features and thermal behaviour of blends.
Effects of UV-accelerated weathering and natural weathering conditions on anti-fungal efficacy of wood/PVC composites doped with propylene glycol-based HPQM
P. Srimalanon, W. Yamsaengsung, A. Kositchaiyong, E. Wimolmala, K. Isarangkura, N. Sombatsompop
Vol. 10., No.4., Pages 289-301, 2016
Vol. 10., No.4., Pages 289-301, 2016
This work studied the mechanical, physical and weathering properties and anti-fungal efficacy of polyvinyl chloride(PVC) and wood flour/polyvinyl chloride composites(WPVC). 2-hydroxypropyl-3-piperazinyl-quinoline carboxylic acid methacrylate (HPQM) in propylene glycol was used as an anti-fungal agent. Propylene glycol-based HPQM was doped in neat PVC and in WPVC containing 50 and 100 pph wood (WPVC-50 and WPVC-100). The flexural properties of PVC decreased when propylene glycol-based HPQM was added. However, adding this component did not affect the flexural properties of WPVC. Fungal growth inhibition test and dry weight technique were used for evaluation of anti-fungal effectiveness. Aspergillus niger was used as a testing fungus. Adding propylene glycol-based HPQM to WPVC-100 led to the most effective anti-fungal performance. Wood flour acted as an anti-fungal promoter for the WPVC composites. The optimal dosages of propylene glycol-based HPQM in PVC, WPVC-50, and WPVC-100 were 50000, 15000, and 10000 ppm, respectively. UV-accelerated weathering aging and natural weathering conditions were found to affect the flexural properties of PVC and WPVC. The change in the anti-microbial performance of WPVC under natural weathering were slower than those under UV-accelerated weathering aging. The anti-microbial evaluation indicated that the samples doped with less than 20000 ppm propylene glycol-based HPQM had a more pronounced effect than the ones doped with higher dosages.
The course of supplemental activator and reducing agent (SARA) atom transfer radical polymerization (ATRP) has been presented in the presence of Cu0. The novelty of this work is that SARA ATRP has been used for the first time to synthesize polystyrene-b-polyurethane-b-polystyrene copolymers by using tetraphenylethane-urethane macroinitiator as transitional products reacting with styrene in the presence of CuIIBr2/TPMA catalyst complex. The influence of copper surface area on the polymerization was examined. It was confirmed that in all cases, both the molecular weight of resulting copolymer increases linearly with increasing conversion as well as the value of ln([M]0/[M]) as a function of polymerization time increases linearly. A successful formation of the urethane-styrene copolymers was confirmed by NMR spectral studies.
The influence of crystalline microstructure and molecular topology on the strain-induced fibrillar transformation of semi-crystalline polyethylenes having various chemical structures including co-unit content and molecular weight and crystallized under various thermal treatments was studied by in situ SAXS at different draw temperatures. The long period of the nascent microfibrils, Lpf, proved to be strongly dependent on the draw temperature but non-sensitive to the initial crystallization conditions. Lpf was smaller than the initial long period. Both findings have been ascribed to the straininduced melting-recrystallization process as generally claimed in the literature. The microfibrils diameter, Df, was shown to depend on the draw temperature and initial microstructure in a different way as Lpf. The evolution of Df was shown to correlate with the interfacial layer thickness that mainly depends on the chemical structure of the chains. It was concluded that, in contrast to Lpf, the microfibril diameter should not be directly sensitive to the strain-induced melting-recrystallization. The proposed scenario is that after the generation of the protofibrils by fragmentation of the crystalline lamellae at yielding, the diameter of the microfibril during the course of their stabilization should be governed by the chain-unfolding and subsequent aggregation of the unfolded chains onto the lateral surface of the microfibrils. The morphogenesis of the microfibrils should therefore essentially depend on the chemical structure of the polymer that governs its crystallization ability, its chain topology and subsequently its fragmentation process at yielding. This scenario is summed up in a sketch.
Segmented linear polyurethanes (PUs) containing Diels-Alder (DA) adduct were synthesized in toluene solution from poly(ε-caprolactone) (PCL, Mn = 10, 25 and 50 kg/mol), diisocyanate (methylene diphenyl diisocyanate (MDI), 2,4-toluene diisocyanate (TDI), 1,6-hexamethylenediisocyanate, (HDI)), furfurylamine (FA) and bismaleimide (BMI). The order of the segments in the PUs was -PCL-MDI-FA-BMI-. The PUs were characterized by size-exclusion chromatography (SEC), different spectroscopic (1H-NMR, attenuated total reflectance Fourier-transform infrared, AT-FTIR), thermal and mechanical analysis (differential scanning calorimetry, DSC, dynamical mechanical analysis, DMA). The DA and retro-DA reactions were identified by 1H-NMR for both the synthesized PU and the coupling components (i.e. FA and BMI). Tensile mechanical and shape memory (SM) properties of the PUs were also determined. The DA coupling in the PU was improved by heat treatment above the melting temperature (Tm) of PCL. DMA traces showed a plateau-like region above Tm of PCL confirming the presence of a physical network the netpoints of which are given by the hard segments including the DA couplers. This feature suggested good SM behavior that was confirmed both qualitatively and quantitatively.
Microchannels embedded polymer composites were fabricated by resin infusion process using carbon fabric, epoxy resin and hollow glass tubes (HGTs). The effect of a range of low-velocity impact (LVI) and mode-I delamination (M1D) damage on the flexural strength of microchanneled carbon- epoxy composites was studied. A self-healing approach was also employed to recover their lost flexural strength due to these damages. Moreover, influence of LVI, M1D damage and healing on the failure behavior of microchanneled carbon- epoxy composites was also investigated. The results of flexural after impact (FAI) and flexural after delamination (FAD) showed that LVI has more deleterious effect on the flexural strength of carbon- epoxy composites than M1D damage. The loss in flexural strength increased linearly with increase in both impact (by higher impact energies) and delamination damage (by longer delamination lengths). Scanning electron microscopic (SEM) study revealed that self-healing agent (SHA), stored in HGTs placed within carbon- epoxy composites, effectively healed both LVI and M1D damage with excellent healing efficiencies.
In this study, the effect of graphene nanoplatelets (GNPs) on the shape memory properties of poly(L-lactic acid) (PLLA) was studied. In addition to thermal activation, the possibility of infrared actuating of thermo-responsive shape memory PLLA/GNPs nanocomposite was investigated. The incorporated GNPs were expected to absorb infrared wave’s energy and activate shape memory PLLA/GNPs. Different techniques such as differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), field emission gun scanning electron microscope (FEG-SEM) and dynamic mechanical thermal analysis (DMTA) were used to characterize samples. DSC and WAXD results indicated that GNPs augmented crystallinity due to nucleating effect of graphene particles. GNPs improved both thermal and infrared activating shape memory properties along with faster response. Pure shape memory PLLA was slightly responsive to infrared light and its infrared actuated shape recovery ratio was 86% which increased to more than 95% with loading of GNPs. Drastic improvement in the crystallinity was obtained in nanocomposites with lower GNPs contents (0.5 and 1 wt%) due to finer dispersion of graphene which resulted in more prominent mechanical and shape memory properties enhancement. Infrared activated shape memory PLLA/GNPs nanocomposites can be developed for wireless remote shape control of smart medical and bio-systems.