Search

The compatibilization by olefin block copolymer (OBC) in the blends of polypropylene (PP)/ethylene-propylene-diene terpolymer (EPDM) and the phase morphology of the ternary blends were investigated by rheology, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) measurements. It was found that the PP/EPDM blends exhibited enhanced mechanical properties in the presence of OBC. The addition of OBC had a significant influence on the phase separation behavior of the blends. For the PP/EPDM-50/50 heterogeneous blends, the addition of 15 phr OBC enabled the two-phase morphology to change from a droplet-matrix structure to a co-continuous one. In the temperature range of 150 to 200 °C, OBC was shown to have a better compatibility with PP than EPDM. The changes in viscosity ratio of the dispersed phase to matrix phase caused by adding OBC might be the dominant factor in controlling the coalescence of the dispersed phase domains. For the crystallizati...

Genomic and transcriptomic sequences of Tagetes erecta are very limited in public databases, despite its nutritional and economical value. In this study, nine cDNA libraries were constructed from leaves, immature and mature flowers and sequenced using Illumina Hiseq 2000. Over 45.66 Gb nucleotides were generated and a total of 72,499 unigenes were assembled, 34,892 (48.13%) of which were annotated in NR, Swiss-prot, COG, GO, KOG, KEGG and Pfam. 11,721 differentially expressed genes were identified in leaves, immature flowers and mature flowers. The differentially expressed genes between immature flowers and mature flowers were mainly involved in photosynthesis and secondary metabolite biosynthesis. Additionally, the catalysis-related unigenes and their expression involved in carotenoids biosynthesis were determined. Using our newly identified reference genes as internal control, the expression profiles of carotenoids biosynthetic genes were verified by real-time qRT-PCR, and four of the unigenes were cloned for full length sequences confirmation. Furthermore, gene expansions occurred among the catalytic gene families in carotenoids biosynthesis pathway, which might explain the high pigment content in T. erecta.

Isothermal and non-isothermal crystallization behaviours of the blends of long chain branched polypropylene (LCB PP) and poly(ethylene-co-octene) (PEOc) with different weight ratios were studied under quiescent and shear flow using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and rheological measurements. Experimental results showed that the crystallization of the LCB PP/PEOc blends were significantly accelerated due to the existence of the long chain branches (LCBs), the blends being able to rapidly crystallize even at 146 °C. The addition of PEOc that acts as a nucleating agent, could also increase the crystallization rate of LCB PP. However, the crystallization rate of LCB PP was reduced when the PEOc concentration was more than 60 wt %, showing a retarded crystallization growth mechanism. The morphology of the binary blend was changed from a sea-island structure to a co-continuous phase structure when the PEOc concentration was increased from 40 to 60 wt %. In comparison with linear isotactic iPP/PEOc, the interfacial tension between LCB PP and PEOc was increased. In addition, flow-induced crystallization of LCB PP/PEOc blends was observed. Possible crystallization mechanisms for both LCB PP/PEOc and iPP/PEOc blends were proposed.

Poly(ethylene-co-octene) (PEOc) has been shown to provide a high toughening contribution to isotactic polypropylene (iPP). The theoretical modeling of flow-induced crystallization (FIC) of blends of iPP and PEOc is not much reported in the literature. The aim of the present work is to clarify the FIC of iPP upon addition of PEOc in terms of theoretical modeling. The crystallization of iPP and PEOc blends in flow is simulated by a modified FIC model based on the conformation tensor theory. Two kinds of flow fields, shear flow and elongational flow, are considered in the prediction to analyze the influence of flow field on the crystallization kinetics of the polymer. The simulation results show that the elongation flow is much more effective than shear flow in reducing the dimensionless induction time of polymer crystallization. In addition, the induction time of crystallization in the blends is sensitive to the change of shear rate. In comparison with experimental data, the modified model shows its validity for the prediction of the induction time of crystallization of iPP in the blends. Moreover, the simulated relaxation time for the blends becomes longer with increasing percentage of PEOc in the blends.

Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with a series of anionic polysaccharides such as carboxymethyl cellulose, sodium hyaluronate, xanthan gum, pectin, gellan gum were prepared by electropolymerization in aqueous solutions. Some other dopants of potassium nitrate, potassium sulfate, sodium poly(styrenesulfonate), and sodium polyacrylate were used in comparison with the anionic polysaccharides. The electrochemical properties and stability of the obtained PEDOT films were also investigated. It was found that indium tin oxide (ITO) conductive glass could be used as the working electrode of the electropolymerization of EDOT and that the dopant had a great influence on polymerization potential and overoxidation potential. These charged biomolecules of anionic polysaccharides were found to facilitate electropolymerization of EDOT instead of common doping anions as counterion. The electroactive PEDOT films doped with anionic polysaccharides showed stable electrochemical properties, good texture, and adhesion properties to the ITO conductive glass.

In the present work aqueous mixtures of polysaccharide of methylcellulose (MC) and conductive polymer of ammonium poly(3-thiophene acetic acid) (PTAA-NH 4 ) were prepared and the effect of PTAA-NH 4 on the rheological and thermal properties of MC solution were investigated. Significant viscous synergism depending on shear rate and concentration of PTAA-NH 4 was found for the mixtures, indicating a special interaction between the two amphiphilic polymers of MC and PTAA-NH 4 . In comparison with pure MC solutions, the mixtures showed much more evident shear thinning characteristics. When the concentration of PTAA-NH 4 added was higher than 0.15%, weak gel-like behavior of the mixtures was also observed at low temperatures. In addition, though the gelation and degelation patterns of MC were not changed by the addition of PTAA-NH 4 , both rheological and calorimetric measurements showed that the presence of PTAA-NH 4 shifted the sol–gel transition temperature of MC solution to higher temperature with increasing of the concentration of PTAA-NH 4 .

In this study, a series of linear- and long-chain branched polylactic acid (PLA) samples was prepared by electron beam irradiation without or with addition of a trifunctional monomer, trimethylolpropane triacrylate (TMPTA). The chain structures of the PLA samples were characterized by size-exclusion chromatography coupled with a light scattering detector (SEC-MALLS) and shear and extensional rheology. PLA tends to degrade while keeps linear structures with increasing irradiation dose and without addition of TMPTA, as evidenced by decreased molecular mass Mw and reductions of storage modulus G′ and the zero shear viscosity η0. Long-chain branched PLA samples were successfully prepared with irradiation and addition of TMPTA, which shows prominent higher η0 and apparent flow activation energy, longer characteristic relaxation time τ, and pronounced strain-hardening behaviors. With increasing amount of TMPTA, Mw dependences of η0 and the root mean square radius of gyration Rg obviously deviate from the scaling relation of linear PLA samples, which strongly indicates the increased long-chain branching degree for the branched PLA samples. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The effect of pre-shear flow on the subsequent crystallization process of polymeric melt was investigated and a flow-induced crystallization (FIC) model based on the conformation tensor incorporating the pre-shear effect was proposed. The model is capable of predicting the overshoot phenomena of the stress and the flow-induced free energy change of the polymeric system at high pre-shear rates. Under the condition of flow, the increase in the activated nuclei number was contributed by the flow-induced free energy change, which showed an overwhelming effect on the nuclei formation during the pre-shear process at high shear rates. The half crystallization time (t1/2) of polypropylene (PP) as functions of pre-shear rate and pre-shear time at different crystallization temperatures was predicted and compared with the experiment data. Both numerical and experimental results showed that t1/2 of PP decreased dramatically when the flow started but leveled off at long times. It was found that two transformation stages in t1/2 existed within a wide range of shear rates. For the first stage where the melting polymer experienced a relatively weak shear flow, the acceleration of crystallization kinetics was mainly contributed by the steady value of free energy change while in the second stage for high shear rates, strong overshoot in flow-induced free energy change occurred and the crystallization kinetics was thus significantly enhanced. The overshoots in stress and flow-induced free energy change reflected an important role of flow on the primary nucleation especially when the flow was strong enough.

In the present work long chain branched polypropylene (LCB PP) polymers were prepared by linear polypropylene and multi-functional monomer through melt grafting reaction. A quantitative rheological method was adopted to analysis the structure parameters of LCB PP. The effects of chain branched level on the crystallization kinetics of PP were investigated by rheology, differential scanning calorimetry, polarized optical microscope and wide-angle X-ray diffraction. The dynamic viscoelastic properties of LCB PP showed that the increase in the chain branched level caused a typically deviation from the terminal behavior and a different distribution of the melt relaxation spectrum in the long relaxation time regime. It was found that the chain branched level had a significant effect on the flow induced crystallization (FIC) process of PP melts. The crystallization of LCB PP was more sensitive to shear flow than that of linear PP during induced period at low shear rates. This result also indicated that the longer relaxation time of the polymer chains played an important role in the nucleation of PP under shear flow fields. LCB PP with high chain branched level showed accelerated crystallization kinetics in comparison with that with low chain branched level.

In this work, the isothermal flow-induced crystallization (FIC) of high- density polyethylene (HDPE) under a simple shear flow was investigated. Two exper- imental modes, including steady shear and preshear treatment, were performed on the polymer melt. Based on the nonequilibrium thermodynamic theory, the FIC pro- cess of HDPE was predicted through the modification of a continuum FIC model. The theoretical predictions of the evolution of both the viscosity in steady shear flow and the complex modulus under preshear treatment were essentially related to the crystallinity of HDPE, in agreement with the experimental findings. Both experimen- tal and predicted results showed that the applied flow field could accelerate the crys- tallization kinetics of HDPE significantly. However, the effect of the intensity of shear flow on the crystallization of HDPE was finite, showing a saturation phenom- enon, namely, the accelerated degree of crystallization tending to level off when the shear rate was large enough. In additional, it was found that the predicted crystal- linity of HDPE was very low in induction period either in steady shear flow or by preshear treatment. V C 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 531- 538, 2009

The crystallization behavior of long-chain branched (LCB) polypropylene (PP) in the supercritical carbon dioxide (scCO2) atmosphere was investigated to show the influences of LCB and CO2 on the formation of y-crystal. The crystallization experiments were performed in CO2 atmosphere with the pressure from 1.3 to 10.4 MPa and temperature between 90 and 130 °C. The effects of LCB level, CO2 pressure, and crystallization temperature on the content of y-crystal were investigated. The results showed that the influence of LCB on the formation of y-crystal was obvious when PP was crystallized in CO2. The content of y-crystal increased with LCB level and reached a maximum of 88.2%. It could be explained that, as LCB increased the chainfolding energy of PP molecular chain and hindered it from folding back into crystal lamella, which made the formation of y-crystal easier. However, CO2 was the key factor in the formation of y-crystal, and the influence of CO2 on y-crystal was much significant than that of LCB. It was believed that the increase of free volume after dissolving of CO2 in PP was helpful in the formation of y-crystal. It was found that the content of y-crystal increased almost linearly with CO2 pressure (CO2 content), and the contribution of CO2 to y-crystal increased with pressure, while that of LCB increased with temperature.

Glycidyl methacrylate (GMA) was grafted onto chlorinated polypropylene (CPP) in the molten state using benzoyl peroxide (BPO) in the presence of styrene (St) as a comonomer. The differential scanning calorimetry (DSC) results indicated that the thermodynamic curve of unpurified grafted CPP was different from the purified, and showed a new broad endothermic peak at 100 degrees C, which may be attributed to the glass transition temperature (T-g) of remained copolymer of GMA and St. Furthermore, transmission electron microscope (TEM) showed that there were two-phase structures in the grafted CPP. Because the grafted CPP was to be used as a hot melt adhesive, so the influence of initiator concentration, monomer concentration, and reaction temperature on peel strength was investigated. The experiment results showed that a higher degree of grafting was obtained by using two kinds of monomers, such as GMA and St. Increasing the monomer concentration led to an initial rapid increase in the peel strength. (c) 2007 Wiley Periodicals, Inc.

The non-isothermal crystallization behaviors of long chain branched isotactic polypropylene (LCB PP), dynamically vulcanized LCB PP/ethylene-propylene-diene monomer (EPDM) blends at various weight ratios were investigated by DSC, rheology and optical microscopy. LCB PP/EPDM blends were found to show a different crystallization behavior in comparison with linear PP/EPDM blends, showing a minimum in the peak temperature of crystallization with increasing the content of EPDM while the latter showing a maximum. The nucleation and the crystallization kinetics of PP were induced and accelerated by long chain branches and EPDM. The acceleration of crystallization kinetics of LCB PP induced by LCB structures was attributed to the grafted efficient nucleation agent. The influence of EDPM on the crystallization combines the effects of enhancement and retardation, depending on its content in the blends. Based on the thermodynamics theory of crystallization, a modified crystallization model was developed to reveal the crystallization mechanism of LCB PP/EPDM blends.

A series of halogen-free intumescent flame retardants (IFR) based on home-made melamine phosphate and pentaerythritol system (MPPER) including polyamid 12, basic nickel carbonate (NiCO3·2Ni(OH)2·4H2O), lanthanum oxide (La2O3), and expandable graphite compounding with MPPER, were adopted for flame retarding olefin block copolymers (OBC). Flame-retardant effects and thermal stabilities of OBC-IFR composites were investigated by limiting oxygen index, vertical burning test (UL-94), and thermogravimetry analysis along with the analysis of morphological structures of the char residue by scanning electron microscopy. The mechanical properties and the flame-retardant mechanism of the final composited materials have been also discussed. The loading of suitable amount of IFR can improve effectively the flame retardancy of the OBC with tolerable decrease in mechanical properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40066.