Poly(&#x3b1;-hydroxyacrylic acid), PHA, is one of the few polymers with biodegradable properties used in mechanical pulp bleaching to stabilize hydrogen peroxide. A new method for the in situ follow-up of the lactone ring formation of PHA has been developed. The results have further been applied to describe the reaction kinetics of the lactonization and hydrolysis reactions through parameter estimation. In addition, the reaction mechanism is elucidated by multivariate data analysis. Satisfactory identification and semiquantitative separation of the lactone ring as well as the acyclic (carboxyl and hydroxyl groups) forms have been established by 1H NMR in the pH range of 1&#x2013;9. The lactonization reaction approaching equilibrium can be described by pseudo-first-order kinetics in the pH range of 1&#x2013;6. The rate constants of the pseudo-first-order kinetic model have been estimated by nonlinear regression. Due to the very low rates of lactonization as well as the weak pH dependency of the reaction, an addition-elimination mechanism is proposed. Additionally, the presence of a transient reaction intermediate during lactonization reaction could be identified by subjecting the measurement data to multivariate data analysis (PCA, principal component analysis). A good correlation was found between the kinetic and the PCA models in terms of model validity.

Heli Virkki

Antti Vuori

Tapani Vuorinen

Intramolecular Lactonization of Poly(&#x3b1;-hydroxyacrylic acid): Kinetics and Reaction Mechanism

Superparamagnetic particles were widely used in medical applications as well as for magnetic sensors and actuators. Generally, the size of the particles is in the range of 10&#x2013;20&#x2009;nm. To use such particles in large-scale applications, a simple processing as well as the use of commercially available particles is required. Therefore superparamagnetic nanoparticles available on the market were incorporated in flexible polymer films and the magnetic properties of the films were investigated. At ambient temperature no significant hysteresis was observed, indicating the superparamagnetic properties. Films containing up to 25&#x25; nanoparticles were prepared. The films show a saturation magnetization of 13.8&#x2009;Am2/kg and a coercivity of 7&#x2009;Oe at ambient temperature.

Kristin Trommer

Carina Petzold

Bernd Morgenstern

Thin Polymer Layers with Superparamagnetic Properties

The main aim of the present work is to correlate the morphological changes observed in the modified PP/PA6 fifty/fifty blends molded at confined flow conditions with both their mechanical and thermal properties and the kind and the amount of the interfacial modifiers used. Both transmitted light optical microscopy in the positive phase contrast mode, PC TOM, and field emission scanning electronic microscopy, FE SEM, were the used techniques for, respectively, general morphology overview and fractures surface analysis. The interfacial modifiers, a succinic anhydride, aPP-SA, and a succinyl-fluorescein, aPP-SF/SA, grafted atactic polypropylenes obtained and well characterized in authors&#x2019; laboratories came from the chemical modification of an atactic polypropylene industrial by-product. The amounts of any of both the interfacial modifiers came coded by the Box-Wilson experiment design methodology applied to the overall PP/PA6 binary system, watching that the interfacial agent was not a third component on a ternary blend but a true interfacial modifier in a binary one. All the studies were carried out over suitable specimens according to each test procedure with no further material manipulations to preserve at any moment the morphology of the blends as they emerge from the compression molding step at confined flow conditions.

E. P. Collar

J. Taranco

S. Areso

Jes&#xfa;s Mar&#xed;a Garc&#xed;a-Mart&#xed;nez

Understanding the Morphological Changes in the Polypropylene/Polyamide 6 Fifty/Fifty Blends by Interfacial Modifiers Based on Grafted Atactic Polypropylenes: Microscopic, Mechanical, and Thermal Characterization

The objective of this work was to prepare hydrogel films, as semi-interpenetrating polymer networks (semi-IPN), based on polyethylene glycol-co-fumarate (PEGF) and chitosan (Ch) blends. Hydrogel films were prepared by free radical cross-linking of PEGF, an unsaturated aliphatic polyester, in the presence of N-vinyl pyrrolidone (NVP), camphorquinone (CQ), and N,N-dimethyl-p-toluidine (DMPT) as a cross-linking, photoinitiating, and accelerating agent, respectively. The effect of NVP concentration on physicochemical and biological properties of semi-IPN film properties was evaluated. The sol fraction, water vapor transmission rate, and swelling degree of the hydrogel films were also investigated. Antibacterial activity against S. aureus was observed for the photocured blend hydrogels of Ch/PEGF with no toxicity to L929 cells according to the cell viability assays. Blend hydrogel films showing 600 &#xb1; 88&#x25; of equilibrium swelling degree in water and the lowest sol fraction (3.14 &#xb1; 1.22&#x25;) were obtained at 20&#x2009;wt&#x25; of NVP content whilst preserving their own cytocompatibility and antibacterial activity. Therefore, this formulation was considered as an optimal semi-IPN blend hydrogel film composition with potential application for wound dressing.

Aazadehsadat Hashemi Doulabi

Hamid Mirzadeh

Nasrin Samadi

Shadab Bagheri-Khoulenjani

Mohammad Atai

Mohammad Imani

Potential Application of a Visible Light-Induced Photocured Hydrogel Film as a Wound Dressing Material

Agrowaste biocomposites were obtained using peanut husk filler and LDPE. The effects of agrofiller content and compatibilizer on the mechanical and biodegradable properties of the composites have been discussed. Mechanical and biodegradable behaviour of LDPE became noticeably worse when it was blended with agrofiller, due to poor compatibility between the two phases. The presence of MAPE in the composites and its compatibility with the agrofiller, led to much better dispersion and homogeneity of agrofiller in the matrix and consequently to improved properties. Water absorption and thickness swelling indices increased with increasing filler content and were reduced on addition of MAPE. Furthermore, weight loss of composites via enzymatic degradation showed that both composites were biodegradable even at high levels of filler addition. However, composites with MAPE exhibited lower weight loss.

Henry C. Obasi

Peanut Husk Filled Polyethylene Composites: Effects of Filler Content and Compatibilizer on Properties

Polypyrrole and silver nanoparticles have been synthesized at 277&#x2009;K by chemical route. Nanoparticles of polypyrrole-silver (PPy-Ag) composites were prepared by mixing polypyrrole and silver nanoparticles in different weight percentages. Dielectric properties as a function of temperature in the range from 300&#x2009;K to 550&#x2009;K and frequency in the range from 50&#x2009;Hz to 1&#x2009;MHz have been measured. Dielectric constant decreased with increase in frequency and temperature. Dielectric loss decreased with increase in frequency and increased with increase in temperature. Using dielectric data AC conductivity has been determined. Conductivity was found to be in the order of 10&#x2212;3&#x2009;(&#x2126;&#x2212;1&#x2009;m&#x2212;1) and it increased with increase in temperature. Temperature variation of conductivity data has been analyzed in the light of Mott&#x2019;s polaron hopping model. Activation energy for conduction has been determined. Activation energy was determined to be in the order of meV and it has increased with increase in frequency and Ag nanoparticles content. This is the first time that PPy-Ag nanocomposites have been investigated for dielectric properties and AC conductivity and data analyzed thoroughly.

K. Praveenkumar

T. Sankarappa

J. S. Ashwajeet

R. Ramanna

Dielectric and AC Conductivity Studies in PPy-Ag Nanocomposites

Once cracks have formed within hydrogel materials, the integrity of the structure is signifcantly compromised, regardless of the application. Here, we demonstrate  cross-linked CMCS hydrogels can be engineered to exhibit self-healing under mild conditions. CMCS hydrogels based on CMCS and acryloyl-6-aminocaproic acid (A6ACA) were synthesized by free radical aqueous copolymerization using ammonium persulfate as initiator. A series of hydrogels was synthesized varying the percentage of A6ACA. The hydrogels were characterized by Fourier transform infrared spectroscopy (FTIR) techniques and their morphologies were investigated by scanning electron microscope (SEM) images. When the proportion of A6ACA was increased, the compressive strength, stress, and strain of hydrogels were increased. The cross-linked hydrogel based on CMCS that can autonomously heal between cut surfaces after 1&#x2009;h was formed under mild conditions. The increase of A6ACA content in the hydrogels will lead to increased mechanical properties and mechanical healing efficiencies for highly cross-linked polymeric networks. Hydrogen bond is the main reason for self-healing ability, and the covalent cross-linkss and noncovalent cross-links both bear loads in the hyrogel. Polymers with the ability to self-repair after sustaining damage could extend the lifetime of materials used in many applications.

Jiufang Duan

Self-Healing Hydrogels Based on Carboxymethyl Chitosan  and Acryloyl-6-aminocaproic Acid

Polymers are subject to oxidative degradation during all steps of their useful cycle. This degradative process is prevented using stabilizers like antioxidant of the type sterically hindered phenols or amines. Lignin, due to the presence of phenolic groups in their structure, can present characteristic as antioxidant agent, in a similar way to the additives used in polymers. Therefore, in this work, the antioxidant capacity of the lignin in a sample of polyethylene is studied. For this reason, in this paper, a method based on nonisothermal differential scanning calorimetry (DSC) to evaluate this property is used. The samples studied were subjected to heat treatment at different scan rates and in presence of oxygen to promote thermooxidation of the material. The antioxidant capacity of different formulations of lignin and additives in the polymer resin was determined from the temperature of onset of oxidation (<svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-3.29108pt" id="M1" height="12.2532pt" version="1.1" viewBox="-0.0498162 -8.96212 10.3582 12.2532" width="10.3582pt"><g transform="matrix(.013,0,0,-0.013,0,0)"><path id="g113-85" d="M620 675H597C578 656 570 650 541 650H144C112 650 104 653 94 675H72C59 618 42 552 23 493L53 491C71 534 88 564 105 585C124 608 144 615 238 615H290L197 121C182 40 174 34 88 28L82 0H361L367 28C275 34 266 38 281 121L374 615H441C522 615 543 608 553 583C562 560 566 531 565 493L597 494C603 551 612 629 620 675Z"/></g><g transform="matrix(.0091,0,0,-0.0091,7.176,3.132)"><path id="g50-106" d="M250 606C250 634 233 656 203 656C168 656 146 618 146 593C146 564 169 545 192 545C227 545 250 573 250 606ZM227 95L212 119C187 98 152 71 135 71C129 71 128 78 134 102L207 373C219 418 217 451 194 451C165 451 92 411 30 351L44 326C77 353 106 371 114 371C124 371 121 357 117 341L55 97C32 5 46 -12 70 -12C108 -12 191 51 227 95Z"/></g></svg>) at different heating rates and adjusting Arrhenius model prediction. The results indicate that the procedure can predict the antioxidant capacity of antioxidant additives in HDPE with good reproducibility and accuracy, according to the Arrhenius model prediction.

I. Pi&#xf1;a

F. Ysambertt

D. Perez

K. Lopez

Study of Antioxidant Effectiveness of Kraft Lignin in HDPE

A kind of polyphosphate modified expandable graphite (EGp) was prepared in graphite oxidation and intercalation reaction with KMnO4 as oxidant, H2SO4 as intercalator, and sodium hexametaphosphate (SHMP) as assistant intercalator. The feasible mass ratio of C&#x2009;:&#x2009;KMnO4&#x2009;:&#x2009;H2SO4 (98&#x25;)&#x2009;:&#x2009;SHMP was determined as 1.0&#x2009;:&#x2009;0.3&#x2009;:&#x2009;4.5&#x2009;:&#x2009;0.6, H2SO4 was diluted to 77&#x2009;wt&#x25; before intercalation reaction, and the reaction lasted for 40&#x2009;min at 40&#xb0;C. Expanded volume and initial expansion temperature of the prepared EGp reached 600&#x2009;mL/g (at 800&#xb0;C) and 151&#xb0;C, respectively. X-ray diffraction spectroscopy testified the intercalation and layer structure of EGp, and Fourier transform infrared spectroscopy illuminated the intercalated functional groups. Flame retardance of the prepared EGp and the referenced EG (with only H2SO4 as intercalator) for linear low density polyethylene (LLDPE) was also investigated. Addition of 30&#x2009;wt&#x25; EGp to the polymer improved the limiting oxygen index (LOI) from 17.5 to 27.3&#x25;. On the other hand, the LOI of the same amount of the referenced EG was only 24.6&#x25;. Assistant intercalation of SHMP improved the dilatability and flame retardancy.

Hongmei Zhao

Xiuyan Pang

Zhixiao Zhai

Preparation and Antiflame Performance of Expandable Graphite Modified with Sodium Hexametaphosphate

The oxidative coupling copolymerization between 2,6-dimethylphenol (DMP) and dihydroxynaphthalenes, such as the 2,3- and 2,6-dihydroxynaphthalenes (2,3- and 2,6-DHN), was carried out using a Cu catalyst under an O2 atmosphere. The polymerization was significantly affected by the structure of the comonomer, and the copolymers were efficiently obtained during the copolymerization of DMP and 2,6-DHN. The obtained copolymers containing hydroxyl groups of the DHN unit were further transformed into polymers containing ester and urethane groups. The obtained copolymers containing various functional groups showed a very different solubility from that of the homopolymer of DMP.

Shigeki Habaue

Ryosuke Ito

Ken Okumura

Yuki Takamushi

Oxidative Coupling Copolymerization of 2,6-Dimethylphenol and Dihydroxynaphthalene Affording Poly(phenylene oxide) Derivatives

This paper describes 3D particle-in-cell simulation of charge injection and transport through nanocomposite film comprised of ferroelectric ceramic nanofillers in an amorphous polymer matrix and/or semicrystalline ferroelectric polymer with varying degrees of crystallinity. The classical electrical double layer model for a monopolar core is extended to represent the nanofiller/nanocrystallite by replacing it with a dipolar core. Charge injection at the electrodes assumes metal-polymer Schottky emission at low to moderate fields and Fowler-Nordheim tunneling at high fields. Injected particles propagate via field-dependent Poole-Frenkel mobility. The simulation algorithm uses a boundary integral equation method for solution of the Poisson equation coupled with a second-order predictor-corrector scheme for robust time integration of the equations of motion. The stability criterion of the explicit algorithm conforms to the Courant-Friedrichs-Levy limit assuring robust and rapid convergence. Simulation results for BaTiO3 nanofiller in amorphous polymer matrix and semicrystalline PVDF with varying degrees of crystallinity indicate that charge transport behavior depends on nanoparticle polarization with antiparallel orientation showing the highest conduction and therefore the lowest level of charge trapping in the interaction zone. Charge attachment to nanofillers and nanocrystallites increases with vol&#x25; loading or degree of crystallinity and saturates at 30&#x2013;40&#x2009;vol&#x25; for the set of simulation parameters.

Meng H. Lean

Wei-Ping L. Chu

Model for Charge Transport in Ferroelectric Nanocomposite Film

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Journal of Polymers