The Role of Particle Surface Functionality and Microstructure Development in Isothermal and Non-Isothermal Crystallization Behavior of Polyamide 6/Cellulose Nanocrystals Nanocomposites

Polyamide 6 (PA6)/cellulose nanocrystal (CNC) and aminopropyl triethoxy silane (APS) - modified CNC nanocomposites were prepared by in situ anionic ring opening polymerization and subsequent melt extrusion. The morphological observation of these hybrid systems revealed that the non-modified nanocrystals developed a network-like fibrillar structure while the APS-modified CNCs were finely dispersed mostly as individual whiskers. The isothermal and non-isothermal crystallization kinetics was extensively studied with emphasis on the effects of CNC surface functionality and the subsequent microstructure development on crystallization behavior of these novel nanocomposite systems. The non-modified CNC particles with corresponding fibrillar microstructure were found significantly hinder the crystallization process and spherultic growth of polyamide 6 chains under both isothermal and non-isothermal conditions. On other hand, the surface modified cellulose nanocrystals with improved sub-micron dispersion enhance crystal nucleation in early stages of crystallization while imposing opposite effect in later stages of crystallization resulting in development of relatively smaller defective spherulitic structures

Rheology of Tin Fluorophosphate Glass/Polyamide 12 Hybrids in the Low Concentration Regime

Phosphate glass (Pglass)/polymer hybrids are a unique material class that promises to help fulfill the growing need for new advanced materials. Rheological investigations into Pglass/polyamide 12 hybrids have shown a strong dependence on temperature and composition. Strong negative deviations from the log-additivity rule are also observed for these materials as well as a reduction in the activation energy for viscous flow. Hybrids containing \u3c 2 vol. % Pglass are theologically simple fluids that display temperature independence in plots of storage modulus versus loss modulus. Hybrids containing \u3e= 2 vol. % Pglass are rheologically complex and do not obey the time-temperature superposition principle. Through application of Han plots, we identified a structural change that occurs in hybrids containing \u3e= 2 vol. % Pglass at temperatures in excess of 220 degrees C. This microstructural change induces an apparent yield stress in the material at these elevated temperatures. It is believed that the microstructural change is due to enhanced interactions that occur at elevated temperatures between the compatible pure components of the hybrids. (c) 2007 The Society of Rheology

Biocompatibility of Synthetic Poly(Ester urethane)/Polyhedral Oligomeric Silsesquioxane Matrices with Embryonic Stem Cell Proliferation and Differentiation

Incorporation of polyhedral oligomeric silsesquioxanes (POSS) into poly(ester urethanes) (PEU) as a building block results in a PEU/POSS hybrid polymer with increased mechanical strength and thermostability. An attractive feature of the new polymer is that it forms a porous matrix when cast in the form of a thin film, making it potentially useful in tissue engineering. In this study, we present detailed microscopic analysis of the PEU/POSS matrix and demonstrate its biocompatibility with cell culture. The PEU/POSS polymer forms a continuous porous matrix with open pores and interconnected grooves. From SEM image analysis, it is calculated that there are about 950 pores/mm2 of the matrix area with pore diameter size in the range 1-15 μm. The area occupied by the pores represents approximately 7.6% of the matrix area. Using mouse embryonic stem cells (ESCs), we demonstrate that the PEU/POSS matrix provides excellent support for cell proliferation and differentiation. Under the cell culture condition optimized to maintain self-renewal, ESCs grown on a PEU/POSS matrix exhibit undifferentiated morphology, express pluripotency markers and have a similar growth rate to cells grown on gelatin. When induced for differentiation, ESCs underwent dramatic morphological change, characterized by the loss of clonogenecity and increased cell size, with well-expanded cytoskeleton networks. Differentiated cells are able to form a continuous monolayer that is closely embedded in the matrix. The excellent compatibility between the PEU/POSS matrix and ESC proliferation/differentiation demonstrates the potential of using PEU/POSS polymers in future ESC-based tissue engineering. Copyright (C) 2010 John Wiley & Sons, Ltd

New Phosphate Glass/Polymer Hybrids - Current Status and Future Prospects

The physical modification of polymer structure and properties via polymer blending and reinforcement is a common practice in the plastics industry and has a large economic advantage over synthesizing new polymeric materials to fulfill new material needs. In this context, a new class of inorganic glass/organic polymer hybrids with enhanced benefits has been recently developed by blending low-Tg phosphate glasses with polymeric materials in the liquid state, to afford new hybrid materials with significant improvements in properties that are impossible to achieve from classical polymer blends and composites. Because of their facile synthesis and desirable characteristics, these phosphate glass/polymer hybrid materials may be model systems for exploring feasibility of new routes for driving inorganic glasses and organic polymers to self-assemble into useful materials. Conceptually, it may even be possible to use block copolymers, with one block being miscible with Pglass, to perform self-directed assembly of nanostructured hybrids, where the Pglass is confined solely to one phase. This article reviews some new insights into the structural dynamics, melt rheology, molecular relaxation processes, and phase behavior of a few representative examples of these unique hybrid materials with prescribed rheological properties, macromolecular structure and function. The unanswered questions are discussed to guide future research directions, and facilitate progress in this emerging area. (C) 2007 Elsevier Ltd. All rights reserved

Mechanism of Unexpected Viscosity Decrease of Nylon 6 Melts by Low-T-g Inorganic Tin Fluorophosphate Glass During Processing

We report unprecedented non-Einstein-like viscosity decrease of polymer melts by special low glass transition, T-g, inorganic tin fluorophosphate glass (Pglass) that is remarkably counter to widely accepted dispersions, suspensions, and composites theories. The well dispersed low-T-g Pglass dramatically decrease the polymer melt viscosity while increasing its Young\u27s modulus in the solid state at low loading (\u3c2%) however decreasing with high loading (\u3e 2%), making the hybrid Pglass/polymer solid material stronger yet easier to process in the liquid state. Disruption of the Nylon 6 melt dynamics, strong physicochemical interactions, and submicrometer nanophase separation (proved by rheometry, FTIR, DSC, SEM, NMR and XRD) are thought to be responsible for this experimental fact. This finding should beneficially impact our abilityto prepare lower viscosity, very highly filled Nylon 6 melts from already existing materials and polymer processing methods such as injection molding and extrusion, making the simple strategy potentially widely applicable in a number of applications such as thinner barrier resistant thin films, composites, and membranes for heterogeneous catalysis

Kinetic Analysis of Fractal Gel Formation In Waterborne Polyurethane Dispersions Undergoing High Deformation Flows

Isothermal and nonisothermal kinetics studies of thermal-induced gelation for waterborne polyurethane dispersions have been investigated rheologically. The change in the viscoelastic material functions such as elastic storage modulus, G\u27, viscous loss modulus, G and complex dynamic viscosity, eta* during the gelation process was evaluated accurately for the first time. The isothermal kinetics reaction was described using a phenomenological equation based on the Malkin and Kulichikhin model that was originally developed for predicting isothermal curing kinetics of thermosetting polymers from differential scanning calorimetery (DSC) data. The Malkin and Kulichikhin model was found to conform excellently well for the rheokinetics data presented here. The rate of the gelation process was found to be a second-order reaction regardless of the temperature and shear frequency, and to be in good agreement with literature data. The isothermal gelation kinetics was also analyzed using a standard isoconversional method that is based on replicated experimental data and model-free kinetics calculations. This isoconversional method evaluates an effective activation energy that is independent of the degree of conversion, indicating that the rate of gelation is controlled by a single step (homogeneous) process with no change in the fractal gel formation mechanism at different degree of conversions. The temperature dependence of the gelation rate constant was well described by an Arrhenius plot with an average apparent activation energy equal to 127 +/- 2 kJ/mol, in reasonable agreement with the value obtained from the temperature dependence of gel time, t(gel). The nonisothermal kinetics reaction rate was interpreted using the classical rate equation, the Arrhenius equation and the time-temperature relationships. A frequency-independent apparent activation energy was evaluated nonisothermally and found to be similar to that obtained from isothermal kinetics data. The high value of activation energy is thought to be due to the strong interaction between the PU-dispersed particles during the gelation process, making a significant contribution to the rate of structure formation. It is noteworthy that, in some respects, these results resemble those from other cross-linking polymer networks and gels measured by DSC, yet in very important ways the aqueous PUDs of the present study is quite unique

Natural Cellulose Fiber-Reinforced Polyamide 6 Thermoplastic Composites Prepared Via \u3ci\u3eIn Situ\u3c/i\u3e Anionic Ring-Opening Polymerization

Thermoplastic polyamide 6 composites reinforced with flax fiber fabric and kraft pulp cellulose mat were prepared by anionic in situ ring‐opening polymerization (ROP) using a special vacuum‐assisted resin infusion process. The effects of the polymerization initiator, fiber alkali pre‐treatment, fiber type, polymerization temperature, and surface modification of fibers with organosilane coupling agents on the ROP reaction, polymer conversion and the physical and mechanical properties of the composites were investigated. The results showed that a combination of alkali pre‐treatment and the use of relatively less reactive magnesium bromide based anionic initiator gave a successful ROP reaction and high polymer conversion. Analysis of the physical and mechanical properties of the composite panels showed that optimal mechanical properties could be achieved by using a polymerization temperature of 150°C while polymerization at higher temperatures lowered both the flexural and tensile properties due to generation of more internal microvoids, as well as, decreased crystallinity of the matrix. In addition, it was found that optimal mechanical properties of the composites could be obtained using 2 wt% aminopropyltriethoxysilane (APS) coupling agent while higher APS concentrations negatively impacted the interfacial adhesion, resulting in lower mechanical properties. POLYM. COMPOS., 2018. © 2018 Society of Plastics Engineer

The Effects of the Interface On Microstructure and Rheo-Mechanical Properties of Polyamide 6/Cellulose Nanocrystal Nanocomposites Prepared By In-Situ Ring-Opening Polymerization and Subsequent Melt Extrusion

Polyamide 6 (PA6) nanocomposites containing cellulose nanocrystals (CNCs) were prepared via a multi-step process consisting of in-situ anionic ring-opening polymerization and subsequent melt extrusion. The effect of surface modification of the CNCs with aminopropyl triethoxysilane (APS) was studied in detail using microscopic, mechanical and rheological techniques and compared with that of the neat CNC nanocomposites. Solid-state 29Si NMR analysis was used to confirm the interfacial bond formation between the PA6 matrix and surface modified CNCs. SEM images showed that upon surface modification, the morphology of CNCs within the matrix transformed from a fibrillar structure towards more individually dispersed nanocrystals with enhanced dispersion and higher interfacial area. The matrix-particle interphase was further investigated using quantitative nanomechanical mapping (QNM) to study the role of interfacial modification on thickness of interphase and development of a broader modulus gradient across the interface. The quality of dispersion and development of the rigid interfacial layer in the modified system resulted in significant improvement in solid-state mechanical properties of the nanocomposites. In addition, melt rheological studies showed significant improvements of melt elasticity and strength in shear and elongational flow in the nanocomposites systems

Rheokinetics of Thermal-Induced Gelation of Waterborne Polyurethane Dispersions

Thermal-induced gelation for waterborne polyurethane dispersion has been studied rheologically under isothermal condition over a wide range of frequencies at different constant temperatures (55, 60, 65, and 70 degrees C). The elastic storage modulus, G\u27, at a constant temperature in the vicinity of the gel point increases abruptly, and the magnitude of the elevation in G\u27 was found to be temperature dependent. Similar behavior has been observed for both the viscous loss modulus, G , and the complex dynamic viscosity, eta*. The gel point, t(gel), was determined from the point of intersection in tan delta vs gelation time for different constant shear frequencies, where tan delta is frequency independent and all curves cross over, indicating the validity of the Winter-Chambon criterion.. The value of tgel obtained from the coincidence of G\u27 and G was in excellent agreement with that obtained from tan delta vs t. At the gel point, G\u27 and G showed a power law with shear frequency, i.e., G\u27 similar to G similar to omega(n) with critical exponents n\u27 and n for G\u27 and G , respectively. The values of n\u27 and n are identical at t(gel) (n\u27 and n similar to 0.58), and both decreased exponentially with gelation time at 70 degrees C. The exponent values n\u27 and n are in good agreement with that predicted from the percolation theory (i.e., n = 2/3). In addition, the temperature dependence of n\u27 and n was investigated in the vicinity of the gel point. Both n\u27 and n decreased with temperature and intersected at the gel temperature, i.e., n\u27 = n at T-gel = 67 degrees C. The value of T-gel = 67 degrees C was in good agreement with that obtained previously from the temperature at which tan delta is frequency independent and also from the temperature at which G\u27 and G coincided. The zero shear viscosity, eta(0), and the equilibrium shear modulus, G(eq), conformed well with power law scaling functions of the relative distance from the gel point, 6, i.e., eta(0) similar to epsilon(-k) and G(eq) similar to epsilon(z) (where k and z are scaling parameters)

Broadband Dielectric Spectroscopy of Nanostructured Maleated Polypropylene/Polycarbonate Blends Prepared By In Situ Polymerization and Compatibilization

The miscibility and molecular dynamics of nanostructured maleated polypropylene (mPP)/polycarbonate (PC) blends prepared by in situ polymerization of macrocyclic carbonates with polypropylene modified with 0.5 wt% of maleic anhydride-reactive groups were investigated over a wide range of frequencies (10(-2) -0.5 x 10(7) Hz) at different constant temperatures using broadband dielectric spectroscopy and scanning transmission electron microscope (STEM). The molecular dynamics of the glass relaxation process of the blend (alpha-relaxation process) appeared at a lower temperature range compared with that of the pure PC. This shift in the molecular relaxation process is attributed to the partial miscibility of the two polymer components in the blends as previously confirmed by the morphology via STEM. Nanoscale morphologies with average domain diameters as small as 50 nm were obtained for the different blend compositions studied. The STEM photographs show that the graft mPP-g-PC prefers to locate at the interfaces as previously reported. The relaxation spectrum of pure PC and mPP/PC blends was resolved into alpha- and beta-relaxation processes using the Havriliak-Negami equation and ionic conductivity. The dielectric relaxation parameters, such as relaxation peak broadness, maximum frequency, f(max), and dielectric strength, Delta epsilon (for the alpha- and beta-relaxation processes), were found to be blend composition dependent. The kinetics of the alpha-relaxation processes of the blends were well described by Vogel-Fulcher-Tammann (VFT) equation. The local process of PC was resolved into two relaxation processes beta(l) and beta(2), associated with the carbonyl groups \u27 motion and the combined motions of carbonyl and phenylene groups, respectively. Only beta(2) shifted to lower frequency in the blend while beta(l) was relatively not affected by blending. The electric modulus of the blends was used to get a sufficient resolution of the different relaxation processes in the samples, i.e., alpha-, beta-relaxation processes, ionic conductivity, and interfacial polarization. In addition, the blending method used was found to increase the d.c. conductivity without affecting the charge carrier transport mechanism, making it possible to develop novel polymer blends with tunable dielectric properties and morphology from existing polymers. Published by Elsevier Ltd