Crystallization of poly(3‐hydroxybutyrate) by exfoliated graphite nanoplatelets

Poly(3‐hydroxybutyrate) (PHB) has been shown to be efficiently nucleated by exfoliated graphite nanoplatelets (xGnP). The nucleating effect of xGnP was investigated using differential scanning calorimetry, optical microscopy and atomic force microscopy. Nonisothermal crystallization of PHB from the melt required lower activation energies for PHB containing 1 wt % and 3 wt % xGnP (?214 and ?102 kJ/mol respectively) than for pure PHB (?60 kJ/mol). A kinetic study of the PHB/xGnP crystallization employing a modified form of the Avrami equation revealed that the presence of xGnP increased the PHB crystallization temperature, as well as the crystallization rates, and generated smaller and more numerous spherulites. Optical microscopy and atomic force microscopy confirmed the incorporation of xGnP into the lamellar structure of the PHB spherulites and provided insight into the influence of xGnP on spherulite size and lamellae thickness. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Use of laser scanning confocal microscopy for characterizing changes in film thickness and local surface morphology of UV-exposed polymer coatings

Laser scanning confocal microscopy (LSCM) has been used to characterize the changes in film thickness and local surface morphology of polymer coatings during the UV degradation process. With the noninvasive feature of LSCM, one can obtain thickness information directly and nondestructively at various exposure times without destroying the specimens or deriving the thickness values from IR measurement by assuming uniform film ablation. Two acrylic polymer coatings were chosen for the study, and the physical and chemical changes of the two systems at various exposure times were measured and analyzed. Those measurable physical changes caused by UV exposure include film ablation, formation of pits and other surface defects, and increases in surface roughness. It was found in both coatings that changes in measured film thickness by LSCM were not correlated linearly to the predicted thickness loss using the changes in the CH band obtained by the Fourier Transform Infrared (FTIR) spectroscopy measurements in the later degradation stages. This result suggested it was not a uniform film ablation process during the UV degradation. At later stages, where surface deformation became severe, surface roughness and profile information using LSCM were also proven to be useful for analyzing the surface degradation process Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 13–14, 2004 in Philadelphia, PA.     

The effect of specific β‐nucleation on morphology and mechanical behavior of isotactic polypropylene

The commercial grade of isotactic polypropylene was modified by a specific β‐nucleating agent in a broad concentration range. The supermolecular structure of the specimens prepared by injection molding was characterized by X‐ray scattering and correlated with mechanical behavior. It was found that at a critical nucleant concentration of 0.03 wt % the content of the β‐modification virtually reaches a saturation level. With further addition of the nucleant, the β‐phase content increases only slightly. The long period passes through a distinct maximum at the same nucleant concentration. This singularity in structure remarkably correlates with a minimum of the yield stress and maxima of strain at break and fracture toughness. Such general behavior is also reflected in the correlation between the β‐phase concentration and fracture toughness profiles along the injection‐molded bars. It is suggested that in the critically nucleated material an optimum thickness of the amorphous interlayer with connecting chains between the β‐crystallites is established, rendering the material the highest possible ductility and toughness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1174–1184, 2002     

PMMA‐modified divinylester/styrene resins: Phase diagrams and morphologies

Binary and ternary experimental cloud‐point curves (CPCs) for systems formulated with a low molar mass synthesized divinylester (DVE) resin, styrene (St), and poly(methyl methacrylate) (PMMA) were determined. The CPCs results were analyzed with the Flory–Huggins (F‐H) thermodynamic model taking into account the polydispersity of the DVE and PMMA components, to calculate the different binary interaction parameters and their temperature dependences. The St‐DVE system is miscible in all the composition range and down to the crystallization temperature of the St; therefore, the interaction parameter expression reported for a higher molar mass DVE was adapted. The interaction parameters obtained were used to calculate the phase diagrams of the St‐PMMA and the DVE‐PMMA binary systems and that of the St‐DVE‐PMMA ternary system at three different temperatures. Quasiternary phase diagrams show liquid–liquid partial miscibility of the St‐PMMA and DVE‐PMMA pairs. At room temperature, the St‐DVE‐PMMA system is miscible at all compositions. Final morphologies of PMMA‐modified cured St‐DVE materials were generated by polymerization‐induced phase separation (PIPS) mechanism from initial homogeneous mixtures. SEM and TEM micrographs were obtained to analyze the generated final morphologies, which showed a direct correlation with the initial miscibility of the system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4539–4549, 2006     

Processing and morphology of molecularly imprinted nylon thin films

The characterization of thin, selectively imprinted films of nylon‐6 was performed. Amino acids were used as template molecules. Spin‐cast films were prepared with sizes ranging from 2 μm to 300 nm, depending on the nylon and template concentration in the casting solution. The morphological characteristics of the film surface were examined by atomic force microscopy, and the structure within the films was observed by freeze‐fracture scanning electron microscopy. The film activity was clearly coordinated with the appearance of nanometer‐sized pores both on the surface and within the film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2919–2926, 2006     

Reply to the Comment by K. Jorgensen et al. to “Analysis of constant rate period of spray drying of slurry”

Previously developed model for spray drying of slurry droplets with high solid content (Liang, 2001) was revised to describe correctly a boundary condition on the outer surface of droplet on basis of the rate of liquid evaporation.     

Morphology,thermal, and mechanical properties of polyamide 66/clay nanocomposites with epoxy‐modified organoclay

A new kind of organophilic clay, cotreated by methyl tallow bis‐2‐hydroxyethyl quaternary ammonium and epoxy resin into sodium montmorillonite (to form a strong interaction with polyamide 66 matrix), was prepared and used in preparing PA66/clay nanocomposites (PA66CN) via melt‐compounding method. Three different types of organic clays, CL30B–E00, CL30B–E12, and CL30B–E23, were used to study the effect of epoxy resin in PA66CN. The morphological, mechanical, and thermal properties have been studied using X‐ray diffraction, transmission electron microscopy (TEM), mechanical, and thermal analysis, respectively. TEM analysis of the nanocomposites shows that most of the silicate layers were exfoliated to individual layers and to some thin stacks containing a few layers. PA66CX–E00 and PA66CX–E12 had nearly exfoliated structures in agreement with the SAXS results, while PA66CX–E23 shows a coexistence of intercalated and exfoliated structures. The storage modulus of PA66 nanocomposites was higher than that of the neat PA66 in the whole range of tested temperature. On the other hand, the magnitude of the loss tangent peak in α‐ or β‐transition region decreased gradually with the increase in the clay loading. Multiple melting behavior in PA66 was also observed. Thermal stability more or less decreased with an increasing inorganic content. Young's modulus and tensile strength were enhanced by introducing organoclay. Among the three types of nanocomposites prepared, PA66CX–E12 showed the highest improvement in properties, while PA66CX–E23 showed properties inferior to that of PA66CX–E00 without epoxy resin. In conclusion, an optimum amount of epoxy resin is required to form the strong interaction with the amide group of PA66. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1711–1722, 2006     

Influence of PS‐b‐PEO diblock copolymers on the compatibility of syndiotactic polystyrene modified epoxy blends

Homogeneous solutions of syndiotactic polystyrene (sPS) in diglycidylether of bisphenol A (DGEBA), containing 2.5, 5 and 7.5 wt % of thermoplastic with or without 0.5 and 1 wt % of poly(styrene‐b‐ethylene oxide) (PS‐b‐PEO) block copolymer, were polymerized using a stoichiometric amount of an aromatic amine hardener, 4,4′‐methylene bis (3‐chloro‐2,6‐diethylaniline) (MCDEA). The dynamic‐mechanical properties and morphological changes of sPS‐(DGEBA/MCDEA) compatibilized with different amount of PS‐b‐PEO have been investigated in this paper. The addition of the block copolymer produced significant changes in the morphologies generated. The size of the dispersed spherical sPS spherulites does not change significantly, but less spherulites of sPS appeared upon network formation in the systems with compatibilizer, what means that addition of compatibilizer in this system delayed crystallization of sPS in sPS‐(DGEBA/MCDEA) systems and change phase separation mechanism from crystallization‐induced phase separation (CIPS) and reaction‐induced phase separation (RIPS) almost only to RIPS. Moreover, PS‐b‐PEO with higher molecular weight of PS block seems to be a more effective compatibilizer than one with lower molecular weight of PS block. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 479–488, 2006     

凝固条件对纤维素/丝素蛋白纤维相形态及性能的影响

蛋白质纤维具有光滑柔顺、透气吸湿等优点,然而天然蛋白纤维产量有限。再生蛋白纤维的制备通常采用与其它成纤高分子接枝或共混的方法,有利于提高再生蛋白纤维的断裂强度。选用同为天然高分子的纤维素为基体,以共溶剂溶解纤维素与蛋白质,进而纺丝成形制得力学性能满足要求的纤维素/丝素蛋白共混纤维。为了探究凝固剂组成对纤维素/丝素蛋白共混纤维相形态及性能的影响,选用水、乙醇、乙醇/1-丁基-3-甲基咪唑氯盐([BMIM]Cl)等作为凝固剂。研究发现:乙醇作为凝固剂时,纤维素与丝素蛋白能很好地同时凝固;而当在乙醇凝固浴中加入适量的[BMIM]Cl径向均匀分散。通过对凝固剂组成的调控能有效提升纤维的力学强度。     

Imide-aryl ether benzoxazole random copolymers

Novel imide-aryl ether benzoxazole copolymers were prepared and their morphology and mechanical properties investigated. A key feature of these copolymers is the incorporation of a benzoxazole moiety by the use of 2,2′-bis[4-(3-aminophenoxy)phenyl]-6,6′-bibenzoxazole or 2,2′-bis[4-(4-aminophenoxy)-phenyl]-6,6′-bibenzoxazole as co-diamines in polyimide syntheses. The preparation of these diamines involved the nucleophilic aromatic substitution of 2,2′-bis(4-fluorophenyl)-6,6′-bibenzoxazole with either 3- or 4-aminophenol in the presence of K₂CO₃. The diamines were co-reacted with various compositions of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) to synthesize the desired poly(amic acids). Films were cast and cured (350°C) to effect the imide formation, affording films with elongations between 40 and 110% and moduli in the 2000–2750 MPa range. The copolymers exhibited good dimensional (T_g in excess of 300°C) and thermal stability. Wide-angle X-ray diffraction measurements on the copolymers showed that the ordered morphology characteristic of PMDA/ODA polyimide was retained. Improvements in the auto-adhesion were observed, particularly in those copolymers which displayed a T_g.