Thermal degradations of chlorinated natural rubber from latex and chlorinated natural rubber from solution

The thermal degradations of chlorinated natural rubbers from latex (CNR‐L) and from solution (CNR‐S) under nitrogen atmosphere were studied with thermogravimetric analysis (TGA). The thermal degradations of CNR‐L and CNR‐S are one‐step reaction. The shapes of the thermogravimetric and derivative thermogravimetric curves are similar. The degradation temperatures of CNR‐L and CNR‐S increase linearly with the increment of heating rates. The heating rate hardly affects the thermal degradation rates of CNR‐L and CNR‐S at the various degradation stages. The thermal degradations of CNR‐S and CNR‐L are dehydrochlonation reactions. The reaction activation energy (E) of CNR, at the first stage, is around 100 kJ/mol. After that, E remains relatively steady (80–140 kJ/mol). At the last stage, E rises rapidly (130–270 kJ/mol). The variation tendency of frequency factor (A) is similar to that of E. As the initial degradation temperature T₀ of CNR‐L is 10.9°C lower than that of CNR‐S, the thermal stability of CNR‐S is better than that of CNR‐L, which may be caused by the difference of molecular structure between CNR‐L and CNR‐S, as FTIR results indicate that there are more ? OH, ? C?O and ? COO? groups in the CNR‐L molecular chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Scanning tunnel microscopy study of rayon‐based carbon‐fiber surfaces

Because of its atomic resolution, scanning tunnel microscopy (STM) was applied to the study of the surface topography, in air, of rayon‐based carbon fibers (RCF) that were not previously studied. By a variety of larger scales, RCF exhibits some rugosities with “peaks” and “valleys.” The surfaces are characterized by stripe‐form crystallite stackings with the diameter of about 10 nm aligned at an angle between 45 and 60° to the fiber axis. A graphitelike structure was first observed on the surface of RCF examined at an atomic resolution scale. Distances between two adjacent carbon atoms of RCF and that between the closest centers of hexagonal carbon rings were estimated. It was also concluded that the hexagonal structure of RCF is deformed graphene (graphitelike) compared with that of highly oriented pyrolytic graphite. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 754–758, 2003     

Formation of Novel Microstructured SiCNO Films from Block Copolymer Micellar‐Templating Approaches

We report the formation of novel microstructured SiCNO films with “smooth,” “egg‐shaped,” and “strawberry‐like” spheres by a block copolymer micellar‐templating approach, in which polyvinylsilazne (PVSZ) swelled F127 micelles are allowed to evaporate at different temperatures over the different periods of time, followed by the cross‐linking at 140°C and the pyrolysis at 800°C. The evolution process of “smooth,” “egg‐shaped,” and “strawberry‐like” spheres in the microstructured SiCNO films is observed by controlling the evaporation temperature and time of the multistep thermal treatment. The SiCNO films with varied internal microstructures have potential for harsh environment applications including high‐temperature sensors and high oxidation/corrosion resistance.     

Effects of dibutyltin dilaurate and epoxidized soya bean oil on the thermal stability of chlorinated natural rubber from latex

The effects of dibutyltin dilaurate (DBTL) and epoxidized soya bean oil (EBO) on the dehydrochlorination reaction of chlorinated natural rubber (CNR) from latex were studied by the measurement of the HCl evolving rate during the thermal degradation of CNR and by the determination of the amounts of cyclic conjugated dienes that formed on the CNR molecular chains. During the early stage of the thermal degradation of CNR at 150°C, HCl was eliminated, and the cyclic conjugated dienes formed on the CNR molecular chains. Under the effects of DBTL and EBO, the HCl evolving rates during the early stage of the thermal degradation of CNR were reduced, whereas the amounts of cyclic conjugated dienes formed on the CNR molecular chains were increased. Under the effects of mixtures from the compounding of DBTL with barium stearate or 2,2′‐methylene‐bis(4‐methyl‐6‐tert‐butyl‐phenol) as well as the compounding of EBO with 2,2′‐methylene‐bis(4‐methyl‐6‐tert‐butyl‐phenol), not only the HCl evolving rate from CNR but also the formation of cyclic conjugated dienes decreased, and this indicated that the compounded mixtures had synergistic functions against the thermal degradation of CNR. However, the mixture from the compounding of EBO with barium stearate had no synergistic effect on increasing the thermal stability of CNR. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1986–1991, 2006     

Preparation and characterization of core–shell polystyrene and polymethylsilsesquioxane structure latex particles by seeded polymerization

Composite polystyrene and polymethylsilsesquioxane (PS‐PMSSQ) latices were prepared by hydrolysis and polycondensation of triethoxylmethylsilane (TEOMS) in the presence of PS seed latices, obtained by gamma ray induced polymerization. Morphology of the composite latex particles was observed by transmission electronic microscopy and their size distribution was measured by dynamic laser light scattering. It was found that if 1 wt% silicon‐containing surfactant (SCS) and 0.4 wt% dodecylbenzene sulphonic acid (DBSA) were both used, core–shell/PS‐PMSSQ latex particles could be prepared at 30 °C. The core–shell structure was further characterized by X‐ray photoelectron spectrometry. With 0.5 wt% SCS or 0.2 wt% DBSA, the capsulation was incomplete. At 0 and 90 °C, the PMSSQ phase penetrated into the seed particles. No core–shell structure was observed when DBSA was replaced by hydrochloric acid or SCS was replaced by poly(ethylene glycol) monooctylphenyl ether. Copyright © 2006 Society of Chemical Industry     

Study on preparation of chlorinated natural rubber from latex and its thermal stability

The effects of pH value of reaction system, reaction time, and reaction temperature on the chlorination reaction in the preparation of chlorinated natural rubber (CNR) from natural rubber latex were discussed. It has been found from the thermal analysis that the thermal degradation of CNR in nitrogen is a one-step reaction, and 30% carbonide with a stable structure remained at 360 to 700°C; whereas the thermo-oxidative degradation of CNR in air is a multistep reaction, and the thermal degradation ratio reaches to 100% at 560°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2863–2867, 1999     

Gating Characteristics of Thermo‐Responsive Membranes with Grafted Linear and Crosslinked Poly(N‐isopropylacrylamide) Gates

Thermo‐responsive porous membranes with grafted linear and crosslinked poly(N‐isopropylacrylamide) (PNIPAM) gates are successfully prepared at temperatures above and below the lower critical solution temperature (LCST) of PNIPAM by using a plasma‐induced grafting polymerization method, and the effects of operation pressure and grafting temperature on the thermo‐responsive gating characteristics of the prepared membranes are investigated systematically. The fluxes of water through the grafted membranes increase simply with increasing the operation pressure no matter whether the environmental temperature is 40 °C or 25 °C. Under high operation pressure (e.g., higher than 0.14 MPa), the grafted linear PNIPAM gates deform to a certain extent, whereas the grafted crosslinked PNIPAM gates do not deform. For both membranes with grafted linear and crosslinked PNIPAM gates, the membranes prepared at 25 °C (below the LCST of PNIPAM) show larger thermo‐responsive gating coefficients than those prepared at 40 °C (above the LCST of PNIPAM), which results from different distributions of grafted PNIPAM gates in the membrane pores. When the PNIPAM gates are grafted at 25 °C, the grafted layer near the membrane surface is much thicker than that inside the membrane pores; on the other hand, when the PNIPAM gates are grafted at 40 °C, the grafted layer is homogeneously formed throughout the whole pore length. Both linear and crosslinked grafted PNIPAM gates in the membrane pores exhibit stable and repeatable thermo‐responsive “open‐close” switch performances under the operation pressure of 0.26 MPa. The results in this study provide valuable guidance for designing, fabricating, and operating thermo‐responsive gating membranes with desirable performances.     

Evaluation of thermo‐viscosity parameters of dextran in polar and nonpolar solvent

Some thermo‐viscosity parameters like Viscosity‐molecular weight constant (K), the short‐range parameter, (A) and long‐range parameter (B) have been evaluated for the polymer “Dextran” of three different molecular weights (M?_w = 19,500, 75,000, and 250,000) in three different solvents like 6 (M) aqueous urea, 2 (M) aqueous glycine, and 50% aqueous glucose at temperatures ranging from 25 to 50°C. The study reveals that the viscosity‐molecular weight constant (K) decreases with increase in temperature for polar solvents like aqueous urea and aqueous glycine. The value of “K” increases with the rise in temperature within the range of 25 to 35°C in case of a nonpolar solvent aqueous glucose and then “K” decreases with the increase in temperature within the range of 40 to 50°C for the nonpolar solvent aqueous glucose. The short‐range parameter (A) shows the same trend as shown by “K” and the long‐range parameter “B” exhibits no definite trend with the variation of temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 440–452, 2001     

Effects of pyrolysis temperature on the chemical composition of refined softwood and hardwood lignins

The current study uses nuclear magnetic resonance, Fourier-transform infrared spectroscopy and Raman spectroscopy to investigate the evolution of refined softwood and hardwood lignins under various pyrolytic exposures. Little chemical change occurred at pyrolysis temperatures of 250 and 300 °C, whereas significant mass loss and chemical change was observed at 400 and 500 °C. These losses were mainly attributed to evolution of methoxyl, hydroxyl, and propyl groups. Mass loss plateaued following pyrolysis at 500 °C, but rearrangements continued to occur at higher temperatures, resulting in char that became increasingly polyaromatic in nature. Following brief pyrolytic exposures at 500 and 600 °C, the refined hardwood and softwood lignins yielded coal-like products. Lignin pyrolyzed at higher temperatures yielded chars with greater order, similar in composition to coke. These coal and coke-like products are called “lignin-based carbon” (LBC). The polyaromatic nature of the LBC after high temperature pyrolysis was perceived as the result of radical formation and recombination, leading to fused aromatic structures, which occurs more readily at higher temperatures.     

Thermal behavior and kinetics during the stabilization of polyacrylonitrile precursor in inert gas

The thermal behaviors of polyacrylonitrile precursor during thermal stabilization in inert gas were investigated by differential scanning calorimetry, thermomechanical analysis, and thermogravimetry. Combining these methods with the tracing of chemical changes by Fourier transform infrared spectroscopy indicated that complex reactions, including cyclization and pyrolytic reactions occurred sequentially. An imine‐enamine tautomeric structure was formed at around 240°C and was converted to a conjugated structure when the temperature was increased to 400°C. A thermal stabilization mechanism was proposed and confirmed experimentally by using a two‐step heating process. The apparent activation energies and the pre‐exponential factors for these stabilization reactions were also estimated by the Kissinger, Ozawa, and “Improved Coats‐Redfern” methods. To obtain a fit to the experiment data, a new kinetic model, named the “Three Regions Kinetic Model,” was proposed using the Improved Coats‐Redfern method. The applicability of this model and the prediction of the stabilization profile at a given heating rate were verified by plotting conversion rate against conversion profiles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Thermal degradation and aging behavior of polytriazole polyethylene oxide-tetrahydrofuran elastomer based on click-chemistry

Polytriazole polyethylene oxide-tetrahydrofuran (PTPET) elastomer was prepared based on the click-chemistry reaction between the  CCH and  N₃ groups. The PTPET exhibits improved thermal stability with an activation energy of 204 kJ/mol compared with hydroxyl-terminated polyethylene oxide-tetrahydrofuran (PET) elastomer. TG-FTIR and pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) were used to analyze the pyrolysis mechanism and products of the PTPET elastomer. The pyrolytic mechanism of PTPET mainly involves breakage of the polyether chains. The main pyrolytic products were identified. The PTPET underwent for 180 days at 50°C and 60°C. The tensile properties, dynamic mechanical analysis (DMA) and TGA of the aged PTPET were investigated. The tensile stress and strain of the aged PTPET increased until 120 days (at 60°C) or 150 days (at 50°C), which could be attributed to the postcuring of the elastomer. The scission of the PTPET chains due to aging could dominate after aging for 120 days (at 60°C) or for 150 days (at 50°C), resulting in the reduction of mechanical properties.     

Nanostructure of potato starch. II. Structure of a highly crystalline gel obtained by retrogradation using X‐ray diffraction techniques

A highly crystalline gel (65% crystal portions) was prepared by retrogradation of injection‐molded potato starch in humid atmosphere. The different components of the nanostructure were identified by means of successive melting processes using “in situ” simultaneous wide and low angle X‐ray diffractions. At low temperatures, structural changes such as annealing phenomena or evaporation of water, giving rise to a thickening of the gel, are observed. In the range of 55–75°C, a first transition due to melting of a layered structure of concentric sphere‐like alternating crystalline and amorphous lamellar shells (amylopectine, AP, being the crystalline component) is detected. Analysis of results reveals that the AP crystallization contributes 25% to the overall crystal fraction. A spherulitic structure of alternating radial lamellae from amylose (AM) or AP melts in a higher temperature region between 75 and 86°C. This modification represents the major contribution to crystallinity of about 40%. Unexpectedly, the crystalline blocks of such a structure are abnormally anisometric; i.e., they are thicker than their width. This has been related to a contraction of the AMAP‐co‐spherulite due to an excessive growth of the AP‐shell crystals. The anisometry of the blocks of the AMAP lamellae vanishes at the beginning of the melting of the AP shell crystals, just when the total crystallinity decreases below 50% at 60°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 689–696, 2007     

Preparation and high‐temperature behavior of HfC–SiC nanocomposites derived from a non‐oxygen single‐source‐precursor

A single‐source precursor for the preparation of HfC‐SiC ceramics was synthesized via a Grignard reaction using bis(cyclopentadienyl)hafnium(IV) dichloride, trans‐1,4‐dibromo‐2‐butene, and (chloromethyl)trimethylsilane as raw materials. The composition, structure, pyrolysis process and high‐temperature behavior of the precursor were investigated. The results show that the precursor with a backbone comprising Hf–C, Si–C and CH=CH groups exhibits good solubility in common solvents, such as tetrahydrofuran, dimethylbenzene, and chloroform. Pyrolysis of the precursor at 1000°C yielded a microcrystalline HfC phase with a ceramic yield of 63.86 wt%. The pyrolytic products at 1600°C were HfC–SiC nanocomposite ceramics, which exhibited good thermal stability up to 2400°C. The formation of a (Hf,Si)C solid‐solution would be beneficial for densification during the sintering process. The non‐oxygen structure, high ceramic yield, homogeneous composition and excellent high‐temperature behavior of the pyrolytic products make the as‐prepared precursor a promising material for the preparation of high‐performance ultra‐high‐temperature ceramics.     

Packing effect on latex film formation: a photon transmission study

A photon transmission method has been used to study interdiffusion processes during film formation from hard latex particles. Films with different latex content were prepared separately by annealing poly(methyl methacrylate) (PMMA) particles above the glass transition temperature. The transmitted photon intensity from these films increases as the annealing temperature is increased. Monte Carlo simulations are performed for photon transmission through a rectangular lattice. The increase in the transmitted photon intensity (I_tr) is attributed to the latex content (film thickness) for the annealed film samples. It is observed that as the latex particles are packed (film thickness is increased) fewer voids or cracks are formed in the films. A negative absorbance coefficient has been measured above the 180 °C annealing temperature. Packing coefficients are obtained for films having various latex contents. © 2000 Society of Chemical Industry     

Fracture toughness evaluation of polytetrafluoroethylene

The objective of this preliminary work was to explore the fracture resistance of polytetrafluoroethylene (PTFE) (DuPont tradename Teflon) as part of materials characterization work related to the development of “reactive” material projectiles. Little mechanical property data is available on this material since it is commonly used only as a coating material with the dominant properties being its low friction coefficient and high application temperature. Additional end products of the “7C” derivative, however, includes sheet, gaskets, bearing pads, piston rings, and diaphragms. In this work, standard ASTM E1820 fracture toughness specimens were machined from a 14‐mm‐thick sheet of this material obtained from NSWC Dahlgren Laboratory. These specimens were tested at three test temperatures and four test rates to determine if fracture would occur in this material, and if so, how the fracture toughness depends on the test temperature and specimen loading rate. Standard axial tensile specimens were also tested at quasi‐static and elevated loading rates at temperatures from ambient to ?73°C. The major results are that while crack extension is difficult at ambient (20°C) temperature, for temperatures slightly below ambient, a rapid degradation of fracture resistance occurs. This reduction in fracture resistance is enhanced by rapid loading, and the material loses approximately 75% of its toughness (fracture energy absorption ability) at ?18°C if the crack opening loading rate of the C(T) specimen approaches 0.25 m/s. Further reductions in temperature or increases in the loading rate appear to result in a reduced rate of degradation of fracture toughness.     

Preparation and thermal response behavior of poly(N‐isopropylacrylamide‐co‐a crylic acid) microgels via soap‐free emulsion polymerization based on AIBN initiator

Poly(N‐isopropylacrylamide‐co‐acrylic acid) (poly(NIPAM‐co‐AA)) microgels with different copolymer compositions were prepared through soap‐free emulsion polymerization at 80°C, and 2, 2′‐azobisisobutyronitrile (AIBN) was used as initiator. Scanning electron microscope (SEM) characterization shows that the prepared microgels are regular and smooth and not easy to distort. Result of ¹H‐NMR characterization shows that with increasing of the initial concentration of AA (AA in feed), the AA content in polymer chains increases. The thermal response of microgels latex was investigated by UV‐3010 spectrophometer through detecting the transmittance of the latex at different temperature in the range of 190–900 nm. The thermal response of the poly(NIPAM‐co‐AA) microgels was tested by dynamic light scattering (DLS). The results show that with the increase of AA content in polymer chains, the low critical solution temperature (LCST) of microgels latex first decreases and then increases. Still, with increasing of AA in poly(NIPAM‐co‐AA) microgels, the LCST of microgels first increases and then decreases. The basic reasons causing the changes of LCST of microgels latex and microgels are interpreted clearly in this article from the perspective of hydrogen bonding interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of grafting polyacrylamide from PET films by SI‐ATRP via water‐borne system

The grafted homopolymer and comb‐shaped copolymer of polyacrylamide were prepared by combining the self‐assembly of initiator and water‐borne surface‐initiated atom transfer radical polymerization (SI‐ATRP). The structures, composition, properties, and surface morphology of the modified PET films were characterized by FTIR/ATR, X‐ray photoelectron spectroscopy (XPS), contact angle measurement, and scanning electronic microscopy (SEM). The results show that the surface of PET films was covered by equable grafting polymer layer after grafted polyacrylamide (PAM). The amount of grafting polymer increased linearly with the polymerization time added. The GPC date show that the polymerization in the water‐borne medium at lower temperature (50°C) shows better “living” and control. After modified by comb‐shaped copolymer brushes, the modified PET film was completely covered with the second polymer layer (PAM) and water contact angle decreased to 13.6°. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical strengths of epoxy resin composites reinforced by calcined pearl shell powders

A series of epoxy resin (EP) composites were prepared using ground pearl shell powders, which had been calcined at various temperatures. The EP composite containing ～ 3% weight content of the calcined pearl shell powder had the highest impact strength and the presence of silane agent was found to be essential for the composite formulation. The impact strengths of the resultant EP composites were highly influenced by the specific surface area, surface morphological structure, and chemical composition of the calcined pearl shell powder. The highest mechanical improvement was obtained for the EP composite prepared with the pearl shell powder calcined at 700°C for 3 h. The layered biopolymeric materials were completely degraded for the pearl shell powder calcined at 700°C, resulting in “sponge‐like” or “net‐like” porous calcium carbonate powder. However, the degradation of the layered biopolymeric materials was not complete for the calcinations at lower temperatures (<600°C), while calcium carbonate decomposed to form calcium oxide at higher temperatures (>800°C). The mechanical improvements of the processed EP composites have been discussed along with the chemical compositions and surface microstructures of the incorporated pearl shell powders. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pyrolytic lignin removal for the valorization of biomass pyrolysis crude bio‐oil by catalytic transformation

BACKGROUND: The catalytic processes for valorizing the bio‐oil obtained from lignocellulosic biomass pyrolysis face the problem that a great amount of carbonaceous material is deposited on the catalyst due to the polymerization of phenol‐derived compounds in the crude bio‐oil. This carbonaceous material blocks the catalytic bed and contributes to rapid catalyst deactivation. This paper studies an on‐line two‐step process, in which the first one separates the polymerizable material and produces a reproducible material whose valorization is of commercial interest. RESULTS: The establishment of a step for pyrolytic lignin deposition at 400 °C avoids the blockage of the on‐line catalytic bed and attenuates the deactivation of a HZSM‐5 zeolite based catalyst used for hydrocarbon production. The origin of catalyst deactivation is coke deposition, which has two fractions (thermal and catalytic), whose content is attenuated by prior pyrolytic lignin separation and by co‐feeding methanol. The morphology and properties of the material deposited in the first step (pyrolytic lignin) are similar to lignins obtained as a by‐product in wood pulp manufacturing. CONCLUSIONS: The proposed reaction strategy, with two steps (thermal and catalytic) in series, valorizes the crude bio‐oil by solving the problems caused by the polymerization of phenolic compounds, which are obtained in the pyrolysis of the lignin contained in lignocellulosic biomass. Given that a by‐product (pyrolytic lignin) is obtained with similar properties to the lignin from wood pulping manufacturing, the perspectives for the viability of lignocellulosic biomass valorization are promising, which is essential for furthering its implementation in biorefinery processes. Copyright © 2009 Society of Chemical Industry     

Stereocomplexed polylactides (Neo‐PLA) as high‐performance bio‐based polymers: their formation,properties, and application

Polymeric materials prepared from renewable natural resources are now being accepted as “bio‐based polymers”, because they are superior to the conventional petroleum‐based polymers in reducing the emission of carbon dioxide. Among them, poly(L ‐lactide) (PLLA) prepared by fermentation and polymerization is paid an immediate attention. Although PLLA exhibits a broad range of physico‐chemical properties, its thermal and mechanical properties are somewhat poorer for use as ordinary structural materials. For improving these inferior properties, a stereocomplex form consisting of PLLA and its enantiomer poly(D ‐lactide) (PDLA) has high potential because of showing high melting nature (230 °C). It can be formed by simple polymer blend of PLLA and PDLA or more easily with stereoblock polylactides (sb‐PLA) which are PLLA/PDLA block copolymers. These novel PLA polymers, named “Neo‐PLA”, can provide a wide range of properties that have never be attained with single PLLA. Neo‐PLA retains sustainability or bio‐based nature, because both monomers L ‐ and D ‐lactic acids are manufactured from starch by fermentation. Copyright © 2006 Society of Chemical Industry