Thermal dehydrochlorination of poly(vinylidene chloride)

The kinetics of the early stages of thermal degradation below 1% dehydrochlorination of emulsion-polymerized poly(vinylidene chloride) (PVDC) is studied by the variation of the pH value of potassium hydroxide aqueous solution between 160 and 190°C in the presence of air and other gas streams. The results turned out that the thermal degradation of PVDC can be divided into three stages, which correspond to an induction period, a period with conversion below 0.1% dehydrochlorination, and that with conversion ranging from 0.1 to 1%. For the induction stage, the induction time depends upon the types of environment gas and degradation temperature. Both of the second and the third stages are zero-order reactions, which also result in the discoloration and crosslinking of the neat polymer. The average apparent activational energy of the zero-order degradation reaction was about 21 kcal/mol, which is independent of the types of environment gas. The whole degrading kinetics data can be well explained by the mechanism of a free-radical-induced dehydrochlorination. The viscosity of the degraded sample increases rapidly with degradation and becomes insoluble in regular solvents. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2035–2044, 1999     

Formation of conjugated polyene and polyyne structure by KrF excimer laser-induced dehydrochlorination on polyvinylidenechloride film

The surface dehydrochlorination of poly(vinyldenchloride) film was performed to produce a conjugated polyyne and polyene structures by photo-irradiation with a KrF excimer laser at 248 nm in a vacuum chamber. The reaction was confirmed by detection of HCl with a mass spectrometer and by measurement of chlorine content on the film with X-ray photoelectron spectroscopy. UV-visible absorption spectroscopy for the laser-treated film showed the formation of new broad absorption bands in the visible and near IR region, indicating that sequential dehydrochlorination induced the formation of conjugated carbon multiple bonds in the polymer chain. Its conjugation number is estimated to be 30 for a triple bond and 10–25 for a double bond from the peak positions on the Raman spectrum of the film. ESR spectra of laser-irradiated PVDC powder also showed long-lived radicals having a narrow band width (ΔH_pp = 0.15 mT), suggesting that the radicals were delocalized on the conjugated bonds. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2483–2487, 1998     

The role of Carica papaya latex bio-catalyst and thermal shock in water on synthesizing rice husk

A bio-catalyst made of natural resources, such as Carica papaya latex, is very challenging for nanoparticle separation. In addition, differences in thermal conditions between nanoparticles affect the movement of substances in the separation process. The study experimentally investigated the role of Carica papaya latex bio-catalyst and thermal shock in water on synthesizing rice husk (RH). The synthesis retained the Mg and C elements attached to SiO₂, which were generally neglected during the process. The study's objective was to evaluate the effectiveness of biocatalysts and thermal effects on the separation of Mg-SiO₂-C from rice husk carbon nanoparticles (CNPs-RH). The research involved various treatment processes, such as RH pyrolysis in obtaining charcoal, High energy milling (HEM) to have carbon particles, and washing to get nano-sized carbon particles. The bonding of elemental compounds to rice husk carbon particles (CPs-RH) was released using NaOH and coagulation using a bio-catalyst. Coagulated CPs-RH was injected into water at a temperature of 60–70 °C to have a thermal shock effect for H₂O clusters in Na⁺ and Mg²⁺ ions attached to the surface of the nanoparticles. Several tests were carried out, such as the SEM-EDX, TEM, XRD, and FTIR tests, to investigate the two nanoparticle clusters formed up to the nanometer scale. The results indicated that CNPs-RH nanoparticles consist of spherical particles with a diameter of 1.2 nm, while Mg-SiO₂-C nanoparticles have a diameter of 0.6 nm. Both are classified as amorphous. Based on the FTIR test, CNPs-RH is hydrophilic, while Mg-SiO₂-C is hydrophobic. Thermal shock in water strengthens the ion's mobility, increasing the interfacial dipole forces between nanoparticles and accelerating the separation process.     

利用高压水射流技术制备天然橡胶复合材料

首先利用超声空化作用将炭黑团聚体破碎、切割、分散在水中制得炭黑悬浮液,然后在高速射流场中,炭黑悬浮液被高速射流卷吸到天然胶乳中,在射流边界,由于二者存在极大的速度差,而形成一个湍流混合层,炭黑在湍流拉伸、剪切作用下微观分散到天然胶乳中.结果表明,与传统干法工艺相比,射流工艺可以使炭黑更均匀的分散到天然橡胶基体中.Payne效应结果表明射流工艺减弱了炭黑与炭黑之间的相互作用,增强了炭黑与橡胶之间的相互作用.同时射流工艺制备的复合材料硫化时间变短,硫化程度增加,硫化胶的撕裂强度提高了78%,回弹性提高了20%,DIN磨耗减小了33%.动态力学性能结果表明,射流工艺制备的复合材料在60℃左右具有更低的损耗因子.     

Polytetrafluoroethylene modification by radiation grafting of vinylidene chloride and its dehydrochlorination

A process has been designed for manufacturing a new composite material consisting of a PTFE matrix with a carbon phase implanted in the surface layer of up to 30 μm thickness. The process involves radiation graft polymerization of vinilydene chloride (VDC) from the vapor phase onto the PTFE matrix followed by dehydrochlorination of implanted PVDC. The VDC grafting kinetics, the distribution of the grafted polymer and the carbon phase, and the mechanical characteristics of the composite material have been investigated. It has been shown that unlike initial PTFE, the composite possesses good adhesive bonding properties and a small contact angle.     

Carbon Blacks Produced by Thermal Plasma: the Influence of the Reactor Geometry on the Product Morphology

Carbon black (CB) nanopowders were obtained by plasma decomposition of methane at various flow rates using inductively coupled thermal plasma torch system of 35 kW. Nitrogen was also introduced in some experiments along with the methane. Using a cylindrical shape reactor the obtained powders were composed mainly of spherical particles, non-uniform in terms of particles size with diameters between 30 and 150 nm. The shape and size of this reactor resulted in the presence of recirculation areas enabling the formation of large CB particles and other secondary volatile compounds. Changing the reactor to a conical geometry resulted in the production of CB powders showing a crystalline and flake-like morphology made of sheets having 6–16 graphitic planes. The conical shape avoids the presence of recirculation areas and promotes the formation of a uniform powder morphology throughout the reactor.     

Effects of thermal stability on the crystallization behavior of poly(vinylidene chloride)

Thermal analysis based on TGA (thermal gravimetric analysis) and DSC (differential scanning calorimeter) shows no significant degradation for PVDC which has been annealed at 210°C for less than 2 min. And the following recrystallization behavior at lower temperature (120°C) is also independent of the thermal treatment and is not affected by the difference of molecular weight. The degradation which includes dehydrochlorination at lower temperature and intramolecular cyclization or intermolecular crosslinking of the polyenes at higher temperature starts when the melting time at 210°C is more than 2 min, which also causes weight loss and heat exchange in the TGA and DSC thermograms. The recrystallization behavior of the degraded PVDC (staying at 210°C for more than 2 min) shows a strong dependence on the molecular weight. The crystallinity is decreased with the melting time at 210°C due to the increase of the degree of crosslinking. However, the POM (polarized optical microscopy) pictures and IR spectra show a favorable nucleation effect is present due to the formation of trichlorobenzene from the cyclization of the polyenes as nuclei. The crystallinity of the PVDC recrystallized at 120°C after staying at 210°C for more than 2 min is actually dependent on the molecular weight, melting time at 210°C, and cyclized or crosslinking types of degradation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3269–3276, 1999     

Effects of thermal annealing on the viscoelastic properties and morphology of bimodal hard/soft latex blends

The effects of thermal annealing on the viscoelastic properties and morphology of films prepared from bimodal latex blends containing equal weight fractions of soft and hard latex particles with controlled sizes were investigated. The thermal and viscoelastic properties of as‐dried and annealed samples were investigated with differential scanning calorimetry and dynamic mechanical analysis (DMA). Throughout the thermal annealing, the latex blend morphologies were also followed with atomic force microscopy and transmission electron microscopy (TEM). A particulate morphology, consisting of hard particles evenly dispersed in a continuous soft phase, was observed in the TEM micrographs of the as‐dried latex blends and resulted in an enhancement of the mechanical film properties at temperatures between the α relaxations of the soft and hard phases in the DMA thermograms. As soon as the thermal annealing involved temperatures higher than the glass‐transition temperature of the hard phase, the hard particles progressively lost their initial spherical shape and formed a more or less continuous phase in the latex blends. This induced coalescence of the hard particles was confirmed by the association of the experimental viscoelastic data with theoretical predictions, based on self‐consistent mechanical models, which were performed by the consideration of either a particulate or cocontinuous morphology for the bimodal latex blends. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2289–2306, 2005     

Tailoring of carboxyl‐decorated magnetic latex particles using seeded emulsion polymerization

In this research, submicron and carboxyl‐functionalized magnetic latex particles were elaborated by using seeded emulsion polymerization technique in presence of oil‐in‐water (o/w) magnetic emulsion as seed. The polymerization conditions were optimized in order to get well‐defined latex particles with magnetic core and polymer shell bearing carboxylic (–COOH) functionality. Starting from (o/w) magnetic emulsion as seed, synthesis process was performed by copolymerization of styrene (St) monomer with the cross‐linker divinylbenzene (DVB) in presence of 4,4′‐azobis(4‐cyanopentanoic acid) (ACPA) as a carboxyl‐bearing initiator. The prepared magnetic latex particles were first characterized in terms of particle size, chemical composition, morphology, magnetic properties, magnetic content, and colloidal stability using various techniques, e.g. particle size analyzer using dynamic light scattering (DLS) technique, Fourier transform infrared, transmission electron microscopy, vibrating sample magnetometer, thermogravimetric analysis, and zeta potential measurements as a function of pH of the dispersion media, respectively. The prepared magnetic latex particles were then used as second seed for further functionalization with methacrylic acid (MAA) in order to enhance carboxylic groups on the magnetic particle's surface. The results showed that final magnetic latex particles possessed spherical morphology with core‐shell structure and enriched carboxylic acid functionality. More importantly, they exhibited superparamagnetism with high magnetic content (58.42 wt%) and high colloidal stability, which considered as the main requirements for their application in the biomedical diagnostic domains. Copyright © 2017 John Wiley & Sons, Ltd.     

Latex film formation studied with the atomic force microscope: Influence of aging and annealing

The surface structure of latex dispersion films was examined with an atomic force microscope. All measurements were done in air on latex films having a minimum film formation temperature of 12°C and a glass transition temperature of 18°C. One aim of this study was to follow structural changes during film formation. Three minutes after spreading the film, its surface layer dried. Afterwards, the structure of the film did not change anymore. Only after 4 months could structural changes be observed: Though individual latex particles could be identified, the particles partly melted into one another.After annealing films at 50° or 60°C for 4 h, the latex particles partly melted into one another, but individual particles could still be identified. When annealing at or above 80°C, no individual latex particles were visible anymore. With increasing temperature the film roughness decreased from 3 nm without annealing to 0.8 nm at 100°C annealing temperature. In addition, islands of 2–4 nm thickness appeared on the film surface. These islands could be scraped off the film by increasing the force between tip and sample, indicating that they are composed of surfactant which was squeezed out of the film.     

Thermal characterization of biomass smoke particles

In this paper we present results on characterization of filter-collected redwood (Sequoia sempevirens)-needle and eucalyptus smoke particles by thermal, optical, and solvent extraction methods. Our results show that black carbon and a significant fraction of organic carbon in biomass smoke particles have similar volatility and combustion temperatures. Combustion temperatures of both black carbon and this organic fraction critically depend on the concentrations of common constituents of biomass smoke such as Na and K. These species are also known to catalyze the combustion and therefore lower the combustion temperatures by more than 100 °C. Consequently, thermal methods that rely on a specific temperature to separate organic from black carbon may either underestimate or overestimate the black and organic carbon concentrations, depending on the amounts of Na and K and on the composition and concentration of organic material present in a sample. These results suggest that more than one method must be used to accurately determine the organic and black carbon concentrations in biomass smoke particles.     

Coassembly of Nanorods and Nanospheres in Suspensions and in Stratified Films

The entropically driven coassembly of nanorods (cellulose nanocrystals, CNCs) and nanospheres (dye‐labeled spherical latex nanoparticles, NPs) was studied in aqueous suspensions and in solid films. In mixed CNC‐latex suspensions, phase separation into an isotropic latex‐NP‐rich and a chiral nematic CNC‐rich phase took place; the latter contained a significant amount of latex NPs. Drying the mixed suspension resulted in CNC‐latex films with planar disordered layers of latex NPs, which alternated with chiral nematic CNC‐rich regions. In addition, fluorescent latex NPs were embedded in the chiral nematic domains. The stratified morphology of the films, together with a random distribution of latex NPs in the anisotropic phase, led to the films having close‐to‐uniform fluorescence, birefringence, and circular dichroism properties.     

Preparation of carbon fibers/carbon/alumina tubular composite membranes and their applications in treating Cu-CMP wastewater by a novel electrochemical process

In this study, the alumina substrate was first prepared by the extrusion method, then followed by poly-vinylydenchloride (PVDC) film wrapping, PVDC carbonization, catalyst precursor coating, and the chemical vapor deposition (CVD) process to grow carbon fibers on the carbon interlayer. The carbon fibers/carbon/alumina tubular composite membranes (CCA-TCMs) thus obtained, with a pore size distribution ranging from 2 to 10 nm, were further characterized by scanning electron microscopy, transmission electron microscopy, and permporometry. A prepared CCA-TCM of this kind was incorporated into a novel simultaneous crossflow electrocoagulation and electrofiltration (EC/EF) treatment module to evaluate its capability in treating Cu-CMP (chemical mechanical polishing) wastewater. Crossflow EC/EF performance tests were carried out based on the 2³⁻¹ fractional factorial design using the electric field strength, crossflow velocity, and transmembrane pressure (TMP) as the experimental factors. Under the optimal operating conditions, the CCA-TCM associated EC/EF treatment module is capable of treating Cu-CMP wastewater in a proper manner. Permeate thus obtained had a turbidity of below 1 NTU and the removal efficiencies of total solids content, total organic carbon, copper, and silicon for Cu-CMP wastewater were 72%, 81%, 92%, and 87%, respectively.     

Preparation of monodisperse reactive styrene-glycidyl methacrylate latexes by the emulsifier-free dispersion copolymerization technique

Latexes based on styrene-glycidyl methacrylate copolymers were prepared by the emulsifier-free dispersion copolymerization technique. The main factors affecting the size and morphology of the latex particles and their distribution are the initiator concentration (K₂S₂O₈), the total ionic strength of the aqueous phase, and the total monomer concentration. The existence of critical values for these variables was demonstrated. In the range in which these factors had values below the critical, the synthesized latex particles were spherical, homogeneous, and in varied sizes, depending on the abovementioned parameters in the range of 220–500 nm. Above the critical values of these variables the latex particles consisted of spherical aggregates of smaller particles. The reactive oxirane groups of the latex particles were modified later by hydrolysis, ammonolysis, reaction with Na₂S, or periodic acid oxidation of the hydrolyzed or ammonolyzed forms of the latex particles.     

纳米SiO_2/聚丙烯酸酯复合乳液的制备与表征

根据核壳乳液聚合理论,以经过硅烷偶联剂表面改性的纳米SiO2为种子,采用适当的乳液聚合工艺,制备了纳米SiO2/聚丙烯酸酯复合乳液,并表征了其性能.结果表明,纳米SiO2经过改性后,硅烷偶联剂接枝在其表面;以其为种子制备的复合乳液具有核壳结构,其热稳定性有所提高.     

Preparation and properties of a thermo-sensitive latex film

Polymer particles with hydrophobic core and hydrophilic shell were prepared via a three-step method. First, poly(butyl methacrylate-co-methyl methacrylate) (p-(BMA-MMA)) latex was prepared through emulsion polymerization. Then, a shell of poly(glycidyl methacrylate) (p-GMA) was introduced around the p-(BMA-MMA) particles by using a redox initiation system under kinetically controlled conditions. Finally, part of the epoxy groups existing in the shell were converted into quaternary ammonium salts, resulting in an ionic hydrophilic shell. The core-shell particles could be redispersed in water to form a stable emulsion. The contact angle of the core-shell latex film with water was around 16° at 25 °C, which became larger than 90° after the film was heated at 150 °C for a short period of time. This showed that the latex film was completely switched from hydrophilicity to hydrophobicity by the action of heat. Additionally, the latex film before heat treatment could be easily washed away from the substrate with neutral water, but it could no longer be removed after the heat treatment. When an IR dye with the maximum absorption at 830 nm was incorporated into the film, it became sensitive to LD laser emitting at 830 nm and gave negative image after exposed by LD laser and developed with neutral water. This showed that the latex film might find uses in chemical-free thermal laser imaging applications.     

Degradation of vinylidene chloride/methyl acrylate/phenylacetylene (VDC/MA/PA) terpolymers. Effect of internal unsaturation on the stability of Saran copolymers

The thermal degradation of vinylidene chloride/methyl acrylate/phenylacetylene (VDC/MA/PA) terpolymers containing a constant 9 wt % methyl acrylate and small but varying amounts of phenylacetylene has been examined in the solid phase and in bibenzyl solution. Thermally promoted degradative dehydrochlorination, largely uncomplicated by methyl chloride formation, readily occurs at temperatures approaching 200°C. Incorporation of phenylacetylene into the polymer structure greatly facilitates degradative dehydrochlorination. Indeed, the presence of phenylacetylene induces the formation of polyene segments during the polymerization so that all the terpolymers, even at very low phenylacetylene loading, are tan in color. The decreased stability of polymers containing internal unsaturation arises from an increased rate of initiation for the degradation reaction. The propagation rate is largely unaffected by the level of unsaturation initially present in the polymer. Thus random double bonds have been identified as the principal defect sites responsible for the facile degradation of Saran copolymers. Species which promote the degradation of Saran polymers probably do so by facilitating the introduction of double bonds into the structure. The ratio of hydrogen chloride to stilbene formed for degradation of the terpolymers in bibenzyl solution is ca. 35:1. This is strongly reminiscent of PVDC degradation and suggests that for degradation of either the homopolymer or Saran copolymers the chain-carrying allylic radical pair does not dissociate to any appreciable extent as dehydrochlorination occurs.     

Templated assembly of polymer particles into mesoscopic clusters with well-defined configurations

We report on the fabrication of colloidal clusters through the combination of spherical particles. Polystyrene latex particles bearing amino groups on their surface were used as building blocks of the clusters. Packing of these particles with diameters of 91 and 154 nm into assemblies with defined configurations was accomplished using narrow dispersed emulsion droplets as templates. The building blocks of the clusters adhered to the oil–water interphase due to the Pickering effect. Subsequent evaporation of the dispersed phase forced them to pack into small clusters. Addition of the particles via the dispersed phase led to higher yields of clusters than if the building blocks were added via the continuous phase. All clusters had well-defined configurations. Because the dimensions of these clusters were below 400 nm, the colloidal assemblies underlay Brownian motion, which resulted in stable suspensions. The number and yields of different species could be controlled via the concentration of the building blocks and surfactant within the emulsions. Moreover, the nature of the dispersed phase itself had a strong impact on the cluster formation. When cyclohexane was used as the dispersed phase, predominately, particle doublets and triplets were obtained. The use of toluene-in-water emulsions resulted into a broader spectrum of clusters of up to 12 constituents. Such clusters could satisfy the demand for particles with complex but defined shapes and special symmetries for the fabrication of novel hierarchically organized materials.     

Synthesis of monodisperse,magnetic latex particles with polystyrene core

A novel method for producing monodisperse, submicron-sized magnetic latex particles is described. The method provides coating of polymer particles with surface-modified magnetic particles during soap-free polymerization. Experiments were performed with styrene monomer, potassium persulfate initiator, Fe ₃O ₄ magnetic particles, and silane-coupling reagents of methacryloxypropyltrimethoxysilane (MPTMS) and methacryloxypropyldimethoxysilane (MPDMS). The morphology of the magnetic particles depended on the silane-coupling reagents. Use of the tri-functional coupling reagent MPTMS produced particles having a disk-like or concave-like shape, whereas use of the di-functional coupling reagent MPDMS produced spherical particles that had a coefficient of variation of 4.4%, which was much smaller than the standard criteria of monodispersity, 10%.     

Dehydrochlorination of polyvinylidene chloride (PVDC) in the presence of crown ether as a phase transfer agent

Films of polyvinylidene chloride (PVDC) were heterogeneously dehydrochlorinated by reacting them with KF-crown and KOH-crown complexes dissolved in benzene. Solutions were in contact with an excess of unhydrous salts. This three-phase reaction was very fast at 80°C and the removal of one chlorine atom per monomer unit was completed within 1 h. Further dehydrochlorination leads to triple-bond formation and to aromatization of the system due to the intramolecular 1,6 elimination. The former reaction is dominant when KOH-crown is used as the dehydrochlorinating agent and the latter is dominant in KF-crown/CaO systems. The apparent energy of activation of the initial dehydrochlorination process is estimated to be 6.7 kcal./mol.