Influence of experimental conditions on the incorporation of water droplets in polystyrene (original) (raw)
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Water-Expandable Polystyrene Using Cross-Linked Starch Nanoparticle as Water-Stabilizing Agent
Industrial & Engineering Chemistry Research, 2015
Despite several attempts to synthesize water expandable polystyrene (WEPS) beads, the product is still far from commercialization. This is mainly due to the inability of the PS beads to preserve the blowing agent (water) during storage which leads to the loss of expandability. Here we report a new generation of WEPS beads with extended shelf-life and good expandability. The beads were synthesized through Pickering emulsion polymerization in which crosslinked starch Page 1 of 31 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 2 nanoparticles (CSTNs) were used as water stabilizing agent. The synthesized beads with different CSTN content could encapsulate 5.0-12 wt.% of the water droplets of 3-4 µm in diameter. The thermogravimetric analysis showed that the entrapped water is mainly bound water with a strong adsorption to the starch nanoparticles. The bound water can be preserved over 88 % of the initial content 3 months after synthesis and therefore prolong shelf-life of the CSTNWEPS beads. The expansion behavior of CSTNWEPS beads were investigated in hot oil and at an optimized temperature of 135 °C. The best results (expansion ratio of ~7 for assynthesized beads and ~3 after 3 months) were obtained for the sample containing 1 wt.% of CSTN and 5.6 wt.% of water in the form of uniformly distributed microdroplets. Finally, the morphological investigation of the expanded beads revealed that the CSTNs not only stabilize the water microdroplets in the beads, but also reinforce the foam during expansion and inhibit the cell wall rupture.
Particle size control in dispersion polymerization of polystyrene
Canadian Journal of Chemistry, 1985
In a dispersion polymerization process, the reaction mixture starts out as 21 honiogeneous solution and the resultins polymer precipitates as spherical particles, stabilized by a steric barrier of dissolved polymer. The final polymer particle size is determined by the inherent polymer aggregation behaviour under a given set of conditions. In the present study styreile polymerization was studied in various solvents using cellulosic derivatives as the steric stabilizer. Some of these solvents in certain combinations allowed the direct preparation of particles in the micron size and thcir size distribution appeared to be highly dependent on the monomer-solvent-initiator system. lnvcstigations of these factors have suggested that monodisperse particles up to 12 p m can be prepared in a single step: studies of several systems are delineated. KAR P. LOK et CHRISTOPHER K. OBER. Can. J . Chem. 63, 209 (1985).
European Polymer Journal, 2019
Synthesis of polystyrene beads containing well-dispersed water microdroplets via surfactant free Pickering emulsion polymerization in water-in-oil emulsion followed by suspension method. The water microdroplets with a diameter of 8-15 µm were stabilized using in situ modified cellulose nanocrystals (CNCs). The morphological investigation revealed that the water droplets were surrounded by a dense layer of the modified CNCs. The thermogravimetric analysis confirmed two types of water inside the beads; free water and bound water with release temperatures of 102 and 118°C, respectively. The bound water was responsible for higher water preservation ability and therefore long shelf-life of the beads, which over 75% of the initial entrapped water was kept 7 months after synthesis. The beads can be expanded at an optimum temperature of 130°C due to water vapour pressure developed inside the beads. The best max expansion ratio of around 15 was found for the beads included 5.45 wt% of water. During the expansion process, the CNCs were located in the cell wall to reinforce it from rupturing. Eventually, we report a new type of water expanded polystyrene beads synthesized by the use of CNCs, named CNCWEPS, with good expandability and extended shelf-life.
Expandable polystyrene without any embedded blowing agent
Journal of Cellular Plastics, 2020
In this research, in-situ suspension polymerization of styrene in the presence of graphene, without any blowing agent, was investigated. Steam used in the expansion process of graphene-filled expandable polystyrene (GEPS). The dispersed graphene nano-sheets in the polystyrene matrix may absorb water in high temperatures, which evaporates by lowering the pressure and expansion precedes. The effects of graphene type and loading and steam temperature on the expansion ratio evaluated. Scanning electron microscopy (SEM) used to reveal the cross-section morphologies before and after expansion. The effect of graphene on the polymerization kinetics evaluated by differential scanning calorimetry (DSC). The results showed that by increasing the graphene loading, the rate of polymerization decreased, and the expansion ratio increased. The highest expansion ratio of about 4.8 was for particles containing 0.4% of graphene. Therefore, it was shown that by using graphene as a dispersed phase, poly...
Dynamics of Foaming of Polystyrene Particles
Macromolecular Symposia, 2006
In this work, we address the industrially relevant problem of the foaming of expandable polystyrene (PS) impregnated by pentane as a traditional downstream processing in the suspension polymerization of styrene. Once the polystyrene foam is formed by means of a proper foaming agent, e.g., pentane or fluoro-or chlorohydrocarbons, the blowing agent diffuses out from the cellular structure. Environmental efforts call for the reduced consumption of blowing agents. The dynamics of foaming of polystyrene particles was recorded video-microscopically in our laboratory as the sequence of images of expanding particle located in the small pressure cell placed under the microscope with sufficient depth of focus. The amount of pentane sorbed in PS was controlled by the length of the impregnation period and was determined independently by gravimetric measurements. Strong dependence of the structure of the produced foam and of the foaming dynamics on the amount of sorbed pentane, temperature and particle size is reported and explanations for some observed foaming phenomena are provided.
Preparation of monodisperse polystyrene spheres in aqueous alcohol system
Materials Letters, 2003
The aqueous methanol/ethanol/n-propyl systems have been exploited as dispersion medium in emulsion polymerizing of polystyrene (PS) using sodium lauryl sulfate and potassium persulfate as emulsifier and initiator, respectively. The diameter of PS spheres synthesized in aqueous methanol/ethanol/n-propyl dispersion media is 80 nm-1.15 Am/150 nm-1.3 Am/260 nm-1.65 Am. The replacement of water dispersion medium with alcohol dispersion medium can lift the upper limit of PS spheres size from 1 to 1.65 Am. A seeded growth technique based on aqueous alcohol dispersion media was developed to improve spheric-shape and monodispersity as well as increasing PS spheres size. In this technique, the styrene added for the growth of seeds is diluted with four times volume absolute alcohol, which makes the swelling process of styrene in seed (which is necessary in the conventional two-step seed growth technique) unnecessary and consequently reduces dramatically the synthesis time.
Polymer, 2006
Free-radical dispersion polymerization of styrene was carried out in ethanol and in ethanol-water mixtures in the absence and presence of carbon tetrabromide (CBr 4) as a chain transfer agent. When CBr 4 was present at the onset of the reaction, particles with a broad size distribution were obtained. If, however, the addition of CBr 4 was delayed ca 1 h, so that the particle nucleation step was complete, then 1-2 wt% chain transfer agent, dissolved in monomer plus solvent, could be added to the reaction without a deleterious affect on particle formation. The particle size and size distribution was essentially identical to that obtained in the absence of CBr 4. When more CBr 4 was added, other problems arose. These problems appeared to be due to solubility of low molar mass polymer in the reaction medium. They could be overcome by running the reaction in ethanol-water mixtures (e.g. 5 wt% water) to decrease the solubility of oligo-styrene at 70 8C, the reaction temperature. In this way, monodisperse particles could be prepared in the presence of 3 wt% CBr 4 based upon total styrene, consisting of polymers with M n Z7060, M w /M n Z2.4.
Macromolecules, 1999
Tetrahydrofuran (THF) and acetonitrile (AN) are good and poor solvents for poly(2cinnamoylethyl methacrylate) (PCEMA) and polystyrene (PS). Their mixtures with AN volume fractions between 80% and 93% are precipitants for PS but slightly solubilize the PCEMA block of a polystyreneblock-poly(2-cinnamoylethyl methacrylate), PS-b-PCEMA, sample with 380 styrene and 210 CEMA units. Immediately after the addition of AN to a THF solution of the diblock, spherical particles with PCEMA shell and PS core are formed due to phase separation. The core-shell particles then grow in size, presumably mainly due to particle coalescence, and transform into the more complex egglike, onionlike, and berrylike particles in THF/AN with 80%-90% AN before precipitation in several weeks. In THF/AN with 93% AN, no structural mutation is seen in 1 week after the formation of the spherical particles despite eventual polymer precipitation. This resistance of the spherical core-shell particles to morphological transitions may be due to the locking in of the PS core in a glassy state.