Amorphous Polymers’ Foaming and Blends with Organic Foaming-Aid Structured Additives in Supercritical CO2, a Way to Fabricate Porous Polymers from Macro to Nano Porosities in Batch or Continuous Processes

Organic polymers can be made porous via continuous or discontinuous expansion processes in scCO₂. The resulting foams properties are controlled by the interplay of three groups of parameters: (i) Chemical, (ii) physico-chemical, and (iii) technological/process that are explained in this paper. The advantages and drawbacks of continuous (extrusion, injection foaming) or discontinuous (batch foaming) foaming processes in scCO₂, will be discussed in this article; especially for micro or nano cellular polymers. Indeed, a challenge is to reduce both specific mass (e.g., ρ < 100 kg·m⁻³) and cell size (e.g., average pore diameter ϕ_average^pores < 100 nm). Then a particular system where small “objects” (coreshells CS, block copolymer MAM) are perfectly dispersed at a micrometric to nanometric scale in poly(methyl methacrylate) (PMMA) will be presented. Such “additives”, considered as foaming aids, are aimed at “regulating” the foaming and lowering the pore size and/or density of PMMA based foams. Differences between these additives will be shown. Finally, in a PMMA/20 wt% MAM blend, via a quasi one-step batch foaming, a “porous to nonporous” transition is observed in thick samples. A lower limit of pore size (around 50 nm) seems to arise.     

微波加热液相均匀沉淀法制备纳米Sb2O3阻燃剂(英)

Antimonyoxide(Sb2O3)isanimportantadditiveflameretardant.Itisextensivelyusedinflameretar鄄danttreatmentofpolyolefine,polyvinylchloride,polyesterandtextiles.TheefficiencyofhalogenatedflameretardantcanbeenhancedbycooperatingwithSb2O3.ThesizeofSb2O3hasgreatef…     

Effect of Supercritical Carbon Dioxide Conditions on PVDF/PVP Microcellular Foams

Supercritical carbon dioxide (ScCO₂) was used as a physical foaming agent to prepare poly(vinylidene f luoride)/poly(N-vinyl pyrrolidone) (PVDF/PVP) microstructure material. The effects of foaming conditions including saturation pressure, foaming temperature and foaming time on PVDF/PVP foams morphology, thermal and electrical behavior were systematically investigated by scanning electron microscope, differential scanning calorimeter and broadband dielectric spectrometer. Small cell and low cell density were achieved at low pressure of 12 MPa, as increasing saturation pressure, the average cell size increased first, and then decreased. The competition between the cell growth and cell nucleation played an important role in average cell size, which was directly related to ScCO₂ processing conditions. With increasing foaming temperature, cell size was increased and cell density was decreased, in a nearly linear manner. The variation of foaming time was considered to be closely related to the time for cells to grow. Thus, the results revealed that the average cell size enhanced with extending foaming time. The thermal properties of PVDF/PVP composites are slightly inf luenced by foaming parameters, and the dielectric constant of PVDF/PVP composite foams decreased with increasing volume expansion ratio.     

A comparison of softwood and birch kraft pulp fibers as raw materials for production of TEMPO-oxidized pulp, MFC and superabsorbent foam

This study compares the suitability of using birch kraft pulp or softwood kraft pulp in the preparation of TEMPO-oxidized pulp, MFC and superabsorbent foam. TEMPO oxidation was performed using five different dosages of primary oxidant. The time of disintegration treatment was varied to study its influence on the properties of the produced MFCs and foams. Both the birch and the softwood pulps could be used for producing superabsorbent foams, depending on the process conditions, the absorption capacities were about the same for the two pulps and varied between 25 and 55 g saline solution/g absorbent. The foams based on birch pulp had, however, on average, 30 % higher retention capacity than the foams based on softwood pulp. The maximum retention capacity obtained was 16.6 g saline solution/g absorbent. The greater retention capacity of birch-based foams is not fully understood, but a smaller pore size may be the reason, which in turn would generate greater capillary forces. In addition to this, it was found that birch pulps, contrary to softwood pulps, had a substantial amount of fibers that were relatively unaffected by the disintegration treatment. These oxidized fibers are likely to reinforce the foam, thereby making the foam more resistant to external pressures, which is in accordance with earlier findings.     

In vitro degradation of porous poly(dl-lactide-co-glycolide) (PLGA)/bioactive glass composite foams with a polar structure

In vitro degradation of porous 50/50, 70/30 and 90/10 PLGA (poly(dl-lactide-co-glycolide)) foams and PLGA/bioactive glass (20 wt%) composite foams was studied up to 16 weeks in TRIS (pH 7.4; 37 °C). Polar PLGA/bioactive glass composite films were prepared by applying the bioactive glass (S53P4) on one side of the composite. Porous foams were made by solvent casting and pressure quenching with CO₂. The fabricated foams had an initial pore size of 50-500 μm and thickness of 2-2.5 mm. In vitro degradation of the prepared foams was evaluated after 1, 2, 4, 6, 8, 12 and 16 weeks. Weight loss, water uptake, molecular mass and the amount of dissolved bioactive glass were measured after each time period. Changes in pore morphology were analysed with SEM. The present in vitro results will be evaluated and compared with the results from ongoing animal studies where comparable implants are used for bone defect treatment under non-load-bearing conditions.     

超声场中均匀沉淀法制备纳米Sb2O3阻燃剂(英)

Sb2O3isanessentialsynergistofalmostallthehalogenatedflameretardants.Themechanicalproper-tiesandflameretardancyofflameretardingmaterialsaregreatlyinfluencedbythesizeofSb2O3.WhennanosizedSb2O3isappliedtotheflameretardingpolymericmaterials,themechanicalprope…     

球磨时间对浆态床CO甲烷化Ni-Al_2O_3催化剂性能的影响

结合行星式球磨机,采用低温固相法制备Ni-Al_2O_3催化剂,考察了球磨时间对Ni-Al_2O_3催化剂晶相结构(XRD)、还原特征(H2-TPR)、孔道结构(BET)、粒径分布(PSD)、表面形貌(SEM)和浆态床CO甲烷化性能的影响.结果表明,球磨时间为60 min,催化剂(CT-60)平均粒径最小,为141 nm;比表面积最大,为329 m2/g.随球磨时间延长,Ni-Al_2O_3催化剂的甲烷化性能(CO转化率、CH_4选择性和CH_4收率)均先增加后减少.其中,球磨时间为60 min制备的催化剂(CT-60)甲烷化性能最佳,其CO转化率、CH_4选择性和CH_4收率分别达87.9%、8 6.8%和74.3%.结合催化剂表征可知,CT-60优异的性能与其具有较小的颗粒尺寸(141 nm)和较大的比表面积(329 m2·g-1)有很大的关联.即,催化剂颗粒尺寸越小,比表面积越大,其性能越好.     

Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel

Hydrophobic porous silica has been prepared by surface modification of TEOS (tetraethylorthosilicate) wet gel with 6 and 12 vol.% of TMCS (trimethylchlorosilane). We characterized the products by using FT-IR, TGA, DTA, N₂ adsorption/desorption, contact angle and SEM. Surface silanol groups of the gel were widely replaced by–Si(CH₃)₃ to result in a hydrophobic SiO₂ powder as confirmed by contact angle measurements with H₂O, 1-butanol and ethanol. The modified dried gels had a surface area of 950–1000 m²/g (average pore size 120 Å), compared to the non-modified surface which had a surface area of 690 m²/g (average pore size 36 Å). The adsorption/desorption isotherm curves indicated they had similar pore characteristics as aerogels prepared by the supercritical drying process.     

Structures and physical properties of rigid polyurethane foams with water as the sole blowing agent

Polyurethane rigid foams have been used for many applications such as pipelines insulation materials, automotive parts, solar water heater and construction materials[1,2], due to their desirable physical properties. Traditional rigid foam is made by the reaction of a polyol and 4,4′-diphenylmethane diisocyanate (MDI) with chlorofluorocarbons (CFCs), in particular tri- chlorofluoromethane (CFC-11) and/or HCFC-141b as blowing agents. However, the CFCs blowing agents contain halogens, whic…     

Synthesis and photocatalytic activity for water-splitting reaction of nanocrystalline mesoporous titania prepared by hydrothermal method

Nanocrystalline mesoporous TiO₂ was synthesized by hydrothermal method using titanium butoxide as starting material. XRD, SEM, and TEM analyses revealed that the synthesized TiO₂ had anatase structure with crystalline size of about 8 nm. Moreover, the synthesized titania possessed a narrow pore size distribution with average pore diameter and high specific surface area of 215 m²/g. The photocatalytic activity of synthesized TiO₂ was evaluated with photocatalytic H₂ production from water-splitting reaction. The photocatalytic activity of synthesized TiO₂ treated with appropriate calcination temperature was considerably higher than that of commercial TiO₂ (Ishihara ST-01). The utilization of mesoporous TiO₂ photocatalyst with high crystallinity of anatase phase promoted great H₂ production. Furthermore, the reaction temperature significantly influences the water-splitting reaction.     

Thermal Stability of Pt/Al2O3 Catalysts Prepared by Sol-Gel

A series of Pt/Al₂O₃ catalysts were prepared using a sol-gel method. The influence of several parameters used in the synthesis including: metal content, identity of the metal precursor, and the water/alkoxide ratio on the structural properties of the fresh (dried) and calcined samples were studied. It was found that the BET surface area decreased with an increase in the platinum content. A surface area of 500 m²/g was obtained following calcination at 773 K. The structure of fresh samples as determined by FTIR corresponded to that of a pseudoboehmite structure. Samples prepared using a water/alkoxide ratio (H₂O/ATB) of 9 showed a well-defined, uniform pore size distribution following calcination at 773 K. Metal dispersions comparable to those obtained using impregnation methods were obtained. Aging studies (calcination at 873 K for 24 h) performed on these catalysts, exhibited sintering behavior which were similar to Pt/Al₂O₃ catalysts prepared by other methods. The sample prepared using a H₂O/ATB ratio of 9 had the highest surface area and was more thermally resistant towards metal sintering. A bimodal metal particle size distribution was observed: some particles exhibited sintering while others of similar size showed a greater thermal stability to sintering. The sample having the largest surface area and the highest thermal stability following thermal treatment was a consequence of a more condensed structure and a higher pore roughness obtained after drying the gel. This enabled the formation of an alumina structure which was more amorphous and limited aggregation of platinum particles due to surface diffusion within the pore structure.     

Formation of TiO2 ceramic foams from the integration of the sol–gel method with surfactants assembly and emulsion

A general and potentially easy method for synthesizing TiO₂ ceramic foams presenting hierarchical architecture of meso and macropores is presented here. The ceramics foaming method is based on the integration of the sol?Cgel process with sodium dodecyl sulfate (SDS) surfactant and oil droplets of isopropyl myristate (IPM) as dual pore templates. The main aim of this study was to evaluate the effect of ionic surfactant on the porous structure and specific surface area. The structural feature of these materials was characterized by analyzes of X-ray diffraction, nitrogen absorption/desorption isotherms, Hg porosimetry, He and Dried-Fluid^? picnometers. Mercury intrusion porosimetry shows that SDS and IPM induce the formation of hierarchical structure composed of two families of pores, namely macro and mesopores. The relative population of each family and the average size of macropores could be finely tuned by adjusting the SDS quantity. In the presence of this surfactant, a single anatase crystalline phase was observed for titania foams fired at 600?°C.     

制备工艺对NiFe2O4分解CO2活性的影响

随着大气中CO2浓度的增加,温室效应日趋严重,促使人们对大气中CO2的转化与消除这一课题更加重视。1990年Yutaka Tamaura[1]发现氧缺位磁铁矿几乎可以100%分解CO2后,为解决温室效应提供了一条新的探索途径。通过对不同铁酸盐MFe2O4(M=Fe,Mn[2],Co[3],Zn[4],Ni[5]等)分解CO2活性的考察,发现铁酸镍在300℃分解CO2的活性比其它铁酸盐都好。NiFe2O4的制备最常采用的是共沉淀法、柠檬酸溶胶凝胶法和水热法,3种方法由于制备     

The effects of silica gel (carrier) on the activity (hydrogen yield) of photocatalytic decomposition of water over [pol-Ti(OBu)4 + CH3OH]-complex

A significant effect of pore size has been found on the yield of photolysis of water to hydrogen, ozone (oxidising product) and methane (decomposing product of catalyst or solvent) using [pol-Ti(OBu)₄ + CH₃OH]-complex/SiO₂. The pore structure of silica gel has been found to provide good conditions for forming this type of catalyst.     

Bioactive ceramics in the CaO-Al2O3-P2O5-ZnO system prepared by the sol-gel technology

The sol-gel method was applied to the synthesis of porous bioactive glass-ceramic materials in the Ca-Al₂O₃-P₂O₅-ZnO system when compositions were chosen in the glass formation range. Aluminium sol and soluble inorganic salts of the other components have been used as starting materials. The sol-gel transition was achieved by controlling the pH value of the medium. After drying the gel products were thermally treated up to 800°C, Phase formation was studied by X-ray diffraction, IR spectroscopy and electron microscopy.It was found that the main crystalline phases in the glass ceramics were C(PO₃)₂ and Ca₂P₂O₇. The amorphous powder was sintered to form ceramic materials with average pore size distribution of 150–200 µm by isostatic pressing and heat treatment at 500–600°C. This glass ceramic is more bioactive than hydroxylapatite in the initial stage after implantation.     

Evidence of mechanisms occurring in thermally induced phase separation of polymeric systems

Thermally induced phase separation is a fabrication technique for porous polymeric structures. By means of easy‐to‐tune processing parameters, such as system composition and demixing temperature, a vast latitude of average pore dimensions, pore size distributions, and morphologies can be obtained. The relation between demixing temperature and morphology was demonstrated via cloud point curve measurement and foams fabrication with controlled thermal protocols, for the model system poly‐l ‐lactide–dioxane–water. The morphologies obtained at a temperature lower than cloud point showed a closed‐pore architecture, suggesting a “nucleation‐and‐growth” separation mechanism, which produced larger pores at higher holding times. Conversely, the porous structures attained when holding the sample above the cloud point exhibited open pores with dimensions independent of time, denoting a phase separation occurring during sample freezing. Finally, the influence of the cooling rate on final morphology was investigated, showing a clear correlation with microstructure and pore size. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 979–983     

Single-Sided Portable NMR Investigation to Assess and Monitor Cleaning Action of PVA-Borax Hydrogel in Travertine and Lecce Stone

In this work, we investigated the potential of PVA-borax hydrogel for cleaning limestones and the dependence of the cleaning on the porosity of the rock and on the action time of the hydrogel treatment. Towards this goal, we used a nuclear magnetic resonance (NMR) spectrometer, developed for non-invasive and non-destructive applications on cultural heritage. T₂-NMR parameters were quantified on different samples of Lecce stone and Travertine cut perpendicular (Pe) and parallel (Pa) to the bedding planes under different experimental conditions: untreated samples, treated with Paraloid B72 and cleaned with PVA-PEO-borax hydrogel applied for 4 min and 2 h. The T₂ results suggest that the effectiveness of the cleaning strongly depended on the porosity of the stones. In Lecce stone, the hydrogel seemed to eliminate both the paramagnetic impurities (in equal measure with 4 min and 2 h treatment) and Paraloid B72. In Travertine Pe, characterized by a smaller pore size compared to Lecce stone, no significant effects were found regarding both the cleaning and the treatment with Paraloid B72. In Travertine Pa, characterized by a larger pore size than the other two samples, the hydrogel seemed to clean the paramagnetic agents (it worked better if applied for a longer time) but it did not appear to have any effect on Paraloid B72 removal.     

以氨水和碳酸铵为沉淀剂制备氧化铝的对比研究

γ-Al2O3，是一种常用的催化剂载体，它具有比表面大和价廉易得等优点。但对于很多高温反应体系，如汽车尾气催化净化，其热稳定性在很大程度上影响了汽车尾气净化催化剂的活性和稳定性，因此提高γ-Al2O3的高温热稳定性对保持汽车尾气净化催化剂的反应活性、延长催化剂的使用寿命非常重要。     

Preparation and structure characterization of carbons prepared from resorcinol-formaldehyde resin by CO2 activation

In this work, carbon xerogels with a high pore volume and surface area (up to 2.58 cm³/g and 3200 m²/g respectively) have been synthesized using the sol-gel polycondensation of resorcinol (R) with formaldehyde (F) in a basic medium of monoethanolamine (MEA), followed by drying and pyrolysis. This medium (MEA) has not been used in previous investigations. The effect of activation with CO₂ on the pore size distribution and the chemical functional groups has been investigated using N₂ (77 K) adsorption, FTIR and elemental analysis techniques. A series of experiments has been conducted to investigate the effect of activation time and activation temperature. Activation of the samples was carried out at 850, 900 and 980 °C for times ranging from one to three hours. Within the range of activation conditions, an increase in activation time at 850 °C results in a continuous steady rise of the BET surface area and total pore volume. However, at the two higher temperatures, the surface area shows a maximum when plotted against activation time. FT-IR results show that the use of MEA as a catalyst leads to the formation of nitrogen functional groups in the surface of the resin.     

Polymer‐Derived Silicoboron Carbonitride Foams for CO2 Capture: From Design to Application as Scaffolds for the in Situ Growth of Metal–Organic Frameworks

A template‐assisted polymer‐derived ceramic route is investigated for preparing a series of silicoboron carbonitride (Si/B/C/N) foams with a hierarchical pore size distribution and tailorable interconnected porosity. A boron‐modified polycarbosilazane was selected to impregnate monolithic silica and carbonaceous templates and form after pyrolysis and template removal Si/B/C/N foams. By changing the hard template nature and controlling the quantity of polymer to be impregnated, controlled micropore/macropore distributions with mesoscopic cell windows are generated. Specific surface areas from 29 to 239 m² g^?1 and porosities from 51 to 77 % are achieved. These foams combine a low density with a thermal insulation and a relatively good thermostructural stability. Their particular structure allowed the in situ growth of metal–organic frameworks (MOFs) directly within the open‐cell structure. MOFs offered a microporosity feature to the resulting Si/B/C/N@MOF composite foams that allowed increasing the specific surface area to provide CO₂ uptake of 2.2 %.