Preparation of high performance copolymer microcapsule encapsulated heat storage material without supercooling

ABSTRACT

The methyl methacrylate (MMA)-based copolymer microcapsules encapsulating Rubitherm®27 (RT27) used as a phase change material were successfully prepared by microsuspension polymerization. The influence of three types of crosslinked comonomers such as ethylene glycol dimethacrylate), trimethylolpropane trimethacrylate, and divinylbenzene (DVB) on the microcapsule formation was studied at various ratios of MMA:crosslinked comonomer. It was found that using MMA:DVB at 70:30 wt% was the optimum ratio. The obtained microcapsules were nonspherical in shape with a dent and high shell strength. In addition, the latent heats of melting and crystallization of the encapsulated RT27 were about 140 J/g-RT27 which were close to those of the original RT27. However, the crystallization temperatures (T_c) of the encapsulated RT27 (14°C) were lower than that of the original RT27 (25°C) which was called supercooling. To prevent supercooling, the effect of nucleating agents (emulgen 150, 1-octadecanol, and RT58) on decreasing supercooling of the encapsulated RT27 was investigated. The results clearly presented that the addition of at least 5 wt% of RT58 significantly increased T_c (25°C) of the encapsulated RT27, whereas the observed latent heats were pretty close to original RT27.     

Nucleation effect of hydroxyl‐purified multiwalled carbon nanotubes in poly(p‐phenylene sulfide) composites

To investigate the nucleation effect of hydroxyl‐purified multiwalled carbon nanotubes (MWNTs‐OH) in poly(p‐phenylenesulfide) (PPS), a series of composites were prepared by blending PPS with MWNTs‐OH at 1, 2, and 3 wt %, respectively. Under SEM observation MWNTs‐OH were found homogeneously dispersed in the PPS matrix. DSC thermograms revealed that the enthalpy (ΔH_c) of the composites increased with increasing MWNT‐OH content, whereas the crystallization temperature (T_c) decreased progressively. The decrease in T_c was in accordance with the smaller crystallite size determined with WXRD characterization, and the increase in ΔH_c was evidenced by FTIR and XPS analyses. The higher ΔH_c shows that MWNTs‐OH serves as a nucleating agent, providing sufficiently multiplied sites for crystal growth. The lowering of T_c was attributed not only to MWNTs‐OH network hindrance to PPS chain fusing rearrangement, but also to a poorer affinity between MWNTs‐OH and PPS; both effects coordinately govern T_c of PPS/MWNTs‐OH composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Characterization of Biomass Adsorbent ZSG-1 through Isopropanol and Water Azeotrope Dehydration

In this work, a compound starch-based adsorbent material known as ZSG-1, which was formulated in a previous work for high-capacity, low-cost ethanol dehydration, was thermodynamically assessed through dehydration of azeotropic aqueous isopropanol. Comparisons of the retention times, heats of adsorption (ΔH _s ), and Gibbs free energies (ΔG) of isopropanol and water confirmed the feasibility of using ZSG-1 in this dehydration process. Retention data were obtained by inverse gas chromatography and revealed the heat of adsorption ΔH _s to be ?55.73 kJ/mol, demonstrating that water entrapment in ZSG-1 is an exothermic physisorption process. After SEM observation, the inner micrographic pore size and surface area of ZSG-1 were calculated and estimated using an approach that combines nitrogen adsorption and mercury porosimetry. Through tests in a fixed-bed column under conditions determined by orthogonal experiment design, the optimal adsorption conditions were determined from breakthrough curves at different bed depths, bed temperatures, and kettle temperatures.     

Polyether-segmented nylon hemodialysis membranes. III. Preparation and properties of new polyether-segmented nylon

In order to apply a blood-compatible polymer to hemodialysis membrane, a new polyether-segmented nylon which dissolved in common organic solvents was designed. The basic polyether-segmented nylon was synthesized by melt polycondensation from sebacic acid, m-xylenediamine, and α,ω-bisaminopropyl-poly(ethylene oxide). To improve the solubility, azelaic acid and hexamethylenediamine were copolycondensed with the basic copolymer. The solubility was correlated with the heat of fusion (ΔH_m) of the copolymer. When ΔH_m is < 30 mJ/mg, the polymer is soluble in dimethylsulfoxide and makes a stable solution. The nonthrombogenicity was investigated in the viewpoint of adhesion of platelet onto the copolymer surface. It is made clear that the surface of the block copolymer, having > 10 wt % of poly(ethylene oxide), suppresses the adhesion of platelet, and the composition of the nylon block has no effect on the adhesion of platelet. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1723–1729, 1997     

Synthesis and characterization of oil sorbers based on docosanyl acrylate and methacrylates copolymers

Docosanyl acrylate (DCA) monomer was copolymerized with different monomer feed ratios of cinnamoyloxy ethyl methacrylate (CEMA) or methyl methacrylate (MMA) monomer to produce different compositions for DCA/CEMA or DCA/MMA copolymer with low conversions.¹H NMR spectroscopy was used to confirm the copolymer structure. DCA was crosslinked with different mol % of CEMA or MMA using dibenzoyl peroxide as initiator and various weight percentages of either 1,1,1‐trimethylolpropane triacrylates or 1,1,1‐trimethylolpropane trimethacrylates crosslinkers. The effects of monomer feed composition, crosslinker concentration, and the hydrophobicity of the copolymer units on swelling properties of the crosslinked polymers were studied through the oil absorbency tests. The network parameters, such as polymer solvent interaction (χ), effective crosslink density (υ_e), equilibrium modulus of elasticity (G_T), and average molecular weight between crosslinks (M_c), were determined and correlated with the structure of the synthesized copolymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Nonisothermal crystallization of s‐PP fractions

Syndiotactic polypropylene (s‐PP) was prepared by metallocene catalyst and was fractionated with the temperature rising elution fractionation (TREF) technique. The nonisothermal behavior of the obtained fractions was investigated. Fractions was first cooled at different rates and then heated at a constant rate. The parameters such as the peak crystallization temperature (T_c), the onset crystallization temperature (T_on), the difference between T_on and T_c (ΔT₁ = T_on − T_c), the crystallization enthalpy (ΔH), the peak melting temperatures (T_m1, T_m2), and the difference between the T_m1 and T_m2 (ΔT₂ = T_m2 − T_m1) were obtained. The dependence of these parameters on cooling rate, syndiotacticity, and molecular weight was discussed. It is found that T_c, T_on, ΔH, T_m1, and T_m2 systematically increase with increasing syndiotacticity and are depressed on increasing the cooling rate. Cooling rate, syndiotacticity, and molecular weight show different influences on ΔT₁. In the melting process of s‐PP, double peaks were observed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 897–901, 1999     

Nonisothermal crystallization of metallocene propylene–decene‐1 copolymers

The nonisothermal crystallization behavior of one metallocene‐based isotactic polypropylene and three propylene–decene‐1 copolymers was studied. The effects of comonomer content and cooling rate were investigated. It was found that comonomer units enchained systematically reduce the crystallization temperature (T_c), melting temperature (T_m), fusion enthalpy (ΔH_f), and crystallinity (X_c). Such an effect becomes more evident at a faster cooling rate. With increasing comonomer content, the supercooling required for crystallization increases and the overall crystallization rate is reduced. The Avrami equation is applicable to describe the nonisothermal crystallization kinetics of propylene–decene‐1 copolymer. It was shown that, although the reduced crystallization rate constant Z_c increases with comonomer content, the Avrami exponent decreases with comonomer content and cooling rate, leading to the smaller overall crystallization rate and larger crystallization half‐time of the copolymer with higher comonomer content. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1724–1730, 2004     

Equilibrium of benzidine inclusion adsorption on cyclodextrin copolymer

Insoluble β‐cyclodextrin (β‐CD) copolymer was prepared by reacting β‐CD with hexamethylene diisocyanate, and its inclusion adsorption behavior was investigated. The physical and chemical properties of CD copolymer were characterized by SEM, FTIR, DSC, TGA, XRD, and BET N₂ adsorption. The effects that shaking time and temperature exerted on the inclusion adsorption of benzidine on CD copolymer have been studied at relative low initial benzidine concentration. The procedure of the inclusion adsorption could be described by the Freundlich equation, and the thermodynamic constants ΔH^θ, ΔS^θ and ΔG^θ were obtained simultaneously. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Margarine-Like Emulsions Prepared with Coconut and Palm Oils: Analysis of Microstructure and Freeze–Thaw Stability by Differential Scanning Calorimetry

The objective was to study the microstructure and freeze–thaw stability of margarine-like emulsions formulated with vegetable fats using differential scanning calorimetry. Emulsions were prepared with 20% w/w dispersed aqueous phase and a continuous lipid phase composed by coconut oil (CO) and/or palm oil (PO) plus polyglycerol polyricinoleate (PGPR) as emulsifier. Mean temperature (T_M) and crystallization enthalpy (ΔH_c) were obtained from the exothermic peaks corresponding to freezing of aqueous phase. Successive cooling–heating–cooling cycles were applied to analyze changes in the exothermic peak. The emulsion prepared with CO (without PO) and 1% w/w PGPR in lipid phase showed higher water droplets size (T_M = −44.8 ± 0.1 °C) and lower quantity of stabilized aqueous phase (ΔH_c = 28.9 ± 1.2 J g⁻¹) prior to application of temperature cycles, while coalescence and (presumably) water transfer processes occurred during the treatment. The use of 2% w/w PGPR was sufficient to accomplish full stabilization of aqueous phase (T_M = −45.9 ± 0.1 °C; ΔH_c = 42.6 ± 0.3 J g⁻¹) before and after the freeze–thaw treatment. The total or partial (50%) substitution of CO by PO in emulsions with 1% w/w PGPR also improved the stability of the system, exhibiting slight microstructural changes. This enhanced stability would be linked to reduced water droplets size because of more rapid crystallization of lipid phase and immobilization of aqueous phase after emulsion preparation. In conclusion, it is possible to obtain margarine-like emulsions prepared with CO and/or PO using relatively low emulsifier concentration and maintaining a desired microstructure after freeze-thawing if the percentage ratio of both fats is controlled.     

Solvent extraction and separation of rare earths from chloride media using α-aminophosphonic acid extractant HEHAMP

Solvent extraction and separation of rare earths (REs: La ~ Lu, plus Y and Sc) by a novel synthesized extractant, (2-ethylhexylamino)methyl phosphonic acid mono-2-ethylhexyl ester (HEHAMP, abbreviated as H₂A₂), were investigated in chloride medium. The favorable separation factors (SFs) between adjacent heavy REs suggested that HEHAMP has a better separation performance than P507. The extracted complex of trivalent REs was determined to be REClH₂A₄ by the slope analysis method. Thermodynamic parameters (ΔH, ΔG, and ΔS) of Lu were calculated as 7.47 kJ mol^?1, ?6.05 kJ mol^?1, and 45.4 J mol^?1 K^?1 at 298.15 K, respectively, which indicate that the extraction reaction of Lu is an endothermic process. The loading capacity of 30% (v/v) HEHAMP toward Lu(III), Yb(III), and Y(III) was about 15.17 g Lu₂O₃/L, 14.46 g Yb₂O₃/L, and 12.64 g Y₂O₃/L, respectively. HCl is the most efficient stripping acid, and 92% of the loaded Yb(III) can be stripped by one-stage stripping with 2 mol/L HCl.     

Effect of formulation variables on the prediction of release from microparticles with experimental design

Different formulations of triamcinolone acetonide (TA) encapsulated in microparticles (MPs) based on poly(D,L ‐lactide‐co‐glycolide) (PLGA), poly(?‐caprolactone) (PCL), and poly(methyl vinyl ether‐co‐maleic anhydride) (Gantrez AN119) blends were obtained by spray‐drying with a mixture experimental design. The goal of this study was to investigate the influence of the mixture composition, particle size, particle shape, enthalpy of melting (ΔH_m) of PCL, enthalpy of depolymerization of PLGA, and glass‐transition temperature of Gantrez on drug release at pH 1.2 and 6.8. The presence of Gantrez in the MPs made PCL more amorphous because of the reduction of its ΔH_m. The determination of the activation energy (E_a) associated with TA release from the MPs was used to calculate the fitting equation of the drug‐release profile, and subsequently, a thermodynamic (Arrhenius‐like) model was established. Drug release increased as E_a and ΔH_m decreased. Our results suggest that this approach was capable of predicting in vitro TA release from these MPs, which allowed us to develop formulations with low‐release patterns at pH 1.2 and to modulate drug release at enteric pH. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4546–4553, 2006     

Taming the Beast: Measurement of the Enthalpies of Combustion and Formation of Triacetone Triperoxide (TATP) and Diacetone Diperoxide (DADP) by Oxygen Bomb Calorimetry

Low‐melting paraffin wax was successfully used as a phlegmatizing agent to perform semi‐micro oxygen bomb calorimetry of spectroscopically pure samples of the sensitive explosive peroxides TATP and DADP. The energies of combustion (Δ_cU) were measured and the standard enthalpies of formation (Δ_fH°) were derived using the CODATA values for the standard enthalpies of formation of the combustion products. Whilst the measured Δ_fH° of DADP (Δ_fH°=−598.5 ± 39.7 kJ mol⁻¹) could not be compared to any existing literature value, the measured Δ_fH° value of TATP (Δ_fH°=+151.4 ± 32.7 kJ mol⁻¹) did not correlate well with the only existing experimental value and confirmed that TATP is an endothermic cyclic peroxide.     

Synthesis and Characterization of Methylmethacrylate-alt-N-vinyl-2-pyrrolidone Initiated by Phosphorus Containing 1,2 Dipolar Compound

Copolymerization of methylmethacrylate (MMA) with 1-vinyl-2-pyrrolidone (N-VP), initiated by p-nitrobenzyl triphenyl phosphonium ylide in dioxane at 60°C for 60 min under inert atmosphere of nitrogen yields alternating copolymer as evidenced by the values of r ₁ = 0.01 and r ₂ = 0.02. The kinetic expression was R_p ∝ [I]^0.75[MMA]^1.2[VP]^1.2. The overall activation energy is 45.4 kJ/mol. The FTIR bands of OCH₃ of MMA at 1725 cm^?1 and –C=O of N-VP at 1679 cm^?1, confirms the incorporation of both the monomers in the copolymer. The glass transition temperature of the copolymer is 133°C. The GPC data shows the polydispersity index at about 1.5. The ESR spectroscopy confirm phenyl radical responsible for initiation.     

Predictions of nucleation theory applied to ehrenfest thermodynamic transitions: II. The effects of pressure and stress

This paper is a sequel to an earlier one on the applicability of classical nucleation theory to second-order transitions in the Ehrenfest sense (1). In each case the approach was to obtain the critical size r_c and energy barrier ΔG_c for the growth of a nucleus of β-phase in an α-phase matrix by a Maclaurin series expansion of the free-energy-density g = (G_β ? G_α)/v_β as a function of θ (in BC-I) and of ΔP and Δσ in this paper where θ = (T ? T_t) is the degree of undercooling and ΔP and Δσ are analogous terms for the hydrostatic pressure shift and tensile stress shift away from the equilibrium transition. The expansion coefficients were determined by the use of thermodynamic relationships. For second-order transitions, r_c = 4γv_β T_t/ΔC_pθ², r_c = 4γ/Δβ(Δp)², and r_c = 4γ/Y_αY_β(Δσ)², respectively, for the three cases. The terms ΔC_p, Δβ, and ΔY denote the differences in heat capacity, compressibility, and Young's modulus, e.g., ΔY = Y_β ? Y_α. The interfacial energy γ_αβ is denoted by γ. The activation energy barriers for the cases developed in this paper were ΔG_c = (16π/3)γ³/(Δβ)² (Δp)⁴ and ΔG_c = (64π/3)γ³Y_α²Y_β²/(ΔY)²(Δσ)⁴. More complicated expressions are given in the paper for the r_c and ΔG_c for first-order transitions. In the long run, these expressions may prove more useful than the ones for second-order because of the modifications expressions for the kinetics of transformations.     

Effects of dilution with PMMA and network formation on fluorescence from benzimidazolylphenylenes linked to PMMA network

N,N′‐5‐(2‐benzimidazolyl)‐1,3‐phenylenebis(methacrylamide) (BIPBMA) was synthesized and copolymerized with methyl methacrylate (MMA) by changing feed BIPBMA/MMA molar ratio. The swelling experiments suggest that these cross‐linked copolymers (c‐copolymers) have a polymer network structure. To compare with c‐copolymers, synthesized 3‐(2‐benzimidazolyl) phenylmethacrylamide (BIPMA) was copolymerized with MMA by changing feed BIPMA/MMA molar ratio. These linear copolymers (l‐copolymers) were dissolved in N,N‐dimethylacetamide (DMA). The fluorescence spectra of c‐copolymers were well fitted by trial‐and‐error contraction with sums of five or less of Lorentzian equations. The fluorescence spectra of l‐copolymers were so distributed that only the initial peak was fitted to a single Lorentzian equation. The fluorescence spectra of BIPBMA/DMA solutions with various concentrations were also fitted to sums of five or less of Lorentzian equations. The fitted coefficients were used to quantify dilution effect. The fluorescence intensity of c‐copolymers is higher than that of l‐copolymers in a same chromophore concentration. A relation between the intensity and the chromophore concentration shows a concentration quenching owing to chromophore aggregating for c‐copolymer, l‐copolymer, and the solution. A critical concentration point before which the intensity increases appeared in the plots of intensity against concentration for the c‐copolymer and the solution. The critical point of the c‐copolymer is higher than that of the solution and that of the l‐copolymer (if observed). This suggests that the network formation and the dilution break up the chromophore aggregates. The fluorescence spectra of c‐copolymers (1/200) adjusted by varying AIBN concentrations suggest that the fluorescence is independent of the extent of cross‐linking. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Characterization of unsaturated polyester resin cured with styrene

In this work, the curing kinetic of an unsaturated polyester resin, mixed with styrene as curing agent, was studied by means of diffential scanning calorimetry (DSC) and infrared (IR) spectroscopy. Investigations were made in situ during curing and post-curing periods. The enthalpy (ΔH_cop) characterizing the styrene homopolymerization and its copolymerization with the polyester chains was determined from isothermal DSC investigations. The residual enthalpy (ΔH_res) was determined from nonisothermal DSC measurements. We find that the quantity (ΔH_res + ΔH_cop) depends on the curing temperature (T_iso). Styrene homopolymerization and/or copolymerization lead to characteristic bonds modifications. The variations of the most characteristic bonds versus curing duration were studied from Fourier transform IR investigations. The data allow the determination of a relationship between transformation rate and curing duration using a time constant (τ) characteristic of each reaction involved during the liquid to solid-state transformation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 695–703, 1998     

Effect of Temperature on Kinetics and Adsorption Profile of Endothermic Chemisorption Process: –Tm(III)–PAN Loaded PUF System

Abstract

The sorption behavior of 3.18×10^?6 mol l^?1 solution of Tm(III) metal ions onto 7.25 mg l^?1 of 1‐(2‐pyridylazo)‐2‐naphthol (PAN) loaded polyurethane foam (PUF) has been investigated at different temperatures i.e. 303 K, 313 K, and 323 K. The maximum equilibration time of sorption was 30 minutes from pH 7.5 buffer solution at all temperatures. The various rate parameters of adsorption process have been investigated. The diffusional activation energy (ΔE_ads) and activation entropy (ΔS_ads) of the system were found to be 22.1±2.6 kJ mol^?1 and 52.7±6.2 J mol^?1 K^?1, respectively. The thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) were calculated and interpreted. The positive value of ΔH and negative value of ΔG indicate that sorption is endothermic and spontaneous in nature, respectively. The adsorption isotherms such as Freundlich, Langmuir, and Dubinin–Radushkevich isotherm were tested experimentally at different temperatures. The changes in adsorption isotherm constants were discussed. The binding energy constant (b) of Langmuir isotherm increases with temperature. The differential heat of adsorption (ΔH_diff), entropy of adsorption (ΔS_diff) and adsorption free energy (ΔG_ads) at 313 K were determined and found to be 38±2 kJ mol^?1, 249±3 J mol^?1 K^?1 and –40.1±1.1 kJ mol^?1, respectively. The stability of sorbed complex and mechanism involved in adsorption process has been discussed using different thermodynamic parameters and sorption free energy.     

Polymeric surfactants for enhanced oil recovery. IV—Thermodynamic properties of ethoxylated alkylphenol formaldehyde polymeric surfactants

The thermodynamic properties of some low molecular weight ethoxylated alkylphenol formaldehyde polymeric surfactants have been investigated. Surface tension as a function of concentration of the surfactants in aqueous solutions was measured at 28, 38, 48 and 58°C, using the spinning drop technique. From these measurements, the minimum area per molecule at the aqueous solution/air interface (A_min) was determined. The thermodynamic parameters of micellization (ΔG_mic, ΔH_mic, ΔS_mic) and of adsorption (ΔG_ad, ΔH_ad, ΔS_ad) for these polymeric nonionics were calculated. Micellization is more sensitive to ethylene oxide chain length while adsorption is more dependent on the length of the alkyl chain.     

Structural and Preliminary Explosive Property Characterizations of New 3,4,5‐Triamino‐1,2,4‐triazolium (Guanazinium) Salts

Two new highly stable energetic salts were synthesized in reasonable yield by using the high nitrogen‐content heterocycle 3,4,5‐triamino‐1,2,4‐triazole and resulting in its picrate and azotetrazolate salts. 3,4,5‐Triamino‐1,2,4‐triazolium picrate (1) and bis(3,4,5‐triamino‐1,2,4‐triazolium) 5,5′‐azotetrazolate (2) were characterized analytically and spectroscopically. X‐ray diffraction studies revealed that protonation takes place on the nitrogen N1 (crystallographically labelled as N2). The sensitivity of the compounds to shock and friction was also determined by standard BAM tests revealing a low sensitivity for both. B3LYP/6–31G(d, p) density functional (DFT) calculations were carried out to determine the enthalpy of combustion (Δ_cH (1) =−3737.8 kJ mol⁻¹, Δ_cH (2) =−4577.8 kJ mol⁻¹) and the standard enthalpy of formation (Δ_fH° (1) =−498.3 kJ mol⁻¹, (Δ_fH° (2) =+524.2 kJ mol⁻¹). The detonation pressures (P (1) =189×10⁸ Pa, P (2) =199×10⁸ Pa) and detonation velocities (D (1) =7015 m s⁻¹, D (2) =7683 m s⁻¹) were calculated using the program EXPLO5.     

Calculation of the Detonation Velocities and Detonation Pressures of Dinitrobiuret (DNB) and Diaminotetrazolium Nitrate (HDAT‐NO3)

The enthalpies of combustion (Δ_combH) of dinitrobiuret (DNB) and diaminotetrazolium nitrate (HDAT‐NO₃) were determined experimentally using oxygen bomb calorimetry: Δ_combH(DNB)=5195±200 kJ kg⁻¹, Δ_combH(HDAT‐NO₃)=7900±300 kJ kg⁻¹. The standard enthalpies of formation (Δ_fH°) of DNB and HDAT‐NO₃ were obtained on the basis of quantum chemical computations at the electron‐correlated ab initio MP2 (second order Møller‐Plesset perturbation theory) level of theory using a correlation consistent double‐zeta basis set (cc‐pVTZ): Δ_fH°(DNB)=−353 kJ mol⁻¹, −1 829 kJ kg⁻¹; Δ_fH°(HDAT‐NO₃)=+254 kJ mol⁻¹, +1 558 kJ kg⁻¹. The detonation velocities (D) and detonation pressures (P) of DNB and HDAT‐NO₃ were calculated using the empirical equations by Kamlet and Jacobs: D(DNB)=8.66 mm μs⁻¹, P(DNB)=33.9 GPa, D(HDAT‐NO₃)=8.77 mm μs⁻¹, P(HDAT‐NO₃)=33.3 GPa.