Latent Heat Enhancement of Paraffin Wax in Poly(divinylbenzene-co-methyl methacrylate) Microcapsule

The preparation of divinylbenzene (DVB)-methyl methacrylate (MMA) copolymer microcapsule encapsulated Rubitherm27 (RT27) P(DVB-co-MMA)/RT27 used as heat storage material by the microsuspension polymerization was studied to improve the latent heats of the encapsulated RT27 with sufficient polymer shell strength. Percent loading of RT27 and DVB:MMA ratio were optimized. The optimal condition was 30% loading of RT27 and 30:70 (% w/w) of DVB:MMA ratio. The nonspherical microcapsules with a dent having core-shell morphology were obtained. The thermal properties of the encapsulated RT27 in the P(DVB-co-MMA)/RT27 capsules were measured by thermogravimetric analyzer and differential scanning calorimeter. The heats of melting (ΔH_m; 153 J/g-RT27) and crystallization (ΔH_c; 164 J/g-RT27) of the encapsulated RT27 in the prepared copolymer capsules were higher than those in PDVB and closed to those of bulk RT27 (162 and 168 J/g-RT27 for ΔH_m and ΔH_c, respectively).     

Poly(divinylbenzene) Microencapsulated Octadecane for Use as a Heat Storage Material: Influences of Microcapsule Size and Monomer/Octadecane Ratio

Poly(divinylbenzene) (PDVB) microencapsulated octadecane (OD) (PDVB/OD) used as heat storage material were prepared by suspension polymerization at 70°C using benzoyl peroxide and polyvinyl alcohol as initiator and stabilizer, respectively. The influence of microcapsule size and divinylbenzene (DVB)/OD weight ratio on the microcapsule shape and thermal properties of encapsulated OD were considered. Thermal properties and thermal stability of PDVB/OD microcapsules were determined using differential scanning calorimeter (DSC) and thermogravimetric analyzer. The optical micrographs and scanning electron micrographs showed that the microcapsules have spherical shape only in the case of 50/50 (%w/w) of DVB/OD whereas they were nonspherical with the decreasing of DVB content. However, the core materials were still well encapsulated even increasing the OD content to 70%wt. From DSC analysis, in all cases, the melting temperature of encapsulated OD (28°C) was almost the same as that of bulk OD (30°C), yet it was quite different in the case of crystallization temperature (≤ 19°C and 25°C for encapsulated and bulk OD, respectively). The latent heats of melting and crystallization of encapsulated OD, in all conditions, were reduced from those of bulk OD (242 and 247 J/g, respectively).     

Innovative and high performance synthesis of microcapsules containing methyl anthranilate by microsuspension iodine transfer polymerization

In this research, preparations of polymer microcapsule encapsulated methyl anthranilate (MA) as an essential oil model by both microsuspension conventional radical polymerization (ms CRP) and microsuspension iodine transfer polymerization (ms ITP) using methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) copolymer as the polymer shell were studied. In the case of ms CRP, a large amount of free polymer particles nucleated in aqueous medium were obtained. Using ms ITP, the free polymer particle formation was significantly depressed. Iodoform (CHI₃) as a chain transfer agent with 0.8 wt% relative to the monomer, such a phenomenon was not observed. Various emulsifiers (oleic acid, Span 80 and PEG 30 dipolyhydroxystearate (DPHS)) with low hydrophile–lipophile balance value were used to retain MA in the monomer droplets or polymerizing particles. DPHS is the most effective emulsifier to retain MA in microcapsules giving 58% encapsulation at 20 wt% of DPHS relative to MA. In addition, from the controlled release study, only 55 wt% of the encapsulated MA was released by 90 days. Polymer microcapsule encapsulated MA using an MMA‐EGDMA copolymer shell with a high percentage of encapsulation and without free polymer particles was successfully prepared for the first time. Based on slow release of the encapsulated MA, the prepared microcapsules could be used in various applications. © 2017 Society of Chemical Industry     

Preparation,characterization, and prominent thermal stability of phase‐change microcapsules with phenolic resin shell and n‐hexadecane core

Microcapsules with phenolic resin (PFR) shell and n‐hexadecane (HD) core were prepared by controlled precipitation of the polymer from droplets of oil‐in‐water emulsion, followed by a heat‐curing process. The droplets of the oil phase are composed of a polymer (PFR), a good solvent (ethyl acetate), and a poor solvent (HD) for the polymer. Removal of the good solvent from the droplets leads to the formation of microcapsules with the poor solvent encapsulated by the polymer. The microstructure, morphology, and phase‐change property as well as thermal stability of the microcapsules were systematically characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimety (DSC), and thermogravimetric analysis (TGA). The phase‐change microcapsules exhibit smooth and perfect structure, and the shell thickness is a constant fraction of the capsule radius. The initial weight loss temperature of the microcapsules was determined to be 330°C in N₂ and 255°C in air, respectively, while that of the bulk HD is only about 120°C both in air and N₂ atmospheres. The weight loss mechanism of the microcapsules in different atmosphere is not the same, changing from the pyrolysis temperature of the core material in N₂ to the evaporation of core material caused by the fracture of shell material in air. The melting point of HD in microcapsules is slightly lower than that of bulk HD, and a supercooling was observed upon crystallization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation of polyacrylate/paraffin microcapsules and its application in prolonged release of fragrance

The purpose of the present work was to develop a fragrance encapsulation system using polyacrylate/paraffin microcapsules. The Polyacrylate/paraffin microcapsules were fabricated by the method of suspension polymerization in Pickering emulsion. Morphology, size distribution, and thermal resistance of polyacrylate/paraffin microcapsules were investigated by scanning electron microscopy, light scattering particle size analyzer, and thermogravimetric analyzer. Results indicated that the crosslinked PMMA/paraffin microcapsules and P(MMA‐co‐BMA)/paraffin microcapsules prepared under optimal conditions presented regular spherical shape and similar size distribution. The crosslinked P(MMA‐co‐BMA)/paraffin microcapsules exhibited better thermal stability, with a thermal resistance temperature up to 184 °C. Fragrance microcapsules were prepared by encapsulating fragrance into crosslinked P(MMA‐co‐BMA)/paraffin microcapsules. The prolonged release performance of fragrance microcapsules was measured by ultraviolet‐visible near‐infrared spectrophotometer. 63.9% fragrance was retained after exposing fragrance microcapsules in air for 3 months, and the fragrance continued to release over 96 h in surfactant solution (sodium lauryl sulfonate, 20 wt %). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44136.     

Relationship between crystallization behavior, microstructure, and mechanical properties in a palm oil-based shortening

In this study, the effects of cooling rate, degree of supercooling, and storage time on the microstructure and rheological properties of a vegetable shortening composed of soybean and palm oils were examined. The solid fat content vs. temperature profile displayed two distinct regions: from 5 to 25°C, and from 25°C to the end of melt at 45–50°C. A peak melting temperature of 42.7°C was determined by DSC. Discontinuity in the crystallization induction time (determined by pulsed NMR) vs. temperature plot at 27°C also suggested the existence of two separate groups of crystallizing material. Isothermal crystallization kinetics were characterized using the Avrami and Fisher-Turnbull models. In using DSC and powder X-ray diffraction, the α polymorph formed upon fast cooling (>5°C/min), and the β′ form predominated at lower cooling rates (<1°C/min). An α to β′ transition took place upon storage. Fractal dimensions (D _f ) obtained by microscopy and image analysis showed no dependence on the degree of supercooling since D _f remained constant (∼1.89) at crystallization temperatures of 5, 22, and 27°C. Crystallization at 22°C at 1°C/min and 15°C/min yielded D _f values of 1.98 and 1.93, respectively. Differences in microstructure were observed, and changes in particle properties increased the parameter λ at higher degrees of supercooling.     

Preparation and Properties of Thermoplastic Expandable Microspheres With P(VDC-AN-MMA) Shell by Suspension Polymerization

Thermoplastic expandable microspheres (TEMs) having core/shell structure were prepared via suspension polymerization with vinylidene chloride (VDC), acrylonitrile (AN), and methyl methacrylate (MMA) as monomers and i-butane as blowing agent. TEMs were about 20 µm in diameter and had a hollow core containing i-butane. The influence of the monomer feed ratio and blowing agent content was researched. When the monomers composition of 58.4 wt% VDC, 28 wt% AN, 13.6 wt% MMA, and 32 wt% i-butane in oil phase, suspension polymerization could yield TEMs having good expansion properties. The maximum expansion volume was 25 times of original volume at about 111–120°C, the blowing agent content in microspheres was about 21.5 wt%. The T_m.e, T_o.e, and T_o.s. of the TEMs increased with the VDC content in the polymerizable monomers decreasing.     

Lamellar thickness transition of melt-crystallized polybuten-1 tetragonal phase: configurational change in chain folding directions

Lamellar crystal thickness l _c of isotactic polybutene-1 (it-PB1) have been investigated for crystallization in the melt over a wide range of crystallization temperature T from 40°C to 90°C by small angle X-ray scattering experiments and density measurements. The crystal thickness l _c demonstrates two linear dependences on inverse supercooling and a transition from one dependence to the other has been observed around T = 65°C. Each of the two dependences obeys the nucleation theory in the high and low supercooling ranges, respectively. Chain folding free energy q determined from the low supercooling range is larger than that determined from the high supercooling range. Possible mechanisms for the transition are discussed taking account of entropy of chain folding directions.     

Thermal Activation of Mendable Epoxy through Inclusion of Microcapsules and Imidazole Complexes

Epoxy resin was encapsulated in poly(urea–formaldehyde) microcapsules using an in situ dispersion polymerization technique. The efficiency of Ni and Cu–imidazole complexes as latent hardeners was compared to that of 2-methylimidazole. Calorimetric studies revealed higher reactivity of the nickel complex toward oxirane functionalities. Both the complexes could effectively cure the epoxy released from within the microcapsules in the event of damage followed by thermal treatment. The curing could be effected at lower temperature (T_onset = 145°C) using [Ni(2-Me-ImidH)₄Cl]Cl as compared to [Cu(2-Me-ImidH)₄Cl]Cl (T_onset = 152°C). A healing efficiency of 100 ± 2% could be achieved at 30% microcapsule loading, irrespective of the type of metal complex used.     

Initiation system effects in the cationic copolymerization of tetrahydrofuran (THF)

Summary Macromonomeric peroxy initiator, poly tetrahydrofuran (poly-THF=inimer) were synthesized via cationic polymerization of THF by the mono- (t-BuBP) and tetra-bromo methyl benzoyl peroxides (BDBP)/ZnCl₂ initiating system. The macromonomers were characterized by ¹H-NMR, IR, and GPC techniques. Methyl methacrylate (MMA) polymerization initiated by poly-THF inimers at 80°C and different times in bulk gave crosslinked poly-THF-b-polymethyl methacrylate block copolymers. Swelling ratios of the crosslinked block copolymers obtained by taking in same amounts of poly-THF inimer and MMA monomer in CHCl₃ were decreased versus time. It was compared the results obtained from t-BuBP-, BDBP-ZnCl₂ initiating systems with t-BuBP-, BDBP-AgSbF₆ initiating systems for THF monomer. Poly(THF-b-MMA) crosslinked block copolymers containing undecomposed peroxide groups initiated the thermal polymerization of styrene, S, were used to obtain poly(THF-b-MM_A-b-S) crosslinked multicomponent copolymers at 90°C. The crosslinked multi component copolymers were investigated sol-gel analysis and swelling ratios in CHCl₃. "Active" poly(THF-b-MM_A) having peroxygen group were used in the free radical coupling reaction of poly butadien (Poly Bd). Poly(THF-b-MM_A)-polybutadien crosslinked blend soluble graft copolymers were obtained. Received: 31 July 2001/Revised version: 16 June 2002/ Accepted: 5 July 2002     

Modification of porous suspension‐PVC particles by stabilizer‐free aqueous dispersion polymerization of absorbed monomers

The modification of porous PVC particles by an in‐situ stabilizer‐free polymerization/crosslinking of a monomer/crosslinker/peroxide solution absorbed within the PVC particles is presented. The modifying crosslinked polymers are polystyrene (PS) crosslinked with DVB (divinyl benzene), polymethyl methacrylate (PMMA) crosslinked with ethylene glycol dimethacrylate (EGDMA), and styrene‐MMA copolymer crosslinked with DVB. The modified PVC particles characterization includes polymerization yield, non‐extractables, ¹³C solid‐state CPMAS NMR, porosity measurements and also morphology and dynamic mechanical behavior (DMTA). The levels of nonextractable fractions found and ¹³C solid‐state CPMAS NMR results are indicative of low chemical interaction in the semi‐IPN PVC particles. Particle porosity levels and SEM observations indicate that styrene and MMA mainly polymerize within the PVC particles' bulk and just small amounts in the pores. MMA polymerization in the PVC pores is as crusts covering the PVC pore surfaces, whereas styrene polymerization in the PVC pores is by filling the pores. Dynamic mechanical studies show that tanδ and the storage modulus curves are influenced by the incorporation of PS and XPS but not by the incorporation of PMMA and XPMMA.     

Biobased composite resins design for electronic materials

Biobased materials developed from triglycerides contain a large variety of structures, which makes it difficult to predict their properties. In this study, we used a structure–property relation to design biobased materials, both theoretically and experimentally. A general equation to predict the crosslink density in terms of the level of chemical functionalities of the triglycerides was derived and used as a design rule for high‐crosslinked polymer materials. The twinkling fractal theory and the Clausius–Mossotti equation were used to guide two approaches of synthesis to improve the properties of the biobased thermosets: the biobased resin acrylated epoxidized soybean oil (AESO) was either crosslinked with divinylbenzene (DVB) or chemically modified by phthalic anhydride. The DVB‐crosslinked resins had a 14–24°C increase in their glass‐transition temperatures (T_g′s), which was dependent on the crosslink densities. T_g increased linearly as the crosslink density increased. Phthalated acrylated epoxidized soybean oil (PAESO) had an 18–30% improvement in the modulus. The dielectric constants and loss tangents of both DVB‐crosslinked AESO and PAESO were lower than conventional dielectrics used for printed circuit boards (PCBs). These results suggest that the new biobased resins with lower carbon dioxide footprint are potential replacements for commercial petroleum‐based dielectric materials for PCBs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of paraffin microcapsules for energy-saving applications

A series of microencapsulated phase-change materials (PCMs) with styrene–divinyl benzene shells composed of an n-octadecane (OD or C₁₈)–n-hexadecane (HD or C₁₆) mixture as the core were synthesized by an emulsion polymerization method. The effects of the core/shell ratio (C/S) and surfactant concentration (C_surf) on the thermal properties and encapsulation ratios of the PCMs were investigated. The chemical structures and morphological properties of the microcapsules were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy analysis, respectively. The characteristic peaks of the paraffin mixtures and shell material located in the FTIR spectrum of the microencapsulated PCMs proved that the encapsulation of the PCM mixture was performed successfully. The thermal properties of the paraffin microcapsules were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis. DSC analysis demonstrated that the microcapsules containing the maximum amount of paraffin mixture (C/S = 2:1) and the minimum C_surf (45 mmol/L) had the highest latent heat value of 88 kJ/kg and a latent heat of temperature of 21.06°C. Moreover, the maximum encapsulation ratio of the paraffin mixture was found to be 56.77%. With respect to the analysis results, the encapsulated binary mixture, which consisted of OD–HD with a poly(styrene-co-divinyl benzene) shell, is a promising material for thermal energy storage applications operating at low temperatures, such as in the thermal control of indoor temperatures and air-conditioning applications in buildings for desirable thermal comfort and energy conservation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47874.     

Crystaline polymers as heat storage materials in passive thermal protection systems

Previous studies have evaluated low molecular weight crystalline materials as latent heat sinks for passive thermal protection systems. This study evaluated crystalline polymers as heat storage materials. Differential scanning calorimetry and Instron thermomechanical analysis are applied in dynamic studies of cumulative histories of melting and recrystallization. Commercially available crystalline polymers with melting temperatures T_m ≥ 100°C can provide fully reversible heats of fusion ΔH_m ≥ 35 cal/gm under programmed heating-cooling cycles. A linear polyethylene (Marlex 6050) is modified by radiation crosslinking to retain shape stability above T_m with-out loss of heat storage capability. The essentially zero vapor pressure and inherent shape stability of crosslinked crystalline polymers may provide unique advantages as uncontained, non-expendable, heat storage materials.     

Preparation of coated thermo‐regulating textiles using Rubitherm‐RT31 microcapsules

Spherical microcapsules with a 49 wt % of Rubitherm^® RT31 were successfully synthesized by means of suspension‐like polymerization to be used for textile applications in summer conditions. Microcapsules were fixed into seven fabric substrates for different textile applications by a coating technique without deteriorating original functionalities of the textiles. Thermal performance of different coated textiles with 35 wt % of microcapsules was evaluated by differential scanning calorimetry (DSC) and infrared thermography (IR) techniques and the physical characteristics of textiles with thermo‐regulating properties were examined by environmental scanning electron microscopy (ESEM). It was observed that all treated textile substrates allow to obtain thermo‐regulating properties with acceptable latent heat storage capacities. Results also indicated that the presence of microcapsules containing Rubitherm^® RT31 produces a significant thermal insulation effect during a cold to warm transition (20–45°C). Thus, this kind of microcapsules can be used to obtain textiles with thermal comfort‐related properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Evaluation of tripalmitin crystallization in sesame oil through a modified avrami equation

Tripalmitin (TP) crystallization in sesame oil solutions (0.98, 1.80, and 2.62%, wt/vol) was investigated by utilizing a modification of the Avrami equation. The modified equation retains the original correspondence to the nucleation process (i.e., n) and crystal growth and simply corrects the value of the crystallization rate constant (z) by eliminating the influence of n. The energy of activation (E _a ) values for TP crystallization in sesame oil solution, calculated with the modified z, were quite similar to those calculated with the reciprocal of time required to achieve 50% of TP crystallization (t _F =0.50⁻¹). However, E _a values calculated with z from Avrami’s original equation were quite different from those obtained with t _F =0.50⁻¹. Thus, z and E _a values calculated through the Avrami equation yield erroneous results, especially when comparing crystallization processes having different magnitudes of n, as in this study. Additional analysis that considered the viscosity of the TP oil solutions concluded that, at equal supercooling conditions (e.g., 22.0–22.5), the magnitude of z and E _a became more dependent upon the crystal growth process as oil viscosity decreased. In contrast, as viscosity of the oil phase increased, the main crystallization process, evaluated through z and E _a′ was nucleation. Furthermore, within the supercooling interval achieved at the temperatures utilized, the increase in supercooling at constant viscosity conditions (e.g., 5.25–5.5 dynes/cm²) would produce a higher degree of nucleation without an appreciable effect on TP crystal size. The results obtained indicate that investigating the effects of supercooling, molecular diffusion (i.e., viscosity) and TP concentration on the magnitude of z and E _a during TP crystallization in sesame oil requires a multiple variable statistical approach.     

Effect of crosslinkers on the preparation and properties of ETFE‐based radiation‐grafted polymer electrolyte membranes

This study concerns a comparative study of three crosslinkers, divinylbenzene (DVB), 1,2‐bis(p,p‐vinylphenyl)ethane (BVPE), and triallyl cyanurate (TAC) crosslinked poly(ethylene‐co‐tetrafluoroethylene) (ETFE)‐based radiation‐grafted membranes, which were prepared by radiation grafting of p‐methylstyrene onto ETFE films and subsequent sulfonation. The effect of the different types and contents of the crosslinkers on the grafting and sulfonation, and the properties such as water uptake, proton conductivity, and thermal/chemical stability of the resulting polymer electrolyte membranes were investigated in detail. Introducing crosslink structure into the radiation‐grafted membranes leads to a decrease in proton conductivity due to the decrease in water uptake. The thermal stability of the crosslinked radiation‐grafted membranes is also somewhat lower than that of the noncrosslinked one. However, the crosslinked radiation‐grafted membranes show significantly higher chemical stability characterized in the 3% H₂O₂ at 50°C. Among the three crosslinkers, the DVB shows a most pronounced efficiency on the crosslinking of the radiation‐grafted membranes, while the TAC has no significant influence; the BVPE is a mild and effective crosslinker, showing the moderate influence between the DVB and TAC crosslinkers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4565–4574, 2006     

Modification of poly(butylene succinate) with peroxide: Crosslinking,physical and thermal properties,and biodegradation

Prior to curing, we evaluated thermal stability of poly(butylene succinate) (PBS). Above 170°C, PBS was severely degraded and the degradation could not be successfully stabilized by an antioxidant. PBS was crosslinked effectively by DCP at 150°C, and the gel fraction was increased as DCP content increased. The major structure of crosslinked PBS is supposed to consist of an ester and an aliphatic group. The tensile strength and elongation of PBS were improved with increasing content of DCP, but tear strength was only slightly affected. The higher the crosslinking, the lower the heat of crystallization (ΔH_c) and heat of fusion (ΔH_f). However, the melt crystallization temperature (T_c) of crosslinked PBS was higher than that of PBS. The viscosity of crosslinked PBS increased and exhibited rubbery behavior as the content of curing agent increased. The biodegradability of crosslinked PBS did not seriously deteriorate. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1115–1124, 2001     

Properties of electropolymerized polycarboxyphenylmethacrylamide matrices/graphite fiber composites: Crosslinking effect

Imide formation from -CONH and -COOH functional groups of 2-carboxyphenylmethacrylamide (2-CPM), 4-carboxyphenylmethacrylamide (4-CPM), 4-carboxyphenyl methacrylamide/methylmethacrylate (4-CPM/MMA) and 4-carboxyphenylmethacrylamide/N-phenylmalemide (4-CPM/NPMI) electropolymerized matrices was investigated. It was found that 2-CPM polymers undergo intramolecular imidization and anhydride formation, which result in a small amount of crosslinked network. On the other hand, the thermally cured 4-CPM polymer demonstrates a significant increase in gel fraction. T_g and dynamic storage modulus, owing to crosslinked network formation. T_gs of 4-CPM/MMA and 4-CPM/NPMI composites measured by thermomechanical analysis after thermal heating were increased and were correlated very well with the preheating time. The 4-CPM/MMA composites with a particle crosslinking (T_g increased to 245°C) maintained a higher Izod impact strength than a typical epoxy composite (200 kJ/m² vs. 100 kJ/m²). Upon heating to promote crosslinking, a lower shear strength (65 MPa) of a 4-CPM/MMA composite increased to a strength of 78 MPa, close to the 80 MPa of an epoxy composite at 67% fiber volume fraction. A lower water absorption of around 1% was associated with the increased crosslinking. The mechanical properties of the 4-CPM/NPMI composites showed a similar trend upon preheating.     

Synthesis and characterization of paraffin/TiO2‐P(MMA‐co‐BA) phase change material microcapsules for thermal energy storage

Microcapsules based on a phase changing paraffin core and modified titanium dioxide–poly(methyl methacrylate‐co‐butyl acrylate) [P(MMA‐co‐BA)] hybrid shell were prepared via a Pickering emulsion method in this study. The microcapsules exhibit an irregularly spherical morphology with the size range of 3–24 µm. The addition of BA can enhance the toughness of the brittle polymer poly(methyl methacrylate) and improve the thermal reliability of the phase change microcapsules. The ratio of BA/MMA is in the range of 0.09–0.14, and the ratio of the monomer/paraffin is varied from 0.45 to 0.60. These microcapsules exhibit a well‐defined morphology and good thermal stability. The actual core content of the microcapsules reaches 36.09%, with an encapsulation efficiency of 73.07%. Furthermore, the prepared microcapsules present the high thermal reliability for latent‐heat storage and release after 2000 thermal cycles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46447.