Synthesis and properties of bulk-biodegradable phase change materials based on polyethylene glycol for thermal energy storage

The bulk-biodegradable solid–solid phase change materials (SSPCMs) based on phase change polyethylene glycol (PEG) were synthesized by solvent-free polyaddition. On the basis of the fact that the water absorption is up to 800 mass% and that the poly(ethylene oxide) molecular chains can be degraded by microorganisms, the bulk-biodegradable mechanism of SSPCMs was put forward and studied. The X-ray diffraction patterns and the polarizing optical microscopy images show the SSPCMs possess the defective crystal and small grain compared with PEG. The differential scanning calorimetry data demonstrate the melting temperature and enthalpy of the synthesized SSPCMs are, respectively, 41 °C and 128 J g^?1. The bulk-biodegradable SSPCMs have the preeminent thermal reliability and the high thermal stability due to the onset thermal degradation temperature above 302 °C, which will give a good insight into bulk-biodegradable PCM system.     

Synthesis and characterization of cellulose-g-polyoxyethylene (2) hexadecyl ether solid–solid phase change materials

A series of novel solid–solid phase change materials, namely, cellulose-g-polyoxyethylene (2) hexadecyl ether (Cellulose-g-E₂C₁₆) copolymers, were synthesized using toluene 2,4-diisocyanate (TDI) as a coupling reagent in the ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). The optimum prepolymerization conditions were determined to be 25 °C and 75 min without catalyst, and the optimum reaction conditions of the grafting step were 90 °C, 6 h and 0.1 wt% dibutyltin dilaurate (DBTDL, weight percent of TDI). The successful grafting was confirmed by FTIR and ¹H-NMR. The properties of the Cellulose-g-E₂C₁₆ copolymers were investigated by DSC, TG and XRD. It is shown that the heat storage ability and phase change temperature of Cellulose-g-E₂C₁₆ copolymers depended on the degree of substitution. The crystalline type of the grafted E₂C₁₆ was not affected by the cellulosic backbone. Compared with E₂C₁₆, Cellulose-g-E₂C₁₆ copolymers showed better thermal stability. They are expected to be widely applied in the area of thermal energy storage.     

Synthesis and thermal energy storage properties of the polyurethane solid–solid phase change materials with a novel tetrahydroxy compound

Based on the phase change theory, a novel tetrahydroxy compound (THCD) was designed and prepared. Depending on the spatial structure of the tetrahydroxy compound, a form-stable thermoplastic polyurethane solid–solid phase change material (TPUPCM) was synthesized via employing PEG as soft segments, while multi-benzene ring structure made by 4,4′-diphenylmethane diisocyanate and tetrahydroxy compound as hard segments. The composition and structure of THCD and TPUPCM, the TPUPCM’s the weight average molecular weight and number average molecular weight, dissolving and melting abilities, phase change behaviors, thermal performances and crystalline morphology were investigated by Fourier transform infrared spectrometer, ¹H nuclear magnetic resonance spectrometer, multiangle laser light scattering apparatus, differential scanning calorimentry, dynamic mechanical thermal analysis, thermogravimetry analysis system, wide-angle X-ray diffraction, polarizing optical microscopy. The results show that the solid–solid phase change material owns excellent phase change properties and a broad processing temperature range. The heating cycle phase change enthalpy is 137.4 J/g, and the cooling cycle phase change enthalpy is 127.6 J/g. The started decomposition temperature and the maximum decomposition temperature are at 323.5 and 396.2 °C, respectively. Furthermore, the solid–solid phase change material is dissolvable, meltable and can be processed directly, and has great potential applications in thermal energy storage.     

Different methods for β-cyclodextrin/triclosan complexation as antibacterial treatment of cellulose substrates

Two different production ways of antibacterial cotton fabrics by means of triclosan inclusion into a β-cyclodextrin cavity have been compared. On the one hand, triclosan has been dissolved into an aqueous solution of a β-cyclodextrin derivative with the aim of including the antibacterial agent into the cavity before grafting the β-cyclodextrin on a cotton fabric. On the other hand, the same β-cyclodextrin derivative has been grafted onto cotton and, subsequently, the fabric has been immersed into a triclosan water–ethanol solution to allow the inclusion complex formation. The antibacterial properties have been evaluated according to AATCC Test Method 100–1993 before and after two washing cycles at 60 °C. It has been shown that the durability of the antibacterial finishing depends on the production method, obtaining a more durable antibacterial action in case of prior triclosan inclusion followed by grafting. This suggests that the immobilization onto the fiber has affected the cyclodextrin cavity accessibility.     

Retrogradation characteristics of high hydrostatic pressure processed corn and wheat starch

High hydrostatic pressure (HHP) has been investigated as an alternative to thermal processing for food preservation. HHP has been known to affect high molecular weight polymers causing phase change. Starch is gelatinized at a pressure on the order of 600–700 MPa, at 25 °C. Gelatinized starch recrystallizes during storage affecting the texture and shelf life of food products. The effect of HHP processing on the crystallization of starches from different botanical origins during storage at 4 and 23 °C was investigated. Crystallization kinetics of HHP treated wheat and corn starch gels were compared using DSC. The effect of crystallization on structure was evaluated in terms of storage modulus. The rate of retrogradation depended on the storage temperature (23 °C and 4 °C) and the botanical origin of the starch. The least crystallization was observed in HHP treated wheat starch stored at 23 °C. The storage modulus increased with crystallization of starch.     

Phase transition of syndiotactic polypropylene in electrospun nanofibers during progressive heating

By means of high-temperature electrospinning process, syndiotactic polypropylene (sPP) nanofibers with an average diameter of 127 nm were obtained using a rotating disc as a collector. The aligned fibers were subjected to progressive heating for fiber melting. During heating, structural evolution of the sPP nanofibers was investigated in situ by means of two-dimensional wide-angle and small-angle X-ray scattering with synchrotron radiation sources. It was found that the as-spun fibers consist of the antichiral form I (9 %), mesophase (31 %), and amorphous phase (60 %), in the absence of isochiral form II. Upon heating, the mesophase started to melt and completely disappeared at 90 °C. The melting of the mesophase directly produced amorphous chains at 35–60 °C, and brought up the isochiral form II at low temperatures (60–70 °C), as well as the antichiral form I at high temperatures (70–110 °C). These events were in accordance with the DSC heating curve, which exhibited a small endotherm centered at 52 °C for the mesophase melting, followed by a shallow and broad exotherm associated with two phase-transition events, i.e., the crystal reorganization and the crystallization of supercooled liquid. The former is likely due to the solid–solid transition of meso→II phase as suggested by Lotz et al. (Macromolecules 31:9253, 1998), and the latter is relevant with crystallization of amorphous chains to develop the thermodynamic stable form I phase at high temperatures.     

Crystallization of polydioxolan. II. Morphology and melting properties

Polydioxolan samples crystallized between 25 and 35°C present two optical phases when viewed on the polarizing microscope. These phases, termed central and external phases, form a spherulite. It is shown in this paper that the central phase of the two-phase spherulite melts at about 63°C, and is made of modification III crystals. The external portion of the two-phase spherulites melts at a lower temperature, around 59°C, and is composed of modification II crystals. Differential scanning calorimeter (DSC) melting curves, photomicrographs, and x-ray results are presented to prove these assertions.     

Pre-irradiation grafting of span 60-IAH onto polyethylene to improve dripping properties of water on polyethylene films

A reactive type dripping anti-condensation agent, Span 60-IAH, was grafted onto linear low density polyethylene (LLDPE) by β-ray pre-irradiation and reactive extrusion. Effects of total dose, monomer concentration and extrusion temperature and rate on the degree of grafting were studied in detail. It was shown that the optimum conditions for grafting were the extrusion temperature of 130–220°C, screw run speed of 90 rpm and total β-ray dose of 12.5 kGy. The structure of the LLDPE-g-(Span 60-IAH) (LS) was characterized by Fourier-transform infrared spectroscopy (FT-IR). The tensile properties and light transmission properties of extruded films were determined. The thermal behavior of the LS was investigated by using differential scanning calorimetry (DSC). Compared with pure LLDPE, the crystallization temperature (T_c) of LS increased about 3°C. Accelerated dripping properties of film samples were investigated. The dripping duration of the LS film and a commercial anti-fog dripping film at 60°C were 45 days and 17 days, respectively, indicating a significant improvement.     

Fast-scan vs conventional differential scanning calorimetry (DSC) techniques in detection of crystallization events of tolbutamide–polyethylene glycol composite

This study investigated the capacity of fast-scan (400 °C min^?1) against conventional (10 °C min^?1) differential scanning calorimetry (DSC) techniques to track crystallization phenomenon in tolbutamide–polyethylene glycol 3000 composites prepared by hot melt method (mass ratios 1:1, 1:5, and 1:9) and stored at 25 and 75 % relative humidities. Drug crystallization in composites was indicated by X-ray diffractometry (XRD) and scanning electron microscopy characterization over 40 days storage. With reference to XRD as gold measurement standard, fast-scan DSC could not map the crystallization events of composites (Pearson correlation: fast-scan DSC peak temperature and enthalpy versus XRD peak intensity and area, p > 0.05). Conventional DSC was able to indicate marked drug crystallization through an increase in endothermic enthalpy value of peaks at high temperature regimes between 250 and 360 °C due to formation of high melting point crystal form.     

Geraniol Based Side Chain Liquid Crystalline Polymer: Synthesis and Characterization

Side chain liquid crystalline (SCLC) polysiloxane polymer with a geraniol mesogenic group and polymethylene spacers were prepared, and their properties were compared with those of an equivalent SCLC polymer, SCLCP's, with phenyl benzoate mesogenic group. The phase behavior was studied by differential scanning calorimetry (DSC) and optical polarizing microscopy (OPM). The DSC curve showed a clear melting temperature and isotropization at 72 and 148°C, respectively, with a glass transition at 25°C. The observation of a fan‐shaped texture confirms the presence Smectic A phase under an optical polarized microscope.     

Characterization and Studies on Grafting of Methyl Methacrylate onto PAN Fibers

The graft copolymerization of methyl methacrylate (MMA) onto commercial acrylic fibers (PAN) has been studied using Azobis(isobutyro)nitrile (AIBN) as an initiator. MMA grafting initiated by radicals formed from thermal decomposition of AIBN. In this study, the effects of monomer and initiator concentration, time and temperature reaction on the grafting yield have been investigated.

The optimum conditions for this grafting reaction were obtained with an MMA concentration of 0.7 M, an AIBN concentration of 0.0073 M, a reaction temperature of T=85°C and with a 60 min reaction time.

The fiber structure has been investigated by different experimental techniques of characterization such as Fourier transform infrared spectroscopy (FT‐IR), calorimetric analysis (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), water absorption and the physical and mechanical properties has also been investigated in this study. The thermal analysis data showed that by increasing grafting yield, little changes have occurred in fibers samples up to 13.5% of grafting yield and the thermal transitions of grafted fibers have approximately the same behavior compared with the raw fibers sample. Grafting also slightly affected the fiber morphology. The experimental data of mechanical properties clearly show that by increasing grafting yield, max extension will decrease but this change up to 13.5% grafting yield is barely noticeable. Grafting of poly MMA improved water absorption.     

聚乙二醇/二醋酸纤维素相变材料的组成与储能性能间的关系

以刚性的二醋酸纤维素 (CDA)链为骨架 ,接枝上聚乙二醇 (PEG)柔性链段 ,可得到一种具有固固相变性能的网状储能材料 .利用该材料的PEG支链从结晶态到无定形态间的相转变 ,可以实现储能和释能的目的 .具体研究了PEG的百分含量及PEG的分子量对材料储能性能的影响 .研究结果表明 ,通过改变PEG的百分含量与PEG的分子量 ,可以得到不同相变焓和不同相变温度的材料     

Thermal and structural characterization of superfine down powder

The thermal degradation of down fiber and down powder was studied using TG, DSC, TG-FTIR, and ATR-FTIR as a function of mass loss. For both down fiber and down powder, two evident mass loss stages were observed. Compared to down fiber, down powder had higher moisture and lower thermal stability. The oxygen in air weakened the mass loss of superfine down powder in the temperature range of 300–530 °C, and accelerated the oxidation–reduction reaction between oxygen and powder when the temperature was over 530 °C. The microstructures of down fiber and down powder were investigated on the analysis of DSC results. As the decrease in the average particle size of down powder, the absorbed energy of the destruction of crystallinity, rupture of crosslinks and thermal degradation of peptide bonds decreased, respectively. The gases evolved during thermal degradation of superfine down powder were inspected by in situ FTIR, and then the solid residues collected at different temperature were analyzed using ATR-FTIR. The color evaluation of superfine down powder hot-pressed at high temperature was discussed to confirm the best hot-processing condition.     

Cotton fabric modification for imparting high water and oil repellency using perfluoroalkyl phosphate acrylate via γ-ray-induced grafting

The perfluoroalkyl phosphate acrylates were grafted onto a cotton fabric via γ-ray irradiation to improve the hydrophobic and oleophobic properties. The change in chemical structure of grafted cotton fabric was detected by the Fourier transform infrared spectroscopy and the X-ray photoelectron spectroscopy. The contact angles for water and sunflower oil were determined to be over 150° and 140°, respectively, after irradiated with a dose range of 471–5664 Gy. The flame retardancy of the fabric with a grafting ratio of over 13.0 wt% was improved, reaching to 24 compared with 18 of which before grafted, according to the limiting oxygen index measurement. The microstructure of the fabric before and after grafted was observed by the scanning electron microscope.     

Fractional crystallization behavior of PCL and PEG in blends

The crystallization behavior of poly(e-caprolactone)/poly(ethylene glycol) (PCL/PEG) blend was investigated by differential scanning calorimetry (DSC) and polarized microscopy (POM). Individual phase transition peaks in the DSC curves for both PEG and PCL in all the polymer blends with different PCL contents were observed. The crystallization and melting peak temperatures of PEG were at 41 and 65°C, respectively; while the crystallization and melting temperatures of PCL located at 28 and 56°C, respectively. In-situ POM results demonstrated that spherulites crystalline morphology was formed for both PCL and PEG homopolymers. In PEG/PCL blend, however, both the phase separation morphology and spherulitic morphology can be observed. In blends with 30 or 50 wt % PCL, the PCL component formed dispersed phase and crystallized at lower temperature. However, in blends with 70% PCL, the phase inversion behavior occurred. The continuous PCL phase crystallized at 35°C, while the PEG dispersed phase crystallized at a lower temperature. Fractional crystallization behavior of PEG and PCL was controlled by temperature. The spherulites growth rate of PEG was greatly influenced by temperature, instead of the content of PCL component in the PCL/PEG blends.     

Effect of fluorinated nematic mesogens on phase behaviors and optical properties of chiral liquid crystalline polysiloxanes

A series of new chiral side-chain liquid crystalline polymers (P₁–P₇) have been synthesized with poly(methylhydrogeno)siloxane, two chiral liquid crystalline monomers, cholesteryl-4-allyloxybenzoate (M₁) and cholesteryl 4-(10-undecylen-1-yloxy) benzoate (M₂), and a nematic liquid crystalline monomer, 4-(trifluoromethyl)phenyl 4-(undec-10-enoyloxy)benzoate (M₃). The chemical structures and liquid crystalline properties of the synthesized polymers have been investigated by FTIR, ¹H-NMR, differential scanning calorimetry (DSC), polarizing optical microscopy (POM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD). All chiral polymers show wide mesophase temperature ranges and a high thermal stability with decomposition temperatures (T _d) at 5 % weight loss greater than 300 °C. P₁–P₄ display a single cholesteric phase, but P₅–P₇ containing more fluorinated units show a smectic A (SA) phase besides a cholesteric phase. The optical properties of the polymers have been characterized by circular polarization spectra and optical rotation analysis. The cholesteric polymers P₃ and P₄ exhibit different colors at room temperature, and the color can remain over 24 months. The maximum reflection bands of polymers P₁–P₄ shift to long wavelength with increasing the content of M₃ in the polymer systems. For P₅–P₇, the reflection wavelengths change sharply around the temperature of the SA–Ch phase transition. The specific rotation value of P₂ smoothly decreases from ?8.2° to ?0.29° when it is heated, but the specific rotation value of polymer P₇ changes from negative value to positive value on heating cycle. The optical properties of the polymers offer tremendous potential for various optical applications.     

Calorimetric analysis of the multiple melting behavior of melt-crystallized poly(l-lactic acid) with a low optical purity

The polymorphous crystallization and multiple melting behavior of poly(l-lactic acid) (PLLA) with an optical purity of 92 % were investigated after isothermally crystallized from the melt state by wide-angle X-ray diffraction and differential scanning calorimetry. Owing to the low optical purity, it was found that the disordered (α′) and ordered (α) crystalline phases of PLLA were formed in the samples crystallized at lower (<95 °C) and higher (≥95 °C) temperatures, respectively. The melting behavior of PLLA is different in three regions of crystallization temperature (T _c) divided into Region I (T _c < 95 °C), Region II (95 °C ≤ T _c < 120 °C), and Region III (T _c ≥ 120 °C). In Region I, an exothermic peak was observed between the low-temperature and high-temperature endothermic peaks, which results from the solid–solid phase transition of α′-form crystal to α one. In Region II, the double-melting peaks can be mainly ascribed to the melting–recrystallization–remelting of less stable α crystals. In Region III, the single endotherm shows that the α crystals formed at higher temperatures are stable enough and melt directly without the recrystallization process during heating.     

New polymer syntheses 16. LC-copolyesters of 3-(4-hydroxyphenyl) propionic acid and 4-hydroxy benzoic acids

The polycondensation of 3-(4-hydroxy phenyl)-propionic acid, 4-Hypp, by means of acetanhydride or acetylchloride was conducted either in the presence or in the absence of a liquid reaction medium. DSC measurements, polarizing microscope, and X-ray diffraction studies indicate poly(4-Hypp) possesses at about 215°C a reversible first order transition between two solid phases. Copolyesters containing various mole ratios of 4-Hypp and 4-hydroxy benzoic acid, 4-Hybe, were prepared by bulk condensation with acetanhydride at 320°C. At 4-Hypp/4-Hybe ratios less than 1.0:1.5 the reaction product was heterogeneous, containing crystals of pure poly(4-Hybe). Neither increasing the reaction time nor the variation of the transesterification catalyst resulted in an entirely homogeneous copolyester. However, for 4-Hypp/4-Hybe ratios greater than 1.0:1.5, ¹³C NMR spectra indicate perfectly random sequences. Also, terpolyesters containing 3-chloro-4-hydroxy- or 3,5-dichloro-4-hydroxy-benzoic acid were heterogeneous with less than 30 mol % 4-Hypp. DSC measurements revealed for all polyesters a glass transition in the range of 55–78°C. Temperature dependent X-ray diffraction studies confirm that the solid phase is a s.c. LC-glss. Correspondingly low heat distortion temperatures were found by thermomechanical analyses. The copolyesters display under the polarizing microscope LC-phase up to temperatures of 450–480°C, where rapid thermal degradation prevents further investigations. In the case of the 4-Hypp/4-Hybe 1:1 copolyester, the LC-phase extends over a temperature range of about 400°C. TGA measurements indicate beginning thermal degradation at temperatures between 350 and 380°C.     

Thermal study of the polyethyleneglycol 6000-triamterene system

This paper examines binary polyethyleneglycol (molecular weight 6000)-Triamterene (PEG 6000-T) solid dispersions (5–40 w/w% of T) prepared by the fusion carrier method, and physical mixtures (5–90 w/w% of T) are studied using DSC and Hot Stage Microscopy (HSM). The use of these combined techniques allows to explain the thermal behaviour on the basis of dissolution of T in the liquid carrier according to the progressive disappearance of the original crystals over a wide range of temperatures (ca. 100°C). The above fact, and possibly the sublimation of T, also could explain that at low T content (<- 30 w/w%), DSC curves exhibited only a single endothermic peak and/or weak endothermic peaks. On the basis of DSC data, a tentative phase diagram of this system is proposed.     

Synthesis and characterization of an environmentally friendly PHBV/PEG copolymer network as a phase change material

Novel environmentally friendly poly(hydroxybutyrate-co-hydroxyvalerate) and poly(ethylene glycol) (PHBV/PEG) copolymer networks were synthesized through free-radical solution polymerization with PHBV diacrylate (PHBVDA) and polyethylene glycol diacrylate (PEGDA) as macromers. The molecular structure of PHBV/PEG copolymer network was characterized by Fourier transform infrared (FT-IR) and ¹H nuclear magnetic resonance (¹H NMR). The morphology of the PHBV/PEG copolymer network was characterized by polarization optical microscopy. Thermal energy storage properties, thermal reliability and thermal stability were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis. The results indicated that the PHBV/PEG copolymer network hindered the growth of PEG crystalline segments or PHBV segments. PHBV/PEG copolymer network had a higher latent heat enthalpy, which didn’t reduce with the components of PHBV increased. Moreover, PHBV/PEG copolymer network still had good thermal stability even at 300 °C. These results suggested that such environmentally friendly copolymer network would have wide applications in phase change energy storage materials.