Temperature and acid/base-driven dual switching of poly(N-isopropylacrylamide) hydrogel with Azo dye

A thermoresponsive poly(NIPAM-co-Azo) hydrogel labeled with azo dye was prepared by typical radical copolymerization. The lower critical solution temperature (LCST) behavior was investigated by means of UV-vis spectroscopy which allows the measurement of the phase transition from 25 to 45 °C in aqueous solution. The poly(NIPAM-co-Azo) copolymer also exhibited sizeable color change when used a acid/base-induced molecular switch. This material can act as water soluble dual sensor for both temperature and acid/base.     

Synthesis and properties of Nylon 4/5 copolymers for hydrophilic fibers

Nylon 4, which can be synthesized by anionic ring-opening polymerization, has good mechanical properties and a very high affinity for water owing to its high polarity. On the other hand, despite its high melting temperature, the polymer has not been commercialized because of its low thermal stability. In this study, copolymerization of 2-pyrrolidone (C4) with 2-piperidone (C5) was performed to reduce the melting temperature of Nylon 4 homopolymer. The copolymerization reaction was controlled by changing the comonomer content, catalyst content, temperature, initiator content, and reaction time. The Nylon copolymers were characterized by ¹H-nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The hydrophilic properties of Nylon 4 and its copolymers were evaluated by surface free energy analysis and moisture regain measurement. The intrinsic viscosity and polymerization yield of Nylon 4 increased with increasing catalyst concentration until 5 mole% and decreased with further increases in catalyst loading. The proton NMR spectrum revealed the composition of the Nylon 4/5 copolymer to be 62.5 % C4 moiety at a 5:5 comonomer feed ratio. The melting temperature of the Nylon 4/5 copolymers decreased considerably according to the composition. The moisture regain of the Nylon 4/5 copolymer was higher than 6.4 % even at 77.3 % C4 in composition.     

Synthesis and properties of acrylonitrile-methyl itaconate copolymers as spun carbon fiber precursors

Acrylonitrile-methyl itaconate (AN-MIA) copolymers were successfully prepared by free-radical solution copolymerization, and then were spun into precursors of carbon fibers by one-step wet-spun method in this study. Effect of methyl itaconate(MIA), itaconic acid (IA) and methyl acrylate (MA) on the characteristics of the copolymers and precursors were studied in contrast. The monomer reactivity ratios for AN/MIA system were determined by Kelen-Tudos (K-T) method with r ₁=0.65, r ₂=1.80. The viscosity test shows that using MIA as a co-monomer is an effective way to decrease the viscosity of PAN solution. During the spinning and stretching processes, polyacrylonitrile (PAN) copolymer with MIA as co-monomer can reach the higher total draw-ratio of 12.0 folds, while PAN copolymer with IA as co-monomer can reach only 8.5 folds. The fineness and elongation at-break of the PAN precursors with MIA as co-monomer improve, but the tenacity decreases. DSC test shows MIA is less effective in improving the thermal property than IA.     

Synthesis and hydrophilicity of poly(trimethylene 2,6-naphthalate)/poly(ethylene glycol) copolymers

Poly(trimethylene 2,6-naphthalate) (PTN)/poly(ethylene glycol) (PEG) copolymers were synthesized by the two-step melt copolymerization process of dimethyl-2,6-naphthalenedicarboxylate (2,6-NDC) with 1,3-propanediol (PD) and PEG. The copolymers produced had different PEG molecular weights and contents. The structure, thermal property, and hydrophilicity of these copolymers were studied by proton nuclear magnetic resonance (¹H-NMR) analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and by contact angle, moisture content, and instantaneous elastic recovery measurements. The intrinsic viscosity and the instantaneous elastic recovery of the PTN/PEG copolymers increased with increasing PEG molecular weight and content, whereas the glass transition, melting, and cold crystallization temperatures, and the heat of fusion of the PTN/PEG copolymers all decreased with increasing PEG molecular weight or content. The thermal stability of the copolymers was not affected by PEG molecular weight or content. The hydrophilicity, as determined by contact angle and moisture content measurements of the copolymer films, was significantly improved with increasing PEG molecular weight and content.     

Synthesis and hydrophilicities of Poly(ethylene 2,6-naphthalate)/Poly(ethylene glycol) copolymers

Poly(ethylene 2,6-naphthalate) (PEN)/Poly(ethylene glycol) (PEG) copolymers were synthesized by two step reaction during the melt copolymerization process. The first step was the esterification reaction of dimethyl-2,6-naphthalenedicarboxylate (2,6-NDC) and ethylene glycol (EG). The second step was the condensation polymerization of bishydroxyethylnaphthalate (BHEN) and PEG. The copolymers contained 10 mol% of PEG units with different molecular weights. Structures and thermal properties of the copolymers were studied by using¹H-NMR, DSC, TGA, etc. Especially, while the intrinsic viscosities of PEN/PEG copolymers increased with increasing molecular weights of PEG, but the glass transition temperature, the cold crystallization temperature, and the weight loss temperature of the copolymers decreased with increasing molecular weights of PEG. Consequently, the hydrophilicities by means of contact angle measurement and moisture content of the copolymer films were found to be significantly improved with increasing molecular weights of PEG.     

Acetylation of wheat straw hemicelluloses in N,N-dimethylacetamide/LiCl solvent system

Hemicellulose acetates were prepared under homogeneous reaction conditions in the system N,N-dimethylacetamide/lithium chloride by reacting the native hemicelluloses with acetic anhydride in the presence of 4-dimethylaminopyridine within 72 h at 60–85°C. The products obtained were characterised by means of Fourier transform infrared chromatography, gel permeation chromatography, and thermal analysis. The degree of substitution of acetylated hemicelluloses ranged between 0.74 and 1.49 as a function of experimental conditions. Under an optimum reaction condition (85°C, 60 h), over 80% hydroxyl groups in native hemicelluloses were acetylated. The molecular weight measurements showed that a significant degradation and hydrolysis of the products appeared at only a prolonging period of 72 h. It was found that the thermal stability of the products increased by esterification.     

Wheat gluten films cross-linked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide

Wheat gluten films were cast from aqueous dispersions containing 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as cross-linking reagents and glycerol as a plasticizer. Cross-linking was carried out to improve film properties such as water sensitivity and tensile strength. Films were characterized by measuring protein and water content, amount of amino groups, swelling of the films in water, and mechanical properties such as tensile strength (σ_max) and strain at maximum stress ( at σ_max). The use of different ratios of EDC to COOH resulted in different tensile properties and different percentage of swelling, which was attributed to the degree of cross-linking in the film. At a ratio of EDC/NHS/COOH=0.5/0.5/1, films had a water content of 10–11.5% and showed the highest σ_max (2.8±0.9 MPa), the lowest at σ_max (142±67%), and the lowest swelling (46%) compared to σ_max=1.7±0.4 MPa, at σ_max=257±63%, and swelling=68% for native gluten films.     

Synthesis and crystallization behaviors of modified PET copolymers

A series of random copolyesters having various compositions were synthesized by bulk copolymerization of bishydroxyethyl terephthalate (BHET) with 1,4-cyclohexane dimethanol (CHDM) or dimethyl isophthalate (DMI). CHDM and DMI content was less than 10 wt%. For the synthesized copolyesters, isothermal crystallization rate, melting behavior, and equilibrium temperature were investigated by calorimetry and by Avrami and Hoffman-Weeks equation. Crystalline lattice and morphology were studied by WAXD and SEM. Regardless of the composition, the value of the Avrami exponent was about 3, which indicates that crystallization mechanism of the copolyester was similar to those of PET homopolymer. Incoporation of CHDM or DMI units in PET backbone decreased the crystallization rate of the copolyesters. Surface free energy of copolyesters was evaluated using the newly proposed equation. The value of surface free energy was about 189×10⁻⁶ J²/m⁴ regardless of comonomer contents. This result is in good agreement with that of PET homopolymer.     

Synthesis and physical properties of pH-sensitive semi-IPN hydrogels based on poly(dimethylaminoethyl methacrylate-co-PEG dimethacrylate) and poly(acrylic acid)

Hydrogels of semi-interpenetrating polymer networks (semi-IPNs) were prepared by two step reactions. Dimethylaminoethyl methacrylate (DMAM) and poly(ethylene glycol)-dimethacrylate (PEGDM) were copolymerized to yield hydrogels, and then acrylic acid (AA) monomer were adsorbed in the hydrogels followed by polymerization of AA to produce semi-IPNs. The swelling behavior of semi-IPNs depends largely on pH of medium, showing that the degree of swelling of the semi-IPNs exhibits a minimum at pH 6.0. It is observed that the elastic modulus of semi-IPNs is closely related to its swelling behavior.     

Moisture-dependent physical properties of Karanja (Pongamia pinnata) kernel

The moisture-dependent physical properties are important to design post harvest equipments of the product. The physical properties of Karanja kernel were evaluated as a function of moisture content in the range of 8.56–22.22% d.b. The average length, width, thickness and 1000 kernel mass were 25.29 mm, 15.58 mm, 7.88 mm and 1036.45 g, respectively, at moisture content of 8.56% d.b. The geometric mean diameter and sphericity increased from 14.55 to 15.97 mm and 0.57 to 0.6 as moisture content increased from 8.56 to 22.22% d.b., respectively. In the same moisture range, the bulk density decreased from 663 to 616 kg/m³, whereas the corresponding true density and porosity increased from 967 to 1081 kg/m³ and 31.44 to 43.02%, respectively. As the moisture content increased from 8.56 to 22.22% d.b., the angle of repose and surface areas were found to increase from 27.69 to 37.33° and 665.74 to 801.63 mm², respectively. The static coefficient of friction of Karanja kernel increased linearly against the surfaces of three structural materials, namely plywood (28.72%), mild steel sheet (29.88%) and aluminium (18.86%) as the moisture content increased from 8.56 to 22.22% d.b.     

Synthesis and characterization of electrically conductive composite films of polypyrrole/poly(acrylonitrile-co-styrene)

Homogeneus Polypyrrole (PPy)/poly(acrylonitrile-co-styrene) (SAN) composite thin films were prepared by chemical polymerization of pyrrole on poly(acrylonitrile-co-styrene) matrix. Ce (IV) is used as an oxidant for in-situ polymerizion of pyrrole on SAN matrix, having an advantageous over the impregnation method. The formation and incorporation of PPy in the copolymer matrix were confirmed by FTIR-ATR and UV-Visible spectrophotometric measurements. Thermal analyses showed that after polymerization of Py in copolymer matrix, thermal behavior of SAN was changed and derivative of weight loss at this temperature was increased by increasing of PPy content. XPS and FTIR-ATR analysis of composite films indicated cerium salt with nitrate ion acted as a dopant. The increase in the AC electrical conductivity of the PPy/SAN composites over pure SAN was observed. At lower frequency up to 10⁵ Hz, conductivity was shown an independent behavior from frequency; but at high frequencies (10⁵–10⁷ Hz), dependence on frequency was explained by polaron and bipolaron formations of PPy. The dispersion of PPy particles in copolymer matrix was proven by SEM, AFM and digital camera. By the increase of PPy content in the composite films, increase in AC conductivities, and decrease in dielectric constants and loss were observed.     

Rheological and thermal properties of acrylonitrile-acrylamide copolymers: Influence of polymerization temperature

An attempt was made to correlate the polymerization temperature and rheological and thermal properties of acrylonitrile (AN)-acrylamide (AM) copolymers. The copolymers were synthesized at different polymerization temperature. The copolymer structure was characterized by gel permeation chromatography (GPC) and Infrared spectrum (IR). The rheological and thermal properties were investigated by a viscometer and differential scanning calorimeter-thermogrametric (DSCTG) analysis, respectively. When the polymerization temperature increased from 41 °C to 65 °C, the molecular weight ([`(M)] <sub>w</sub> )(\overline M _w ) of copolymers decreased from 1,090,000 to 250,000, while its conversion increased from 18% to 63%, and the polymer composition changed slightly. To meet the requirements of carbon fibers, the rheological and thermal properties of products were also investigated. It was found that the relationship between viscosity and [`(M)] _w\overline M _w was nonlinear and the viscosity index (n) decreased from 3.13 to 2.69, when the solution temperature increased from 30 °C to 65 °C. This suggests the dependence of viscosity upon [`(M)] _w\overline M _w is higher at lower solution temperature. According to the result of activation energy, the sensivity of viscosity to solution temperature is higher for AN-AM copolymers synthesized at higher polymerization temperature. The result of thermal analysis shows that the copolymers obtained at higher polymerization temperature are easier to cyclization evidenced from lower initiation temperature. The weight loss behavior changed irregularly with polymerization temperature due to irregular change of liberation heat.     

Thermomechanical properties and shape memory effect of PET-PEG copolymers cross-linked with pentaerythritol

Poly(ethylene terephthalate) (PET) and poly(ethylene glycol) (PEG) copolymers cross-linked with pentaerythritol, a four-way cross-linker, are prepared to compare their mechanical and shape memory properties with the one cross-linked by glycerol. Composition of PEG and pentaerythritol is varied to search for the one with the best mechanical and shape memory properties. The highest shape recovery rate is observed for the copolymer composed of 30 mol% PEG-200 and 2.5 mol% pentaerythritol. Four-way cross-linking by pentaerythritol significantly improves shape recovery rate and retention of high shape recovery rate after repeated use compared to the one cross-linked by glycerol, a three-way cross-linker, and difference and advantage of additional cross-linking point are discussed.     

Thermal and structure properties of biobased cellulose nanowhiskers/poly (lactic acid) nanocomposites

Cellulose nanowhiskers were used to improve the performance of poly (lactic acid) (PLA). The nanocomposites mixed with three different molecular weight of poly (ethylene glycol) (PEG) were characterized by mechanical testing, thermal gravimetry and differential scanning calorimetry. The tensile test showed an increase in tensile strength and elongation at break with the addition of PEG to PLA/CNW nanocomposites, the thermal analysis results showed an increase of crystallization temperature (T _c) and crystallization compatibility (larger crystallization and melting areas), which indicated that the cellulose nanowhiskers (CNW) and PEG or CNW alone should not be considered as nucleating agents for the PLA matrix; The CNW was homo-dispersed which contributed to decreasing mobility of polymer chain segments. The compatibility between hydrophobic PLA matrix and the hydrophilic CNW was improved by the addition of different molecular weight polymeric-PEG. The thermo gravimetric analysis indicated that the thermal stability of the different composites were reflected well in the region between 25 °C and 245 oC. The structure of the PLA/CNW/PEG composites was characterized by AFM, which showed that the CNW dispersed in the PLA matrix evenly.     

Effect of aldehydes crosslinkers on properties of bacterial cellulose-poly(vinyl alcohol) (BC/PVA) nanocomposite hydrogels

The effects of the aldehydes crosslinkers on properties of the BC/PVA nanocomposite hydrogels were investigated. BC as the reinforcement and PVA as the matrix materials of the BC/PVA nanocomposite hydrogels, the hydrogels were prepared in coagulating bath of sodium sulfate and cross-linked with kinds of aldehydes. The hydrogels were characterized by Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), Equilibrium swelling ratio (ESR) tests, mechanical properties tests, thermo-gravimetric analysis (TGA) and X-ray diffraction (XRD) analysis. It was found that the dialdehyde (glyoxal, glutaraldehyde) crosslinkers were more efficient than monoaldehyde (formaldehyde, acetaldehyde) crosslinkers. The ESR, mechanical properties of the BC/PVA nanocomposite hydrogels were obviously influenced by aldehydes crosslinkers. However, their thermo stability and crystallinity were scarcely influenced. The nanocomposite hydrogels described in this study provides information for further development and optimization of a variety of nanofiber-polymer matrix composite hydrogels.     

Synthesis, characterization, and protonation of poly(2-N,N-dimethylamino-4,6-bis(2-furan)-pyrimidine)

A new monomer (2-N,N-dimethylamino-4,6-bis(2-furan)-pyrimidine) was synthesized and its homopolymer was successfully prepared by using ferric trichloride as an oxidant. The structure of monomer and polymer were fully characterized by ¹H-NMR, FT-IR, UV, fluorescent spectroscopy, and X-ray diffraction. The N,N-dimethylformamide solution of the polymer showed a UV-Vis peak at 387 nm and the PL spectrum gave a peak at 517 nm. We have observed that the polymer was sensitive to inorganic acids and the protonation behavior was investigated applying inorganic acids such as HCI and H₂SO₄. The corresponding UV-Vis peaks were observed at 464 and 357 nm, respectively. X-ray diffraction data shows that polymer had a certain crystalline region. The polymer exhibited an [η] value of 0.21 dl/g at 25 °C in H₂SO₄ (w=98 %).     

茶叶多糖铁的合成及其铁含量的测定

用热水浸泡法从粗老茶叶中提取茶叶多糖,在碱性条件下,茶叶多糖水溶液与三氯化铁反应合成茶叶多糖铁配合物(TPC),并用邻菲罗啉分光光度法和原子吸收光谱法测定TPC中铁(Ⅲ)的含量。实验结果表明:TPC是深棕红色无定型粉末,易溶于水,在pH值3~12范围内不沉淀,不水解。TPC中铁(Ⅲ)的含量:邻菲罗啉分光光度法测定结果为20.71%,原子吸收光谱法测定结果为20.13%。     

Composition and physical properties of cress (Lepidium sativum L.) and field pennycress (Thlaspi arvense L.) oils

The fatty acid profiles and tocopherol and phytosterol contents of crude oils of cress (Lepidium sativum L.) and field pennycress (Thlaspi arvense L.) are reported, along with yields from the corresponding seeds. The physical properties of these oils were also determined, which included oxidative stability, kinematic viscosity, viscosity index, low temperature fluidity, specific gravity, acid value, lubricity, and iodine value. The oil content of dried cress and field pennycress seeds was 22.7 and 29.0 wt%, respectively. The primary fatty acids found in cress oil were oleic (30.6 wt%) and linolenic acids (29.3 wt%), whereas field pennycress oil was principally composed of erucic (32.8 wt%) and linoleic (22.4 wt%) acids. Cress oil contained high concentrations of γ- (1422 ppm) and δ- (356 ppm) tocopherols, whereas α-tocopherol (714 ppm) was the primary tocopherol discovered in field pennycress oil. The overall tocopherol concentrations of cress and field pennycress oils were 1799 and 851 ppm, respectively. The primary phytosterols elucidated in cress and field pennycress oils were sitosterol and campesterol, with avenasterol also present in significant quantity in cress oil. The total phytosterol concentration in cress oil (14.41 mg/g) was greater than that in field pennycress (8.55 mg/g) oil. Field pennycress oil exhibited excellent low temperature fluidity, whereas cress oil was more stable to oxidation and over a range of temperatures displayed lower kinematic viscosities as well as a higher viscosity index. The acid and iodine values of field pennycress oil were lower than those for cress oil, but both oils had excellent lubrication properties.     

Synthesis of core-shell fluorinated acrylate copolymers and its application as finishing agent for textile

Core-shell fluorinated acrylate copolymers emulsion was thus synthesized via the core-shell emulsion polymerization with the fluorinated monomers and acrylic monomers as the main raw materials and its properties were studied. PFMA, the fluorinated acrylate monomers, was synthesized by the esterification of perfluorooctanoyl chloride (PFOC) and hydroxypropyl methacrylate (HPMA). Then the core-shell fluorinated acrylate copolymers emulsion with a poly(MMA/BA/St) core and a poly(PFMA/MMA/BA) shell was synthesized via a starved semi-continuous core-shell emulsion polymerization method by using KPS and sodium bicarbonate as the initiator/buffer system and SDS/Twain 80 as the commixture emulsifier. Lastly, the synthesized copolymers was applied as textile finishing agent for cotton textile. The results of FT-IR and NMR indicated that PFMA had been synthesized as expected and effectively combined in the emulsion copolymerization. The GPC, zeta potential, TEM and DSC showed that the particles had uniform spherical core-shell structure with a diameter of 65-150 nm, and the distribution and emulsion stability was satisfactory. As XPS, FESEM and AFM shown, a hydrophobic structure which was similar to the structure of the lotus leaf were formed and the surface hydrophobicity of the films can be improved. Based on the analysis of DSC, thermal stabilities of the films were enhanced with the increase of fluorine content. Besides, FESEM of textiles showed that the surface of treated textiles were smooth and the edges were clear and visible, indicating significant improvement of the performance on water and oil repellent.