Study of the thermal behaviour of alipharomatic polyesters around the glass–rubber transition region by thermomechanical analysis: the mobile and rigid amorphous fraction

The objective of this work was the study using thermomechanical analysis (TMA) of a peculiar behaviour, which was observed some years ago, around the glass–rubber transition region in some thermoplastic alipharomatic polyesters. For this purpose a series of nine alipharomatic polyesters was prepared by the two‐stage melt polycondensation method in a glass batch reactor and subjected to TMA in both penetration and expansion mode. Differential scanning calorimetry (DSC) was additionally used and the results are discussed focusing mainly on the first derivative curve of TMA thermograms in the penetration mode. From this curve, which shows two distinct peaks, the first peak could be attributed to the glass transition temperature (T_g) of the mobile amorphous fraction, since the value coincides with that obtained from DSC and is due to the abrupt shrinkage of the amorphous part of the sample. The second peak (up to 40 °C higher than T_g) is due most probably to the softening of the rigid amorphous fraction and the passage of the polymeric sample from the glass region to the cold crystallization region. When the sample is more crystalline than amorphous then the first peak is smaller or is completely absent. Copyright © 2006 Society of Chemical Industry     

端羧基超支化聚合物-铝无铬鞣剂的制备及应用

根据超支化聚合物官能团度大,反应活性高的特点,利用端羧基超支化聚合物(HPAE-C)的末端羧基与Al3+络合,制备一种新型的无铬鞣剂(HPC-Al),通过单因素实验考察了反应条件对成革收缩温度的影响,确定了最佳合成条件:m(HPAE-C)∶m〔Al2(SO4)3〕=2∶1,反应温度30℃,pH=3,反应时间3 h。采用IR、XRD对产品分子结构进行表征,并采用热重分析仪测试了产品的热性能,HPC-Al的热分解温度为243℃。将产品应用于皮革鞣制中,其单独鞣革收缩温度为76.6℃,铬复鞣后收缩温度大于95℃,且物理力学性能明显提高。     

Water-soluble sulfonated amino–formaldehyde resins. IV. Melamine–urea resins: Synthesis and properties

The factors affecting the preparation and the properties of sulfonated melamine urea–for-maldehyde resins were studied. The resins weresynthesized using a four-step procedure previously used in preparing sulfonated melamine formaldehyde resins. The melamine–urea resins required higher hydroxymethylation and condensation temperatures as the percentage of urea increased. The molecular weight distribution of the prepared resins revealed the formation of low molecular weight species in increasing amounts with higher percentages of urea. The effectiveness of the prepared resins as dispersants for concrete mixes was found to be lower than the pure melamine resins; however, it was possible to enhance them by raising the ratio of sulfonated groups in the resins.     

三聚氰胺树脂鞣剂的研究(Ⅱ)——应用性能研究

丁醇醚化改性的胺树脂鞣革,成革粒面细致、丰满柔软,能促进对油脂、铬的吸收。紫外—可见光扫描,电子探针及电子扫描分析发现,树脂与铬生成了新的化学键。纯树脂鞣革,树脂在革内填充紧密,成革板硬;Cr—树脂结合鞣,铬在革断面分布趋于均匀,树脂包裹在纤维四周。鞣剂用量为削匀革重3％最佳。     

Synthesis and application of methyl methacrylate/butyl acrylate copolymer nanoemulsions as efficient retanning and lubricating agents for chrome‐tanned leather

Two different nano‐emulsions based on methyl methacrylate/butyl acrylate copolymers have been synthesized to be used as retanning and lubricating agents for chrome‐tanned leather. The main difference and characteristics of the two prepared copolymers were studied. The nano particle size of the two copolymers was confirmed using transmission electron microscope (TEM). The influence of the prepared copolymers on chrome‐tanned leather as retanning agents was investigated. The properties of the retanned leather, namely, physicomechanical properties as tensile strength, elongation at break and water absorption, were measured. Thermal gravimetric analysis (TGA) technique was used to examine the thermal stability of the retanned leather. Also, the texture of the grain surface and fibers were inspected using scanning electron microscope (SEM). The retanned leather showed an improvement in its physicomechanical properties, as well as enhancement of its thermal stability as compared with the chrome‐tanned leather. Furthermore, the retanned leather has uniform dyestuff, softness, and firmness of grain. All these promising results provide evidence to the applicability of the prepared copolymer emulsions as efficient retanning and lubricating agents for chrome‐tanned leather. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

FTIR studies of the curing reactions of palm oil alkyd–melamine enamels

Three alkyds of high hydroxyl numbers with oil lengths of 21, 30, and 41 were prepared from crude palm oil. The excess hydroxyl groups provided good compatibility with melamine resins, and also served as sites for crosslinking reactions. They were made into baking enamels by blending with 20% of a commercial melamine resin. All of them could be cured at temperatures below 200°C although thermodecomposition might occur above 290°C. The dry‐hard time of these enamels cured at temperatures between 140–180°C ranged from 10 to 180 min. Fourier transform infrared spectroscopy could be used to follow the major curing reactions. The absorbance of ? O? H and ? N? CH₂? OCH₃ groups showed significant reduction. The changes in the absorbance of these peaks with time and temperature were investigated. The predominant reaction was identified as the formation of methylene ether linkages. However, the self‐condensation reactions of the amino resin and ester linkages did not occur to any noticeable extent. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2309–2315, 2001     

Pyrogallol–formaldehyde thermosetting adhesives

A new thermosetting wood adhesive system from pyrogallol has been developed. Pyrogallol can be easily obtained from tara pods (Caesalpinia spinosa) a native leguminosae of low cost widely distributed in Peru. In this work, polymerization of formaldehyde with pyrogallol was carried out at different pH values and optimal conditions were determined to establish the adhesive formulation. The reactivity of this resin was characterized by differential scanning calorimetry (DSC) and the results were compared with those obtained with resins made with tara tannin, gallic acid, and phenol. The results show that tara tannin and gallic acid are less reactive due to the presence of deactivating groups (i.e., carboxylates) in the phenolic moieties while their polymerization is limited to that of a bidimensional network upon curing. In contrast, pyrogallol–formaldehyde kinetic parameters (Ea and ΔH) were determined and they are comparable with those of phenol-formaldehyde adhesives. In addition, mechanical property values (MOR, MOE, and IB) of particleboards prepared with pyrogallol–formaldehyde compare favorably to those of Canadian standard requirements (CSA). Main assets of the new thermosetting adhesive is lower pressing times and temperatures than those currently used in the industry. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:399–408, 1997     

Effects of alpha‐tocopherol addition to polymeric coatings on the UV and heat resistance of a fibrous collagen material—chrome‐free leather

The US is the world's 3rd largest hide producing country and currently produces approximately 35 million cattle hides annually. The majority of hides are tanned into leather, which is composed of collagen fibers interwoven into fibrous networks. Most leather products are constantly exposed to outdoor environments, therefore UV and heat resistance are very important qualities, particularly for nonchrome‐tanned (chrome‐free) leather. In recent years, we have focused on using environmentally friendly antioxidants that will improve the UV and heat resistance of chrome‐free leather. Tocopherols are well‐known antioxidants commonly used in the cosmetic and food industries. They are known as potent free radical scavengers and highly protective agents for collagen fibers against UV damage. We have investigated their potential to improve the UV and heat resistance of chrome‐free leather. Experiments were conducted by adding 5–12% α‐tocopherol to the polymeric topcoat on the grain of chrome‐free leather. The treated samples were tested in a weatherometer, where they were exposed to artificial sunlight. Colorfastness and mechanical property tests showed that α‐tocopherol significantly improved UV and heat resistance of leather. Dynamic mechanical tests showed that α‐tocopherol reduced the hardening effects on leather caused by UV irradiation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

New melamine–formaldehyde–ketone resins. VI. Preparation of filled molding compositions and compression‐molding materials from reactive solvents based on cyclohexanone

The conditions and a method of preparing new molding compositions and filled compression‐molding materials from melamine–formaldehyde–cyclohexanone resins are described. The resins were obtained from melamine solutions in a reactive solvent prepared by the reaction of 1 mol of cyclohexanone with 7 mol of formaldehyde. The fillers were wood powder and sulfite cellulose. The thermal properties of the samples prepared from the compositions were studied with dynamic thermal analysis, thermogravimetry, and differential scanning calorimetry analysis. Selected mechanical properties [Brinell hardness, unnotched impact strength (Charpy method), and bending strength] of the cured resins were also measured. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Analysis of variations in porosity of metal crosslinked collagen matrix

The fundamental knowledge of the porous nature of crosslinked collagen matrix such as tanned leather is an aid to design appropriate chemicals for leather making. It would also help to target a particular area of matrix to improve its uniformity and other functional properties. The purpose of this study is to analyze the variations in pore sizes of chromium crosslinked collagen matrix, chrome tanned leather, from different animal species and different areas of the same species. In this study, chrome tanned leather from goat and sheep were investigated for surface area, pore size, and distribution. Thermoporometry results show that average pore radius of goat leather is around 2–30 nm and that of sheep is 2–20 nm. Nitrogen adsorption result shows that average surface area of goat (8.24 m²/g) leather is higher than sheep (6.73 m²/g), but the average pore diameter of goat (289 nm) is smaller than sheep (385 nm) leather. It has been found that more numbers of smaller pores are present in goat than sheep leather and all the leather samples including goat and sheep obeyed type‐III adsorption isotherm. Capillary flow porometry analysis gives the smallest, largest, and mean‐flow‐diameter of through‐pores. The average size of largest throat pore diameter of sheep (1313 nm) is smaller than that of goat (1385 nm) leather. In general, the pore volume distribution of sheep leather is higher than that of goat leather. Morphological analysis using scanning electron microscopy shows that pore mouth of goat is deeper than that of sheep. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40835.     

New melamine–formaldehyde–ketone polymers. II. Dissolution of melamine in reactive solvents prepared from cyclohexanone

Reactive solvents of melamine were prepared from cyclohexanone and excess of formaldehyde in the presence of triethylamine catalyst. The solubility of melamine in the solvents was evaluated and the mechanism of dissolution explained on the basis of ¹H‐NMR and IR spectroscopy. Attempts to cure the melamine solutions resulted in melamine–formaldehyde–cyclohexanone polymers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 77–85, 2005     

New melamine–formaldehyde–ketone polymers. III. Coatings from melamine and reactive solvents based on cyclohexanone

The conditions and methods of preparing novel melamine–formaldehyde–cyclohexanone coatings are presented. The coatings were prepared by dissolving melamine in reactive solvents based on formaldehyde and cyclohexanone. The latter were prepared at different molar ratios of the components. The water resistance of the resulting coatings was measured. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1083–1092, 2006     

New melamine–formaldehyde–ketone polymers. IV. Dissolution of melamine in reactive solvents prepared from methyl ethyl ketone

Reactive solvents of melamine were prepared from methyl ethyl ketone and formaldehyde in the presence of the catalyst triethylamine. The solubility of melamine in the resulting solvents was determined, and the mechanism of dissolution was explained with ¹H‐NMR and IR spectroscopy. Preliminary experiments aimed at curing the melamine solutions in reactive solvents into melamine–formaldehyde–butanone resins are reported. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1496–1505, 2006     

Synthesis and properties of high-sulfonated melamine–formaldehyde resin

High-sulfonated melamine–formaldehyde (HSMF) resins were prepared with 1.0–2.0 of sulfite/melamine (S/M) molar ratio. The factors affecting the preparation and the properties of the resin were studied. Chemical analysis indicated that there are 0.98–1.96 sulfonate groups per unit of the polymeric chain. The viscosity of HSMF resins is lower than that of sulfonated melamine–formaldehyde (SMF) resins, and the HSMF resins are more effective superplasticizers at small dosages of admixture. © 1995 John Wiley & Sons, Inc.     

Flame‐retardant materials: synergistic effect of halloysite nanotubes on the flammability properties of acrylonitrile–butadiene–styrene composites

Novel well‐dispersed nanocomposites of halloysite nanotubes and acrylonitrile–butadiene–styrene were prepared. The fire retardancy and thermal stability of these new nanocomposites were improved. A synergistic effect was observed between the halloysite nanotubes and an intumescent flame‐retardant system consisting of ammonium polyphosphate, melamine polyphosphate and pentaerythritol in the acrylonitrile–butadiene–styrene composites. The incorporation of the intumescent flame‐retardant material into the halloysite–polymer nanocomposite system also improved the thermal stability and reduced the peak heat release rate by up to 56.2%, and it significantly reduced the emission of CO and CO₂ gases. The morphology and dispersion of the halloysite nanotubes were characterized using scanning and transmission electron microscopy. The thermal stability and flammability properties were investigated using thermogravimetric analysis and cone calorimeter tests. © 2013 Society of Chemical Industry     

Synthesis and characterization of leather impregnated with bismaleimide (BMI)–Jeffamine® resins

Leather/polymer composites were prepared by impregnating chrome-tanned cattlehide with a solution containing 1,1′-(methylenedi-4,1-phenylene)bismaleimide and Jeffamine® D-230. The mechanical properties in tension, glass transition temperatures, dynamic storage moduli, and moisture absorption of the composites were measured. Impregnated samples showed significant changes in tensile properties, such as the Young's modulus and strain at break, when compared with chrome-tanned cattlehide. In addition, impact energy increased significantly upon formation of the leather/polymer composite over that of the bismaleimide–Jeffamine® resin itself. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1019–1027, 1998     

基于一步法制备含羧基环氧树脂/纳米二氧化锆复合材料

选用乙烯基三乙氧基硅烷改性纳米二氧化锆,与烯丙基缩水甘油醚、甲基丙烯酸通过自由基共聚法制备了含羧基环氧树脂/纳米二氧化锆复合材料。采用傅里叶红外光谱、X射线衍射分别对改性纳米二氧化锆和含羧基环氧树脂/纳米二氧化锆复合材料进行了表征。结果表明:纳米二氧化锆表面引入了双键;纳米二氧化锆较为均匀地分散在聚合物基体中,其表面灰色部分可能是聚合物形成的包裹。将含羧基环氧树脂/纳米二氧化锆复合材料应用于制革鞣制工艺中,应用结果表明:含羧基环氧树脂/纳米二氧化锆复合材料配合酸皮质量3%的铬粉鞣制坯革收缩温度为102.6℃,增厚率为67.26%,与酸皮质量8%的铬粉鞣制坯革相比,柔软度明显提高,鞣制后废液中的Cr_2O_3含量降低了73.2%。     

Syntheses and properties of low‐level melamine‐modified urea–melamine–formaldehyde resins

Syntheses of urea–melamine–formaldehyde (UMF) resins were studied using 2–12% melamine levels and UF base resins that were preadvanced to various different extents. The melamine reaction was carried out at pH 6.3 with F/(U + M) mole ratio of 2.1 until a target viscosity of V was reached (Gardener–Holdt) and then the second urea added at pH 8.0 to give a final F/(U + M) mole ratio of 1.15. Analyses with ¹³C‐NMR and viscosity measurements showed that MF components react fast and the UF components very slowly in the melamine reaction. Therefore, as the extent of preadvancement of UF base resin was decreased, the reaction time to reach the target viscosity became longer and the MF resin components showed high degrees of polymerization. The overpolymerization of MF components resulted in increasingly more opaque resins, with viscosity remaining stable for more than a month. As the preadvancement of UF base resin was increased, the extent of advancement of MF components decreased, to give clearer resins, with viscosity slowly increasing at room temperature. Overall, preadvancing the UF base resin components to an appropriate extent was found to be a key to synthesizing various low‐level melamine‐modified UMF resins. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2559–2569, 2004     

New thermosets obtained by cationic copolymerization of DGEBA with γ‐caprolactone with improvement in the shrinkage. II. Time–temperature–transformation (TTT) cure diagram

Mixtures of diglycidylether of bisphenol A (DGEBA) with different proportions of γ‐caprolactone (γ‐CL) were cured with ytterbium triflate as initiator. The curing was studied with differential scanning calorimetry (DSC) and thermo mechanical analysis (TMA). The results are presented in the form of a time–temperature–transformation diagram. The kinetic analysis was performed by means of the isoconversional integral procedure and the kinetic model was also determined using the Coats–Redfern method. Gelation was determined by means of combined experiences of DSC and TMA. The relationship between the glass transition temperature (T_g) and the degree of conversion α was determined by DSC. Using the isoconversional lines and the T_g‐α relationship, the vitrificacion curve was obtained. The methodology developed makes it possible to obtain the TTT diagram using only no‐isothermal experiments with equivalent results to those using classical isothermal procedures. The addition of γ‐CL accelerates the curing and reduces the shrinkage after gelation and consequently the internal stresses in the material. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Master curve and time–temperature–transformation cure diagram of lignin–phenolic and phenolic resol resins

The aim of this work is to generate both a master curve of resol resins based on the time–temperature superposition principle and their TTT cure diagrams. The samples used for this purpose were lignin–phenolic and phenol–formaldehyde resol resins. A TMA technique was employed to study the gelation of resol resins. In addition, a DSC technique was employed to determine the kinetic parameters through the Ozawa method, which allowed us to obtain isoconversional curves from the data fit to the Arrhenius expression. Establishing the relationship between the glass‐transition temperature and curing degree allowed the determination of the vitrification lines of the resol resins. Thus, using the experimental data obtained by TMA and DSC, we generated a TTT cure diagram for each of resins studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3362–3369, 2007