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Separate stages of mathematical processing of thermogravimetric data, the difficulties most often encountered, and typical error sources are considered. A complex procedure of automatic acquisition and editing of experimental data, including calculation of effective kinetic parameters, is described and an appropriate algorithm for the 15 BCM-5 microcomputer is presented. The computer calculation of the kinetic parameters of the multistage thermal decomposition of a polyamide fibre is given as an example.
Abstract
The copolyamides consisting of ε-caprolactam and 6.1–24.5 wt.% of nylon salt prepared from adipic acid and 1-(2-aminoethyl) piperazine were synthesized. Physical and thermal characteristics of polyamide 6 and the copolyamides were compared. Nylon salt does not influence the polyreaction equilibrium so it is possible to prepare the copolyamides with high molecular weight and with the content of low-molecular compounds comparable with that of pure PA 6. Melting temperatures of the copolyamides are lower in comparison with PA 6 and decrease proportionally to the amount of the nylon salt. The thermal stability of the copolyamides is good and equal to that of PA 6. The melting enthalpies indicate that the process of crystallization of the copolyamides is influenced by the time of crystallization and the amount of comonomer present. Longer time of the crystallization assures higher degree of crystallization. The kinetics and the level of crystallization are positively influenced by the mobility of copolyamide segments mainly up to 10 wt.% of comonomer.
TLC and HPLC have been used for preliminary evaluation of the phenolic acids occurring in the leaves, inflorescences, and rhizomes of Silphium perfoliatum L. Free phenolic acids and those released after acidic and basic hydrolysis were subjected to chromatographic analysis. Qualitative TLC analysis was performed by one- and two-dimensional ascending development on plates coated with cellulose, polyamide 11 F 254 , and silica-gel 60 F 254 . Reversed-phase HPLC was performed with photodiode-array detection.Seven phenolic acids were present, in the free and bonded forms, in the raw material studied. Caffeic and protocatechuic acids occurred in all the fractions analyzed. p -Coumaric and p -hydroxybenzoic acids were identified in all the free phenolic acid fractions. Ferulic acid was found in inflorescences and rhizomes and vanillic acid in leaves and inflorescences. After acidic hydrolysis chlorogenic acid was identified in leaves and p -hydroxybenzoic and vanillic acids in inflorescences. After basic hydrolysis phenolic acid fractions isolated from leaves also contained p -coumaric acid; those isolated from inflorescences contained p -coumaric, ferulic and p -hydroxybenzoic acids. It was found that caffeic acid was the most predominant phenolic acid in S. perfoliatum (from 67.8% in the leaves to 94.4% in the rhizomes).
Relationships between R M values and mobile phase composition have been determined for the six antihyperlipidemic agents-bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil. The drugs were separated on silica gel, CN, and Diol plates using mobile phases containing n -hexane as weakly polar diluent and five polar modifiers: acetone, dioxane, ethyl methyl ketone, ethyl acetate, and tetrahydrofuran. The optimum mobile phases were also investigated on alumina, NH 2 , and polyamide phases for comparison. The linearity of relationships between R M and modifier volume fraction, molar fraction, and logarithm of molar fraction was calculated. Plates were developed in horizontal chambers, visualized under UV irradiation at λ = 254 nm, and scanned with a densitometer in the multi-wavelength scan mode. Most results fitted the Snyder-Soczewinski equation with r > 0.9; for approximately half r > 0.99. Separation of all the drugs was achieved on Diol plates with mobile phases containing 20–30% of each modifier in n -hexane, and with hexane-acetone, 9 + 1, on CN plates. Five drugs were separated using the same mobile phases on silica gel. The best separation was obtained on Diol plates with tetrahydrofuran-hexane, 2 + 8, as mobile phase.
Summary
The aim of this work was to establish qualitative and quantitative methods for studying Guyinye residue extracts and Turkish gall (TG) cream. This study involved qualitative and quantitative analyses of gallic acid and methyl gallate and determined their preliminary antioxidant activity by high-performance thin-layer chromatography (HPTLC) and thin-layer chromatography-1,1-diphenyl-2-trinitrobenzene hydrazine (TLC-DPPH) in Guyinye residue extracts and TG cream. The thin-layer plate was a polyamide film and glacial acetic acid, methanol, ethyl acetate, and formic acid (10:6:2:1, volume ratio) were used as the developing agent. The scanning wavelength was 280 nm. Results showed that the RF values of gallic acid and methyl gallate were 0.57 ± 0.05 and 0.72 ± 0.05, respectively, and their linearity ranges were 0.001–0.005 and 0.00025–0.00125 mg with correlation coefficients of 0.9990 and 0.9994, respectively, which indicated a good linear relationship. The detection limits of gallic acid and methyl gallate were 3 and 75 ng, respectively, and their quantification limits were 10 and 250 ng, respectively. The average recovery was 98.59% and 98.33%, and the relative standard deviation (RSD) was 2.49% and 3.55%, respectively. Gallic acid was more remarkable than methyl gallate in antioxidant activity. Thus, HPTLC combined with TLC-DPPH, which can rapidly and accurately determine gallic acid and methyl gallate in Guyinye residue extracts and TG cream, is a simple, accurate, and rapid qualitative and quantitative method.
Influence of transcrystallinity on DSC analysis of polymers
Experimental and theoretical aspects
Abstract
Intense parasitic nucleation has been observed at the surface of differential scanning calorimetry samples for various polymers, whereas their crystallization traces exhibit complex shapes. Revisited overall kinetics theories and computer simulation, taking into account small thickness of samples and transcrystallinity effects, allow to explain and reproduce experimental ‘double peaks’, currently observed with polyamide 6-6. The beginning of the transformation and the main peak are attributed to surface and bulk nucleations, respectively. As a consequence, any DSC experiment should be followed by a microscopic observation and more accurate models including thermal gradients and resistances should be developed for their interpretation.
Abstract
Liquid crystalline polymer/polyamide 66 (LCP/PA66) and LCP/poly(butyl terephthalate) (LCP/PBT) blends were compounded using a Brabender Plasticorder equipped with a mixing chamber. The LCP employed was a semi-flexible liquid crystalline copolyesteramide based on 30 mol% of p-amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). The Flory-Huggins interaction parameters (χ12) of the LCP/ PA66 and LCP/PBT blends are estimated by melting point depression from DSC measurement. The results indicate that c12 values all are negative for LCP/PA66 and LCP/PBT blends, and when the LCP content in these blends is more than 10 mass%, the absolute value of χ12 decreases. Thereby, we can conclude that LCP/PA66 and LCP/PBT blends are fully miscible in the molten state, the molecular interaction between the LCP and PA66 is stronger than that between LCP and PBT. As the LCP content in LCP/PA66 and LCP/PBT blends is more than 10 mass%, the molecular interaction between LCP and matrix polymer decreases.
In this study, pressed apricot (Prunus armeniaca L.) juice was concentrated using complex membrane technology with different module combinations: UF-RO-OD, UF-RO-MD, UF-NF-OD and UF-NF-MD. In case of the best combination a cross-flow polyethylene ultrafiltration membrane (UF) was applied for clarification, after which preconcentration was done using reverse osmosis (RO) with a polyamide membrane, and the final concentration was completed by osmotic distillation (OD) using a polypropylene module. The UF-RO-OD procedure resulted in a final concentrate with a 65-70 °Brix dry solid content and an excellent quality juice with high polyphenol content and high antioxidant capacity.Nanofiltration (NF) and membrane distillation (MD) were not proper economic solutions.The influence of certain operation parameters was examined experimentally. Temperatures of UF and RO were: 25, 30, and 35 °C, and of OD 25 °C. Recycle flow rates were: UF: 1, 1.5, and 2 m3 h−1; RO: 200, 400, and 600 l h−1; OD: 20, 30 and 40 l h−1. The flow rates in the module were expressed by the Reynolds number, as well. Based on preliminary experiments, the transmembrane pressures of UF and RO filtration were 4 bar and 50 bar, respectively. Each experimental run was performed three times. The following optimal operation parameters provided the lowest total cost: UF: 35 °C, 2 m3 h−1, 4 bar; RO: 35 °C, 600 l h−1, 50 bar; OD: 20, 30 and 40 l h−1; temperature 25 °C.In addition, experiments were performed for apricot juice concentration by evaporation, which technique is widely applied in the industry using vacuum and low temperature.For description the UF filtration, a dynamic model and regression by SPSS 14.0 statistics software were applied.
Abstract
The injection moulding of semi-crystalline thermoplastic polymers requires an exact knowledge of the thermodynamic data and of the crystallization kinetics. The behaviour of the polymer melt during rapid cooling in the mould determines, to a great extent, the quality and usability of a final product. Technical raw materials are often equipped with nucleating agents in order to obtain crystallization within the desired temperature range and at the required rate. The use of recycled material (regranulate) shows an analogous effect such as the addition of nucleating agents, i.e. crystallization begins at a higher temperature and a higher crystallization rate is detected compared to materials without added regranulate. Heat flux DSC was used to study the crystallization of polyamides, polyolefins and polyoxymethylene during cooling at various cooling rates. Although the temperature gradients and pressures which occur in the proceesing machine cannot be realised in DSC tests, the DSC results reproduce the direction of influence of the regranulate additive very clearly.
Poly(2-methylpentamethylene terephthalamide) (Nylon M5T) is a new high temperature aromatic polyamide developed by Hoechst Celanese. In this paper thermal properties of Nylon M5T chips, as well as as-spun and drawn fibers were studied by DSC, DMA, hot stage microscopy and WAXS.T g of the fully amorphous Nylon M5T is 143°C when measured by DSC;T g increases with crystallinity to 151°C. The temperature dependence of the solid and melt specific heat capacities has also been determined. The heat capacity increase at the glass transition of the amorphous polymer is 103.9 J °C−1 mol−1.T g by DMA for the as-spun fiber is 155°C, for a drawn fiber is 180°C. Three secondary transitions were observed by DMA in addition to the glass transition. These correspond to a local mode relaxation of the methylene groups at −120°C, onset of rotation of the amide-groups at −65°C and the onset of the rotation of the phenylenegroups (at 63°C). The crystallinity of Nylon M5T strongly depends on the rate of cooling from the melt. The isothermal crystallization data are melt temperature dependent: two-dimensional crystallization takes place when the samples are crystallized from higher melt temperatures, and this phase changes into a spherulitic structure during cooling to room temperature. Spherulitic crystallization occurs when lower melt temperatures are used. This polymer has three crystal forms as indicated by DSC, DMA and WAXS data. The crystal to crystal transitions are clearly visible when amorphous samples are heated in the DSC, or the DMA curves of as-spun fibers are recorded. It is experimentally shown that a considerable melting of the lower temperature crystal forms takes place during the crystal to crystal transitions. The equilibrium melting point as measured by the Hoffman-Weeks method, has been determined to be 339°C.
