On-line direct determination of the second virial coefficient of a natural polysaccharide using size-exclusion chromatography and multi-angle laser light scattering

By combining a size-exclusion chromatographic (SEC) separation and an on-line multi-angle light scattering (MALLS) analysis, we have elaborated an original methodology permitting on-line direct determination of the second virial coefficient of molar mass fractions of polydisperse polysaccharides. By assimilating the SEC-MALLS data to a batch mode acquisition, we have obtained on-line the complete Zimm plot of the eluted fractions, leading to knowledge of their weight-average molar mass Mw, radius of gyration r(g) and second virial coefficient A2. Our methodology was successfully applied to a iota carrageenan sample in LiCl 100 mM, EDTA 1 g/l.     

Molecular weight determination of hypromellose phthalate (HPMCP) using size exclusion chromatography with a multi-angle laser light scattering detector

The molecular weight of hypromellose phthalate (HPMCP), a polymer used for enteric coating, was determined using size exclusion chromatography with a multi-angle laser light scattering detector. The values of weight-average molecular weight (Mw) of commercially available grades (HP-55, HP-55S, and HP-50) were 45600, 60200, and 37900, respectively. Their inter-day precisions expressed in terms of the coefficient of variation were less than 3%. A correlation curve between Mw and solution viscosity was prepared so that Mw could be easily estimated from the solution viscosity measured by the compendial method.     

Molecular weight determination of hypromellose acetate succinate (HPMCAS) using size exclusion chromatography with a multi-angle laser light scattering detector

The molecular weight of hypromellose acetate succinate (HPMCAS), a polymer used for enteric coating, was determined by means of size exclusion chromatography with a multi-angle laser light scattering detector. The weight-average molecular weight (Mw) of several lots and grades ranged approximately from 17000 to 20000, and the number-average molecular weight (Mn) was around 13000. The inter-day precision of measurement, in terms of the coefficient of variation, was less than 5%.     

Molar mass characterization of cationic methyl methacrylate-ethyl acrylate copolymers using size-exclusion chromatography with online multi-angle light scattering and refractometric detection

Size-exclusion chromatography (SEC) combined with online multi-angle light scattering (MALS) and refractometric (RI) detection has been employed for the molar mass characterisation of water-insoluble cationic methyl methacrylate-ethyl acrylate copolymers (Eudragit RS and RL). Due to their positive charge, cationic polymers are particularly difficult to separate on a SEC column, in worst cases being completely adsorbed on the oppositely charged packing material. This work has examined how a careful addition of salt (LiCl) to the copolymer solution in ethanol decreases the electrostatic interactions, clearly seen as a decrease in elution volume from the SEC column as well as an improved recovery. At a certain level of ionic strength, typically about 50 mM, the copolymer recovery from the SEC column reached 100% and molar mass distributions corresponding to the complete sample could be obtained. The combined MALS/RI detection gives the opportunity to measure the absolute molar mass independent of recovery and retention. Thus, in this study, it turned out to be a favourable tool for tracing the changes in elution behaviour of the charged copolymer as the ionic strength was increased.     

Comparative study of natural rubber and acrylonitrile rubber reinforced with aligned short aramid fiber

The aims of this paper are three-fold. The first is to determine the reinforcement of high performance short aramid fiber in two representative rubber matrices, namely natural rubber and acrylonitrile rubber. The second is to ascertain the effect of rubber polarity on the reinforcement. The third is to establish a pattern of reinforcement for use with less studied fibers. The rubbers were reinforced either with only aramid fiber or with a hybrid of aramid fiber and carbon black. The fiber contents were varied at 0, 2, 5 and 10 parts (by weight) per hundred rubber (phr) while those of carbon black were 0, 10, 20 and 30 phr. Conventional sulfur vulcanization was used. It was found that aramid fiber can reinforce both rubbers in the low strain region effectively, although to a significantly different degree. The hybrid carbon black provides additional reinforcement at low to medium strains and allows high strain stress upturn to occur in both rubber matrices. The findings enable the preparation of rubber composites having a wide, controllable range of mechanical behavior for specific high-performance engineering applications. Significantly, they also serve as a benchmark for developing reinforced systems from alternative fibers, particularly those from natural sources.     

Equilibration of mixtures of polyamic acids studied using size-exclusion chromatography and light scattering

The transamidation reaction in a polyamic acid solution has been investigated using size-exclusion chromatography and low-angle light scattering. Mixtures of a high-molecular weight (DP = 150) and a low-molecular weight (DP = 10) polymer and of the high-molecular weight polymer with monomer were studied. Mixtures were made at high and low concentrations. The polyamic acid studied is the product of the polycondensation of 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) with oxydianiline (ODA). In all cases the molecular weight distribution equilibrated with time to a most-probable distribution with a DP consistent with the stoichiometry of the mixture. Equilibration required about 2 weeks for mixtures of 10% by weight at ambient temperatures. The effect of addition of a small amount (5%) of low-molecular weight material to sample of high-molecular weight is dramatic; for DP = 150 the molecular weight is decreased by more than one-half. In an entangled solution or melt, this would reduce the viscosity by an order of magnitude.     

Liquid natural rubber (LNR) as a compatibiliser in NR/LLDPE blends—II: the effects of electron-beam (EB) irradiation

Electron-beam (EB) irradiation technique has been used to improve the properties of 60/40 blends of NR/LLDPE in the presence of compatibilisers such as LNR-6 and LNR-16. Improvement in the physical properties of the blend correspond with the increase in the interactions created by EB irradiation as measured by gel content. For this blend ratio, the radiation dose of 200 kGy is found to be optimum. While LNR-6 shows some complimentary effects when it is used together with EB irradiation technique; LNR-16, however, causes an imperfection effect in the blend. The crosslinking process that takes place as a result of EB irradiation occurs at the expense of crystalline arrangement of the semi-crystalline LLDPE. For the morphological fixation purposes EB irradiation technique is found to be very effective.     

Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber-organoclay nanocomposites

Nanocomposites containing natural rubber (NR) as matrix, epoxidized natural rubber (ENR) as compatibilizer and organophilic layered clay (organoclay) as filler were produced in an internal mixer and cured using a conventional sulphuric system. The effects of ENR with 25 (ENR 25) and 50 mol% epoxidation (ENR 50), respectively, were compared at 5 and 10 parts per hundred rubber (phr) concentrations. The organoclay content was fixed at 2 phr. Cure characteristics, clay dispersion, (thermo)mechanical properties of the nanocomposites were determined and discussed. Incorporation of ENR and organoclay strongly affected the parameters which could be derived from Monsanto MDR measurements. Faster cure and increased crosslink density were attributed to changes in the activation/crosslinking pathway which was, however, not studied in detail. The organoclay was mostly intercalated according to X-ray diffraction (XRD) and transmission electron microscopic (TEM) results. The best clay dispersion was achieved by adding ENR 50. This was reflected in the stiffness of the nanocomposites derived from both dynamic mechanical thermal analysis (DMTA) and tensile tests. The tensile and tear strengths of the ENR 50 containing nanocomposites were also superior to the ENR 25 compatibilized and uncompatibilized stocks.     

Size‐exclusion chromatography coupled to multiangle light scattering detection of long‐chain branching in polyethylene made with phillips catalyst

Size‐exclusion chromatography coupled to multiangle light scattering (SEC‐MALS) has been used to detect long‐chain branching (LCB) in polyethylene (PE) from Cr/silica catalysts for the first time. The observed LCB response to several catalyst and reactor variables mostly confirms earlier conclusions drawn from rheological measurements. However, SEC‐MALS has also shed additional light on a few previously unanswered questions. Above all, SEC‐MALS shows the placement of branching within the MW distribution, which was not previously known, and which may explain some of the unique molding behavior of Cr‐derived PE. This new SEC‐MALS data also provide insight into the mechanism of LCB formation, which is discussed. Like earlier studies based on rheology, this new study demonstrates that the commonly accepted view of macromer incorporation may be overly simplistic. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Stabilization effect of lignin in natural rubber

A series of carbon black filled natural rubbers containing lignin was tested from the view point of their thermo-oxidative aging. Lignin is biopolymer that belongs to the main components of wood. Mechanical properties and crosslink density of lignin stabilized vulcanisates were measured before and after thermo-oxidative aging for 24, 72, 168, 240 and 408 h at 80 °C. The results were compared with those from NR vulcanisates stabilized with the commercial rubber antioxidant N-phenyl-N-isopropyl-p-phenylene diamine (IPPD). The results obtained show that lignin exerts a stabilizing effect in carbon black filled natural rubber. Its effect is comparable with that of conventional synthetic antioxidant. Moreover, the addition of lignin increased the stabilizing effect of IPPD.     

Study of the analysis of alkoxyglycerols and other non-polar lipids by liquid chromatography coupled with evaporative light scattering detector

An HPLC method with evaporative light scattering detection (ELSD) for the simultaneous analysis of various lipid classes, particularly alkoxyglycerols and acylglycerols with very similar structure and polarity, has been developed. These lipid classes are frequently found in numerous fats and oils such as shark liver oils and can serve as substrates for lipase-catalyzed reactions. This method utilizes a silica column and a gradient elution of isooctane, methyl tert-butyl ether and 2-propanol in different proportions. Separation between squalene, sterol esters, and fatty acid ethyl esters has been achieved in a time of analysis slightly higher than 8 min. In addition, a good resolution between 1,3-diacylglycerols and free sterols was also attained in the same run, with a broad range of concentrations. Excellent precision regarding the retention times was obtained. The limit of detection for the different lipid classes studied was below 1 microg. Intra-day and inter-day variation of retention times and areas was also evaluated. The relative standard deviation of intra-day variation for retention times and areas never exceeded of 0.1 and 10, respectively. The HPLC-ELSD method was also optimized to separate and quantify the hydrolysis products of alkoxyglycerols and acylglycerols (mono-esterified and non-esterified alkoxyglycerols and mono-esterified and di-esterified acylglycerols) at the same time, rendering a useful method for the study of lipase-catalyzed reactions and a wide variety of fats and oils. The present methodology not only separates 18 different lipid classes with a good reproducibility, but it is also able to estimate the relative proportion in which they are found in a broad range of concentrations.     

Improving the mechanical properties of short pineapple leaf fiber reinforced natural rubber by blending with acrylonitrile butadiene rubber

This work proposes a simple method for improving the rubber to filler stress transfer in short pineapple leaf fiber-reinforced natural rubber (NR). This was achieved by replacing some of the non-polar NR by polar acrylonitrile butadiene rubber (NBR). The amount replaced was varied from 0% to 20% by weight. The mixing sequence was designed so that the fiber would be coated with polar NBR before being dispersed in the NR matrix. A comparison system in which the mixing was carried out in a single step was also examined. Despite the fact that the two rubbers are immiscible, it was found that significant improvement of the stress transfer in the low strain region can be obtained. The mixing sequence affected the mechanical properties of the resulting composites. It is concluded that frictional stress transfer between the immiscible rubbers contributes more to the total stress transfer than does the frictional stress transfer between non-polar NR and polar cellulose fiber.     

Oxidation of natural rubber using a sodium tungstate/acetic acid/hydrogen peroxide catalytic system

A catalytic system based on Na₂WO₄/CH₃COOH/H₂O₂ effectively oxidizes natural rubber (NR) to prepare telechelic epoxidised liquid natural rubber (TELNR). The Na₂WO₄/CH₃COOH/H₂O₂ catalytic system possesses a much higher epoxidation efficiency than the traditional CH₃COOH/H₂O₂ system: the epoxidation degree (X_epoxy) of products increases from merely 5.6% (CH₃COOH/H₂O₂) to values as high as 52.1% (Na₂WO₄/CH₃COOH/H₂O₂) by reacting for 24 h at 60 °C. Moreover, this catalytic system also induces hydrolytic degradation so that the weight average molecular weight of NR decreases, e.g., from 14.10 × 10⁵ Da (NR) to 0.57 × 10⁵ Da (TELNR) after reacting for 30 h.The catalytic process probably proceeds via a mononuclear tungsten peroxo-species with coordinated peracetyl/acetyl group, as suggested by ESI-MS measurements. During oxidation, the tungstic anion [W(CH₃COOO)(O)(O₂)₂]⁻ not only catalyzes NR epoxidation, but also induces a further oxidation of epoxy groups to form ketones and aldehydes.     

Quantitative analysis of isoprene units in natural rubber and synthetic polyisoprene using 1H-NMR spectroscopy with an internal standard

Isoprene units in natural rubber (NR) and its synthetic analogues were quantified by ¹H-NMR spectroscopy using polyethylene glycol (PEG) as an internal standard. The effect of PEG and rubber concentrations, molar ratio of rubber/PEG, measuring temperature and scan number on the quantification was investigated to establish the respective working range. Analysis of commercial grades of NR revealed that the differences in 1,4 isoprene content is caused by the production process and feedstock, in which proteins and lipids were found to be the major impurity in NR. Gel fraction of NR has insignificant effect on the measurement of 1,4 isoprene content. Furthermore, the new method was found to produce good results for the quantification of 1,4 and 3,4 units of synthetic polyisoprenes.     

Degradation of polychloroprene/natural rubber (PCP/NR) blends by photo-Fenton process

The effect of light and FeCl₃·6H₂O on polychloroprene (PCP)/natural rubber (NR) blends in toluene solution were investigated to demonstrate the influence of each polymer on the degradation process. The contributions of total polymer concentration (C_p), temperature (T) and polychromatic light exposure (L) on the degradation process were investigated through a 2³ factorial design approach. Degradation kinetics was examined by solution viscosity time data. FTIR spectroscopy and TGA were used to characterize the degradation. The exposure of the PCP/NR blend solution containing FeCl₃·6H₂O to light induces degradation in the polymers. A decrease of up to 70% in solution efflux time at constant temperature and without aggregation or phase separation was observed. PCP degradation by-products amplify the degradation of NR, as evidenced by the decrease in the PCP/NR 1:99 (w/w) solution efflux time, which was larger than that of the pure NR solution. The film cast from the solution exposed to light was thermally less stable than the one which was cast without FeCl₃·6H₂O.     

The morphology and thermal properties of liquid natural rubber (LNR)-compatibilized 60/40 NR/LLDPE blends

The effects of LNR as a compatibilizer in binary blends of 60/40 NR/LLDPE have been investigated by means of differential scanning calorimetry, dynamic mechanical analysis and scanning electron microscopy. Special emphasis was given to the role of LNR in inducing interactions between NR and LLDPE. It has been observed that increasing LNR content decreases T_m and ΔH_f which are indicators of the crystalline part of the blends. The decrease reflects a reduction in the degree of crystallinity which is due to the interference in the form of NR dissolution into the LLDPE phase. The phenomenon leads to a shift in T_g of the amorphous part of LLDPE to higher temperatures as observed by DMA thermograms. The dissolution effect creates better interactions between the phases leading to improvements in the compatibility of the blends. Further confirmation was obtained through SEM examination.     

微流蒸发光散射检测器与毛细管液相色谱的联用及其在银杏叶提取物分析中的应用

将微流蒸发光散射检测器( μELSD)与毛细管液相色谱(cLC)联用,应用于中药银杏叶提取物及其分散片制剂的分离检测领域。首先对 μELSD仪器参数进行优化。通过调节漂移管温度与载气流量,提高了分析物的响应,并减小了噪声。然后,搭建了cLC-μELSD分离检测平台,其相对常规LC可大大减小实验试剂消耗。流动相A为0.05%(体积分数,下同)三氟乙酸(TFA)水溶液,流动相B为含0.05% TFA的甲醇溶液。最优的洗脱梯度条件为:0~10 min,5%B~25%B;10~25 min,25%B~38%B;25~35 min,38%B;35~40 min,38%B~42%B;40~55 min,42%B~50%B。银杏叶提取物和复杂中药制剂银杏叶提取物分散片都得到了较好的分离,并在其中鉴定到紫外波段几乎无吸收的重要内酯类活性成分白果内酯以及银杏内酯A、B和C。测定了不同厂家银杏叶提取物中萜类内酯洗脱时间的相对标准偏差,结果均不大于2.42%,表明该体系在目标物的分析上具有良好的重现性。实验证明所建立的cLC-ELSD体系在复杂中药体系的分离检测中有良好的应用性。     

Alkanolamide as an accelerator,filler-dispersant and a plasticizer in silica-filled natural rubber compounds

A feasibility study was carried out on the utilization of Alkanolamide (ALK) on silica reinforcement of natural rubber (NR) by using a semi-efficient cure system. The ALK was incorporated into the NR compound at 1.0, 3.0, 5.0, 7.0 and 9.0 phr. An investigation was carried out to examine the effect of ALK on the cure characteristics and properties of NR compounds. It was found that ALK gave shorter scorch and cure times for silica-filled NR compounds. ALK also exhibited higher torque differences, tensile modulus, tensile strength, hardness and crosslink density of up to 5.0 phr of ALK loading, and then decreased with further increases of ALK loading. The resilience increased with increased ALK loading. Scanning electron microscopy (SEM) micrographs proved that 5.0 phr of ALK in the silica-filled NR compound exhibited the greatest matrix tearing line and surface roughness due to higher reinforcement level of the silica, as well as better dispersion and cure enhancement.     

Natural rubber/clay nanocomposites: Influence of poly(ethylene glycol) on the silicate dispersion and local chain order of rubber network

A novel preparation of natural rubber (NR)/Na⁺-montmorillonite (MMT) nanocomposites in only one step by using poly(ethylene glycol) (PEG) has been investigated. PEG behaves as dispersing agent favouring the intercalation of rubber chains into the silicate galleries and providing substantially improved clay dispersion. Intercalated/exfoliated miscible hybrids were observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of PEG on the network structure has also been evaluated by static proton double-quantum nuclear magnetic resonance spectroscopy (¹H DQ NMR) at low-field. Silicate nanoparticles with a high aspect ratio (clay tactoids) and a more crosslinked rubber network have been obtained for an optimum PEG/MMT ratio. Both effects were responsible of the enhancement on mechanical properties.