Rheological and mechanical properties of percolated cyanate ester nanocomposites

The rheological properties and mechanical properties of percolated cyanate ester monomer/layered silicate mixtures are reported. A number of different cation exchanged montmorillonites were examined in an effort to achieve maximal montmorillonite delamination. The dispersion throughout the cyanate ester of a montmorillonite with phenylated ammonium cations (2MBHT MMT) results in the formation of a percolated network. The rheology of this percolated network undergoes a viscous liquid to elastic solid transition at 4 wt% montmorillonite. The percolation of the montmorillonite in the cyanate ester results in a significant improvement in crack resistance (80%) without a sacrifice of flexural strength.     

Physical properties of fish gelatin-based bio-nanocomposite films incorporated with ZnO nanorods

Well-dispersed fish gelatin-based nanocomposites were prepared by adding ZnO nanorods (NRs) as fillers to aqueous gelatin. The effects of ZnO NR fillers on the mechanical, optical, and electrical properties of fish gelatin bio-nanocomposite films were investigated. Results showed an increase in Young''s modulus and tensile strength of 42% and 25% for nanocomposites incorporated with 5% ZnO NRs, respectively, compared with unfilled gelatin-based films. UV transmission decreased to zero with the addition of a small amount of ZnO NRs in the biopolymer matrix. X-ray diffraction showed an increase in the intensity of the crystal facets of (10^ī1) and (0002) with the addition of ZnO NRs in the biocomposite matrix. The surface topography of the fish gelatin films indicated an increase in surface roughness with increasing ZnO NR concentrations. The conductivity of the films also significantly increased with the addition of ZnO NRs. These results indicated that bio-nanocomposites based on ZnO NRs had great potentials for applications in packaging technology, food preservation, and UV-shielding systems.     

Optical and thermo-mechanical properties of composite films based on fish gelatin/rice flour fabricated by casting technique

Packaging films based on fish gelatin-rice flour (FG-RF) at different blend ratios (FG-RF ≈ 10:0, 8:2, 6:4, 5:5 and 0:10, w/w) using 30% (w/w) glycerol as plasticiser were prepared and characterised. FG-RF composite films exhibited lower tensile strength (TS) and elongation at break (EAB), compared to FG film (P < 0.05). Higher water vapour permeability (WVP), but lower water solubility (WS) was obtained for FG-RF composite films having the increased proportion of RF (P < 0.05). Light transmission in ultraviolet (UV) and visible regions (200–800 nm) was lowered in all FG-RF composite films, indicating excellent light barrier characteristics. Based on FTIR spectra, significant changes in molecular structure and lower intermolecular interactions between FG and RF molecules were found in FG-RF (8:2) composite film. Thermogravimetric analysis indicated that FG-RF (8:2) composite film had only 7.61% (w/w) heat-stable mass residues in the temperature range of 50–600 °C. DSC thermograms suggested that FG-RF (8:2) composite film consisting of amorphous/microcrystalline layers of partially miscible aggregated junction zones and the coexisting two different order phases of unbound domains. SEM micrographs elucidated that FG-RF (8:2) composite film was rougher than FG film, but no signs of phase separation between film components were observed, thereby confirming their potential use as packaging material.     

Rheological properties of cement pastes: A discussion of structure formation and mechanical property development

The objective of this paper is to examine the evolution of rheological properties (e.g. yield stress) and to evaluate the use of these properties as a method to monitor structure formation and mechanical property development (i.e. setting) in cementitious materials. The authors utilize the stress growth technique to assess the development of a solid structure in cement pastes. An increase in the yield strength of the system due to cement hydration is identified to occur near the end of the dormant period as identified by chemical shrinkage. The transition from a fluid to a solid state and the development of elastic properties in the material are both noted to occur prior to the time of initial set as identified by the Vicat needle.     

Mechanical properties of native and crosslinked gelatins in a bending deformation

Gelatin samples, native and chemically crosslinked with three different diisocyanates, were studied by bending‐creep measurements. These samples were characterized by the number‐average molecular weight of a chain segment between two points of crosslinkage M_c. The chemical network was found to contribute to a marked extent to the mechanical behavior of the samples. The dependence of the creep compliance on the time for different loads was determined. The experimental results were compared with calculated ones according to a model, comprising four parameters, to obtain a better understanding of structure–property relationships for these materials. A very good agreement between the model and experimental data was found. Two of the fitting parameters, however—the relaxation time and η (which is connected with the viscosity)—were found to strongly depend on the time of the experiment. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2041–2048, 2000     

Rheological and thermal properties of m-LLDPE blends with m-HDPE and LDPE

The dynamic and steady state behavior of metallocene linear low density polyethylene (m-LLDPE) blended with metallocene high density polyethylene (m-HDPE) and with low density polyethylene (LDPE) were measured in parallel plate rheometer at 160, 180, and 200 °C. The composition dependence of zero shear viscosity η₀, the characteristic relaxation time τ₀ and the characteristic frequency ω₀ of m-LLDPE/m-HDPE blends show a linear variation in the whole range of weight fraction, which indicates that m-LLDPE/m-HDPE blends are miscible blend. At the same time, m-HDPE showing a ‘dissident’ rheological behavior should possess a certain very low degree of LCB. Two calculation methods of LCB verify this point. In contrast, the composition dependence of zero shear viscosity η₀ of m-LLDPE/LDPE blends shows a positive deviation from the log-additivity rule, which can be well fitted by using the immiscible blend equation of Utracki. The characteristic relaxation time τ₀ and the characteristic frequency ω₀ have a sharp variation with the small amounts of LDPE in the blends, which also indicates a phase separation in the system. The thermal properties of m-LLDPE/m-HDPE blends are very similar to a single-component system. However, m-LLDPE/LDPE blends are immiscible in both melt and crystal states. DSC results are consistent with the rheological properties of these two series of blends.     

柠檬酸交联可食用红薯淀粉膜的制备和性能

本文采用浇铸法制备了柠檬酸交联红薯淀粉膜,并对膜的机械性能、吸水性、水溶性、抗甲酸溶解性等进行了测试。结果发现交联后的淀粉膜的拉伸力显著提高、吸水性增强、水溶性降低、抗甲酸溶解性增强。膜的机械性能的改善与柠檬酸的浓度、交联温度、交联时间有关,实验发现,当柠檬酸的浓度为淀粉浓度的5％,165℃处理5分钟时,膜的拉伸力比未...     

Thermophysical and mechanical properties of novel polymers prepared by the cationic copolymerization of fish oils, styrene and divinylbenzene

New polymeric materials have been prepared from the cationic copolymerization of fish oil ethyl ester (NFO), conjugated fish oil ethyl ester (CFO) or triglyceride fish oil (TFO) with styrene and divinylbenzene initiated by boron trifluoride diethyl etherate (BF₃·OEt₂). These materials are typical thermosetting polymers with crosslink densities ranging from 1.1×10² to 2.5×10³ mol/m³. The thermogravimetric analysis of the new fish oil polymers exhibits three distinct decomposition stages at 200–340, 340–500 and >500°C, respectively, with the maximum weight loss rate at approximately 450°C. Single glass-transition temperatures of T_g=30–109°C have been obtained for the fish oil polymers. As expected, these new polymeric materials exhibit tensile stress–strain behavior ranging from soft rubbers through ductile to relatively brittle plastics. The Young's modulus (E) of these materials varies from 2 to 870 MPa, the ultimate tensile strength (σ_b) varies from 0.4 to 42.6 MPa, and the percent elongation at break (ε_b) varies from 2 to 160%. The failure topography indicates typical fracture mechanisms of rigid thermosets, and the unique fibrillation on the fracture surface gives rise to relatively high mechanical properties for the corresponding NFO polymer. The new fish oil polymers not only exhibit thermophysical and mechanical properties comparable to petroleum-based rubbery materials and conventional plastics, but also possess more valuable properties, such as good damping and shape memory behavior, which most petroleum-based polymers do not possess, suggesting numerous, more promising applications of these novel fish oil-based polymeric materials.     

疏水缔合聚合物交联弱凝胶流变性能研究

疏水缔合聚合物交联弱凝胶体系含有化学交联和物理缔合双重性能,采用Bohlin CVO流变仪测试了该体系的流变性,并采用Carreau模型和幂律模型对测试数据进行拟合。结果表明,疏水缔合聚合物交联弱凝胶体系完全满足这些模型,其零剪切粘度和稠度系数均随着交联剂和聚合物浓度的增加而增加。     

Effects of cross-linking in nanostructure and physicochemical properties of fish gelatins for bio-applications

The development of advanced materials from proteins requires their modification to improve functional properties, mainly barrier properties. In order to obtain the improvement of properties desirable for some bio-related uses, such as food, pharmaceutical and biomedical applications, Maillard reaction, a natural and non-enzymatic reaction between proteins and sugars, can be promoted and controlled by sugar contents and heating treatments. In this paper, Maillard reaction improves the barrier properties of fish gelatin films, providing an excellent protection against UV light and decreasing solubility due to the cross-linking induced by heating and lactose addition. Furthermore, a fluorescence compound is formed during this reaction and can be used as an indicator of the reaction progress. The knowledge of reaction kinetics as well as the changes observed in the nanostructure as a consequence of the cross-linking between fish gelatin and lactose provides the scientific information needed to spread the field of application of the products that can be manufactured using these natural reactive polymers.     

Rheological properties of sepiolite ground in acid and alkaline media

Effects of different acids (HCl, H₂SO₄ and citric acid) on rheological properties of brown sepiolite from the Eskisehir region of Turkey have been determined. The optimum apparent viscosity value was obtained at the natural pH of the suspension. Below the natural pH, partial collapse of the structure due to the release of Mg ions causes a significant decrease in viscosity values. However, below pH 1, there is a substantial increase in viscosity values owing to gel formation. On the other hand, above the natural pH of suspension, increased amounts of OH ions lead to a decrease in viscosity values and inhibit gel formation. The reversible nature of sepiolite was tested by changing the pH of acid and alkaline treated sepiolite suspensions back to its natural pH by washing with water and acid, respectively. In summary, from a practical point of view, there is no favorable effect of acid treatment of sepiolite on its rheological properties. On the contrary, reducing the pH to natural pH after grinding in a basic environment led to an improvement in rheological properties.     

Tailoring the mechanical properties of polyacrylamide-based hydrogels

Here, we studied the mechanical properties of polyacrylic acid-co-polyacrylamide (pAAc/pAAm) and polyacrylate-co-polyacrylamide (pNaAc/pAAm)-based hydrogels as a function of composition and total polymer content. While both polyacrylate and polyacrylic acid are weakly-charged polyelectrolytes with carboxylate side groups, they exhibit different behavior as copolymers with polyacrylamide. In swelling studies the highest degree of volumetric expansion occurs in the polyacrylate-rich hydrogels. Rheological measurements indicate that the shear storage modulus of the hydrogels typically increases with the percentage of polyacrylamide for a given polymer volume fraction; however, the simultaneous strengthening and embrittling effects of polyacrylamide as a copolymer are more dramatic for the pNaAc/pAAm hydrogels.     

Rheological properties of cement paste: Thixotropic behavior and structural breakdown

In this work, a new material model is presented to simulate rheological behavior of cement paste. This material model is among others based on combined concepts by Hattori and Izumi and by Tattersall and Banfill. More precisely, coagulation, dispersion and re-coagulation of the cement particles (giving a true thixotropic behavior) in combination with the breaking of certain chemically formed linkages between the particles (giving a so-called structural breakdown behavior) are assumed to play an important role in generating the overall time-dependent behavior of the cement paste. The model evaluation is done by comparing experimental data with model prediction.     

Rheological properties of cementitious materials containing mineral admixtures

The rheological properties of cementitious materials containing fine particles, such as mineral admixtures (MA), were investigated using a Rotovisco RT 20 rheometer (Haake) with a cylindrical spindle. The mineral admixtures were finely ground blast furnace slag, fly ash and silica fume. The cementitious materials were designed as one, two and three components systems by replacement of ordinary portland cement (OPC) with these mineral admixtures. The rheological properties of one-component system (OPC) were improved with increasing the dosage of PNS-based superplasticizer. For two-components systems, yield stress and plastic viscosity decreased with replacing OPC with blast furnace slag (BFS) and fly ash (FA). In the case of OPC-silica fume (SF) system, yield stress and plastic viscosity steeply increased with increasing SF. For three components systems, both OPC-BFS-SF and OPC-FA-SF systems, the rheological properties improved, compared with the sample with SF. In the two and three components systems, the rheological properties of samples containing BFS improved much more than with FA replacement alone.     

Rheological and mechanical properties of recycled polypropylene

In order to verify the possibility of manufacturing good quality articles by recycled polypropylene (PP), a study on the effect of many recycling operations on the rheological and mechanical properties of PP was conducted. The amount of degradation occurring during the reprocessing was estimated in the melt state by means of rheological measurements and the results obtained were correlated with the weight average molecular weight M_w and the molecular weight distribution MWD. Since the properties in the solid state are strictly dependent upon the molecular structure parameters and the morphology, mechanical properties were checked on films produced from virgin and recycled PP with a cast technology. Moreover, in order to estimate the effect of film composition and of the number of reprocessings on the final properties of the manufactured articles, blend films having different percentages of PP recycled several times and virgin PP were prepared.     

Rheological and mechanical properties in polyethylene blends

Melt rheology and mechanical properties in linear low density polyethylene (LLDPE)/low density polyethylene (LDPE), LLDPE/high density polyethylene (HDPE), and HDPE/LDPE blends were investigated. All three blends were miscible in the melt, but the LLDPE/LDPE and HDPE/LDPE blends exibiled two crystallization and melting temperatures, indicating that those blends phase separated upon cooling from the melt. The melt strength of the blends increased with increasing molecular weight of the LDPE that was used. The mechanical properties of the LLDPE/LDPE blend were higher than claculated from a simple rule of mixtures, whiele those of the LLDPE/HDPE blend conformed to the rule of mixtures, but the properties of HDPE/LDPE were less than the rule of mixtures prediction.     

Rheological properties of organoclay suspensions in epoxy network precursors

This paper deals with the evolution of the state of dispersion of organically modified montmorillonites in epoxy or amine precursors. The epoxy prepolymer is a diglycidyl ether of bisphenol A (DGEBA) and the curing agent is an aliphatic diamine with a polyoxypropylene backbone (Jeffamine D2000). The clay dispersion is evaluated at the platelet scale (nanoscopic scale) from X-ray spectrometry [wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS)] and at the aggregates scale (microscopic scale) from rheological analysis. The organoclays used form gels in the monomers above the percolation threshold if no shear is applied and present a mechanical gel/sol transition when shear stress increases. Gel strength and viscosity at high shear rates are linked to the nanometric state of dispersion and reveal the existence of two different organizations depending on organoclay/monomer interactions:

(i) When the clay shows good interactions with the monomer, a significant swelling of the clay galleries by the monomer is obtained. These swollen particles lead to formation of weak gels which after shearing give high relative viscosity fluids.

(ii) When the clay develops poor interactions with the monomer, the clay tends to reduce its exchange surface with the monomer and leads to a strongly connected gel. Shear breaks down this physical network leading to a very low relative viscosity fluid composed of nonswollen particles keeping a high aspect ratio.

     

Rheological properties of guar and its methyl, hydroxypropyl and hydroxypropyl-methyl derivatives in semidilute and concentrated aqueous solutions

We report on a comparative study of the rheological properties of guar [GG], methyl guar [MG], hydroxypropyl guar [HPG] and hydroxypropyl-methyl guar [MHPG] polymers aqueous solutions in semidilute (both unentangled and entangled) and concentrated regimes, using oscillatory and steady-shear techniques. In the dilute regime, molecular weights and radii of gyration have been investigated by means of light scattering measurements.Data obtained from steady-shear rheology were satisfactorily analyzed according to Cross model and the effects of polymer concentration and temperature on the rheological behaviour of guar and guar derivatives have been investigated and discussed in terms of rheological parameters, such as the zero-shear viscosity η₀, the characteristic time τ and critical coil-overlap concentration C^∗.The storage and loss moduli of guar and guar derivatives aqueous solutions have been measured using angular frequencies in the range between 10⁻³ and 10 rad/s. The data have been analyzed using the “blob” model for semidilute solutions and the scaling approach proposed by Rubinstein, Dobrynin and Colby for concentrated solutions. These rheological parameters obey a time-concentration superposition principle, so that master curves can be constructed over a wide frequency range. Moreover, we show that, at lower temperatures, these systems behave as thermo-rheological simple systems, in that the oscillatory shear response at different temperatures can be superimposed according to the empirical time-temperature superposition principle. Although these systems can be conveniently described within a unifying scaling model, the behaviour of guar derivatives are somewhat different. At higher temperatures, relatively small deviations from the scaling behaviour of the storage modulus of MG and MHPG polymers were observed. These findings can be justified by a structural re-organization of the macromolecular network, due to the hydrophobic interactions.     

Rheological properties of hydrophobic ethoxylated urethane (HEUR) in the presence of methylated β-cyclodextrin

Hydrophobic ethoxylated urethane (HEUR) is one type of hydrophobically modified polyethylene glycol, which could form a transient network structure in aqueous solution via intermolecular hydrophobic associations. The viscosity of HEUR solution is dependent on two parameters; namely the effective elastic chain density and the relaxation time. In the present study, different amounts of methylated β-cyclodextrin (m-βCD) were added into aqueous HEUR solutions, and significant reduction in the solution viscosity was observed when the m-βCD concentration exceeds a critical value. Oscillatory shear indicated that the plateau modulus does not decrease appreciably with the addition of m-βCD, however a large reduction in relaxation time was observed. At low m-βCD concentrations, addition of m-βCD does not decouple the hydrophobic association. The ring-shaped hydrophobic inner cores of m-βCD interact with the hydrophobic moiety of looping HEUR chains, leading to a reduction in the relaxation time, which weakens the transient network. However, at higher m-βCD concentrations, bridging chains are decoupled, thereby disrupting the transient network and produce smaller isolated aggregates.     

Rheological and optical properties of polypropylene filled with synthetic silicates and calcium carbonate

The rheology of PP filled with three different types of fillers, namely synthetic sodium aluminium silicate (SSAS), aluminium silicate (AS) and calcium carbonate (CaCO₃), at concentrations up to 40% was studied. Variation of shear and extensional viscosity was evaluated for all the compositions. When filler loading was less than 20%, the shear viscosity at low shear rates was less than that of virgin PP. Flow curves are described by the Ellis model. The onset of non-Newtonian shear thinning behaviour is related to parameter η₁₀/τ_1/2. Although fillers are white, they imparted a yellowish tone at lower loadings. At higher loadings, this yellowing effect was masked, yielding a lower yellowness index.