Hysteresis temperature dependence in filled rubbers. II. Mechanical mixing,filler microdispersion,and polymer–filler interactions

The effects of mechanical mixing and filler–filler (F–F) and polymer–filler (P–F) interactions on the normalized state of a filler microdispersion [d(x)] and the viscoelastic properties of silica‐filled rubbers were studied. The rubbers were prepared with or without the addition of n‐octyl‐triethoxysilane (OTES) to modify F–F interactions or coupling agents such as 3‐mercaptopropyl‐trimethoxysilane and 3‐mercaptopropyl‐triethoxysilane (MPTES) to increase P–F interactions. Increased mixing improved d(x) and enhanced the hysteresis temperature dependence (HTD) by giving a higher tan δ value near the compound glass‐transition temperature (T_g) but lowered tan δ at elevated temperatures for stocks containing a coupling agent. The changes in P–F and F–F interactions in rubbers with mixing and subsequent thermal treatment were shown to be responsible for the property differences observed among stocks containing different silanes. Attempts were made to quantify the efficiency for improving d(x) with various silanes. The increased P–F interactions in compounds containing MPTES showed better efficiency for improving d(x) and enhancing HTD in comparison with OTES. It was also demonstrated that the change in hysteresis near T_g was mainly governed by the degree of filler networking, whereas elevated‐temperature hysteresis was strongly influenced by the P–F interactions in compounds. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Attrition of Victorian brown coal during drying in a fluidized bed

Analyzing the attrition of Victorian brown coal during air and steam fluidized bed drying, the change in particle size distribution over a range of initial moisture contents (60% to 0%) and residence times (0 to 60 minutes) was determined. Dried at a temperature of 130°C with a fluidization velocity 0.55 m/s and an initial particle size of 0.5–1.2 mm, both fluidization mediums show a shift in the particle size distribution between three and four minutes of fluidization, with a decrease in mean particle size from 665 µm to around 560 µm. Using differential scanning calorimetry (DSC), the change in particle size has been attributed to the transition between bulk and non-freezable water (approximately 55% moisture loss) and can be linked to the removal of adhesion water, but not to fluidization effects. This is proved through the comparison of air fluidized bed drying, steam fluidized bed drying, and fixed bed drying—the fixed bed drying is being used to determine the particle size distribution as a function of drying. The results show the three drying methods produce similar particle size distributions, indicating that both fluidization and fluidization medium have no impact upon the particle size distribution at short residence times around ten minutes. The cumulative particle size distribution for air and steam fluidized bed dried coal has been modeled using the equation P_d = A₂ + (A₁ ? A₂)/(1 + (d/x₀)^p), with the resultant equations predicting the effects of moisture content on the particle size distribution. Analyzing the effect of longer residence times of 30 and 60 minutes, the particle size distribution for steam fluidized bed dried coal remains the same, while air fluidized bed dried coal has a greater proportion of smaller particles.     

Analysis of strain bursts during nanoindentation creep of high‐density polyethylene

Nanoindentation creep experiments on polyethylene were carried out in order to investigate dislocation‐based plastic deformation mechanisms. Similarly to that reported in a recent paper (Li J and Ngan AHW, Scr Mater 62 :488–491 (2010)), discrete deformation processes occur during nanoindentation creep tests which again seem to arise from the break‐off of dislocation avalanches. That interpretation is supported from systematic studies of the effect of variations of the loading rate and of the applied load on the number and the height of bursts. © 2015 Society of Chemical Industry     

Mechanical properties of polymer‐ceramic nanocomposite coatings by depth‐sensing indentation

The mechanical properties of antimony‐doped tin oxide (ATO) nanoparticle/poly (vinyl acetate‐co‐acrylic) (PVAc‐co‐acrylic) coatings with various ATO contents were investigated using depth‐sensing indentation. These coatings were prepared from aqueous dispersions of ATO and PVAc‐co‐acrylic latex. Three types of methods, including a prolonged load holding time, analysis of the pull‐off portion of the unloading curve, and dynamic indentation, were used to characterize the mechanical properties of these composite coatings. As compared to dynamic indentation, quasistatic conventional indentation even with a prolonged load holding time and analysis of the pull‐off portion of unloading curves generate more scattered coating modulus data. This is due to the effect of creep deformation and inconsistency of the pull‐off portion dimension, respectively. The results obtained using dynamic indentation are more reliable because the technique minimizes the effect of creep deformation using a combination load including static and dynamic components. The dynamic indentation results indicate that the addition of the ATO nanoparticles made the composite coatings stiffer and more elastic solid–like. For example, the storage indentation modulus of the PVAc‐co‐acrylic coating is ～1 GPa and tan δ is ～1.6; the addition of 0.50 volume fraction of ATO increased the modulus to ～5 GPa and reduced the tan δ to ～0.01. POLYM. ENG. Sci. 45:207–216, 2005. © 2005 Society of Plastics Engineers.     

Interferometric study of creep deformation and some structural properties of polypropylene fiber at three different temperatures

Influence of temperature on creep deformation for polypropylene PP fiber under a constant load was studied interferometrically. The automated multiple‐beam Fizeau system in transmission was equipped with a mechanical creep device attached to a wedge interferometer. This system was used to determine the optical properties (n^∥, n^?, and Δn) of PP fiber during the creep process at constant loading with varying temperature. The creep compliance was drawn as a function of both time and temperature. An empirical formula was suggested to describe the creep compliance curves for PP fibers and the constants of this formula were determined. Two Kelvin elements combined in series were used to provide an accurate fit to the experimental compliance curves. The stress–strain curve via creep was studied to determine some mechanical parameter of PP fibers, Young's modulus E, yield stress σ_y, and yield strain ε_y. The optical orientation function f(θ), the dielectric constant d, the dielectric susceptibility χ, the surface reflectivity , and the average work per chain W′ were also calculated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Radiation-crosslinked polypropylene: Physical and dielectric properties

Irradiation of two stereoregular polypropylenes and a polyallomer via ⁶⁰Co in the presence of 3–8% allyl methacrylate (AMA) monomer, to does up to 5 Mrad, lead to an improvement in mechanical properties. With irradiation, heat resistance, tensile strength, and gel fractions increased, and creep compliance decreased. The decrease in creep compliance was revealed by measurements of irradiated samples at 185⁰C (at constant load and monomer level), a temperature above the T_m of polypropylene. Dielectric properties (dielectric constant K and dissipation factor tan δ) were virtually unaffected by irradiation of 0.3 to 5.0 Mrad in nitrogen when AMA was absent. In the presence of monomer, small but generally tolerable increases in tan δ resulted if the monomer concentration was not too great. To obtain improvements in mechanical properties while not simultaneously altering the dielectric losses, it was necessary to keep the AMA concentration to a maximum of 4%.     

Nanoindentation and Morphological Studies of Epoxy Nanocomposites

Summary: This paper investigates the mechanical properties of the epoxy–organoclay nanocomposites by the nanoindentation technique. The nanocomposites were prepared by in situ polymerization and a mixture of exfoliated and intercalated composites structure was obtained as evidenced by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The hardness, elastic modulus, and the creep behavior of the nanocomposites have been evaluated as a function of clay concentration. It has been found that incorporation of 7.5 wt.‐% of clay nanofiller enhances the elastic modulus and hardness of the epoxy matrix by about 20 and 6%, respectively. The elastic modulus data calculated from indentation experiments are comparable with those obtained from a tensile test. An optimum clay loading level was found to be 2.5 wt.‐% to maximum enhance the creep resistance of the epoxy matrix. The lowered creep resistance with higher clay loading could be due to the reduced crosslinking density near the clay surface caused by the plasticizing effect from the pending of alkyl ammonium chains on the clay surface. An attempt has been made to correlate the fracture toughness of the nanocomposites with the ratio of modulus to hardness obtained from nanoindentation experiments.

Ratio of modulus to hardness (E/H) and the fracture toughness (K_IC) versus clay loading for the epoxy nanocomposites.     

Compatibilizing Effect of SEBS for Electrical Properties of LDPE/PS Blends

Summary: In the previous study, we observed compatibilizing effects of low density polyethylene (LDPE)/polystyrene (PS) with polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene (SEBS), a triblock copolymer. Blends consisting of 70 wt.‐% LDPE and 30 wt.‐% PS were prepared with a SEBS concentration of up to 10 wt.‐%. This study examined the electrical properties such as the electrical breakdown, water tree length, permittivity and tan δ in the blends. The possibility of using these blends as insulating material substitutes for LDPE was investigated. The electrical breakdown strength reached a maximum of 66.67 kV/mm, which is superior to 50.27 kV/mm of the LDPE used as electrical insulators for cables. In addition, the water tree length decreased with increasing SEBS concentration. The water tree lengths of the blends containing SEBS were shorter than that of the LDPE. The permittivity of the blends was 2.28–2.48 F/m, and decreased with increasing SEBS concentration with the exception of S‐0. Tan δ of the blends increased smoothly with increasing SEBS content.

Breakdown strength , water tree length, permittivity and tan δ of the LDPE/PS/SEBS blends and raw materials.     

Polypropylene/multiwall carbon nanotubes nanocomposites: Nanoindentation,dynamic mechanical,and electrical properties

Polypropylene (PP)/Multiwall carbon nanotubes (MWCNTs) nanocomposites were fabricated via melt compounding that utilizes a corotating twin‐screw extruder. Two commercially available MWCNTs, Baytubes C150P and C70P, were incorporated into PP matrix at concentration of 3 wt %. The nanocomposites samples were analyzed using scanning electron microscopy, dynamic mechanical analysis (DMA), nanoindentation test, and picoammeter. It was found that both MWCNTs types were well distributed and dispersed in the PP matrix and no agglomeration of MWCNTs was observed. The DMA analysis results showed that the incorporation of MWCNTs enhanced the storage modulus and thermal stability of the PP matrix. Whereas, nanoindentation creep results showed that the creep rate and displacement of the PP/MWCNTs nanocomposites was lower than the neat PP, in which C70P < C150P < PP. The reduction of creep rate and creep displacement was associated to the improvement of creep resistance. There were also improvements on hardness and stiffness of the nanocomposites. Additionally, the electrical resistivity of the neat PP decreased with the incorporation of MWCNTs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45293.     

Influence of ageing on viscoelastic properties of PMMA/ATH modified bitumen

This article deals with the influence of the ageing treatment on the viscoelastic behavior of PMMA/ATH modified paving bitumen. Waste composite powder (polymethyl methacrylate filled with aluminium trihydrate)—PMMA/ATH and Fischer–Tropsch wax were used as modifying agents for 70/100 paving grade bitumen. Measurements in intermediate temperature range were carried out under oscillatory shear conditions on a dynamic shear rheometer (DSR). Creep testing in low temperature range was conducted on a bending beam rheometer (BBR). The time‐dependent behavior of investigated samples was presented in a form of relaxation moduli G(t) and E(t). Dynamic moduli, i.e., G′(ω) and G″(ω), were converted to relaxation modulus G(t) using the Schwarzl method. The interconversion between tensile creep compliance D(t), and tensile relaxation modulus E(t) was performed using the Hopkins and Hamming approach. It was found that modified binders are less susceptible to the oxidation process during bitumen ageing, since the viscoelastic properties changed less than for the base bitumen. Our results indicate that the use of waste PMMA/ATH in the selected bitumen altered the time‐dependent deformation behavior of asphalt binder. The effect of ageing treatment on material functions was particularly manifested at longer times. Different stress relaxation behavior of modified binders could result in higher deformation resistance of asphalt mixture. POLYM. COMPOS., 36:1738–1747, 2015. © 2014 Society of Plastics Engineers     

Thermal expansion transients of a cis-1,4 polybutadiene elastomer at various levels of strain

The length-temperature behavior of elongated elastomeric networks of cis-1,4 polybutadiene was observed following abrupt, nearly step-function changes in the temperature of the specimen environment. The thermal expansion behavior is reversible, and the transient length changes are in the direction anticipated from rubber elasticity theory, i.e., dL(t)/dT is negative. The observed long-time values of the thermal expansion coefficient are in good agreement with equilibrium length-temperature coefficients reported for other elastomers. Results indicate that both thermal diffusion and retarded creep deformation contribute to the transient phenomenon, with the latter mechanism dominating.     

Oxidative Stability and Volatile Formations in Linoleic Acid-D<Subscript>2</Subscript>O Models in the Presence of Deuteron or Electron Donors

Effects of deuteron (D⁺) and electron donors on the oxidative stability in linoleic acid–water model systems were evaluated by analyzing headspace oxygen content and headspace volatiles. Acetic acid‐d and tetrakis(dimethylamino)ethylene (TDAE) were selected as a deuteron and an electron donor, respectively. Samples containing acetic acid‐d had significantly lower headspace oxygen content than controls while those containing TDAE had significantly higher headspace oxygen content (p < 0.05). Combination of acetic acid‐d and TDAE accelerated the consumption of headspace oxygen. Volatiles including t‐2‐heptenal, 2‐octenal, or 2,4‐octadienal had higher mass to charge ratio (m/z) of (molecular weight +1)/molecular weight in samples with deuterium oxide than in samples with deuterium free water. However, no significant difference was observed in the m/z ratio of (molecular weight +1)/molecular weight of those volatiles among samples with or without deuteron or electron donors. Also, lipid hydroperoxides with deuterium, were not found in samples containing deuterium oxide and acetic acid‐d. Therefore, added acetic acid‐d may not be involved on the formation of lipid hydroperoxides and volatiles directly.     

In situ pultrusion of urea–formaldehyde matrix composites. I. Processability,kinetic analysis,and dynamic mechanical properties

We conducted a feasibility study on the pultrusion of a glass‐fiber‐reinforced urea–formaldehyde (UF) composite using a proprietary method. The UF prepolymer synthesized in this study was prepared from blends of UF monomer and a curing agent (NH₄Cl).The process feasibility, kinetic analysis, and dynamic mechanical properties of the glass‐fiber‐reinforced UF composites by pultrusion were investigated. From investigations of the long pot life of the UF prepolymer, the high reactivity of the UF prepolymer, and excellent fiber wet‐out, we found that the UF resin showed excellent process feasibility for pultrusion. A kinetic model, dα/dt = A exp(?E/RT)α^m(1 ? α)ⁿ, is proposed to describe the curing behavior of a UF resin. Kinetic parameters for the model were obtained from dynamic differential scanning calorimetry scans with a multiple‐regression technique. The dynamic storage modulus of the pultruded‐glass‐fiber‐reinforced UF composites increased with increasing die temperature, filler content and glass‐fiber content and with decreasing pulling rate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1242–1251, 2002     

Research on starch‐g‐polyvinyl acetate and epoxy resin‐modified corn starch adhesive

A new corn starch adhesive modified by starch‐g‐polyvinyl acetate (starch‐g‐PVAc) and epoxy resin is described in this study. Starch‐g‐PVAc is used as high cohesive energy component to improve the dry shear strength of the starch adhesive. Although the epoxy resin, which can easily crosslink with the oxidized starch, is used as water‐resistant component to improve the wet shear strength. Because there is no chemical reaction happening between polyvinyl acetate and epoxy resin, both the dry shear strength and the wet shear strength of the corn starch adhesive are notably increased. Considering all the related factors, the optimum of the modification is achieved when the dosage of starch‐g‐PVAc and epoxy resin is 70% of the oxidized starch latex with m(Ep): m(starch‐g‐PVAc) = 1:2. That is, the epoxy resin is 23% in mass fraction and starch‐g‐PVAc 47% in mass fraction. The dry shear strength is 4.50 MPa, and the wet shear strength is 2.51 MPa. The modified corn starch has a broad prospect in the application of plywood industry. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers     

Rheological behaviors of PVA/H2O solutions of high‐polymer concentration

The dynamic viscoelastic properties of poly(vinyl alcohol) (PVA)/H₂O solutions with concentrations of 10 to 25 wt % have been characterized by controlled‐stress rheometry at 30°C. Parameters relating to the linear and nonlinear viscoelasticities include complex viscosity (η*), storage modulus (G′), loss tangent (tan δ), relaxation time (λ), thixotropy, and creep. Change curves of η*, G′, tanδ, and λ with frequency (ω) have been obtained for the PVA/H₂O solutions. Creep and recovery testing yielded compliance (J′) curves with loading and unloading. Shear stress versus rate profiles of the PVA solutions have been obtained through thixotropic measurements. The PVA concentration has been found to have a profound influence on the rheological properties of the aqueous solutions. Four aqueous solutions of 10, 15, 20, and 25 wt % PVA at 30°C exhibited shear‐thinning and showed different transition behaviors of η* and G′ with frequency, and different degrees of creep under constant stress to recovery with time. The 10 wt % PVA solution was viscous and displayed the lowest η* and G′; the 25 wt % PVA solution was viscoelastic and displayed the highest η* and G′; the 15 and 20 wt % PVA solutions showed η* and G′ values and creep to recovery behaviors intermediate between those of the 10 wt % and 25 wt % PVA solutions. The different rheological properties of these PVA/H₂O solutions are considered to correlate with interchain hydrogen bonds and shear‐induced orientation in the solutions. Shearing is able to break the intrachain and interchain hydrogen bonds, and, at the same time, the orientation creates new interchain hydrogen bonding. The reorganization of hydrogen‐bonding mode contributes to the transitions of the macroscopic viscoelasticity with frequency. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Creep behavior of PLA‐based biodegradable plastic exposed to a hydrocarbon liquid

This study explores the effect of hydrocarbon liquid on creep behavior of polylactic acid (PLA)‐based plastic. Evolution of the mechanical properties of the material was investigated experimentally by measurement of creep under tensile load. Tensile creep behavior was studied with a constant load over a temperature range from 30 to 50°C using specimens containing different levels of liquid. It was shown that the hydrocarbon liquid diffusion obeys the Fickian law of diffusion. The viscoelastic properties vary with temperature and these properties dramatically decrease above the glass transition temperature (T_g). Significant decreases in modulus and in the peak of tan δ were observed with an increase in liquid concentration at low temperatures. In contrast, at high temperatures, drier material recorded lower storage modulus. However, only small changes of T_g were recorded. Dependence of compliance on temperature was observed in the creep test at all levels of liquid content. With respect to drier samples, it was noted that the high liquid content material had a lower rate of increasing creep strain with temperature. Therefore, at elevated temperatures, higher creep strain of dry specimens was observed compared to those with a higher liquid content. The improvement of creep resistance and stiffening of material at high temperatures can be attributed to the significant increase of crystallinity fraction induced by liquid absorption. Understanding the effect of liquid diffusion in conjunction with temperature provides useful information for assessment of the potential use of this biodegradable plastic in load‐bearing applications exposed to an organic liquid. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the structure of silane‐coupling agent on dynamic mechanical properties of dental resin‐nanocomposites

This work was aimed at the study by dynamic mechanical analysis (DMA) of dental composites consisted of a Bis‐GMA/TEGDMA (50/50 wt/wt) matrix and silica nanoparticles (Aerosil OX50) as filler, silanized with various silanes. The silanes used were 3‐[(1,3(2)‐dimethacryloyloxypropyl)‐2 (3)‐oxycarbonylamido] propyltriethoxy‐silane (UDMS), 3‐methacryloxypropyl‐trimethoxysilane (MPS), octyltrimethoxysilane (OTMS), blends of UDMS/OTMS (50/50 wt/wt), or MPS/OTMS (50/50 wt/wt). The total amount of silane was kept constant at 10% by weight fraction relative to the filler weight. The silanized nanoparticles were mixed with the dimethacrylate matrix (60% filler by weight fraction). The composites were light cured and tested by DMA for the determination of storage modulus (E′), loss modulus (E″), tangent delta (tan δ), and glass transition temperature (T_g). Measurements were performed in samples immediately after curing and samples stored in water at 37°C for 1, 7, 30, or 120 days. OTMS‐composite in which OTMS does not form covalent bond with the dimethacrylate matrix showed lower elastic modulus both in dry and wet conditions. The ability of bifunctional UDMS for crosslinking was found not to increase the elastic behavior of the composite, as it was expected, compared with that of MPS‐composite, because of the high amount of the silane used. After immersion in water the elastic modulus of OTMS‐composite remained constant, while that of the other composites increased after 1 day and then remained constant up to 120 days. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polymers based on N,N‐diglycidylaniline. I. Investigations of the curing kinetics by dynamic differential scanning calorimetry measurements

N,N‐Diglycidylaniline was reacted with aniline (yielding polymer EP‐1) and the newly synthesized chromophore 4‐(phenylazo)aniline (yielding polymer EP‐2). The curing kinetics of these two epoxy resin systems was studied in dynamic experiments by means of differential scanning calorimetry. Kinetic parameters such as the activation energy and frequency factor were estimated with the Ozawa method [E(O) and A(O), respectively], the Kissinger method [E(K) and A(K), respectively], and the modified Avrami method [E(A) and A(A), respectively]. The activation energy and frequency factor of EP‐1 were much lower than those of EP‐2 estimated with the Ozawa, Kissinger, and Avrami methods. The activation energy and frequency factor for EP‐1 determined with the Ozawa method [E(O) = 55.8 kJ/mol, A(O) = 10 × 10³ 1/s] and the Avrami method [E(A) = 56.4 kJ/mol, A(A) = 9.2 × 10³ 1/s] were higher than those determined with the Kissinger method [E(K) = 51.0 kJ/mol, A(K) = 2 × 10³ 1/s]. In the case of EP‐2, the kinetic parameters calculated with the Ozawa model [E(O) = 140.4 kJ/mol, A(O) = 12.3 × 10¹³ 1/s] and the Kissinger model [E(K) = 139.9 kJ/mol, A(K) = 10.9 × 10¹³ 1/s] were higher than those calculated with the Avrami model [E(A) = 130.4 kJ/mol, A(A) = 7.9 × 10¹² 1/s]. The obtained polymers were characterized with Fourier transform infrared, ¹H‐NMR, differential scanning calorimetry, and ultraviolet–visible spectroscopy. The polymers exhibited low glass‐transition temperatures in the range of 57–79°C and good solubility in common organic solvents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of the comonomer content on the solid‐state mechanical and viscoelastic properties of poly(propylene‐co‐1‐butene) films

In this study, we quantified the thermal and solid‐state mechanical and viscoelastic properties of isotactic polypropylene (i‐PP) homopolymer and poly(propylene‐1‐butene) copolymer films having a 1‐butene ratio of 8, 12, and 14 wt %, depending on the comonomer content. The uniaxial tensile creep and stress‐relaxation behaviors of the samples were studied in a dynamic mechanical analyzer at different temperatures. The creep behaviors of the samples were modeled with the four‐element Burger equation, and the long‐term creep strains were predicted with the time–temperature superposition method. The short‐term mechanical properties of the samples were also determined with tensile and impact testing at room temperature. We found that the Young's modulus and ultimate strength values of the samples decreased with increasing amount of 1‐butene in the copolymer structure. On the other hand, the strain at break and impact strength values of the samples improved with increasing amount of 1‐butene. Creep analysis showed that i‐PP exhibited a relatively lower creep strain than the poly(propylene‐co‐1‐butene)s at 30 °C. However, interestingly, we discovered that the temperature increase resulted in different effects on the creep behaviors. We also found that short‐chain branching improved the creep resistance of polypropylene at relatively high temperatures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46350.     

A kinetic evaluation of the anaerobic digestion of two‐phase olive mill effluent in batch reactors

A comparative kinetic study was carried out on the anaerobic digestion of two‐phase olive mill effluent (TPOME) using three 1‐dm³ volume stirred tank reactors, one with freely suspended biomass (control), and the other two with biomass supported on polyvinyl chloride (PVC) and bentonite (aluminium silicate), respectively. The reactors were batch fed at mesophilic temperature (35 °C) using volumes of TPOME of between 50 and 600 cm³, corresponding to chemical oxygen demand (COD) loadings in the range of 1.02–14.22 g, respectively. The process followed first‐order kinetics and the specific rate constants, K₀, were calculated. The K₀ values decreased considerably from 2.59 to 0.14 d^?1, from 1.93 to 0.23 d^?1 and from 1.52 to 0.17 d^?1 for the reactors with suspended biomass (control) and biomass immobilized on PVC and bentonite, respectively, when the COD loadings increased from 1.02 to 14.22 g; this showed an inhibition phenomenon in the three reactors studied. The values of the critical inhibitory substrate concentration (S*), theoretical kinetic constant without inhibition (K_A) and the inhibition coefficient or inhibitory parameter for each reactor (n) were determined using the Levenspiel model. Copyright © 2004 Society of Chemical Industry