Fabrication, characterization and invitro bioactivity evaluation of QPSU/TiO2 composite membranes

Quaternized Polysulfone (QPSU) is a widely investigated material in the industry because of its unique properties such as resistance to corrosion and high mechanical properties. The ionic nature of the compound can be exploited for medical applications such as in haemodialysis, drug delivery and tissue engineering. In this study, composite membranes of QPSU with varying concentrations of Titanium oxide (TiO₂) were prepared and characterized using FT-IR, ¹H-NMR, XRD, TGA and SEM. The bioactivity of the membranes was studied by immersing them in simulated body fluid (SBF) for 7 days and subsequently observing under SEM for the formation of calcium-phosphate (Ca–PO₄) layer on the surface of the membranes. The formation of Ca–PO₄ on the samples was confirmed using FT-IR and EDAX. The results were compared with those obtained for QPSU membranes and the effect of TiO₂ concentration on the membrane properties was analyzed. It was observed that the percentage crystallinity of the composites increased upto a filler concentration of 5 wt% beyond which it decreased. TGA studies revealed an increase in the thermal stability of the composites with increasing filler concentrations. While optimum bioactivity was observed in the samples containing 5 wt% of TiO₂, higher filler content resulted in the formation of denser calcium—phosphate layer on the surface of the composites. The study shows that quaternized polysulphone/TiO₂ composites are promising bio composites having great potential for application in health care.     

Hydrophilicity and crystallization behavior of PVDF/PMMA/TiO<Subscript>2</Subscript>(SiO<Subscript>2</Subscript>) composites prepared by in situ polymerization

Composites with enhanced hydrophilicity were prepared by adding TiO₂ or SiO₂ nanoparticles during the in situ polymerization of methyl methacrylate (MMA) in poly(vinylidene fluoride) (PVDF). The hydrophilicities of the PVDF/PMMA/TiO₂(SiO₂) composites generated in this manner were characterized by contact angle measurements and atomic force microscopy (AFM). The hydrophilicity was dependent on nanoparticle content; it gradually increased with increasing TiO₂ (or SiO₂) content when the TiO₂ (or SiO₂) content was no more than 4 wt% of PVDF. A homogeneous dispersion of the TiO₂ (or SiO₂) nanoparticles in the composite matrix was observed in scanning electron microscope (SEM) images. Based on Fourier transform infrared (FTIR) spectra and wide angle X-ray diffraction (WAXD) analyses, the crystalline phase composition of PVDF was not influenced by the addition of TiO₂ (or SiO₂); PVDF crystallized predominantly in the α phase after in situ polymerization. Nevertheless, the nanoparticles can promote the formation of the β phase of PVDF in composites; the β-phase content increased with increasing TiO₂ content, while it was almost independent of SiO₂ content.     

Influence of TiO2-Modification on the Mechanical and Thermal Properties of Sugarcane Bagasse–EVA Composites

The effect of nano-particles of TiO₂ on the mechanical and thermal properties of sugarcane bagasse (SCB)–ethylene co-vinyl acetate (EVA) composite was investigated. Composite materials were prepared using a melt-mix intercalation method on a rheomex mixer coupled with a single screw extruder. differential scanning calorimeter (DSC), thermogravimetric (TG) analyser and an Instron, were used to probe the thermal and mechanical properties of the samples. Composites with TiO₂ were compared with those without TiO₂ but with the same content of sugarcane bagasse (SCB). After the addition of TiO₂, the tensile strength increased by 10%, from 11.26 MPa for neat EVA, which correlated with the enthalpy of fusion, however, the tensile strength decreased by 18% at higher SCB loading. Elongation at break decreased from 463 to 0% as the filler (SCB) was increased which was inversely proportional to the modulus. The composite showed an improved thermal stability with the addition of TiO₂.     

Tensile properties of TiO2-filled poly(vinyl acetate) in the transition region

The stress–strain properties of TiO₂-filled poly(vinyl acetate) have been studied at filler percentages of 0, 10, 20, 30, and 40% TiO₂ over a strain-rate range of 100–5000%/ min at 24°C. Tensile strength, Young's modulus, and offset yield strengths all were found to increase with higher strain rates and higher TiO₂ contents. Ultimate elongations decreased with greater TiO₂ content and higher strain rates. Shift factors for volume fraction of filler were estimated for tensile properties as function of test rate. Stress relaxation studies have shown a reduction in relaxation times with increasing TiO₂ content. Calculations of the out-of-phase Young's modulus were made as a function of filler content employing a box-type of distribution of relaxation times. A possible explanation for the stress–strain behavior observed is that introduction of TiO₂ changes the internal viscosity of the system, similar to the effect of temperature. This would also mean that the ultimate properties would be dependent on filler content and strain rate because viscous resistance to chain deformation would be altered. The effect of filler on stress relaxation could be thought of being due to an increase in short-range chain motion.     

Poly(hydroxybutyrate‐co‐hydroxyvalerate)/titanium dioxide nanocomposites: A degradation study

Nanocomposites, based on a poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV) matrix and titanium dioxide (TiO₂) nanoparticles and fabricated with a solvent‐casting technique, were characterized with differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. The content of TiO₂ nanoparticles varied between 0.5 and 10 wt %. Degradation studies, including hydrolytic degradation in a strong base medium (1N NaOH) and degradation under ultraviolet light at 365 nm, were performed. It was confirmed that the inorganic filler had no great influence on thermal properties such as the melting and crystallization temperatures. Improved degradation temperatures were also confirmed with the increase in the filler content. Degradation observations confirmed significant increases in hydrolytic erosion with the filler content increasing in comparison with the degradation of a pure PHBV film. Also, the photocatalytic activity of the inorganic filler TiO₂ in all investigated composites [irradiated at λ = 365 nm and immersed in a liquid medium (H₂O)] was evaluated. The degraded samples were analyzed with Fourier transform infrared spectroscopy, which confirmed their increased crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Mechanical,thermophysical, and diffusion properties of TiO2‐filled chlorobutyl rubber composites

The mechanical and thermophysical properties of TiO₂‐filled chlorobutyl rubber composites were investigated. These materials exhibited enhanced mechanical properties such as increased modulus, tensile strength, and hardness. The morphology of filler dispersion in the matrix was analyzed by scanning electron microscopy and atomic force microscopy. Moreover, the effect of TiO₂ content on the molecular transport of solvents was examined by means of degree of swelling, volume fraction of rubber, penetration rate of solvent, mean diffusion coefficient, etc. A periodic method was used to estimate the thermophysical behavior of samples. It was shown that the thermal conductivity and diffusivity of composites increase with increasing of TiO₂ filler content. Finally, the utilization of the material as effective chemical protective clothing against volatile organic chemicals was analyzed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Effects of particle type on thermal and mechanical properties of polyoxymethylene nanocomposites

The effects of particle size of titanium dioxide (TiO₂) on mechanical, thermal, and morphological properties of pure polyoxymethylene (POM) and POM/TiO₂ nanocomposites were investigated and compared with the results for nanoparticle ZnO in the same matrix, reported in a previous paper. POM/TiO₂ nanocomposites with varying concentration of TiO₂ were prepared by the melt mixing technique in a twin screw extruder, the same method that used for blending the homogeneous ZnO nanocomposites. The dispersion of TiO₂ particles in POM nanocomposites was studied by scanning electron microscopy (SEM). The agglomeration, as observed by the mechanical properties of TiO₂ particles in the polymer matrix, increased with increasing TiO₂ content, a result not found for ZnO even at lower particle sizes. Increasing the filler content of POM/TD32.4 and POM/TD130 (130 nm) nanocomposites resulted in a decrease in tensile strength. The Young modulus, stress at break and impact strength of TiO₂ nanocomposite did not improve with increasing filler contents, in opposition to the better agglomeration conditions of ZnO nanocomposite even at lower particle sizes. Because of agglomeration, the POM/TD32.4 nanocomposites had lower mechanical properties and lower degradation temperature than the POM/TD130 ones. The sizes of nanoparticles determined the agglomeration, but however, the agglomeration also depended on the type of nanoparticles, even when using the same matrix (POM) and the same mixing method. TiO₂ nanoparticles were more difficult to mix and were more agglomerated in the POM matrix as compared to ZnO nanoparticles, regardless of the size of the nanoparticles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of TiO2 Doping on the Sintering Process,Mechanical and Magnetic Properties of NiFe2O4 Ferrite Ceramics

TiO₂‐doped NiFe₂O₄ samples were prepared via ball‐milling and two‐step sintering processes. Besides NiFe₂O₄ phase, two new phases, NiTiO₃ and Fe₂TiO₅, formed in TiO₂‐doped samples. The temperature of sintering onset for 1.0 wt% TiO₂‐doped samples is 230°C lower than that of undoped samples. Early‐stage synthesis process of TiO₂‐doped NiFe₂O₄ ceramics is controlled by grain boundary diffusion mechanism. Increasing TiO₂ content from 0 to 1.0 wt%, the apparent activation energy decreased from 813.919 KJ/mol to 639.361 KJ/mol. The values of relative density and bending strength reached their maximum value with 1.0 wt% TiO₂. Saturation magnetization, residual magnetization ratio and coercivity decrease with increasing TiO₂ content.     

Dynamic mechanical study of the transition from swollen particles to hydrogel caused by neutralization

Summary The copolymer of 2-(2-carboxybenzoyloxy)ethyl methacrylate (CEM) with butyl methacrylate (BMA) (BMA/CEM = 40/60 wt.) and terpolymers CEM/BMA/ 2-hydroxyethyl methacrylate (HEMA) ((BMA + HEMA)/CEM = 40/60 wt.; HEMA/BMA = 35/5, 30/10, 20/20 and 10/30) were prepared by emulsion radical copolymerization in water in the presence of sodium dodecyl sulfate and their dynamic mechanical behaviour was investigated as a function of the degree of neutralization α. Main attention was devoted to the transition from swollen particles to physical gel with increasing degree of neutralization and to the structure of formed hydrogels. From the results it followed: (a) the transition from swollen particles to the gel state occurs in a narrow neutralization interval at α∼ 0.45 for BMA/CEM copolymer; increasing the HEMA content shifts the transition to lower α values; (b) with increasing shear strain γ, the hydrogels passed from the gel to liquid state and this transition at the critical strain γ_c, was reversible; (c) junctions in the gel state are probably formed by the hydrophobic interactions of the ends of CEM units which form clusters and the junction concentration is independent of the HEMA content and degree of neutralization α; (d) increasing degree of neutralization α and the HEMA content (increasing polarity of the system) stabilizes the junctions and the critical γ_c values increase; (e) the values of the low-strain storage G′₀ and loss G″₀ moduli together with critical strains γ_c did not depend on angular frequnecy ω in the interval 10⁻¹− 10 rad/s. Received: 5 January 2000/Accepted: 23 May 2000     

Synthesis and characterization of sol–gel derived PVA-titanium dioxide (TiO<Subscript>2</Subscript>) nanocomposite

Novel PVA/TiO₂ polymer nanocomposites have been prepared at low temperature via sol–gel route. XRD analysis showed the particles to be elongated along a- and b-direction but contracted along c-direction. PVA-assisted TiO₂ nanocomposite samples dried at a temperature of 35 °C were found to have ~12 nm particle size. It was found that the composite nanoparticles had an increased degree of crystallinity in comparison to pure TiO₂ dried at 80 °C. TEM analysis depicted the formation of highly dense nanorods (and prism)-like structure of increasing length and diameter depending on PVA concentration. Our studies revealed that by increasing the concentration of PVA in TiO₂ the band gap was lowered from 3.55 to 1.65 eV. The photoluminescence studies showed that emission shifts towards higher wavelength (417–457 nm) accompanied by a reduction in impurity centres with increasing concentration of PVA in TiO₂.     

X‐ray diffraction study of iPP/cand iPP/TiO2 composites relating to micromechanical properties

Composites of isotactic polypropylene with various contents of white clay or titanium dioxide TiO₂ were prepared by extrusion molding. The extruded composites were melt‐pressed at two different temperatures, and, thereafter, either slowly cooled, or quenched to room temperatures. It is shown that the structure of all the samples, as revealed by wide‐angle X‐ray scattering and small‐angle X‐ray scattering (SAXS), depends on the processing conditions. The lack of SAXS maxima in the composites suggests that the presence of the microadditives hinders the stacking of iPP lamellae. Furthermore, the microindentation hardness H in the slowly cooled composites is influenced by the type and amount of the filler used. However, in the quenched samples H depends only on the amount of the filler used, and not on its type. In case of the quenched iPP/clay composites, the relationship between H and the Young's modulus E is found to be H/E ≈ 0.12, in good agreement with Struik's theoretical predictions of σ_e ≈ E/30, in consonance with results previously obtained for a series of polyethylene samples with different morphology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The influence of titanium dioxide on the rheological and extrusion properties of polymer melts

An experimental study of the influence of titanium dioxide (TiO₂) on the rheological and extrusion properties of five polymer melts (two low-density polyethylenes, two high-density polyethylenes, and a polystyrene) has been carried out. Increasing TiO₂ loading increases the shear viscosity η, with the extent of increase being greater at lower shear rates. At moderate and high TiO₂ loadings, the filled melts may possess yield values. Empirical equations relating viscosity to filler loading have been developed. The first normal stress difference was measured for the melts and found to increase with increasing TiO₂ loading. However, the extent of increase was less than found for the viscosity function and interpretation in terms of the theory of viscoelasticity suggests that the characteristic relaxation time of the melts decreases with increasing TiO₂ level. Empirical equations relating the first normal stress difference coefficient to volume fraction of the filler have been developed. Addition of TiO₂ is found to decrease extrudate swell and retard the occurrence of extrudate distortion.     

Dynamic mechanical properties of a TiO2-filled crosslinked epoxy resin from 20–90°C.

Dynamic mechanical measurements were made with a torsional pendulum of a TiO filled epoxy polymer (crosslinked with hexamethylene diamine) over a temperature range from 20–90°C., at filler concentrations of 0–40 wt.-%. The second-order transition temperature (T_g) was raised as the filler content increased. The behavior of TiO₂ filler results in a long-range immobilization of the highly crosslinked system with resultant increases in shear modulus (higher G′) as well as decreased capacity for energy dissipation (lower damping factor). The out-of-phase modulus (G″) increased with filler content as well. The magnitudes of the slope parameters H_r (representing G′ data above T_g) and H_g (representing G′ data below T_g) decreased with greater filler content. The possibility is set forth that the TiO₂ filler causes a different distribution of mobility around the nitrogen junction as well as a change in the effective number of CH₂ units between crosslinks.     

Crystallization behavior of poly(ϵ‐caprolactone)/Tio2 nanocomposites obtained by in situ polymerization

Poly(?‐caprolactone) (PCL)/titanium dioxide (TiO₂) nanocomposites were prepared by in situ polymerization of ?‐caprolactone in the presence of modified‐TiO₂ nanoparticles as initiators. The molecular weight of PCL matrix was dependent on the amount of the TiO₂ fillers. The incorporation of TiO₂ did not significantly affect the crystalline structure of PCL. Moreover, a tendency of the nanoparticles to form aggregates was observed, especially at higher fillers contents. The analysis of the crystallization process showed that the addition of TiO₂ nanoparticles accelerated the crystallization rate of PCL, and the crystallization rates increased by increasing the filler content. The crystallization activation energy dependence on the filler content observed here is probably the consequence of the two competing factors. The tendency of activation energy obtained by nonisothermal crystallization is similar to that of isothermal crystallization. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Boosting TiO2-anatase antimicrobial activity: Polymer-oxide thin films

TiO₂ incorporation into an isotactic polypropylene (iPP) polymeric matrix was achieved via a straightforward and cost-effective melting process using laboratory-made nanometric anatase-TiO₂ and an industrial polymer. The structural characteristics of the resulting nanocomposite thin films as a function of the inorganic component content were examined using wide and small angle X-ray scattering (WAXS/SAXS) and vibrational Raman spectroscopy. Electron scanning and transmission microscopy (SEM/TEM) studies were also performed to provide evidence of the nanometric dispersion of the oxide within the polymer matrix, showing the presence of average aggregates of ca. 80 nm. TiO₂ incorporation into the iPP renders self-sterilized nanocomposite films upon light excitation, the activity of which was tested against Gram negative (P. aeruginosa) and positive (E. faecalis) bacteria. TiO₂ displays maximum activity for a sample containing a 2 wt.% of anatase-TiO₂ irrespective of the microorganism nature. The antimicrobial activity of the nanocomposite films is significantly enhanced with respect to that of the oxide alone. This key fact is interpreted on physical basis with the help of a complete optical (UV–vis and photoluminescence) and electron paramagnetic resonance (EPR) characterization.     

Enhancing Photophysical Properties of MDMO-PPV-DMP Conjugated Polymer via Incorporation Anatase Titania Nanoparticles

Improving photophysical properties of poly[2-methoxy-5-(3,7-dimethyl-octyloxy)-1,4-phenylenevinylene]-end capped with dimethylphenyl, MDMO-PPV-DMP, was achieved via incorporation anatase titania nanoparticles (TiO₂ NPs). Various contents of TiO₂ NPs (up to 50 wt%) were dispersed into fixed concentration of the MDMO-PPV-DMP (5 mg/mL) via solution blending method followed by spin coating onto cleaned glass substrates to form their thin films. The formation of MDMO-PPV-DMP/TiO₂ nanocomposites was evidenced from the results of X-ray diffractograms and Fourier transform infrared spectra, while the homogeneity of the films was detected by field emission-scanning electron microscopy (FE-SEM). Increasing the contents of TiO₂ NPs resulted in a slight decrease (up to ~?0.07 eV) in both direct and indirect energy band gaps of the MDMO-PPV-DMP in the nanocomposite thin films. A higher degree of disorder in the electronic structure of the MDMO-PPV-DMP/TiO₂ nanocomposite and increasing the localized states density within the forbidden gap can be achieved by increasing the energy tail values and decreasing the steepness parameter with rising the TiO₂ NPs content. The enhancement in emission intensity and broadening of emission spectra with increasing the TiO₂ NPs content can be explained by the charge trapping effect and particle size distribution, respectively. Moreover, the incorporation of TiO₂ NPs into the MDMO-PPV-DMP led to tuning its emitted light color which is of distinct interest in optoelectronic devices.

     

Morphology,crystallization, and thermal behavior of isotactic polypropylene/polystyrene blends: Effects of the addition of a graft copolymer of propylene with styrene

Optical microscopy, differential scanning calorimetry, and small‐angle X‐ray scattering techniques were used to study the influence of crystallization conditions on the morphology and thermal behavior of samples of ternary blends constituted by isotactic polypropylene (iPP), atactic polystyrene (aPS), and a novel graft copolymer of unsaturated propylene with styrene (uPP‐g‐PS) with the purpose of assessing the uPP‐g‐PS capability to act as a compatibilizer for iPP/aPS materials. It was shown that the presence of the uPP‐g‐PS copolymer affects the interfacial tension between the iPP and aPS phases in the melt state, with the aPS particle size and the particle‐size distribution being, in fact, strongly modified. In samples of iPP/aPS/uPP‐g‐PS blends, isothermally crystallized from the melt at a relatively low undercooling in a range of the crystallization temperature of the iPP phase, the addition of the uPP‐g‐PS copolymer induced a drastic change both in the aPS mode and the state of dispersion and in the iPP spherulitic texture and inner structure of the spherulite fibrils. In particular, the phase structure developed in the iPP/aPS/uPP‐g‐PS materials was characterized by a crystalline lamellar thickness of the iPP phase comparable to that shown by the plain iPP. The extent of the induced modifications, that is, the degree of compatibilization achieved, resulted in a combined effect of composition and undercooling. Also, relevant thermodynamic parameters of the iPP phase, such as the equilibrium melting temperature (T_m) and the folding surface free energy (ς_e) of the lamellar crystals, were found to be influenced by the presence of the uPP‐g‐PS copolymer. A linear decrease of the T_m and ς_e values with increasing uPP‐g‐PS content was, in fact, observed. Such results have been accounted for by an increase of the presence of defects along the iPP crystallizable sequences and by the very irregular and perturbed surface of the crystals with increasing copolymer content. The observed decrease in T_m values revealed, moreover, that, in the iPP/aPS/uPP‐g‐PS blends, the iPP crystal growth occurs under comparatively lower undercooling, in line with higher crystalline lamellar thickness shown by SAXS investigation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1429–1442, 1999     

The effect of propylene–ethylene copolymers with different comonomer content on melting and crystallization behavior of polypropylene

The effect of propylene–ethylene copolymers (PEc) with different ethylene‐unit contents on melting and crystallization behaviors of isotactic‐polypropylene (iPP) were investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The results show that the addition of PEc decreases significantly crystallization temperature (T_c) of iPP, but slightly affects melting temperature (T_m). With increasing the ethylene‐unit content of the propylene–ethylene copolymers, the decrease in crystallization temperature of iPP is smaller. The PLM results show that the spherulite growth rate decreases with increasing crystallization temperature for iPP and iPP/PEc blends. The higher the ethylene‐unit content of the copolymers is, the lower the spherulite growth rate (G) of iPP/PEc blends is. The influence of the PEc on nucleation rate constant (K_g) and fold surface energy (σ_e) of iPP was examined by nucleation theory of Hoffman and Lauritzen. The results show that both K_g and σ_e of iPP/PE20(80/20) and iPP/PE23(80/20) blends are higher than those of iPP, demonstrating that the overall crystallization rate of iPP/PEc blends decreased as compared to that of iPP, resulting from the decrease of the nucleation rate and the spherulite growth rate of iPP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polypropylene/nTiO2 nanocomposites using melt mixing and its investigation on mechanical and thermal properties

This study investigates the preparation of nTiO₂ particle using green chemistry approach and its subsequent effect on the properties of isotactic polypropylene (iPP) nanocomposites, which is one of the most suited thermoplastic polymer. The nanocomposite of iPP with TiO₂ nanoparticle (0.5, 1, 1.5, 2, and 2.5 wt%) were prepared on Brabender plasticorder, which was then subjected to injection molding to get a dumbbell‐shape specimens. Meanwhile, TiO2 nanoparticles (nTiO₂) were prepared using ultrasonic cavitation technique using leaf extract of Murraya koenigii . The extraction of leaf was carried out using distilled water as a solvent. The size and shape of nTiO₂ particle was confirmed using transmission electron microscope and found to be spherical shape of diameter ∼10–45 nm. The mechanical properties of nTiO₂ reinforced iPP composites were studied using universal testing machine. Moreover, thermal properties were studied using Vicat softening temperature, thermogravimetric analyzer, and differential scanning calorimeter. The extent of dispersion of nTiO₂ in iPP matrix was studied using field‐emission scanning electron microscope and X‐ray diffractometer. The mechanical and thermal properties of nTiO₂‐iPP composites were found to be improved significantly with increasing amount of nTiO₂ particles except elongation at break, which is a marginal increment. This improvement in properties (mechanical and thermal) was due to the uniform dispersion of nTiO₂ in iPP matrix, which means that chains of polymers were well adhered with the spherical shaper particles. POLYM. COMPOS., 38:1273–1279, 2017. © 2015 Society of Plastics Engineers     

Effects of steeping conditions during wet-milling on the retentions of tocopherols and tocotrienols in corn

Vitamin E is a natural antioxidant that plays significant roles in food preservation and disease prevention. There are eight naturally occurring vitamin E isomers (tocols): α-, β-, γ-, and δ-tocopherols and α-, β-, γ-, and δ-tocotrienols. Corn oil is a major source of vitamin E. Most of the corn oil produced in the United States is a co-product of corn wet-milling. There is limited knowledge about the effects of corn wet-milling on the retention of these vitamin E isomers. A high-performance liquid chromatography method was developed for simultaneous determinations of tocols in steeped corn samples. Effects of steeping conditions (steeping time and SO₂ concentration) on retention of tocols in corn were investigated. α-Tocopherol, γ-tocopherol, α-tocotrienol, and γ-tocotrienol are the predominant vitamin E isomers in the corn variety used in the study. Steeping conditions had little effect on the concentration of α-tocopherol and α-tocotrienol. However, a higher concentration of SO₂ and a shorter steeping time gave a slightly higher γ-tocotrienol content and lower γ-tocopherol content. Corn kernels steeped in a vitamin C solution had a much higher concentration of the tocols than those steeped in SO₂ solution.