Superheated Steam Treatment Research Articles

Tensile properties of recycled carbon fibers subjected to superheated steam treatment under various conditions

A new treatment condition involving superheated steam (SHS) was proposed to achieve optimal carbon fiber recovery with a minimal decrease in fiber strength. Unidirectional carbon fiber reinforced sheets were exposed to SHS at 650 °C for 1 h with the addition of N2 or CO2 as process gas. The recovery was assessed based on mass change and using thermogravimetry and differential scanning calorimetry. The results showed that the addition of N2 efficiently suppressed the decrease in fiber strength and achieved optimal recovery. Weibull parameters indicated that lower strength fibers tended to present a narrower strength distribution. The observation of fracture surfaces and oblique sections indicated that the presence of intrinsic defects and corrosion of surface crystallites under the oxidative condition are responsible for the deterioration of and the changes in the distribution of strength.

Inactivation of Bacillus cereus Spores on Stainless Steel by Combined Superheated Steam and UV-C Irradiation Treatment

Bacillus cereus spore contamination on food contact surfaces is of great concern in the food industry. Thus, in the present study, superheated steam (SHS) was used alone or combined with UV-C irradiation for inactivation of B. cereus spores inoculated on stainless steel coupons. Temperatures higher than 250°C were needed to effectively inactivate B. cereus spores by SHS treatment alone, while a synergistic bactericidal effect resulted from the sequential treatment of SHS before or after UV-C irradiation. The increased dipicolinic acid ratio obtained by the combined treatment had a significant role in the synergistic bactericidal effect. Therefore, the combined treatment of SHS and UV-C could be used effectively to inactivate B. cereus on stainless steel. It is recommended to use hurdle technology with reduced energy consumption to ensure microbiological safety on food contact surfaces.

Inactivation of Staphylococcus aureus Biofilms on Food Contact Surfaces by Superheated Steam Treatment

The objective of this study was to compare the inactivation efficacy of saturated steam (SS) and superheated steam (SHS) on Staphylococcus aureus biofilms on food contact surfaces, including type 304 stainless steel coupons with No. 4 finish (STS No. 4), type 304 stainless steel coupons with 2B finish (STS 2B), high-density polyethylene (HDPE), and polypropylene (PP). In addition, the effects of the surface characteristics on the inactivation efficacy were evaluated. Biofilms were formed on each food contact coupon surface using a three-strain cocktail of S. aureus. Five-day-old biofilms on STS No. 4, STS 2B, HDPE, and PP coupons were treated with SS at 100°C and SHS at 125 and 150°C for 2, 4, 7, 10, 15, and 20 s. Among all coupon types, SHS was more effective than SS in inactivating the S. aureus biofilms. S. aureus biofilms on steel coupons were more susceptible to most SS and SHS treatments than the biofilms on plastic coupons. S. aureus biofilms on HDPE and PP coupons were reduced by 4.00 and 5.22 log CFU per coupon, respectively, after SS treatment (100°C) for 20 s. SS treatment for 20 s reduced the amount of S. aureus biofilm on STS No. 4 and STS 2B coupons to below the detection limit. With SHS treatment (150°C), S. aureus biofilms on HDPE and PP needed 15 s to be inactivated to below the detection limit, while steel coupons only needed 10 s. The results of this study suggest that SHS treatment has potential as a biofilm control intervention for the food industry.

Thermal inactivation of lipoxygenase in soya bean using superheated steam to produce low beany flavour soya milk.

Time and temperature parameters of superheated steam (SHS) treatment were optimised using response surface methodology (RSM) for specific lipoxygenase (LOX) activity in soya beans and crude protein content in soya milk. The optimal SHS treatment was obtained at 9.3min and 119°C. The predicted values of specific LOX activity and crude protein content by RSM were 0.0098μmol/(minmg protein) and 3.2%, respectively. These values were experimentally verified to be 0.0081 ± 0.0002μmol/(minmg protein) and 3.0 ± 0.1%, respectively. Sensory evaluation showed that the beany flavour of soya milk produced from SHS treated soya beans was significantly weaker (P < 0.05) than that of untreated soya beans. The results showed that the optimised SHS treatment could reduce the beany flavour in the soya milk significantly (P < 0.05) by reducing the specific LOX activity in the soybean, while ensuring the crude protein content in the soya milk complied with Malaysian Food Regulations 1985.

Superheated steam treatment of rubberwood to enhance its mechanical, physiochemical, and biological properties

ABSTRACT This research was aimed to investigate mechanical properties, color and cell-wall components changes, and durability of pre-dried rubberwood (Hevea brasiliensis) after superheated steam (SS) treatment. Wood samples were treated at different SS temperatures (140–180°C) for 1–3 h. The highest compression strength parallel-to-grain, hardness and impact strength were found for samples treated at 160°C for 3 h (30.7% higher than untreated), at 150°C for 1 h (26.6% higher than untreated) and at 150°C for 2 h (52.6% higher than untreated), respectively. The surface color became darker after each treatment in comparison with the untreated wood. The number of accessible hydroxyl groups decreased and the relative cellulose crystallinity increased with SS temperature, indicating decreased hygroscopicity of the treated wood. Also, SEM micrographs of wood surface showed consistent decrease in starch particles with treatment temperature. Both decay and termite resistances of treated rubberwood improved with treatment temperature. All the analyzes showed that dried rubberwood treated with SS had some improvements in the mechanical properties, decreased hygroscopicity, and increase resistance to decay.

Effect of Superheated Steam Treatment on the Mechanical Properties and Dimensional Stability of PALF/PLA Biocomposite.

The effectiveness of superheated steam (SHS) as an alternative, eco-friendly treatment method to modify the surface of pineapple leaf fiber (PALF) for biocomposite applications was investigated. The aim of this treatment was to improve the interfacial adhesion between the fiber and the polymer. The treatment was carried out in an SHS oven for different temperatures (190–230 °C) and times (30–120 min). Biocomposites fabricated from SHS-treated PALFs and polylactic acid (PLA) at a weight ratio of 30:70 were prepared via melt-blending techniques. The mechanical properties, dimensional stability, scanning electron microscopy (SEM), and X-ray diffraction (XRD) for the biocomposites were evaluated. Results showed that treatment at temperature of 220 °C for 60 min gave the optimum tensile properties compared to other treatment temperatures. The tensile, flexural, and impact properties as well as the dimensional stability of the biocomposites were enhanced by the presence of SHS-treated PALF. The SEM analysis showed improvement in the interfacial adhesion between PLA and SHS-treated PALF. XRD analysis showed an increase in the crystallinity with the addition of SHS-PALF. The results suggest that SHS can be used as an environmentally friendly treatment method for the modification of PALF in biocomposite production.

Combination effect of saturated or superheated steam and lactic acid on the inactivation of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes on cantaloupe surfaces

The purpose of this study was to evaluate the effectiveness of the combination treatment of lactic acid immersion and saturated or superheated steam (SHS) on inactivation of foodborne pathogens on cantaloupes. Saturated steam (SS) treatments were performed at 100 °C, while SHS treatments were delivered at either 150 or 200 °C. Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes-inoculated cantaloupes were exposed to 2% lactic acid or sterile distilled water for 1 min followed by a maximum of 20 s of SS or SHS. Populations of each of the three pathogens on cantaloupes were reduced to under the detection limit (1.0 log CFU/cm2) after the combination treatment of 2% lactic acid and 200 °C steam for 20 s. To compare the effect of the lactic acid treatment method, we conducted spray application with 2% lactic acid combined with SS or SHS treatment; however, no significant log reduction differences were found between immersion and spraying techniques. After combination treatment of cantaloupes for 20 s, color and maximum load values (a characteristic of texture) were not significantly different from those of untreated controls. The results of this study suggest that the combination treatment of lactic acid and SHS can be used as an antimicrobial intervention for cantaloupes without inducing quality deterioration.

Interfacial adhesion of recycled carbon fibers to polypropylene resin: Effect of superheated steam on the surface chemical state of carbon fiber

The interfacial adhesion between polypropylene resin and recycled carbon fibers (RCFs) subjected to superheated steam (SHS) treatment was examined by performing microdroplet tests on the recovered single fibers. As-received virgin carbon fibers were selected as reference material for the evaluation. The interfacial shear strength (IFSS) was calculated to quantify the interfacial adhesion between the fiber and matrix. By comparing the IFSS of RCFs to those of corresponding virgin fibers, we found that 1 h SHS treatment at 650 °C improved the interfacial adhesion. X-ray photoelectron spectroscopy was employed to characterize the element composition and the content of functional groups on fiber surface. The SHS introduced extrinsic oxygen-containing functional groups on the fiber surface during the treatment. The increase in the IFSS value after SHS treatment is considered to be due to the chemical interaction at the interface between these functional groups and the resin.

Disintegration and Recycling of Multi-layered Glass Fiber Reinforced Polymer Composites via Superheated Steam

To increase viability of recycling of robust and large-scale multi-layered glass fiber reinforced polymer composites (GFRPs), disintegration of the multi-layered GFRPs and recovery of fibers/resin-derived materials were investigated using superheated steam (SHS) under normal pressure where a very quick heat transfer to GFRP was possible. The SHS treatment of 4 different types of multi-layered GFRP products were conducted at 350 °C in an oxygen-free environment up to 3 hours. The SHS treated GFRPs were easily disintegrated into each layer. The separated layers were divided into components: glass fibers, oligomers, and inorganic fillers after subsequent thermal and ultrasonication processes. Finally, clear glass fibers were recovered, and matrix resin was also recovered as soluble oligomers consisting of phthalates, glycols, and styrene units due to partial chain cleavage of cured resin. These results clearly showed the viability for the recycling of actual large-scale multi-layered GFRP products.

Specific oligomer recovery behavior from cured unsaturated polyester by superheated steam degradation

To examine the specific oligomer recovery behavior from cured unsaturated polyester resin (cUPR), super-heated steam (SHS) was employed as a reactant. The cUPR was treated by SHS in a temperature range of 300–350 °C and solubilized, resulting in recovery of solvent extracted residues (SE-SDRs). From size-exclusion chromatography analysis, an interesting finding was that the molecular weight (MW) value of SE-SDR, increased gradually with degradation time. This specific recovery behavior was analyzed by FT-IR and 1H NMR spectroscopies. Based on the analytical results, a proposed SHS degradation mechanism was that first orthophthalate and glycol ester groups were degraded and removed as short length fragments, after which cleavage of styrene unit crosslinkers induced collapse of the 3-D network structure with the resulting solubilizing cUPR as SE-SDR. This mechanism can explain the specific oligomer recovery behavior whereby an increase in MW of SE-SDR occurred with SHS-degradation time. Obtained styrene-fumarate copolymer having Mn 2550 and Mw 9480 was recovered in a maximum 57 wt% yield after SHS treatment at 325 °C for 180 min.

Sandwich compression of wood: effects of preheating time and moisture distribution on the formation of compressed layer(s)

Wood sandwich compression technology can on the one hand effectively improve the physical and mechanical properties of low-density fast-growing wood, on the other hand it saves at least 25 vol% of raw materials (compared to the traditional wood compression technology) by controlling the position of compressed layer(s). In this study, white poplar (Populus tomentosa) lumbers were firstly soaked in water for 2 h, then preheated at 180 °C for 0–600 s. After the preheating process, radial compression was applied to obtain sandwich-compressed wood, and the compression was fixed by superheated steam treatment. Moisture distribution along the wood thickness and density distribution in the compressed wood were characterized. Furthermore, effects of preheating time on moisture distribution, position and thickness of the compressed layer(s) were investigated. Results indicated that the position of the compressed layer(s) moved from the wood surface to the center as a result of preheating time extension. The initial moving speed of the compressed layer(s) was 0.040 mm/s, which was sharply reduced to 0.014 mm/s with the extension of preheating time to 120 s. Further extension of preheating time above 120 s did not extensively reduce the compressed layer(s) moving speed. When the preheating time was 480 s, two compressed layers in the compressed wood converged to one at the center along the thickness in the compressed wood. More importantly, it was found that the positions of the compressed layer(s) highly matched up with high moisture content (MC) regions in the preheating process. A significant linear correlation between positions of the MC peak in high MC region of the preheated lumbers and density peak in the compressed layer(s) was built. In addition, moisture distribution along the thickness of wood can be controlled by adjusting the preheating time to eventually control the position and thickness of the compressed layer(s) in the sandwich-compressed wood. Superheated steam treatment after wood sandwich compression contributed to the reduced set recovery percentage of 1.58% after conditioning at 40 °C and relative humidity of 90%.

Effects of superheated steam treatment on moisture adsorption and mechanical properties of pre-dried rubberwood

Rubberwood (Hevea brasiliensis) was treated with superheated steam (140–160 °C) for 1–3 h and then its adsorption ability, mechanical properties, and color changes were investigated. The results of adsorption show decreased equilibrium moisture content (EMC) for all heat-treated cases throughout the hygroscopic range. The Hailwood–Horrobin model was used to analyze the sorption isotherms and determine the monolayer and polylayer moisture contents for untreated and heat-treated rubberwood. The monolayer moisture content clearly decreased with treatment temperature and duration, whereas the reduction in polylayer moisture was relatively smaller. Moreover, the least density of water adsorption sites was found in wood after treatment at 160 °C for 3 h, indicating this as the cause for reduced equilibrium adsorption. All treatment conditions had improved mechanical properties, including compression parallel-to-grain, hardness, and tensile strength. The total color difference of the wood surface increased with increasing temperature and treatment duration.

Changes in Granular Swelling and Rheological Properties of Food Crop Starches Modified by Superheated Steam

Conventional hydrothermal modification of starches is a time‐ and energy‐consuming process. In this study, superheated steam treatment (SST) is used to modify the granular swelling and rheological properties of rice, corn, wheat, and potato starches, and the dependence of these modifications on starch sources is investigated. SST causes a decrease in granular swelling and structural recovery of gel network regardless of the starch source. The long‐term stability of all the starch gels is improved by SST, but their daubing performance may be degraded. In contrast, the responses of the starch gels to deformation and shear vary depending on the starch sources. The deformability, structural strength, and viscosity of corn, wheat, and potato starch gels are decreased by SST, while those of rice starch gel are increased. The shear‐thinning behavior of rice and wheat starch gels is strengthened and that of corn and potato starch gels is weakened by SST. Considering the high thermal efficiency of SS and the short treatment time (1 h) used in this study, SS treatment can be a superior alternative to conventional hydrothermal modification.

Effect of Precooking and Superheated Steam Treatment on Quality of Black Glutinous Rice

Consumption of glutinous rice has been increasing. Leum Pua rice (Oryza sativa Linn.) is black glutinous rice containing high nutrition, but its cooking process is time-consuming. This study aimed at decreasing cooking time by changing rice properties using superheated steam treatment. The black glutinous rice was subjected to pretreatment: uncooking and precooking before superheated steam treatment at 250°C and 300°C. Drying rate constant (k) of uncooked rice was 0.0301–0.0744 s−1. Precooking rice prior to superheated steam treatment at 300°C reduced the kinetic rate constant to 0.0596 s−1. From SEM, porosity of the treated rice was observed. However, superheated steam treatment reduced ferric reducing antioxidant power and total phenolic content, compared with control. From X-ray diffraction, A-type crystalline structure of the treated rice was disappeared. Cooking time of the superheated steam-treated rice was reduced to 1–5 min. Their hardness and overall liking scores were comparable to control.

Effects of superheated steam treatment on the physical and mechanical properties of light red meranti and kedondong wood

Effects of superheated steam treatment on the physical and mechanical properties of light red meranti and kedondong wood

Modification of potato starch by using superheated steam

Conventional hydrothermal modification of starches is a time- and energy-consuming process. In this study, superheated steam (SS) at different temperatures (100–160 ℃) was used to modify the structural and physicochemical properties of potato starch (PS). The long- and short-range molecular structures were disrupted without affecting the granular structure of PS and the degree of disruption could be regulated by simply changing the treatment temperature. The swelling power, solubility, transparency, peak viscosity and breakdown of PS were positively correlated with each other and were significantly decreased by SS treatment, while the pasting temperature, final viscosity and setback were significantly increased. Considerable amount (>9%) of slowly digestible starch was converted to resistant starch by SS treatment at 100 and 120 °C. Considering the high thermal efficiency of SS and the short treatment time (1 h) used in this study, SS treatment could be a superior alternative to conventional hydrothermal modification.

Characteristics of cellulose from oil palm mesocarp fibres extracted by multi-step pretreatment methods

Characteristics of cellulose isolated from oil palm mesocarp fiber (OPMF) using multi-step pretreatment methods were determined in this study. It was postulated that the succession of pretreatment steps for cellulose extraction from lignocellulosic biomass may affect the cellulose properties. Pretreatment steps involved in cellulose extraction were superheated steam (SHS) treatment, enzymatic hydrolysis and alkaline treatment. OPMF was subjected to SHS treatment to open up the fibres wall structure followed by enzymatic hydrolysis using xylanase for effectiveness enhancement the alkaline treatment afterwards. In order to obtain bleached cellulose, peracetic acid, a totally chlorine free (TCF) chemical was used. Cellulose obtained from these multi-step pretreatment methods had purity of 87.5 %, with crystallinity of 69.2 % and thermally stable up to 360°C.

Inactivation of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on cherry tomatoes and oranges by superheated steam

This study was performed to compare the effectiveness of saturated steam and superheated steam for the inactivation of Escherichia coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on the surface of cherry tomatoes and oranges. It also determined the effect of the steam processes on the color, texture, Vitamin C content, and antioxidant capacity and changes in these parameters during chilled storage. Cherry tomatoes and oranges inoculated with the three foodborne pathogens were treated with saturated steam at 100 °C and superheated steam at 125, 150, 175, and 200 °C for various time intervals. After the cherry tomatoes and oranges were exposed to superheated steam at 200 °C for 3 or 20 s, all tested pathogens were reduced to below the detection limit (1 or 1.7 log, respectively) without significant changes in color, texture, vitamin C content, and antioxidant capacity (P > .05) at 4 °C for up to 9 days. Our results suggest that superheated steam treatment can be effective at decreasing pathogen populations when compared to saturated steam, without significant quality deterioration, and thus, this technique demonstrates great potential to improve the microbial safety of fresh produce.

Depolymerization of Cellulose with Superheated Steam: Remarkable Obstruction Effects of Sodium and High Reactivity of Crystalline Cellulose

A superheated steam (SHS) treatment was found to be effective for conversion of cellulose to levoglucosan (LG) and other organic compounds. Yields of water-soluble organic compounds (TOC) and LG reached 88% and 41%, respectively, with the SHS treatment at 300 °C for 30 min. The reaction temperature was far lower than temperatures employed in conventional pyrolysis treatments (≥500 °C), and the TOC and LG yields were comparable to values reported for pyrolysis. Product distributions were significantly altered by sodium content in the parent cellulose. Sodium at 0.05 wt % or more in cellulose lowered the LG yield to almost zero, giving approximately constant TOC values other than LG, and increased solid residue, which indicated that sodium greatly reduced the reactivity of cellulose to form LG. In the absence of sodium, the reactivity of the crystalline phase of cellulose was much higher than the amorphous phase, indicating that the widely reported phenomena in which amorphous cellulose has higher reactivit...

Instrumental analyses of nanostructures and interactions with bound water of superheated steam treated plant materials

Using multi-scale instrumental analyses, nanostructural changes due to superheated steam treatments were compared between Japanese cedar (Cryptomeria japonica) and bamboo (Phyllostachys pubescens Mazel). The lower amounts of aromatic carboxylic acids contained in lignin and hemicellulose/lignin in Japanese cedar suppressed not only the formation of pyrolysis products from hemicellulose but also fragmentation of cell walls. Variable temperature solid-state NMR spectra and relaxation time analyses were carried out on the nanostructures of the plant materials in order to examine molecular motions and interaction with bound water for the biomass constituents of the plant materials. The untreated and steam treated bamboos strongly interacted with bound water to change the 1H spin-lattice relaxation time (T1H) values depending on the content of bound water. Because the interaction between the biomass constituents and bound water in Japanese cedar was weaker than that in bamboo, the T1H values of Japanese cedar were reduced less than those of bamboo in the humid conditions. The difference in the interaction with bound water between bamboo and Japanese cedar also affected the amount of the pyrolysis products and the decomposition rate of hemicellulose in the superheated steam treated materials. Furthermore, the pyrolysis products caused little change in the molecular mobility of Japanese cedar although they restrained that of bamboo.