Removal Of Hemicellulose Research Articles

Ozonolysis of wheat bran in subcritical water for enzymatic saccharification and polysaccharide recovery

The destarched wheat bran was pretreated with ozonolysis, subcritical water (SW), and their combinations to improve its enzymatic digestion and hemicellulose solubilization. Ozonolysis caused lignin destructions and partial leach of hemicelluloses, leading to the formation of oxalic acids. Taking advantage of these effects, the sequential combinations of ozonolysis and SW showed synergy, resulting in a 3-fold hydrolysis outcome relative to the individual SW treatment. Eventually, the combined pretreatment achieved a high hemicellulose removal (86%) and saccharification yield (85% for glucose) under a mild SW condition (160 °C for 30 min). Apart from morphological destructions, FTIR and TGA results indicated different structural changes caused by ozonolysis and SW. Hemicellulose was shown as the major factor hindering enzymatic hydrolysis. Additionally, the soluble polysaccharides generated by these pretreatments were characterized, showing that the single SW pretreatment was better for polysaccharide recovery. These findings may help to maximize the benefits of wheat bran biorefinery.

The Effect of Alkaline Treatment onto Physical, Thermal, Mechanical and Chemical Properties of Lemba Leaves Fibres as New Resources of Biomass

The main purpose of this paper is to investigate the effect of alkaline treatment on the physical, thermal, mechanical and chemical properties of pristine lemba leaves fibres (LeLeFs). LeLeFs were treated with 6, 8, and 10 wt% sodium hydroxide (NaOH) solution at room temperature for 24 h. In order to determine the functional group presence after the alkaline treatment, LeLeFs were analyzed using Fourier Transform Infrared (FTIR) Spectroscopy. The density of LeLeFs treated with 10 wt% NaOH solution recorded the highest density with 1.168 g/cm³. Morphology study showed that the diameter of fibre reduced with the increment of NaOH concentration. The removal of lignin and hemicellulose could be observed in the thermogravimetric analysis (TGA). Alkaline treatment enhanced the tensile properties of fibre and 10 wt% alkaline treated fibre resulted in the highest tensile strength, modulus and elongation of the fibre at 511.10 MPa, 11.76 GPa and 3.69% respectively. Chemical resistance analysis found that the treated fibre had better chemical resistance compared to untreated fibre. Therefore, it is substantiated that alkaline treatment affects the properties of LeLeF.

Physical techniques shed light on the differences in sugarcane bagasse structure subjected to steam explosion pretreatments at equivalent combined severity factors

Significant improvements in pretreatments and a deeper understanding of changes in the physical structure and chemical composition of pretreated lignocellulosic materials are required to guarantee the technical and economic sustainability of second-generation ethanol technologies. In present work, several biophysical techniques were applied to characterize sugarcane bagasse samples that have been subjected to autocatalytic, phosphoric acid and sulfuric acid catalyzed steam explosion under equivalent combined severity factors (CSF). Confocal laser scanning microscopy and fluorescence lifetime imaging studies demonstrated unequal changes in lignin distribution in the plant cell wall that could be nicely correlated with substrate susceptibility to enzymatic hydrolysis. Furthermore, solid state nuclear magnetic resonance corroborated these observations by showing the differences in biomass composition primarily associated with hemicellulose removal, whereas X-ray diffraction analysis revealed changes in crystallinity indexes and average crystallite sizes. Thus, the impact of pretreatment temperature on the physical structure and chemical composition of CSF-equivalent steam-exploded sugarcane bagasse was identified as the key factor for developing substrate accessibility. This calls for caution in using combined severity factor as a chief parameter for comparison of different pretreatment conditions.

Insights into delignification behavior using aqueous p-toluenesulfonic acid treatment: comparison with different biomass species

Exploring an efficient delignification technique is imperative for further advance on biorefinery, together with elucidation on affecting factors and mechanism of delignification. Biomass fractionation using the aqueous p-toluenesulfonic acid (p-TsOH) changed tremendously with biomass species. Herein, effect of biomass species on delignification using the aqueous p-TsOH treatment was investigated. Compared to cellulose and hemicelluloses removal, delignification was greatly affected by biomass species, and delignification of softwood was the toughest. The dissolved lignin and residual lignin in the pretreated biomass, together with the original lignin without pretreatment were determined, analyzed and compared using various techniques. Essentially, the active linkages and groups in the dissolved lignin decreased compared to the original lignin from TGA and GPC analysis. However, the primary structure of lignin was not drastically altered after treatment from FTIR results. The high content of phenolic hydroxyl and the hydrophilic carboxyl in the original lignin of hardwood and grass were detected, which mainly accounted for their super solubility during the aqueous p-TsOH treatment. Moreover, the active aryl ether linkages reduced and C–C linkages increased for softwood after treatment. Compared with the guaiacyl unit, dissolution of the syringyl and p-hydroxyphenyl units were readily achieved. Therefore, the ideal feedstocks for the aqueous p-TsOH treatment are hardwood and grass species.

Optimization of Chemical Pretreatments Using Response Surface Methodology for Second-Generation Ethanol Production from Coffee Husk Waste

Within the strategies of substitution of energy from fossil fuels by renewable energies, the research is based on second-generation ethanol production (2G ethanol). One of the raw materials considered for this is residual biomass of the coffee industry, being the subject of study here. The cellulose contained in the coffee husk (coffee husk or coffee skin or coffee exocarp or pericarp) was maximized using pretreatment processes. In dilute acid hydrolysis (DAH), using a fixed 1:6 w:v solid to liquid ratio (SLR), process times (35, 45, 55 min) and H2SO4 concentrations (3, 4, 5% v/v) were evaluated, achieving 53.63% hemicellulose removal. A delignification process resulted in 58.82% lignin removal, evaluating the effect of process times (30, 35, 40 h) and SLR (1:8, 1:10, 1:12 w:v) at a fixed concentration of 8% v/v H2O2. A 115.59 g/L glucose concentration was obtained with an interaction of fixed concentrations of 4–6% w/w Cellic CTec3 enzyme and 6:1 to 1:12 v:w SLR. The fermentation process considered the composition variation of the culture medium (enriched culture C1 and non-enriched culture C2), generating ethanol at 48.19 and 29.02 g/L concentrations, respectively. Fermentation efficiency (ηf) was improved from 21.99 to 81.74% with the addition of inorganic nutrients (KH2PO4, (NH4)2SO4, and MgSO4·7H2O). These results confirmed that the optimization of the pretreatments in coffee husk waste favored the cellulose production and facilitated the enzymatic process to produce a high glucose concentration, revealing these residues as a carbon source promising for second-generation ethanol production.

Deep eutectic solvent pretreatment of Bambara groundnut haulm for enhanced saccharification and bioethanol production

Five deep eutectic solvents (DES) were screened for their effectiveness in improving biosugar yield in Bambara groundnut haulm (BGH) for bioethanol production. Choline chloride-lactic acid (ChCl-LA) treatment provided the most promising result and was further optimised by investigating the effect of temperature and time on cellulose loss and enzymatic sugar yield. ChCl-LA pretreatment at 100 °C for 1 h was observed to be the best condition for hemicellulose (54.5%) and lignin (60.7%) removal along with optimum sugar recovery of 94.8%. The resulting hydrolysate was concentrated and fermented for 72 h with Saccharomyces cerevisiae BY4743, and a maximum ethanol concentration of 11.57 g/L was achieved with an ethanol yield of 0.38 g/g sugar and productivity of 0.19 g/L/h. From the results obtained, it is evident that deep eutectic solvents are effective for breaking the recalcitrance in BGH due to their high delignification capacity. Furthermore, a recovery of the amorphous glucose and xylose in the BGH prior to DES pretreatment is vital to prevent sugar loss, thereby improving the biosugar yield for bioethanol production.

Combination of ethanol and Fe3O4@C‐SO3H pretreatment of Eucalyptus for glucose release via enzymatic saccharification

AbstractBACKGROUNDEnzymatic hydrolysis of lignocellulose is regarded as the most efficient route to producing fermentable sugars, one kind of promising future biofuel, while physiochemical pretreatment is the initial but most critical step for the efficient utilization of lignocellulose.RESULTSIn this study, a recoverable carbonaceous solid acid catalyst Fe3O4@C‐SO3H was used in combined organosolv pretreatment of Eucalyptus biomass at 140–180 °C with 50 vol% ethanol. The introduction of solid acid in ethanol pretreatment remarkably alleviated the requirement of smaller biomass size, but provided less influence on cellulosic degradation, which benefited the subsequent enzymatic hydrolysis to glucose. After the pretreatment using 50 vol% ethanol and 20% catalyst at 160 °C, 60.3% hemicellulose and 52.6% lignin were removed from Eucalyptus (75–250 μm) within 60 min, which resulted in a cellulose retention ratio of >90% and improved hydrolysis efficiency by nearly 20 and 2 folds, respectively, compared to untreated and ethanol pretreated materials.CONCLUSIONThis study explored a novel pretreatment technique to improve the efficiency of enzymatic saccharification. It also demonstrated that the hydrolysis yield of cellulose had significantly positive correlation with the removal of lignin and hemicellulose in Eucalyptus, but was less affected by cellulose crystallinity. © 2020 Society of Chemical Industry

Effects of redox environment on hydrothermal pretreatment of lignocellulosic biomass under acidic conditions

The effects of the redox environment on acidic hydrothermal pretreatment were investigated in experiments with sugarcane bagasse (190 °C, 14 min) and Norway spruce (205 °C, 5 min). To modulate the redox environment, pretreatment was performed without gas addition, with N2, or with O2. Analyses covered pretreated solids, pretreatment liquids, condensates, enzymatic digestibility, and inhibitory effects of pretreatment liquids on yeast. Addition of gas, especially O2, resulted in increased severity, as reflected by up to 18 percent units lower recoveries of pretreated solids, up to 31 percent units lower glucan recoveries, improved hemicellulose removal, formation of pseudo-lignin, improved overall glucan conversion, and increased concentrations of several microbial inhibitors. Some inhibitors, such as formaldehyde and coniferyl aldehyde, did not, however, follow that pattern. TAC (Total Aromatic Content) values reflected inhibitory effects of pretreatment liquids. This study demonstrates how gas addition can be used to modulate the severity of acidic hydrothermal pretreatment.

Effect of integrated treatment on improving the enzymatic digestibility of poplar and the structural features of isolated hemicelluloses

Herein, a two-step hydrothermal pretreatment combined with alkali extraction method was applied to deconstruct the poplar cell walls for enzymatic hydrolysis. Results revealed that 88.1 % of hemicelluloses and 77.6 % of lignin were removed during the integrated treatment performed at 180 °C and a maximum enzymatic hydrolysis efficiency of 96.1 % was achieved. Confocal Raman microscopy suggested that the removal of hemicelluloses from cell walls was inhomogeneous, and most hemicelluloses were released from the secondary wall. In addition, 35.2–56.8 % of hemicelluloses were isolated from the integrated treatment. Detailed structural analysis revealed that the water-soluble hemicelluloses possessed more branched structure than the alkali-soluble hemicelluloses and the hemicelluloses isolated from the poplar were mainly composed of a linear backbone of (1→4)-β-d-Xylp with 4-O-Me-α-d-GlcpA attached as side chains. This work provides an efficient pathway to transform poplar into fermentable sugars and hemicelluloses with considerable yield.

Characterization on chemical and mechanical properties of silane treated fish tail palm fibres

A novel cellulosic fibre was extracted from the peduncle portion of the fish tail palm tree and the extracted fish tail palm fibre was treated with different concentrations (1%, 5%, and 9%) of silane solution. The characteristic analysis on chemical, functional, mechanical and surface property of the extracted fish tail palm fibres were investigated through chemical composition analysis, Fourier Transform InfraRed spectroscopy (FT-IR), single fibre tensile test, and Scanning Electron Microscopy (SEM). Chemical analysis results indicate that silane treatment improved the cellulose content of the fish tail palm fibre. The highest cellulose content of 72.51% was observed in the 9% silane treated fish tail palm fibre. Also, it improved crystallinity index value of 62.5% for 5% silane treated fibre, which is confirmed through the X-ray diffraction analysis. FT-IR result indicates the removal of hemicellulose at characteristic wavelength of 1745 cm−1 for 5% silane treated fish tail palm fibre. Tensile property of the silane treated fish tail palm fibre (1, 5, and 9%) shows an increased tensile strength of 7.3%, 12%, and 6.6% as compared to raw fish tail palm fibre. Moreover, this type of novel natural fibres can reduce the cost while offering competent performance during the polymer-based product development.

Catalytic co-pyrolysis of torrefied poplar wood and high-density polyethylene over hierarchical HZSM-5 for mono-aromatics production

The catalytic co-pyrolysis of torrefied poplar wood sawdust (TPW) and high-density polyethylene (HDPE) was investigated over hierarchical HZSM-5. Compared with raw PW/HDPE, the bio-oil yield from co-pyrolysis of TPW/HDPE decreased gradually while the quality of bio-oil was upgraded. With increasing torrefaction temperature from 220 to 280 °C, the amounts of acids, furans, and anhydrosugars in bio-oil were significantly reduced due to the removal of hemicellulose, whereas the production of phenols and alkenes were improved due to the enhanced hydrogen transfer reaction. In the catalytic co-pyrolysis, increasing torrefaction temperature caused an enhanced production of mono-aromatics as well as the selectivity of BTX (benzene, toluene, and xylene). Nevertheless, severe torrefaction (280 °C) lead to a rapid reduction of aromatic yield and selectivity due to the loss of cellulose. Compared to parent HZSM-5, hierarchical HZSM-5 treated with alkaline concentration (0.2–0.3 mol/L) favored the formation of mono-aromatics at the expense of polyaromatics. The maximum mono-aromatics yield of 71.75% was obtained during catalytic co-pyrolysis of 260-TPW/HDPE over 0.3-HZSM-5. The present work suggests that torrefaction pretreatment followed by the catalysis of hierarchical HZSM-5 is an efficient way to promote the production of valuable mono-aromatic hydrocarbons from biomass and plastic wastes.

Optimization of wheat‐straw‐extracted cellulose via response surface methodology and mechanical properties of its poly(lactide)‐based biocomposites

AbstractIn view of environmental footprints and growing demand for green energy materials, employing biomass by eliminating lignin and hemicellulose has been topic of recent interests due to their applications in food packaging, textile, automobile, and polymer industries. Herein, we report on optimization of the cellulose extraction (removal of lignin and hemicellulose) from agro‐waste (wheat straw) by the response surface methodology (RSM), where, the Box Behnken Design has been implemented to study the effect of sodium hydroxide/sodium hypochlorite amount, temperature, and time on the extraction process. Fourier transform infrared spectroscopy, X‐ray diffraction study, and thermal degradation analysis indicate the successful isolation of cellulose with maximum (56%) removal of hemicellulose and lignin under optimal conditions. Furthermore, nano‐indenter analysis and tensile strength have been examined for cellulose/poly(lactide) biocomposites at different wt.% of cellulose, which indicated better tensile strength (28.15 MPa), tensile modulus (2430.24 MPa), and elongation at break (1.89%) as compared to intrinsic poly(lactide). Such studies on the cellulose extraction with optimized conditions and their mechanically stable biocomposites will pave the way for their utilization in polymer industrial applications.

Co-production of soluble sugars and lignin from short rotation white poplar and black locust crops

Co-production of sugars and lignin from short rotation white poplar and black locust crops is evaluated. Acid-catalyzed ethanol/water organosolv and dilute acid pretreatments are analyzed. Resulting pretreated materials are hydrolyzed enzymatically for sugar production, whereas solubilized lignins from pretreatment liquors are precipitated, analyzed by analytical standard, and characterized by FTIR spectroscopy, SEC chromatography, and solid-state 13C NMR. Organosolv produces in both materials a high delignification degree (46–50%) and a considerable hemicelluloses removal (62–67%), while acid hydrolysis is more efficient at removing hemicelluloses (86–90%), showing a delignification of 43% (white poplar) and 31% (black locust). Organosolv followed by enzymatic hydrolysis results in 37.8% (white poplar) and 38.2% (black locust) total sugars yields, whereas acid pretreatment and subsequent saccharification show higher sugars yields for white poplar (43.3%) and lower for black locust (29.1%). Regarding lignin samples, higher concentrations are recovered from organosolv liquors of both materials (67.8% and 44.9% yields for white poplar and black locust, respectively) compared to the quantities extracted from acid liquors of white poplar (4.6%) and black locust (6.8%). Organosolv lignins display a lower content of S units and phenols, and higher molecular weights. Contrary, acid lignins consist mainly of phenolic fragments with a higher content of S units and lower molecular weights.

An innovative plasma pre-treatment process for lignocellulosic bio-ethanol production

ABSTRACT In this work, glow discharge plasma pre-treatment was used for bio-ethanol production from a mixture of waste surgical cotton and cardboard. After compositional analysis, the plasma pre-treatment for the biomass mixture resulted in 68 ± 1% lignin removal and 22.2 ± 1.2% hemicellulose removal. The pre-treated mixture was analyzed using Fourier Transform-Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). After saccharification using in-house cellulases (saccharification – 43.6 ± 0.5%), bio-ethanol fermentation was performed using Saccharomyces cerevisiae RW 143. 48 ± 0.5 g/L bio-ethanol (0.4 g bio-ethanol/g of glucose) was obtained (cellulose conversion – 56.5 ± 0.2%). 90% (v/v), 180 proof pure bio-ethanol, was dehydrated to 99.9% (v/v) and 200 proof purity using molecular sieves. E-10 and E-20 blends containing 10% (v/v) and 20% (v/v) bio-ethanol with diesel fuel, respectively, were prepared. In an Internal Combustion engine, the combustion and emission characteristics were studied for E-10, E-20, and commercial diesel fuels.

Comparison of dilute acid pretreatment of agave assisted by microwave versus ultrasound to enhance enzymatic hydrolysis

A comparison between microwave and ultrasound irradiations in the agave pretreatment using dilute sulfuric acid as catalyst was assessed for the first time. Pretreatments were performed using a Taguchi Orthogonal Array L9 (34) to improve the hemicellulose removal and the agave digestibility. The results showed that under optimal conditions, the hemicellulose removal was superior in the pretreatment assisted with microwave (77.5%) compared to ultrasound (28.2%). Enzymatic hydrolysis yield of agave pretreated with microwave (MWOC) was 2-fold higher than agave pretreated with ultrasound (USOC). The relatively mild conditions of pretreatment with MWOC allowed to obtain a hydrolyzed free of inhibitors with a high glucose concentration (47.7 g/L) at low solids loading (10% w/v). However, these conditions did not have a significant effect over the agave pretreated with ultrasound. The pretreatment assisted with MWOC allowed to reduce time and temperature of the process compared to pretreatment with conventional heating.

A novel approach for isolation of nanofibers from sugarcane bagasse and its characterization for packaging applications

AbstractA novel approach including only one stage of ecofriendly treatment, by sodium bicarbonate, followed by mechanical grinding was used to isolate the nanofibers from waste sugarcane bagasse subjected to its characterization for the packaging applications. The result of dynamic light scattering (DLS) analysis was found in line with the result of transmission electron microscopy (TEM) to confirm the nanosize of developed nanofibers. The X‐ray diffraction analysis showed the highest crystallinity of nanofibers than those of untreated and treated fibers. The removal of hemicelluloses and lignin from treated fibers and nanofibers was confirmed by Fourier transform infrared (FTIR) analysis. Moreover, a good thermal stability of nanofibers was also confirmed by thermogravimetric analysis (TGA). The optical properties (ie, absorbance and transmittance) in wavelength range 200 to 700 nm were also measured using UV‐visible spectroscope. An excellent optical and antibacterial property against Escherichia coli (E. coli) and Bacillus bacteria along with better strength and stiffness was offered by the isolated nanofibers, which makes them the most suitable reinforcement to be used in polymeric composites for the packaging applications.

Greener extraction of highly crystalline and thermally stable cellulose micro-fibers from sugarcane bagasse for cellulose nano-fibrils preparation

This study aims to assess Na2CO3 treatment as a potential pre-treatment for extracting cellulose micro-fibers and subsequently cellulose nano-fibrils (CNF) from sugarcane bagasse. For cellulose micro-fibers extraction, Na2CO3 concentration, reaction time, and temperature were critical factors influencing reaction kinetics. It was concluded from statistical analysis of crystallinity index (CrI) that temperature was the most significant factor. Moreover, reaction time and Na2CO3 concentration were minimized while maximizing temperature to get an increase of 33 % and 115.2 % in the CrI and activation energy of thermal degradation, respectively. FTIR analysis of cellulose micro-fibers indicated the removal of hemicellulose and lignin. For the preparation of CNF, ionic liquid (IL) 1-n-butyl-3-methylimidazolium chloride was used. The CNF diameter was in the range of 4–35 nm, and the length was in a few micrometers. Hence Na2CO3 treatment in the combination of IL treatment is an efficient and environmentally friendly approach to valorize sugarcane bagasse into high-value CNF.

Impact Properties of the Chemically Treated Hemp Fibre Reinforced Polyester Composites

Plant based hemp fibre properties were found to be highly influenced by changes in the amounts of cellulose, hemicellulose and lignin constituents within the fibre. These fibre constituents play a major role for effective interfacial adhesion between the fibre and the matrix. Chemical treatments such as alkali (NaOH), acetyl (acetic acid & acetic anhydride) and silane (siloxane) treatments have the potential to react with constituent contents by varying their amounts. In this study, hemp fibre was treated with alkali (0–10 % NaOH), acetyl and silane chemicals. Treated fibres were mixed with polyester matrix to produce composites. The effects of chemical treatments on hemp fibres and the resulted polyester matrix composite were analysed through impact testing of the composite samples. Alkali treatments on hemp fibres enhanced the impact resistance properties (around 43 % lower absorbed energy and 40 % higher rebounded energy) of its composites compared to the untreated cases. Lower absorption energy and higher rebounded energy indicates strong interfacial bonding between the fibre and matrix. Improvements are governed by the removal of hemicellulose and lignin from the fibre, which provides a platform for better chemical reactions between fibres and matrix. On the other hand, acetyl treatments on the higher concentrations of NaOH pre-treated fibres reduced the fibres’ ability to support impact loadings (22 % higher rebounded energy compared to the untreated cases). In the two treatment conditions, fibre lessen their strength due to excessive removal of hemicellulose and lignin constituents, and composites exhibited lower impact properties compared to the NaOH treated samples. Similar impact properties were also recorded for alkali pre-treated silanised composites. As alkali pre-treatment removed the hydroxyl groups from the fibre, further silane treatment could not develop silanols to create strong interface bonding. As a result, composites failed under lower impact resistance compared to the NaOH treated samples.

Pseudo-Lignin Content Decreased with Hemicellulose and Lignin Removal, Improving Cellulose Accessibility, and Enzymatic Digestibility

The sugarcane bagasse is a heterogeneous material and needs a pretreatment to breakdown its complex structure to make cellulose accessible to enzyme action. This study aimed to evaluate pseudo-lignin formation, enzymatic hydrolysis of sugarcane fractions (leaf, external fraction, internode, and node), and bagasse after partial delignification and acid pretreatment. The leaf and external fraction presented the highest content of lignin, and external fraction was the most recalcitrant material resulting in lower glucose release. Pretreatment with diluted sulfuric acid (20% m/m or 2% m/v) generated 5 g/L of acetic acid and 2.07 g/L of 5-hydroxymethylfurfural (external fraction in natura and leaf extractive-free, respectively). Furfural ranged between 0.11 g/L (node delignified) and 0.06 g/L (leaf, external fraction, and node in natura). A decrease was observed in pseudo-lignin formed with extractive-free and delignified biomasses, with different structure compared with non-delignified samples. The biomass partial delignification and subsequent pretreatment with dilute acid generate a material with fragmented anatomical structure, with improved cellulose accessibility, favoring enzymatic hydrolysis achieving more than 90% of glucose yield (up to 12 g/L). This study has shown strategies to decrease material heterogeneity and avoid pseudo-lignin formation as it results in lower recalcitrance and better efficiency of the enzymatic hydrolysis.

Effect of two-stage sodium hydroxide pretreatment on the composition and structure of Napier grass (Pakchong 1) (Pennisetum purpureum)

ABSTRACT Sodium hydroxide is ideal in removing lignin from lignocellulosic materials at an effective operational cost. Two-stage NaOH pretreatment was employed herein to investigate lignin and hemicellulose removal and understand the morphology of Napier grass (Pakchong 1) (Pennisetum purpureum), which is considered lignocellulosic due to its high carbohydrate content. NaOH was used at different concentrations (0, 1, 2, 3, and 4 wt.%) and presoak times (1, 2, 3, and 4 h). The results demonstrated that 3 wt.% NaOH at 121°C without presoak resulted in 83.5% lignin removal, with a cellulose to lignin ratio of 3.0. Moreover, the treated samples showed cracking and irregular patterns at optimal conditions.