Xylan Films Research Articles

Significantly improve film formability of acetylated xylans by structure optimization and solvent screening

Acetylated xylans have great potential in fabricating functional film and coating materials, which need a good solubility/dispersibility and film formability in an easily evaporable solvent. However, the changes of film formability with degree of substitution by acetyls (DSAc) in different solvent systems for xylans have not been extensively studied, which limit the application of acetylated xylans in film materials. In this study, acetylated xylans with DSAc of 0–2 were prepared and the effects of acetyl groups on solubility/dispersibility, crystallinity and film formability of xylans in water and chloroform solvent systems were investigated. Due to the change of polarity, xylans with DSAc of 0–0.62 are only soluble in water solvents, while xylans with DSAc of 1.13–2 are only soluble in chloroform/ethanol (70/30 v/v) organic solvents. We have found that the film formability of acetylated xylans is highly related to their solubility and crystallization. Film formable xylans all had good solubility in the cast solvents. However, although with good solubility, xylans with DSAc of 0–0.3 and DSAc of 1.76–2 cannot form intact films, which is due to the forming of xylan hydrate crystals and xylan diacetate crystals. With the increase of DSAc, the mechanical property of xylan film increases initially at low DSAc and decreases at high DSAc. This study provides theoretical basis for applying xylans and their derivatives in advanced functional film and coating materials with great biocompatibility and biodegradability.

Nano-SiO2-modified xylan-PVOH-based composite films: Mechanical and barrier properties investigation

Hemicellulose from a wide range of sources and abundant reserves shows good biocompatibility, degradability, and renewability. Because of its low degree of polymerization and a large amount of hydroxyl groups, hemicellulose-based films exhibit low strength and tend to be hydrophilic, which hinders some potential applications. Therefore, hemicellulose-based films with improved strength and barrier properties are needed. In this study, nano-SiO2 was incorporated into polyvinyl alcohol/xylan matrix for the purpose of preparing an inorganic-organic hybrid composite film with elevated mechanical and barrier performance. The addition of nano-SiO2 can serve this purpose. A 1% nano-SiO2 loading resulted in an increase of contact angle of the composite film from 89.6° to 110.4°, an increase of the tensile strength from 11.2 to 14.8 MPa, and a decrease of oxygen permeability from 1.83 to 0.27 (cm3⋅µm)/(m2·d·kPa), which corresponds to a contact angle that was increased by 23%, tensile strength increased by 32%, and oxygen permeability decreased by 85%. These results indicated that the nano-SiO2 modified xylan film might have great application prospects as a barrier film in food packaging.

Preparation of xylan bio-composite films reinforced with oxidized carboxymethyl cellulose and nanocellulose

Despite the vast availability and potential for use in biomaterials, application of xylan is highly restricted due to their hygroscopic nature and low mechanical strength. In this work, the xylan (Xy) from hot water extract of bagasse was successfully valorized by integration with carboxymethyl cellulose (CMC), oxidized carboxymethyl cellulose (OCMC) and cellulose nanofibers (CNFs). This work was conducted to blend different ratios of xylan, CMC, OCMC and CNF to provide compact bio-composite films with multi-functional characteristics. Xylan was isolated by using hot water treatment from bagasse, and OCMC was provided from selective oxidation of CMC with sodium periodate. The FTIR and XRD results confirmed the introduction of hydrogen bonding and electrostatic interaction in prepared bio-composite films. The tensile strength of the blended films improved by incorporation of the Xy-CMC with OCMC and CNF, and the WVP of the bio-composite films decreased. The maximum value of achieved tensile strength was 30 and 32 MPa for Xy-CMC/OCMC (codes A1–A8) and Xy-CMC/CNF (codes B1–B8), respectively. The thermal stability of bio-composite films had been improved compared to the neat xylan films. The overall results advised that the blended films potentially could be used in the coating and packaging applications. Preparation of xylan bio-composite films reinforced with oxidized carboxymethyl cellulose and nanocellulose.

Development of a carboxymethyl xylan film containing licorice essential oil with antioxidant properties to inhibit the growth of foodborne pathogens

Antioxidant and antibacterial edible films based on carboxymethyl xylan with licorice essential oil incorporated were successfully developed. The films were prepared by the casting method and characterized using FTIR. The grammage, thickness, contact angle, mechanical and optical properties of the films were measured, together with the evaluation of their antioxidant, antibacterial and anti-biofilm properties against common foodborne pathogens. The FTIR spectra of the films clearly show the successful incorporation of the essential oil. The antioxidant properties of the films linked to scavenging free radicals and lipid peroxidation inhibition were maintained even after a storage period at room temperature (20 days, 25 °C). Moreover, the capacity of these films to inhibit the growth of Enterococcus faecalis and Listeria monocytogenes was demonstrated. The results also suggest the anti-biofilm potential of films incorporated with licorice essential oil. Therefore, these biodegradable films can be used in active packages for food, improving the overall shelf life.

Functionalized xylans in the production of xylan-coated paper laminates

Two functionalized xylans, namely a carboxymethyl xylan (CMX) and a 2-dodecenyl succinic anhydride-modified xylan (X-2-DSA) were, i) synthesized from beechwood xylan (BX) and characterized for their structural properties, thermal behaviour and molar mass and, ii) used in the production of paper/xylan laminates for food packaging. Films prepared from the functionalized xylans by solvent casting were applied onto paper employing the calendering moulding under pre-selected conditions in order to produce the laminates. The obtained laminates, as well as the starting base paper and the xylan-derived films, were characterized for their mechanical and barrier properties. The novel type of laminates demonstrated a synergistic effect with respect to its individual constituents, as the Young's modulus, tensile, tear and burst strengths of laminates were significantly improved in comparison to those of the starting paper or the xylan films. The xylan-coated paper laminates showed good moisture barrier properties, reducing up to 30-fold the water vapor permeability of the paper. At the same time, despite of fairly good oxygen barrier properties of the bio-based films from functionalized xylan, their application in paper laminates did not permit maintaining the same order of magnitude of oxygen transfer rates, which were, however, comparable to those reported for packaging papers coated by polyethylene films.

Development of carboxymethyl xylan films with functional properties.

The aim of this work was focused on the development of carboxymethyl xylan (CMX) formulations with functional properties to produce edible films. Beechwood Xylan was firstly derivatized into carboxymethyl xylan and thereafter was blended with Agar (Ag), Ammonium zirconium carbonate (AZC) and linoleic acid (La) to produce CMX:Ag, CMX:AZC, CMX:Ag:La films. Mechanical, barrier, optical and thermal properties of the produced films and their antimicrobial activity against food pathogenic bacteria were evaluated. The obtained films were transparent and yellowish. Agar and AZC improved the tensile strength at break of the control CMX film from 4.79 to 27.67 and 20.95MPa respectively, and the CMX:AZC film exhibited the greatest elastic modulus. Barrier properties of the films decreased when any of the components was incorporated into the CMX and all blended films were thermally more stable than control. The CMX:Ag:La film revealed a good antimicrobial activity against B. cereus and S. aureus.

Effect of Humidity on the Permeability of Alcohols in Hydroxypropyl Xylan Films

Inverse gas chromatography (IGC) was used to study the effect of humidity on the permeability of selected low molecular weight alcohols (methanol, ethanol, propanol, and butanol) through films made up of a hydrophilic polymer hydroxypropyl xylan (HPX). The thin films used consisted of a neat HPX film and a HPX film with sorbitol, a commonly used food grade plasticizer, (HPX/Sorbitol) and a HPX film with sorbitol and cellulose nanocrystal (CNC) (HPX/Sorbitol/CNC). Diffusivity and solubility of the alcohols at infinite dilution were measured at relative humidity (RH) values of 30%, 50%, and 70% of the carrier gas (helium). Permeability was then calculated using the measured diffusivity and solubility. Solubility coefficients of the alcohols were more or less insensitive to the RH. Increasing humidity from dry to 50% RH increased diffusion coefficients of the alcohols due to plasticization and swelling of the films whereas at higher RH, diffusion coefficient of the alcohols decreased. Based on the water contents of the films estimated from the weight-fraction-based Henry’s constant, at 70% RH, water clustering was the reason for the reduced diffusion coefficient in the neat HPX films while alcohol–water clustering was suggested for HPX/sorbitol and HPX/Sorbitol/CNC films. Permeability coefficients of the alcohols exhibited a maximum at around 50% RH as well suggesting that diffusion, not dissolution, dominated the permeability behavior. The findings suggest that due to sensitivity of the films to humidity, films should be used along with water barrier films to control humidity of the environment for applications used as barrier to alcohols.

Inverse Gas Chromatography Study of the Permeability of Aroma through Hydroxypropyl Xylan Films

Inverse gas chromatography (IGC) was used to study the permeability of a series of aromas through neat hydroxypropyl xylan (HPX) film and HPX films containing sorbitol, a commonly used food grade plasticizer, and cellulose nanocrystal (CNC), a nanosized filler. The aroma used included methanol, ethanol, propanol, and butanol. Also, their solubility and diffusion coefficients at infinite dilution were measured over the temperature range 120–160 °C, and the corresponding permeability coefficients were calculated. It was observed that the alcohols exhibited lower solubility (3 orders of magnitude) and diffusivity (2–3 orders of magnitude) than those of water in the neat HPX film. Solubility coefficient showed a minimum over the range of the molecular weight of the aforementioned alcohols. However, the diffusion coefficient decreased monotonically with increasing the alcohol’s molecular weight. Adding sorbitol (40 wt %) decreased solubility coefficients slightly but increased diffusion coefficients by about 1...

Rapeseed straw as a renewable source of hemicelluloses: Extraction, characterization and film formation

Polymeric hemicelluloses were extracted by autohydrolysis and alkali from a biomass feed consisting of the stems of rapeseed straw according to a full statistical factorial screening design. Water extraction yielded fractions rich in galactoglucomannan, while alkaline extraction yielded primarily xylan. The extracted galactoglucomannan and xylans had similar molecular weights, while the yield of xylan was higher than the yield of galactoglucomannan. The extracted hemicellulose fractions also contained some lignin (7–15%) and traces of Ca, K, Na, and Si. Free-standing films were prepared from the hemicellulose fractions with different xylan:galactoglucomannan ratios. The rapeseed xylan films showed strain-to-break values >60% without any added plasticizers.

Combination of internal and external plasticization of hydroxypropylated birch xylan tailors the properties of sustainable barrier films

To develop functional and sustainable products from future wood biorefineries, birch kraft pulp xylan was alkali-extracted and modified in aqueous solvent with hydroxypropylation to enhance its processability to films. For the first time, the roles of internal vs. external plasticization in the mechanical, thermal, and barrier performance of xylan films were systematically evaluated as a function of the degree of substitution (DS) of hydroxypropyl (HP) groups (internal plasticizer) and the added sorbitol (external plasticizer). In addition, the moisture uptake and the degree of crystallinity of hydroxypropyl xylan (HPX) films were characterized. Internal plasticization of xylan with HP groups enabled cohesive film formation, but did not form barrier materials alone. The addition of sorbitol as external plasticizer was necessary to obtain gas barrier films. The combinations of internal and external plasticization at selected ratios enabled the tailoring of film properties. Low to medium DS of HP and the addition of 10% or 20% sorbitol resulted in promising barrier properties. The tensile strength of the HPX films was rather high between 27 and 43MPa, depending on the level and type of plasticization. The thermal stability of HPXs increased and the degree of crystallinity of xylan in the films decreased as the internal plasticization increased. The glass transition temperature of HPXs and HPX films decreased more with external than with internal plasticization. The studied concept would benefit the sustainable exploitation of natural resources. The promising material properties, high degree of biobased raw materials, and non-food origin make HPX-based films an interesting option for multilayer paperboard coating for food packaging, for example.

Diffusion Behavior of Water at Infinite Dilution in Hydroxypropyl Xylan Films with Sorbitol and Cellulose Nanocrystals

Inverse gas chromatography (IGC) was used to measure the infinite dilution diffusion coefficients of water in hydroxypropyl xylan (HPX) films containing sorbitol, a commonly used plasticizer, and cellulose nanocrystals (CNC) at temperatures above their glass transition temperatures (Tg). HPX forms transparent but relatively rigid films and has the potential to be used for certain food-packaging applications. Sorbitol and CNC were added to HPX films to reduce Tg and to reduce the water diffusivity, respectively. It was found that almost 40 wt % of sorbitol was needed to yield a HPX film to have the desired flexibility, as quantified by its Tg, and that addition of a small amount of CNC (1–5 wt %) while maintaining the total concentration of sorbitol and CNC at 40 wt % (39–35 wt % of sorbitol) slightly increased the Tg but significantly decreased the diffusivity of water. In particular, the infinite dilution diffusion coefficient of water for the HPX film with 35 wt % of sorbitol and 5 wt % CNC was comparable to that of the bare HPX film. The diffusion data suggest that effects of sorbitol and CNC on the water diffusivity follow the free volume theory.

Quaternized and sulfated xylan derivative films

Xylan quaternized sulfate films were prepared from beech xylan (X) and compared with fully sulfated xylan films (XS). When quaternized xylan (QX) was prepared in the first step (DSQ=0.55), than by sulfation of QX in the second step the fully substituted ampholytic derivative (QXS; DSQ=0.33; DSS=1.67) could be obtained. By sulfation in first step, xylan sulphate (SX, DSS=0.70) was obtained and by subsequent quaternization, SXQ film with DSQ=0.55 and DSS=0.33 which contained partially unsubstituted hydroxyls. The molar masses (Mn) of the film's soluble parts were increasing in order X<SX<SXQ<QX<XS<QXS. In all films there were some insoluble particles present as determined by the amount of recovered masses by SEC-MALS. The materials were further characterized by AFM, XRD, TG/DTG/DTA, NMR and mechanical testing. QXS and SXQ could form mechanically more stable films than XS specimens.

Carboxymethylation of alkali extracted xylan for preparation of bio-based packaging films

This study describes the synthesis of carboxymethylxylan (CMX) and investigates its suitability as a film for packaging applications. High-purity polymeric xylan was extracted from commercial bleached birch kraft pulp and converted to CMX with three different degrees of substitution (DSs). The water vapor sorption, mechanical, and barrier properties of the films prepared from CMX were tested. Increasing DS of CMX films resulted in an increase in elongation at break and a decrease in tensile strength and Young's modulus. The DS also affected the barrier properties of the films. CMX films with higher DS showed improved (reduced) oxygen permeability (OP), and the water vapor permeability (WVP) increased with DS. It was demonstrated that the carboxymethylation of xylan recovered from industrial side-streams and its conversion to packaging films could be a viable option to valorize xylan.

Long-Chain Anhydride Modification: A New Strategy for Preparing Xylan Films

Xylan, which is a widely abundant plant polymer, has been considered as an alternative for film preparation. Up to now, however, xylan films have suffered from brittleness, low mechanical strength, and humidity sensitivity. This paper describes a new and effective strategy to prepare xylan films with high mechanical strength and less moisture-sensitive properties by introducing long carbon chains into the xylan backbone. Furthermore, this work revealed some important details on the relationships between structure (molecular structure, aggregation behaviors, and surface morphology) and properties (film-forming performance, flexibility, tensile strength, and hydrophilicity) of xylan film. It was found that the hydrophobic carbon chains (2-octenylsuccinic anhydride half-ester groups) in the xylan backbone acted as steric hindrance and could effectively prevent xylan chains from aggregation. 2-Octenylsuccinic anhydride (2-OSA) modified xylan (2-OSA-X) demonstrated amorphous structure and had better film-forming performance than the unmodified xylan. 2-OSA-X films were smooth, flexible, and less moisture-sensitive and showed significantly increasing tensile strength at a low degree of substitution.

Specific enzymatic tailoring of wheat arabinoxylan reveals the role of substitution on xylan film properties

To increase understanding of the applicability of agro biomass by-products as biodegradable film formers, the effect of wheat arabinoxylan (WAX) fine structure on film properties was studied by applying specific enzyme modifications. WAX was selectively modified to mimic the natural variations of different arabinoxylans, particularly the degree of mono and disubstitution of α-l-arabinofuranosyl (Araf) units in β-d-xylopyranosyl (Xylp) backbone residues. The resulting modified WAX samples had similar arabinose-to-xylose (Ara/Xyl) ratios, but they differed in the number of unsubstituted Xylp units. The substitution of WAX was found to affect, in particular, tensile strength, crystallinity, and oxygen permeability properties of the films, as statistically significant decreases in tensile strength and oxygen permeability took place after WAX de-branching. An increase in the number of unsubstituted Xylp units decreased the temperature of relaxation of small-scale molecular motions of WAX (β-relaxation) and increased the degree of crystallinity of the films.

Moisture barrier properties of xylan composite films

Moisture barrier properties of films based on xylan reinforced with several cellulosic resources including nanocrystalline cellulose, acacia bleached kraft pulp fibers and softwood kraft fibers have been evaluated. Measurements of water vapor transmission rate (WVTR) were performed by a modification of the wet cup method described by ASTM E 96-95, indicating that membranes with 10% nanocrystalline cellulose, prepared using a sulfuric acid, exhibited the lowest permeability value of 174gmil/hm2 among the composite films studied. Both the acacia and the softwood kraft pulp fibers when used for xylan film formation exhibited higher water vapor transmission rates at addition levels of 50% and no improvement at lower levels of 5% and 10%, in comparison to control xylan films. Reinforcement of xylan with hydrochloric acid made nanocrystalline cellulose yielded films that showed a reduction in water transmission but the reduction was not as significant as with the reinforcement of xylan with sulfuric nanocrystalline cellulose. The results showed that xylan films reinforced with 10% sulfuric nanocrystalline cellulose exhibited reductions in water transmission rates of 362%, 62% and 61% over films prepared with 10% softwood kraft fibers, 10% acacia fiber and 10% hydrochloric acid prepared nanocrystalline cellulose, respectively. The morphology of the resulting nanocomposite films was examined by SEM and AFM which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan–sorbitol films containing sulfuric nanocrystalline cellulose. The results from FT-IR suggested strong interactions occurred between the nanocrystalline cellulose and the matrix.

High oxygen nanocomposite barrier films based on xylan and nanocrystalline cellulose

The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan, sorbitol and nanocrystalline cellulose. The morphology of the resulting nanocomposite films was examined by scanning electron microscopy and atomic force microscopy which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan-sorbitol films containing sulfonated nanocrystalline cellulose. The average pore diameter, bulk density, porosity and tortuosity factor measurements of control xylan films and nanocomposite xylan films were examined by mercury intrusion porosimetry techniques. Xylan films reinforced with nanocrystalline cellulose were denser and exhibited higher tortuosity factor than the control xylan films. Control xylan films had average pore diameter, bulk density, porosity and tortuosity factor of 0.1730 µm, 0.6165 g/ml, 53.0161% and 1.258, respectively as compared to xylan films reinforced with 50% nanocrystalline cellulose with average pore diameter of 0.0581 µm, bulk density of 1.1513 g/ml, porosity of 22.8906% and tortuosity factor of 2.005. Oxygen transmission rate tests demonstrated that films prepared with xylan, sorbitol and 5%, 10%, 25% and 50% sulfonated nanocrystalline cellulose exhibited a significantly reduced oxygen permeability of 1.1387, 1.0933, 0.8986 and 0.1799 cm3·µm/m2·d·kPa respectively with respect to films prepared solely from xylan and sorbitol with a oxygen permeability of 189.1665 cm3·µm/m2·d·kPa. These properties suggested these nanocomposite films have promising barrier properties.

Synthesis and characterization of birch wood xylan succinoylated in 1-n-butyl-3-methylimidazolium chloride

The chemical modification of birch wood xylan was undertaken in the ionic liquid 1-n-butyl-3-methylimidazolium chloride (C4mimCl) using three different long-chain succinic anhydrides: n-octenyl succinic anhydride (n-OSA), n-dodecenyl succinic anhydride (n-DDSA) and n-octadecenyl succinic anhydride (n-ODSA). Reactions were performed at temperatures of 80–100 °C and reaction times of 0.5–22 hours resulting in a degree of substitution (DS) of 0.08–0.27. The formation of the desired products was confirmed through the use of 1H NMR and FT-IR, while DS was determined by titration. Thermogravimetric analysis of the modified and native xylans showed a slight lowering of thermal stability with functionalization. Contact angle measurements on spin-coated surfaces of modified xylan films showed a significant increase in hydrophobicity with the introduction of the alkenyl-functionalized succinic anhydride moieties.

High Oxygen Nanocomposite Barrier Films Based on Xylan and Nanocrystalline Cellulose

Abstract The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan, sorbitol and nanocrystalline cellulose. The morphology of the resulting nanocomposite films was examined by scanning electron microscopy and atomic force microscopy which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan-sorbitol films containing sulfonated nanocrystalline cellulose. The average pore diameter, bulk density, porosity and tortuosity factor measurements of control xylan films and nanocomposite xylan films were examined by mercury intrusion porosimetry techniques. Xylan films reinforced with nanocrystalline cellulose were denser and exhibited higher tortuosity factor than the control xylan films. Control xylan films had average pore diameter, bulk density, porosity and tortuosity factor of 0.1730 µm, 0.6165 g/ml, 53.0161% and 1.258, respectively as compared to xylan films reinforced with 50% nanocrystalline cellulose with average pore diameter of 0.0581 µm, bulk density of 1.1513 g/ml, porosity of 22.8906% and tortuosity factor of 2.005. Oxygen transmission rate tests demonstrated that films prepared with xylan, sorbitol and 5%, 10%, 25% and 50% sulfonated nanocrystalline cellulose exhibited a significantly reduced oxygen permeability of 1.1387, 1.0933, 0.8986 and 0.1799 cm3·µm/m2·d·kPa respectively with respect to films prepared solely from xylan and sorbitol with a oxygen permeability of 189.1665 cm3·µm/m2·d·kPa. These properties suggested these nanocomposite films have promising barrier properties.

Positively and negatively charged xylan films

Xylan was 2-hydroxypropylsulfonated and/or 2-hydroxypropylquaternized for film application. All the products were water soluble with molar masses of the derivatives between M n of 3.8 and 948.9 kg/mol with polydispersity index D from 1.7 to 26.8. At the range from 100 to 250 μm of thickness the material developed reproducible mechanical properties. When mixed solutions of quaternized and sulfonated samples were used for film preparation, they disrupted although their thickness was 234 ± 18 μm as determined by SEM. The thermal and thermo-oxidative stability of the mixed derivative increased in comparison to unmodified xylan film as determined by TG and DTA analysis. The measured tensile strength values were the best on quaternized films (64.3 MPa) while the Young's modulus values were higher on hydroxypropylsulfonated xylan film (3350 MPa). The mixed derivative gave values close to average between the two derivatives and according to SEM observation also the smoothest surface on the fracture.