3.1. Film
In recent years, significant progress has been made in developing high-performance hemicellulose-based films. Hemicellulose, as natural biopolymers, have garnered considerable attention in the domain of environmental materials owing to its exemplary biodegradability [
85], which is capable of rapid decomposition under natural conditions, significantly mitigating environmental impacts when juxtaposed with traditional plastics [
86]. However, due to the structural properties of hemicellulose, there are challenges in its compatibility with traditional plastics, as well as in the thermal stability, mechanical properties, and water vapor permeability of hemicellulose materials [
76]. Xylan with a more complete structure has a higher elongation at break. Svärd
, et al. [
87] used optimized hydrothermal alkaline extraction conditions to extract high-purity hemicellulose, primarily consisting of galactoglucomannan and xylan, from rapeseed straw. The Film with an elongation at break exceeding 60%. Enhancing the performance of films can be effectively achieved through the addition of plasticizers. Azeredo
, et al. [
88] used citric acid (CA) as a plasticizer to promote ester bond formation between CA and wheat straw hemicelluloses, this process results in improved water resistance and water vapor barrier properties of the films. Kocabaş
, et al. [
89] used combining acid hydrolysis and mechanical defibrillation techniques with sodium alginate and added CA as a plasticizer. The extracted hemicellulose and cellulose from barley bran could form excellent mechanical properties and gas barrier performance bio-composite films. The study results indicated that the addition of CA not only acted as a plasticizer but also improved the flexibility and processability of the material by forming ester bonds with the hemicellulose chains. Kapil
, et al. [
90] chemically modified rice straw xylan into acetylated xylan (AX) and carboxymethylated xylan (CMX), and created biocomposite films with polyvinyl alcohol (PVA) and CA. the introduction of AX and CMX enhanced the mechanical strength of the biocomposite films. In CMX biocomposite films, the unreacted CA contained undissociated carboxylate ions (COO-) that could kill bacteria by disrupting their cell membranes. However, high concentrations of AX and CMX could lead to uneven intermolecular cross-linking, reducing the elongation at break of the films. The acetylation process reduced the number of free hydroxyl groups, thereby decreasing the antioxidant activity [
90]. This suggests the need to prepare different modified hemicellulose-based materials according to specific requirements.
Hemicellulose and cellulose nanofillers composites have gained significant attention. Pereira
, et al. [
91] innovatively modified wheat straw hemicellulose films by incorporating varying concentrations of cellulose nanocrystals (0-8 wt%) and citric acid (0-30 wt%), they found that the optimal addition of 5.9 wt% CNC and 30 wt% citric acid significantly enhanced the film’s physical properties, the enhancement included improvements in tensile strength, water vapor barrier properties, and water resistance. The research of Xu
, et al. [
92] utilized Artemisia selengensis straw to extract hemicellulose and cellulose nanocrystals, creating enhanced composite films with polyvinyl alcohol, resulting ina substantial increase in tensile strength by 80.1% to 36.21 MPa with a 9% inclusion of cellulose nanocrystals, additionally, the water vapor transmission rate of these films decreased by 15.45% when enhanced with 12% cellulose nanocrystals. These advancements suggest the potential use of these films in applications like biomedicine packaging materials and humidity sensors. ncers for films. Hemicellulose nanocrystals and nanocellulose filled the pores of the films, forming a dense structure that significantly enhanced the mechanical properties, thermal stability, and gas barrier performance of the composite films. The presence of hemicellulose nanocrystals can somewhat slow down the degradation process of the material; however, due to their inherent biodegradability, the overall material can still naturally degrade in the environment. Rice straw hemicellulose was processed into nanoparticles with an average particle size of 141 nm through acid hydrolysis and intense ultrasonic treatment. The intense ultrasonic treatment caused the breaking of cellulose and hemicellulose molecular chains, forming spherical nanoparticles. These nanoparticles exhibited good dispersibility and stability and were used to enhance starch-based composite films. This significantly improved the mechanical properties, gas barrier performance, and thermal stability of the films while maintaining good biodegradability [
93].
3.2. Hydrogel
Compared to other lignocellulosic biomasses (cellulose, lignin), hemicelluloses are characterized by their low molecular weight, low degree of polymerization, and high degree of branching [
94]. They also possess numerous active hydrophilic functional groups (hydroxyl, carboxyl), making them easily soluble and modifiable, thus serving as excellent natural substrates for developing functional biomass-based hydrogels [
95]. However, their low molecular weight and degree of polymerization can impact the strength and usage stability of hemicellulose-based hydrogels [
75]. Researchers have conducted in-depth studies to improve strength and enrich functionalities, categorizing hemicellulose-based hydrogels into physically and chemically cross-linked types [
6].
Physical cross-linking refers to the formation of physical cross-linking points between macromolecular chains under physical conditions such as heating, high pressure, freezing, irradiation, and ultrasound through hydrogen bonding, hydrophobic interactions, host-guest interactions, electrostatic effects, polymer chain entanglement, and crystallization [
75,
96,
97]. Meena
, et al. [
98] studied the properties of mixed hydrogels of κ-carrageenan (kC) and oat bran xylan (OSX). The mixed gels, with 50-90% (by weight) OSX, showed significantly reduced segregation in kC gels and a notable increase in swelling capacity. The gels with kC/OSX50-90 had lower gelation and melting temperatures. The addition of OSX formed a more stable interpenetrating network structure, enhancing the stability of the hydrogels. Higher solution concentrations increasing the physical cross-linking points for denser and more stable gel structures [
97]. Talantikite
, et al. [
99] mixed cellulose nanocrystals (CNC) with arabinoxylan (AX) to synthesize fully bio-based hydrogels with tunable mechanical properties (
Figure 6). The amount of AX adsorbed on the surface of CNCs was positively correlated with the AX concentration.
Chemical cross-linking typically involves the initiation of hydroxyl groups in hemicellulose to produce oxy radicals, which undergo free radical graft copolymerization with polymer molecular chains, ultimately forming a three-dimensional network structure under heat, light, radiation, or cross-linking agents [
5]. Graft copolymerization enhances the molecular weight and thermal stability of hemicellulose, introducing new functional groups to improve strength and expand functionalities [
5]. As illustrated in
Figure 7, Sun
, et al. [
100] introduced acrylic acid (AAc) into the hemicellulose structure through a radical copolymerization reaction, successfully preparing pH-sensitive hydrogels based on wheat straw hemicellulose. The acrylic acid chains formed cross-links with the hemicellulose backbone. These hydrogels exhibited significant swelling differences under various pH conditions. In acidic environments, most carboxyl groups remained non-ionized, resulting in low charge density, with water diffusion primarily controlled by the concentration gradient. In neutral and alkaline conditions, the ionization of carboxyl groups generated strong electrostatic repulsion, causing the hydrogel to relax and absorb more water, thus exhibiting a higher swelling ratio. The swelling ratio was positively correlated with the drug release rate, indicating the hydrogel’s potential in drug delivery applications. The incorporation of Fe
3O
4 nanoparticles imparted magnetic properties to the wheat straw hemicellulose hydrogel. The porous structure and uniformly distributed Fe
3O
4 nanoparticles enhanced the adsorption capacity and rate. The magnetic properties of the hydrogel enable it to be easily separated from the solution under the influence of a magnetic field. The prepared hydrogel exhibited significant swelling behavior in aqueous solutions and displayed superparamagnetic characteristics. The saturation magnetization was 4.21 emu/g. At pH 8, the hydrogel achieved an adsorption capacity of 65.28 mg/g for methylene blue, with a removal rate of 95.58%. However, at higher pH values, Na+ ions in the solution occupy the adsorption sites, thereby reducing the adsorption efficiency [
101]. Wang
, et al. [
102] studied the molecular characteristics and gelation ability of functional hydrogels formed by oxidative cross-linking of arabinoxylan extracted from three types of wheat bran. The study found that high molecular weight and high ferulic acid content contribute to the formation of hydrogels with good elasticity, and high concentrations of arabinoxylan can form stable gel networks more quickly. Li
, et al. [
103] used carboxymethylated arabinoxylan (CMAX) from wheat bran, which was cross-linked with Fe3+ ions through the carboxyl groups (COO−) of CMAX using a reverse emulsion polymerization method to form microgels. The resulting CMAX microgels were regular spherical particles with sizes ranging from 30 to 80 μm. These microgels exhibited high stability under acidic conditions (pH 2.2) and significant swelling behavior under neutral conditions (pH 7.0). This pH sensitivity allows CMAX microgels to exhibit excellent controlled release characteristics in simulated gastrointestinal environments, making them suitable as delivery carriers. [
104] synthesized chemically cross-linked composite hydrogels based on acetylated corn cob xylan and silanized oxidized graphene. The acetylation and silanization modifications of graphene oxide (GO) and xylan introduced hydroxyl and carboxyl functional groups into the hydrogels, aiding in the adsorption of metal ions.
Enzymatic reactions are a popular method for preparing hydrogels, As shown in
Figure 8, during the cross-linking process of xylan (especially arabinoxylan), laccase oxidizes ferulic acid (FA) residues to generate phenoxy radicals. Through coupling reactions, di-ferulic acid (di-FA) and tri-ferulic acid (tri-FA) are formed, resulting in the formation of numerous covalent bonds between the molecular chains of arabinoxylan, particularly phenol-phenol bonds (such as 5-5′, 8-5′, 8-O-4′ di-ferulic acid structures). This initiates the polymerization reaction, forming a cross-linked network [
45]. Chimphango
, et al. [
105] prepared oat bran xylan hydrogels through selective enzymatic hydrolysis. Recombinant α-L-arabinofuranosidase (AbfB) was used to selectively remove arabinose side chains from oat bran xylan. The removal of arabinose reduced steric hindrance between molecules, promoting the aggregation of xylan molecules and hydrogel formation. Zhang
, et al. [
106] extracted arabinoxylan (CAX) from corn bran using an alkaline solution and cross-linked it through laccase treatment. At low pH, the carboxyl groups on the arabinoxylan chains were protonated, promoting hydrogen bond formation and reducing repulsion between polymer chains, thus facilitating gel formation. Higher ferulic acid content resulted in a higher degree of cross-linking, increasing the strength of the formed SCCAX gels. The authors also noted that the gel formation mainly relied on reversible non-covalent interactions. The increased carboxyl and ferulic acid groups on the arabinoxylan chains after cross-linking added negative charges, contributing to the gel’s formation and stability. SCCAX gels have broad applications in food and drug delivery systems, particularly in low-sugar, low-pH gels or applications requiring gel formation in the stomach to delay gastric emptying and increase satiety. Spasojevic, Prokopijevic, Prodanovic, Zelenovic, Polovic, Radotic and Prodanovic [
35] prepared tyrosine carboxymethyl corn cob xylan (Tyr-CMX) hydrogels through cross-linking reactions with horseradish peroxidase (HRP) and hydrogen peroxide. Starch was immobilized in Tyr-CMX hydrogel microbeads via emulsion polymerization. The microbeads formed by emulsion polymerization had smaller diameters, reducing diffusion limitations and improving enzyme activity retention. The introduction of high-functional groups and smaller microbead diameters reduced enzyme leakage, enhancing operational stability and reusability of the enzyme. Li
, et al. [
107] found that subcritical water extraction effectively extracted high molecular weight and high ferulic acid content AX, retaining more ferulic acid esters, which could significantly enhance its oxidative cross-linking ability. They then used laccase to cross-link corn bran arabinoxylan (AX) to form gels. Chen [
24] also used a subcritical water extraction and laccase-induced oxidative cross-linking method to prepare hydrogels from arabinoxylan of corn and rye bran. The study pointed out that ferulic acid content and molecular weight are key factors determining the cross-linking performance of arabinoxylan. Munk
, et al. [
108] treated glucuronoxylan-rich arabinoxylan extracted from corn bran with laccase from Myceliophthora thermophila. The laccase catalyzed the oxidative cross-linking of ferulic acid groups to form covalent diferulic acid cross-links, producing strong hydrogels. Li [
64] used laccase (derived from Trichoderma and oyster mushrooms) as a cross-linker to cross-link hydroxycinnamic acid-esterified corn bran arabinoxylan at 25°C. The author noted that methoxy and hydroxyl groups provide a higher cross-linking density, and the hydrogels exhibited good mechanical properties and biocompatibility, with broad application prospects in antioxidant skincare products and functional foods. Yilmaz-Turan
, et al. [
109] extracted arabinoxylan (FAX) from wheat bran and formed functional hydrogels through laccase oxidative cross-linking. Laccase induced the conversion of ferulic acid (FA) units into various dimer forms, increasing the crystallinity and molecular weight of FAX and allowing FAX chains to pack more tightly. The hydrogels could be reused by freeze-drying and re-suspension. Freeze-drying converted the water molecules in the hydrogels directly into gas through sublimation, avoiding the presence of liquid water, forming a porous dry structure that facilitated rapid water absorption and restored the swelling properties of the hydrogels. Re-suspension in specific pH buffers strengthened the chemical bonds and physical interactions within the hydrogels, restoring the original structure of the hydrogels.
The development trend of hemicellulose-based hydrogels focuses on enhancing mechanical properties, incorporating multifunctionality, and expanding potential applications. Innovations primarily involve the combination of hemicelluloses with various other components to improve strength, self-healing capabilities, and functionality [
110]. Methods have evolved to include physical cross-linking, chemical modifications, and the utilization of nanoparticles, indicating a shift towards creating materials with specific attributes such as conductivity, biodegradability, and suitability for biomedical and environmental applications [
96]. This progression signifies a growing interest in sustainable and versatile materials that can be customized according to diverse application needs.
3.3. Three-Dimensional (3D) Printing
Currently, there is great interest in exploring natural and renewable polymers for manufacturing various 3D printed products [
111]. Hemicellulose, with its environmentally friendly, biodegradable, renewable, and biocompatible properties, has shown significant potential in 3D printing to applied in various fields such as microelectronics, photovoltaics, energy, tissue engineering, and food manufacturing [
112]. Bahcegul
, et al. [
113] developed a 3D printing technology based on corn cob hemicellulose. The hemicellulose was prepared using a 10% KOH solution for extraction, followed by acetic acid and ethanol precipitation. The study found that the viscosity of the slurry was highly sensitive to changes in water content and temperature. Adding NaOH reduced the viscosity of the slurry, making the printing process smoother and more continuous. The optimal printing conditions were found to be 65% water content, 80°C printing temperature, and an extrusion multiplier of 1.5. Although the mechanical properties of the 3D-printed materials were not as good as those produced by traditional methods, the ease of processing and cost advantages made this approach competitive for specific applications. Bahcegul
, et al. [
114] developed a more environmentally friendly method, using a 5% KOH solution to extract hemicellulose from corn cobs and forming a gel by evaporating the water, without the need for further purification. The resulting product exhibited similar mechanical strength to the product from the previous study [
113].
Although 3D printing technology provides a new avenue for the processing of hemicellulose and its derivatives, research in this aspect remains incomplete. Firstly, using hemicellulose and its derivatives directly as raw materials for 3D printing bio-materials is extremely challenging. This is due to the less than ideal mechanical properties, stability, and resolution of 3D printed products made from hemicellulose materials [
115]. Therefore, it is necessary to adjust the composition of composite materials and adapt different 3D printing techniques. Additionally, cost-effectiveness and environmental impact are also important considerations. Traditional solvents used in preparing 3D printing materials can be harmful or expensive, so there is a need to research environmentally friendly and cost-effective solvents.
3.4. Adsorbent
With industrial development, the threat of harmful pollutants is increasingly serious, and effectively removing these toxic chemicals has become a global challenge. Among various treatment methods, adsorption is gaining more attention due to its ability to target a wide range of pollutants and relatively low cost. Hemicellulose-based materials, with their unique physicochemical properties, can be used to prepare hydrogels and activated carbon materials. Hydrogels are highly effective in adsorbing heavy metal ions, organic dyes, water and salt solutions while active carbon are particularly suitable for adsorbing gaseous substances.Mohammadabadi and Javanbakht [
116] prepared a hydrogel by mixing barley straw hemicellulose with sodium alginate for the removal of lead ions from aqueous solutions. Under conditions of pH 5, an adsorbent dosage of 0.4 g/L, an initial lead ion concentration of 210 mg/L, and a temperature of 55°C, the maximum adsorption capacity reached 277.78 mg/g, with a removal efficiency exceeding 99%. The strong interactions between hemicellulose and calcium alginate formed an adsorbent material with a high specific surface area and porous structure, effectively increasing the adsorption sites for lead ions. Additionally, regeneration treatment with 0.01 M nitric acid effectively removed lead ions from the adsorbent surface, restoring its activity. After five adsorption-desorption cycles, the adsorbent maintained a high lead ion adsorption capacity. The study of Sun, Xie, Shan, Li and Sun [
104] chemically cross-linked composite hydrogels based on acetylated corn cob xylan and silanized graphene oxide (GO) were synthesized through radical polymerization. The chemical cross-linking of acetylated xylan and silanized GO formed a stable three-dimensional polymer network, providing numerous adsorption sites. The hydrogel maintained a high Cu²⁺ removal rate even after multiple cycles of use, with a desorption rate still reaching 77.3% after six cycles.
Aerogels are also common adsorbent materials, Guan
, et al. [
117] prepared a wheat straw hemicellulose-chitosan aerogel containing Fe
3O
4 through oxidation and cross-linking reactions. Fe
3O
4 not only imparted magnetic properties to the aerogel but also acted as a cross-linking agent to enhance its structural stability. The magnetic aerogel efficiently adsorbed Congo red dye and could be quickly recovered under an external magnetic field, demonstrating good reusability. Sharma
, et al. [
118] developed a 3D multifunctional fluorescent aerogel (CS@DAHCA) based on rice straw hemicellulose for the ultrasensitive detection and removal of arsenic ions (As(III)) and ciprofloxacin (CPR) from water. By oxidizing with NaIO
4, the C2 and C3 hydroxyl groups of hemicellulose were converted to aldehyde groups, increasing its reactivity and forming a more stable cross-linked structure. Through Schiff base reactions, DAHC formed a three-dimensional porous network with chitosan, providing numerous active sites. The detection limits for As(III) and CPR were 3.529 pM and 55.2 nM, respectively. This high sensitivity was mainly due to the aerogel’s high surface area and abundant functional groups. CS@DAHCA maintained over 95% adsorption efficiency after 10 cycles, demonstrating excellent regeneration capacity and adsorption performance. Aside from forming hydrogels and aerogels, hemicellulose tends to decompose into H
2O, CO
2, and CO during biomass thermal treatment, leading to a structure rich in micropores. Chen
, et al. [
119] developed a mild and straightforward method to decompose lignocellulose from corn straw into cellulose, hemicellulose, and lignin, utilizing these monomers to fabricate three types of porous carbon materials. Through carbonization and chemical activation, the resulting cellulose (PCCC), hemicellulose (PCHC), and lignin (PCLC)-based porous carbons exhibited exceptional surface area and porosity. Notably, the hemicellulose-based porous carbon (PCHC) demonstrated significant adsorption performance, proving the effective strategy of breaking down lignocellulosic biomass into its components for creating enhanced porous carbon materials. This approach not only offers a new pathway for the comprehensive utilization of agricultural waste like corn straw but also contributes fresh insights into the development of materials for water treatment and environmental remediation.