Multi-technique surface characterization of bio-based films from sisal cellulose and its esters: a FE-SEM, μ-XPS and ToF-SIMS approach

Bio-based films were prepared from LiCl/DMAc solutions containing sisal cellulose esters (acetates, butyrates and hexanoates) with different degrees of substitution (DS 0.7–1.8) and solutions prepared with the cellulose esters and 20 wt% sisal cellulose. A novel approach for characterizing the surface morphology utilized field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle analysis. XPS and ToF-SIMS were a powerful combination while investigating both the ester group distribution on the surface and effects of cellulose content on the film. The surface coverage by ester aliphatic chains was estimated using XPS measurements. Fibrous structures were observed in the FE-SEM images of the cellulose and bio-based films, most likely because the sisal cellulose chains aggregated during dissolution in LiCl/DMAc. Therefore, the cellulose aggregates remained after the formation of the films and removal of the solvent. The XPS results indicated that the cellulose loading on the longer chain cellulose esters films (DS 1.8) increased the surface coverage by ester aliphatic chains (8.2 % for butyrate and 45 % for hexanoate). However, for the shortest ester chains, the surface coverage decreased (acetate, 42 %). The ToF-SIMS analyses of cellulose acetate and cellulose hexanoate films (DS 1.8) revealed that the cellulose ester groups were evenly distributed across the surface of the films.     

Regenerated cellulose film with enhanced tensile strength prepared with ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIMAc)

In this study, environmentally friendly regenerated cellulose films with enhanced tensile strength were successfully prepared by incorporation of plasticizer agents using 1-ethyl-3-methylimidazolium acetate as solvent. The results of morphology from scanning electron microscopy and atomic force microscopy showed that cellulose films possessed homogeneously, and exhibited smooth structure. ¹³C CP/MAS NMR spectra showed that the regenerated cellulose films were transferred from cellulose I to cellulose II. Moreover, the incorporation of plasticizer agents, especially in the presence of glycerol, significantly improved the tensile strength of cellulose film (143 MPa) as compared to the controlled sample. The notable properties of the regenerated cellulose films are promising for applications in transparent packaging.     

Chiral Nematic Cellulose Acetate Films; Reflectivity and Effect of Deacetylation

Cellulose acetate samples with a range of degrees of substitution (DS) were prepared by deacetylation of cellulose acetate (DS = 2.5). Chiral nematic solutions of the samples were prepared in formic acid. A handedness reversal from left to right was observed as the DS used to prepare the mesophase increased from 1.8 to 2.4. By selection of a suitably long-pitch mesophase, chiral nematic films cast from a CA (DS = 2.2)/formic acid solution showed a feint reflection of circularly polarized blue light. Deacetylation of this CA film gave a chiral nematic cellulose film with a more intense reflection band at the same wavelength. The improvement in intensity is attributed to the higher intrinsic birefringence of cellulose compared to cellulose acetate.     

Biobased films prepared from NaOH/thiourea aqueous solution of chitosan and linter cellulose

In the present study, films based on linter cellulose and chitosan were prepared using an aqueous solution of sodium hydroxide (NaOH)/thiourea as the solvent system. The dissolution process of cellulose and chitosan in NaOH/thiourea aqueous solution was followed by the partial chain depolymerization of both biopolymers, which facilitates their solubilization. Biobased films with different chitosan/cellulose ratios were then elaborated by a casting method and subsequent solvent evaporation. They were characterized by X-ray analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), thermal analysis, and tests related to tensile strength and biodegradation properties. The SEM images of the biofilms with 50/50 and 60/40 ratio of chitosan/cellulose showed surfaces more wrinkled than the others. The AFM images indicated that higher the content of chitosan in the biobased composite film, higher is the average roughness value. It was inferred through thermal analysis that the thermal stability was affected by the presence of chitosan in the films; the initial temperature of decomposition was shifted to lower levels in the presence of chitosan. Results from the tests for tensile strength indicated that the blending of cellulose and chitosan improved the mechanical properties of the films and that an increase in chitosan content led to production of films with higher tensile strength and percentage of elongation. The degradation study in a simulated soil showed that the higher the crystallinity, the lower is the biodegradation rate.     

Nanocomposite films based on cellulose reinforced with nano-SiO2: microstructure, hydrophilicity, thermal stability, and mechanical properties

Microcrystalline cellulose/nano-SiO₂ composite films have been successfully prepared from solutions in ionic liquid 1-allyl-3-methylimidazolium chloride by a facile and economic method. The microstructure and properties were investigated by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, water contact angle, thermal gravimetric analyses, and tensile testing. The results revealed that the well-dispersed nanoparticles exhibit strong interfacial interactions with cellulose matrix. The thermal stability and tensile strength of the cellulose nanocomposite films were significantly improved over those of pure regenerated cellulose film. Furthermore, the cellulose nanocomposite films exhibited better hydrophobicity and a lower degree of swelling than pure cellulose. This method is believed to have potential application in the field of fabricating cellulose-based nanocomposite film with high performance, thus enlarging the scope of commercial application of cellulose-based materials.     

Characteristics of thin cellulose ester films spin-coated from acetone and ethyl acetate solutions

Spin-coated films of cellulose acetate (CA), cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB) and carboxymethylcellulose acetate butyrate (CMCAB) have been characterized by ellipsometry, atomic force microscopy (AFM) and contact angle measurements. The films were spin-coated onto silicon wafers, a polar surface. Mean thickness values were determined by means of ellipsometry and AFM as a function of polymer concentration in solutions prepared either in acetone or in ethyl acetate (EA), both are good solvents for the cellulose esters. The results were discussed in the light of solvent evaporation rate and interaction energy between substrate and solvent. The effects of annealing and type of cellulose ester on film thickness, film morphology, surface roughness and surface wettability were also investigated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Blend films of natural wool and cellulose prepared from an ionic liquid

Natural wool/cellulose blends were prepared in an ionic liquid green solvent, 1-butyl-3-methylimidazolium chloride (BMIMCl) and the films were formed subsequently from the coagulated solutions. The wool/cellulose blend films show significant improvement in thermal stability compared to the coagulated wool and cellulose. Moreover, the blend films exhibited an increasing trend of tensile strength with increase in cellulose content in the blends which could be used for the development of wool-based materials with improved mechanical properties, and the elongations of the blends were considerably improved with respect to the coagulated films of wool and cellulose. It was found that there was hydrogen bonding interaction between hydroxyl groups of wool and cellulose in the coagulated wool/cellulose blends as determined by Fourier transform infrared (FTIR) spectroscopy. The ionic liquid was completely recycled with high yield and purity after the blend film was prepared. This work presents a green processing route for development of novel renewable blended materials from natural resource with improved properties.     

纳米纤维素晶须的表面醋酸酯化改性及复合材料的力学性能

采用硫酸水解法制备纳米纤维素晶须, 再以冰醋酸为分散介质, 浓硫酸为催化剂, 醋酸酐为酯化剂对纳米纤维素晶须进行不同程度醋酸酯化改性, 得到醋酸酯化的纳米纤维素. 采用红外光谱(FTIR)、 X射线光衍射(XRD)、 透射电子显微镜(TEM)和X射线光电子能谱(XPS)等手段对改性产物进行分析和表征. 结果表明, 改性纳米纤维素晶须中醋酸酯基的平均取代度过小或过大时均不适宜用作复合材料的增强相. 当改性纳米纤维素晶须中醋酸酯基的平均取代度为0.05时, 醋酸酯化反应只发生在纳米纤维素晶须的表面. 此时, 晶须能在丙酮中稳定悬浮, 表现出流动双折射现象, 并保持了改性前纳米纤维素晶须的棒状形态和高结晶度. 将这种改性后的纳米纤维素晶须作为增强相与醋酸纤维素通过溶液浇铸法制成纳米复合膜, 结果显示, 与空白醋酸纤维素膜相比, 添加改性纳米纤维素晶须后, 纳米复合膜的拉伸强度、 杨氏模量和断裂伸长率都得到了提高. 在玻璃化转变区间纳米复合膜储能模量的降低幅度小于空白膜.     

Water resistance, mechanical properties and biodegradability of methylated-cornstarch/poly(vinyl alcohol) blend film

The main shortcomings of biodegradable starch/poly(vinyl alcohol) (PVA) film are hydrophilicity and poor mechanical properties. With an aim to overcome these disadvantages, cornstarch was methylated and blend films were prepared by mixing methylated-cornstarch (MCS) with PVA. The mechanical properties, water resistance and biodegradability of the MCS/PVA film were investigated. It was found that MCS/PVA film had higher water resistance than the native starch/PVA film. However, the water resistance of MCS/PVA films did not have significant difference with the increase in the degree of substitution (DS) of the methylated starch from 0.096 to 0.864. Enzymatic, microbiological and soil burial biodegradation results indicated that the biodegradability of the MCS/PVA film strongly depended on the starch proportion in the film matrix. The degradation rate of starch in the starch/PVA film was hindered by blending starch with PVA. Both tensile strength and percent elongation at break of the MCS/PVA film were improved as DS of the methylated starch increased. Conversely, increasing the methylated starch proportion in film matrix deteriorated both tensile strength and percent elongation at break of the film.     

纤维素/甲壳素共混膜的结构表征与抗凝血性能

以 6wt %NaOH 4wt%尿素为纤维素的新溶剂 ,采用溶液共混法制备出纤维素 甲壳素共混膜 ,为甲壳素在碱性溶液中制膜提供了新的方法 .红外光谱、X 射线衍射、扫描电镜和力学性能、抗凝血性能测试结果表明 ,共混膜中甲壳素含量低于 4 0wt%时 ,纤维素与甲壳素分子间具有良好的相容性 ;在纤维素中引入适量甲壳素可提高共混膜的抗张强度 ,共混膜的干、湿态抗张强度在甲壳素含量 10wt%时最大 ,其值分别为 89 1MPa和 4 3 7MPa ,比纯态纤维素膜的干、湿态抗张强度分别提高了 6 7%和 11 5 % ;甲壳素的引入可明显降低血小板在共混膜表面的粘附、凝聚与变性 ,增大共混膜的抗凝血参数 ,甲壳素含量达到 5 0wt%时 ,该共混膜具有良好的抗凝血性能     

Properties and Applications of Cellulose Acetate

Cellulose acetate is one of the most important esters of cellulose. Depending on the way it has been processed cellulose acetate can be used for great varies of applications (e.g. for films, membranes or fibers). The properties of the applied cellulose acetates are very important for these applications. A special field for using cellulose acetate is the synthesis of porous, spherical particles, so called cellulose beads. Different types of technical cellulose acetates were used and their ability to form such cellulose beads was characterized. First the different types of cellulose acetates were characterized by means of solubility; turbidity and degree of substitution. In addition the molar mass and the distribution of substituents along the polymeric chain were analyzed. Next, the cellulose beads were synthesized within an emulsion process using these different cellulose acetates. Then the properties (particle size, porosity, morphology) of the cellulose beads were determined. Finally, the relationship between the characteristic of cellulose acetates and properties of cellulose beads was investigated.     

Properties of cellulose films prepared from NaOH/urea/zincate aqueous solution at low temperature

Cellulose films were successfully prepared from NaOH/urea/zincate aqueous solution pre-cooled to −13 °C by coagulating with 5% H₂SO₄. The cellulose solution and regenerated cellulose films were characterized with dynamic rheology, ultraviolet–visible spectroscope, scanning electron microscopy, wide angle X-ray diffraction, Fourier transform infrared (FT-IR) spectrometer, thermogravimetry and tensile testing. The results indicated that at higher temperature (above 65 °C) or lower temperature (below −10 °C) or for longer storage time, gels could form in the cellulose dope. However, the cellulose solution remained a liquid state for a long time at 0–10 °C. Moreover, there was an irreversible gelation in the cellulose solution system. The films with cellulose II exhibited better optical transmittance, high thermal stability and tensile strength than that prepared by NaOH/urea aqueous solution without zincate. Therefore, the addition of zincate in the NaOH/urea aqueous system could enhance the cellulose solubility and improve the structure and properties of the regenerated cellulose films.     

Interfaces study of all-polysaccharide composite films

Films made of xylan (X) and quaternized chitosan (QC) were prepared and the interactions of the polysaccharides on interfaces were discussed. According to elemental analysis, the X film contained also cellulose (31%) which could not be separated from the water suspension. The QC sample was soluble in water due to the presence of quaternized glucosamine units (4%) despite the presence of equal amounts of chitosan (CS, 48%) and chitin (CT, 48%). According to mechanical tests on QC/X = 1/3 composite film, the modulus and tensile strength values were the best from all mixtures measured, but still not better than on the film from X. We assume this is due to the sorption of xylan onto the surface of insoluble cellulose fibrils in the X film. Cyclic voltammetry indicates that the incorporation of X into the QC film decreases the overall positive charge provided by the QC. The X composite with net negative charge is indeed a barrier against the diffusion of ferricyanide anions. Based on TG/DTG/DTA analysis, the onset temperatures (OT) are decreasing with increasing X content in the blended films. X and QC films exhibited the highest OT values in comparison with the blended samples. The lowest OT temperature was observed at QC/X = 1/3. We think it is due to the thermocatalytic effect of the 4-O-methyl-d-glucuronate in X and the QC quaternary groups on the thermolysis–thermo-oxidation mechanism. According to AFM, the QC/X = 1/3 film exhibited the largest roughness values on both sides of the films, likely due to having the highest density of electrostatic interactions. XRD profiles of the films indicate some crystalline residues of cellulose in the xylan component as well as some chitin in the QC component. We assume that the properties are the result of the combination of the electrostatic interactions of carboxyl and quaternary groups of the soluble components of X and QC bonded to the surface of insoluble cellulose fibrils by hydrogen bonds. This probably results in both synergistic and antagonistic effects expressed by the improved or diminished values of determined properties.     

Cationic surface modification of nanocrystalline cellulose as reinforcements for preparation of the chitosan-based nanocomposite films

Nanocrystalline cellulose (NCC) is a promising nanofiller for reinforcing chitosan (CTS) film. The flocculation of the NCC suspension in acidic CTS solution is the key problem that makes many properties such as the tensile strength bad. A derivative of nanocellulose, namely cationic dialdehyde cellulose (CDAC), is synthesized in the current study to avoid the flocculation. A CDAC suspension is prepared in a successive oxidation-reductive amination process of NCC. The oxidation of NCC led to smaller rod-like nanocrystals with a reduced crystallinity. The suspension with 1.0% CDAC is well mixed with 1.0% CTS solution. Besides, the tensile strength and anti-swelling properties of CDAC-filled CTS nanocomposite films are improved because of the uniform distribution of CDAC in the CTS matrix plus the intermolecular chemical cross-linking between CDAC and CTS. The tensile strength of CTS-based nanocomposite film with 12% CDAC is about 58.4% higher than that of the pure CTS film.     

纤维素/全硫化弹性纳米粒子复合膜的制备与性能

利用碱脲溶剂低温溶解纤维素,在该体系中掺杂一定比例的全硫化羧基丁苯弹性纳米粒子,制备了纤维素/全硫化弹性纳米粒子复合膜.通过透射电镜、扫描电镜、WAXD、固体核磁共振、热分析和力学性能测试等对该复合膜的结构和性能进行了表征.结果表明,全硫化羧基丁苯弹性纳米粒子(CSB ENP)均匀的分散在具有微纳孔洞结构的纤维素基体中.CSB ENP的引入对纤维素再生过程中的结晶性影响不大.纤维素/全硫化弹性纳米粒子复合膜具有良好的透光性,并且热稳定性也有所提高.加入少量的CSB ENP可以增韧纤维素膜,且能保持良好的力学性能.当CSB ENP的含量为5 wt%时复合膜的断裂拉伸强度和断裂伸长率同时得到了提高.     

Cationic wood cellulose films with high strength and bacterial anti-adhesive properties

In this work, periodate oxidized birch wood pulp and microfibrillated cellulose (MFC) were cationized using Girard’s reagent T or aminoguanidine. Cationic celluloses were used to obtain films via solvent-casting method, and the effects of the cationization route and the cellulose fiber source on the properties of the films were studied. Thermal and optical properties of the films were measured using differential scanning calorimetry and UV–Vis spectrometry, and the morphology of the films was examined using an optical microscope and a field emission scanning electron microscope. Bacterial anti-adhesive properties of the films were also studied using a modified leaf print method and against Staphylococcus aureus and Escherichia coli. Both cationizing agents exhibited similar reactivity with periodate oxidized celluloses, however, MFC had significantly higher reactivity compared to birch pulp. The films with high tensile strength (39.1–45.3 MPa) and modulus (3.5–7.3 GPa) were obtained from cationized birch pulp, aminoguanidine modification producing a film with slightly better mechanical properties. Modulus of the films was significantly increased (up to 14.0 GPa) when MFC was used as a cellulose fiber source. Compared to the unmodified MFC films, the cationic MFC films were less porous and significantly more transparent; however, they had slightly lower tensile strength values. It was found that aminoguanidine modified celluloses had no culturable bacteria on its surface and also exhibited resistance to microbial degradation, whereas there were culturable bacteria on the surface of Girard’s reagent modified films and they were partially degraded by the bacteria.     

The transparency and mechanical properties of cellulose acetate nanocomposites using cellulose nanowhiskers as fillers

Cellulose nanowhiskers (CNWs) were chemically modified by acetylating to obtain acetylated cellulose nanowhiskers (ACNWs) which could be well dispersed in acetone. The chemical modification was limited only on the surface of CNWs which was confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). Surface substitution degree of ACNWs was evaluated to be 0.45 through X-ray photoelectron spectroscopy (XPS). Fully bioresource-based nanocomposite films were manufactured by incorporation of ACNWs into cellulose acetate (CA) using a casting/evaporation technique. Scanning electron microscope (SEM) demonstrated that ACNWs dispersed well in the CA matrix, which resulted in high transparency of all CA nanocomposites. The tensile strength, Young’s modulus and strain at break of all CA nanocomposites exhibited simultaneous increase in comparison with neat CA matrix. At the content of 4.5 wt% ACNWs, the tensile strength, Young’s modulus and strain at break of the CA nanocomposite film were increased by 9, 39, and 44 % respectively.     

Strength and barrier properties of MFC films

The preparation of microfibrillar cellulose (MFC) films by filtration on a polyamide filter cloth, in a dynamic sheet former and as a surface layer on base paper is described. Experimental evidence of the high tensile strength, density and elongation of films formed by MFC is given. Typically, a MFC film with basis weight 35 g/m² had tensile index 146 ± 18 Nm/g and elongation 8.6 ± 1.6%. The E modulus (17.5 ± 1.0 GPa) of a film composed of randomly oriented fibrils was comparable to values for cellulose fibres with a fibril angle of 50°. The strength of the films formed in the dynamic sheet former was comparable to the strength of the MFC films prepared by filtration. The use of MFC as surface layer (0–8% of total basis weight) on base paper increased the strength of the paper sheets significantly and reduced their air permeability dramatically. FEG-SEM images indicated that the MFC layer reduced sheet porosity, i.e. the dense structure formed by the fibrils resulted in superior barrier properties. Oxygen transmission rates (OTR) as low as 17 ml m⁻² day⁻¹ were obtained for films prepared from pure MFC. This result fulfils the requirements for oxygen transmission rate in modified atmosphere packaging.     

Preparation of LDPE-acetylated/butyrylated starch blend blow films and characterization

Development of modified plastics has been studied through the LDPE-acylated starch blend films to examine the effect of different acyl groups and degrees of substitution(DS) on properties of films.Corn starch was modified with acetyl and butyryl groups and films were prepared by blending acylated starch with low density polyethylene(LDPE).Systematic studies were done to observe the effect of acyl groups,DS and starch concentration on the properties and biodegradability of the blend films.It was observed that blend films containing 5% acetylated and butyrylated starches of high DS(2.5,1.7) maintained 75% and 83% of tensile strength of LDPE films.Thermal analysis results indicated that acetylated and butyrylated starch blend films decomposed at 370 °C and 389 °C which were higher than the decomposition temperature of native starch film(349 °C).Scanning electron micrographs of blend films containing high DS acylated starch showed well dispersed starch particles due to improvement in dispersion between starch and LDPE.Water absorption capacity of high DS acetylated and butyrylated starch blend films(4.18% and 3.76%,respectively) was lower than that of native starch films(5%).This study has an advantage because of blown films prepared can be integrated with the present manufacturing systems without any other requirement.     

Efficient alternative of antimicrobial nanocomposites based on cellulose acetate/Cu-NPs

The current research presents an efficient, cheap, and safe antimicrobial material for widespread use based on copper nanoparticles (Cu-NPs) loaded on cellulose acetate (CA) matrix. A reduction process of CuSO₄·5H₂O has been performed to prepare Cu-NPs. The nanosized copper particles included oxidized Cu (15–20 nm). Two different loads of Cu-NPs were used in this study, 2% and 6% mol.%. The presence of Cu-NPs incorporated with CA films slightly affected the tensile index of the films, where low and high-loaded Cu-NPs enhanced the tensile index by small values ranged from 0.640 to 0.650 and 0.667, respectively. A study on the antibacterial activity of these nanocomposites was carried out for Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. It has been found that CA containing Cu-NPs (2%) exhibited the highest antimicrobial activity against all test microbes including S. aeureus (21 mm), P. aeruginosa (18 mm), C. albicans (19 mm), and Aspergillus niger (15 mm). Results also revealed that CA film with 6% exhibited lower activity than film with 2% Cu-NPs. The morphological properties of CA/Cu-NPs films were characterized by scanning electron microscopy and transmission electron microscope in addition to X-ray diffraction. Low-loaded Cu-NPs showed homogenous distribution through CA matrix while, the high-loaded Cu-NPs were agglomerated through CA matrix. Thermal properties illustrated the enhancement of thermal stability of the film with increasing the loaded Cu-NPs.