Regenerated Cellulose Films Research Articles

Ultrathin ultrastrong transparent films made from regenerated cellulose and epichlorohydrin

Thin films used in electronic devices are often petroleum-based, non-biodegradable, and non-renewable polymers. Herein, ultrathin ultrastrong regenerated cellulose films were made with a facile method by applying a solution of mildly carboxylated nanocellulose and various amounts of epichlorohydrin (ECH) as a crosslinker. The morphology and physiochemical properties of films were measured using FE-SEM, TEM, FTIR, NMR, UV–Vis, XRD, DLS, and TGA. Carboxylated cellulose with a charge content of 1.5 mmol/g was prepared to make alkaline dopes containing nanocrystalline cellulose (CNC). Then, ECH (0–50%) was added and the dope was blade cast, dried in an oven, regenerated in an acid bath, washed, and air dried to make uniform films approximately 1 μm thick. The tensile stress and elastic modulus of the films were measured and found to be 100–300 MPa and 5–12.7 GPa, respectively. Higher amounts of ECH led to stronger films. All films were over 96% transparent, insoluble in water, and absorbed 24–28% moisture. TGA analysis showed ultrathin films were thermally resistant up to 250 °C and were stable and unchanged over a month at 105 °C showing excellent thermal aging resistance. Overall, films with 5–10% ECH are extremely strong, which makes them promising bioresource-based candidates for flexible electronic applications.

Efficient Cellulose Dissolution and Film Formation Enabled by Superbase Amino Acid Ionic Liquids.

Cellulose is a promising feedstock for the production of sustainable materials. To fully utilize its potential, exploring efficient cellulose solvents is a paramount prerequisite. In this study, ten superbase amino acid ionic liquids (SAAILs) are synthesized using 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with different amino acid anions via a simple neutralization method. The properties of these SAAILs, such as viscosity and glass transition temperature, varied with their cation and anion structures. The ability of the SAAILs to dissolve cellulose is related to their Kamlet-Taft parameters, particularly hydrogen bond basicity (β). The main driving force for cellulose dissolution in SAAILs is thought to be hydrogen bonding interactions between SAAILs and cellulose hydroxyl groups. Four SAAILs composed of DBN or DBU cations and proline, or aspartic acid anions are identified as promising solvents for preparing regenerated cellulose films (RCFs). The RCF prepared from [DBN]Proline(Pro) showed a favorable combination of high tensile strength (76.9MPa), high Young's modulus (5201.2MPa), good transparency (≈70% at 550nm), and smooth surface morphology. These halogen- and metal-free SAAILs show the potential to provide a new avenue for cellulose processing.

Hydrophobic, Sustainable, High-Barrier Regenerated Cellulose Film via a Simple One-Step Silylation Reaction.

With the increasing importance of environmental protection, high-performance biopolymer films have received considerable attention as effective alternatives to petroleum-based polymer films. In this study, we developed hydrophobic regenerated cellulose (RC) films with good barrier properties through a simple gas-solid reaction via the chemical vapor deposition of alkyltrichlorosilane. RC films were employed to construct a biodegradable, free-standing substrate matrix, and methyltrichlorosilane (MTS) was used as a hydrophobic coating material to control the wettability and improve the barrier properties of the final films. MTS readily coupled with hydroxyl groups on the RC surface through a condensation reaction. We demonstrated that the MTS-modified RC (MTS/RC) films were optically transparent, mechanically strong, and hydrophobic. In particular, the obtained MTS/RC films exhibited a low oxygen transmission rate of 3 cm3/m2 per day and a low water vapor transmission rate of 41 g/m2 per day, which are superior to those of other hydrophobic biopolymer films.

Oxygen permeability of regenerated cellulose films with different water regains

The effect of water regain on the oxygen permeability coefficient (OP) of regenerated cellulose film was investigated. The OP of the dry film was extremely low, which was classified as a “very high” performance gas barrier; however, the OP increased with increasing water regain, and reached to the OP similar to that of low-density polyethylene film, which was categorized as a “poor” gas barrier. The film thickness increased with increasing water regain, and edge-view small-angle X-ray scattering revealed widening of the space between microcrystals in the thickness direction. Oxygen molecules likely passed through the space between cellulose molecules, which was widened with increasing water regain. The viscoelastic measurements indicated that regenerated cellulose existed in a rubbery state under wet conditions. Overall, the OP of regenerated cellulose was increased because of the widening and micro-Brownian motion of cellulose main chains caused by water.

Surface Engineering of Regenerated Cellulose Nanocomposite Films with High Strength, Ultraviolet Resistance, and a Hydrophobic Surface

Regenerated cellulose packaging materials can alleviate the environmental pollution and carbon emissions caused by conventional plastics and other chemicals. They require regenerated cellulose films with good barrier properties, such as strong water resistance. Herein, using an environmentally friendly solvent at room temperature, a straightforward procedure for synthesizing these regenerated cellulose (RC) films, with excellent barrier properties and doping with nano-SiO2, is presented. After the surface silanization modification, the obtained nanocomposite films exhibited a hydrophobic surface (HRC), in which the nano-SiO2 provided a high mechanical strength, whereas octadecyltrichlorosilane (OTS) provided hydrophobic long-chain alkanes. The contents of the nano-SiO2 and the concentrations of the OTS/n-hexane in regenerated cellulose composite films are crucial, as they define its morphological structure, tensile strength, UV-shielding ability, and the other performance of these composite films. When the nano-SiO2 content was 6%, the tensile stress of the composite film (RC6) increased by 41.2%, the maximum tensile stress was 77.22 MPa, and the strain-at-break was 14%. Meanwhile, the HRC films had more superior multifunctional integrations of tensile strength (73.91 MPa), hydrophobicity (HRC WCA = 143.8°), UV resistance (>95%), and oxygen barrier properties (5.41 × 10-11 mL·cm/m2·s·Pa) than the previously reported regenerated cellulose films in packaging materials. Moreover, the modified regenerated cellulose films could biodegrade entirely in soil. These results provide an experimental basis for preparing regenerated-cellulose-based nanocomposite films that exhibit a high performance in packaging applications.

Fully transparent and flexible antibacterial packaging films based on regenerated cellulose extracted from ginger pulp

Full transparent and bendable multifunctional composite films were successfully prepared using regenerated cellulose extracted from ginger pulp. Ginger pulp was chemically treated to obtain the highly purified cellulose. The purified cellulose was dissolved in DMAc/LiCl and regenerated in coagulants such as water, ethanol, and acetone to produce transparent cellulose films with high flexibility. Zinc oxide nanoparticles (ZnO NPs) and curcumin were further incorporated into the regenerated cellulose films to give antioxidant, antibacterial, and UV barrier properties. The regenerated cellulose film prepared in ethanol (RCE) showed the highest tensile strength of 51.4 MPa as well as the highest transmittance of 70.0% at 280 nm (UV) and 90.1% at 660 nm (visible light). The RC film incorporated ZnO NPs and curcumin (RC/ZC) imparted strong antioxidant and antibacterial activities. The antioxidant activity of the RC/ZC films ranged from 56% to 64% but there is no significant difference by types of coagulants. In addition, the RC/ZC films showed strong antibacterial activity of more than 99% against six bacteria.

Highly transparent, hydrophobic, and durable anisotropic cellulose films as electronic screen protectors

Cellulose films have attracted extensive interest in the field of burgeoning electronic devices. However, it remains a challenge to simultaneously address the difficulties including facile methodology, hydrophobicity, optical transparency, and mechanical robustness. Herein, we reported a coating-annealing approach to fabricate highly transparent, hydrophobic, and durable anisotropic cellulose films, where poly(methyl methacrylate)-b-poly(trifluoroethyl methacrylate) (PMMA-b-PTFEMA) as low surface energy chemicals was coated onto regenerated cellulose films via physical (hydrogen bonds) and chemical (transesterification) interactions. The resultant films with nano-protrusions and low surface roughness exhibited high optical transparency (92.3 %, 550 nm) and good hydrophobicity. Moreover, the tensile strength of the hydrophobic films was 198.7 MPa and 124 MPa in dry and wet states, respectively, which also showed excellent stability and durability under various conditions, such as hot water, chemicals, liquid foods, tape peeling, finger pressing, sandpaper abrasion, ultrasonic treatment, and water jet. This work provided a promising large-scale production strategy for the preparation of transparent and hydrophobic cellulose-based films for electronic device protection as well as other emerging flexible electronics.

Dissolution of lignocellulose with high lignin content in AlCl3/ZnCl2 aqueous system and properties of the regenerated cellulose film

Herein, a novel method for dissolving lignocellulose at room temperature is proposed by combining deep eutectic solvents (DES) pretreatment and subsequent dissolution in AlCl3/ZnCl2 aqueous system. Results showed that DES pretreatment could significantly increase the dissolubility of lignin-containing cellulose (CL) samples in AlCl3/ZnCl2 aqueous system. The dissolution ratio of the CL sample with 15.6 % lignin content in AlCl3/ZnCl2·3H2O solvent was as high as 90 %. Besides, the mechanism for the remarkable dissolution of CL samples in low water AlCl3/ZnCl2 aqueous solvent was also proposed. Moreover, the dissolved CL sample was regenerated for the production of lignocellulose films, which have excellent ultraviolet (UV) blocking, hydrophobic, mechanical strength, and natural degradation properties. In particular, the films could be completely naturally degraded after 10 days, which provided a promising way to prepare biodegradable lignocellulose materials, and to encourage the potential utilization of renewable lignocellulose in packaging industry.

Performance-enhanced regenerated cellulose film by adding grape seed extract

Eco-friendly packaging material with intelligent colorimetric performance has been a requirement for food safety and quality. This work focused on a food packaging material from regenerated cellulose films that added the grape seed extract (GSE) and polyethylene glycol 200 (PEG). FTIR and SEM techniques were employed to prove the compatibility of GSE with cellulose matrix. The composite film showed an enhanced elongation at break (16.61 %) and tensile strength (33.09 MPa). The addition of PEG and GSE also improved the water contact angle of regenerated-cellulose film from 53.8° to 83.8°. Moreover, the composite films exhibited UV-blocking properties while maintaining adequate transparency. The GSE induced the regenerated films with a macroscopic change in color under different pH conditions. Furthermore, the loading of GSE slowed down the decomposition of strawberries and delayed the self-biodegradation compared with the control for more than 3 days and 18 days. The present study showed a regenerated cellulose film with acceptable mechanical and hydrophilia properties, pH-responsiveness, anti-decomposition, and delayed biodegradation performances, indicating a potential color sensor in food packaging.

Effect of pulp prehydrolysis conditions on dissolution and regenerated cellulose pore structure

When producing regenerated cellulose materials, e.g., fibers and films, pulp fibers are first dissolved in a solvent and then regenerated in an antisolvent. The pulp properties have a significant impact on the dissolution. This study examines the effect of pulp prehydrolysis conditions on pulp structure, subsequent dissolution in cold aqueous NaOH/ZnO solvent, and regenerated cellulose film properties. The fiber and regenerated cellulose swelling and pore structure is addressed. Once-dried kraft pulp was activated in acid hydrolysis at two temperatures, 60 and 80 °C. The hydrolysis primarily affected the cellulose degree of polymerization (DP), and its reduction dramatically improved the pulp dissolution. Surprisingly, higher hydrolysis temperature did not increase the fiber hornification. DP reduction marginally effected the pulp swelling properties but had a significant effect on the regenerated film swelling. The regenerated films contained cellulose II, and their wet porosity correlated inversely with the DP. Low hydrolysis temperature films remained more porous after critical point drying.

Rheological characteristics of novel cellulose/superbase-derived ionic liquid solutions and the coagulation process towards regenerated cellulose films

This work details the rheological characteristics of cellulose/[DBUH][CH3CH2OCH2COO] solutions and the coagulation process for constructing high-performance regenerated cellulose films.

Regenerated cellulose films from jute fibers applied in conductive nanocomposites

This work studied the sheet resistance and conductivity of nanocomposite of regenerated cellulose films (RCFs) and silver nanoparticles (AgNPs). The novelty is associated with obtaining conductive nanocomposite films from jute fibers, which can be promising for application in electronic devices. A combination of chemical treatments was conducted to obtain bleached jute cellulose, which was used to obtain RCFs. The fibers were characterized by X-ray diffraction, Fourier-transform infrared (FTIR) spectroscopy and thermal analysis. Nanocomposites films were produced containing 0.070, 0.145 and 0.290% (w/w) of AgNPs, compared to a pure RCF. Further, FTIR, ultraviolet-visible spectroscopy, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and sheet resistance using the van der Pauw were used to characterize the films. The chemical treatments removed lignin and hemicellulose present in the fiber, increased the crystallinity index and increased the thermal stability. Additionally, the treated fibers were more thermally stable than raw jute. The RCF thermal stability was approximately 225 °C. SEM-EDS of the films showed dense structures and a homogeneous AgNPs dispersion. The regenerated cellulose/AgNPs films showed an increase in conductivity in the range of 10 -2 S/cm and decreased transmittance with increasing nanoparticle content, with the 0.290% AgNPs sample being the most conductive. • Chemical treatments allowed the removal of lignin and hemicellulose of jute fibers. • Bleached cellulosic fibers enabled the production of regenerated cellulose films. • Bleached cellulose was dissolved in aqueous NaOH to production of nanocomposite films. • Increase of AgNPs in nanocomposite films increased the conductivity of the samples. • The conductivity of the nanocomposite films was in the range of 10 -2 S/cm.

Effect of accelerated aging on properties of biobased polymer films applicable in printed electronics

AbstractThe growing interest in sustainable, lightweight, bendable roll‐to‐roll manufactured printed electronics applied to packaging, textiles or medical healthcare has led to the need for materials that can withstand various environmental conditions. In this work, the studied materials were polyethylene terephthalate (PET), typically used as a substrate for printed electronics, and it was compared to biobased polymeric substrates bio‐PET, polylactic acid (PLA), cellulose acetate propionate (CAP) and regenerated cellulose film Natureflex™. Films were exposed for 500 h to heat (50.5°C); heat and humidity (50 RH%); heat, humidity, and light (UV‐A 300–400 nm, 42 W/m2) and temperature cycles in the range of −45°C to 65°C. Changes in film transparency and mechanical properties were analyzed. The main findings were that during the exposure to only elevated temperature and temperature with humidity, the analyzed properties were retained in all film materials. UV‐A caused less or no changes in Natureflex™, bio‐PET and PLA. The most stable in thermal cycling was Natureflex™, CAP, and PET. These results may open new possibilities for biopolymers in printed electronics applications.

Surface Modification of a Regenerated Cellulose Film Using Low-Pressure Plasma Treatment with Various Reactive Gases.

There is a growing interest in the fabrication of membranes and packaging materials from natural resources for a sustainable society. A regenerated cellulose (RC) film composed solely of cellulose has outstanding advantages including biodegradability, transparency, mechanical strength, and thermal stability. To expand the application of the RC film, various surface modification methods have been proposed. However, conventional chemical methods have disadvantages such as environmental burden and difficulty in controlling the reaction. In this work, low-pressure plasma treatment, a green, solvent-free, and easily controllable approach, was performed for surface modification of the RC film. The effects of three different plasma species (O2, N2, and CF4) and treatment conditions on the surface properties of RC films were investigated based on water contact angle measurements, chemical composition analysis, and surface topography. O2 and N2 plasma treatment slightly enhanced the surface wettability of RC films due to the etching by the plasma reactive species and the formation of new hydrophilic functional groups. In CF4 plasma treatments, the hydrophobic surface with a contact angle of 120.6° was obtained in a short treatment time (60 s) owing to the deposition of fluorocarbon groups on the surface. However, the treated surface in a longer reaction time resulted in increased wettability due to the diffusion and degradation of fluorine-containing bonds. The new insights could be valuable for further studies of surface modification and functionalization of RC films.

Wood cellulose films regenerated from NaOH/urea aqueous solution and treated by hot pressing for food packaging application

Cellulose films made from ‘green’ solvent provide the possibility to mitigate environmental pollution caused by non-degradable plastic packaging. Herein, regenerated cellulose films were prepared from five wood pulps in NaOH/urea aqueous solution, dried either at ambient conditions or by hot pressing, and tested as biodegradable packaging materials. The results revealed that different wood origins did not cause much difference in the structure of cellulose films. However, hot-pressing could not only efficiently remove water from wet films, but also significantly improve the tensile strength and water vapor barrier property of regenerated films. The RC-P-HP film had the tensile strength of 85.00 ± 3.26 MPa, Young's modulus of 6.45 ± 0.36 GPa, and water vapor permeability of 3.59 ± 0.14 × 10−7 gm−1h−1Pa−1, and exhibited the similar capacity as the commercial plastic wrap during the preservation of cherry tomatoes for up to 16 days. Therefore, this study demonstrates a feasible strategy to fabricate wood cellulose films for biodegradable food packaging.

High oxygen barrier materials from paper to regenerated cellulose films

AbstractA transparent, bendable, high oxygen barrier cellulose‐based film was prepared, which has far better oxygen barrier properties than conventional polyethylene, polypropylene and cellophane materials. A series of regenerated cellulose films (RCs) were prepared from filter paper lacking oxygen barrier properties under different cellulose concentrations and gelation times. It was shown that the cellulose concentration and gel time had a greater effect on the oxygen barrier properties of RCs. When the cellulose concentration was 4 wt% and the gel time was 3 h, the RCs obtained the lowest oxygen permeability coefficient (OPC) down to 2.21 × 10−17 cm3 cm cm−2 s−1 Pa−1. The films have a tensile strength of 109.5 MPa, an elongation at break of 27.3% and a light transmission rate of 89%. In further, molecular dynamics simulations showed that when the filter paper was converted to RCs, the increase in hydrogen bonding and the decrease in free volume between cellulose chains caused a decrease in the diffusion coefficient of oxygen. As a novel biobased high oxygen barrier material, the film has broad application prospect in packaging and chemical industry.

Glutaraldehyde-assisted crosslinking in regenerated cellulose films toward high dielectric and mechanical properties

Developing the green dielectric materials satisfies the requirement of the sustainable development of society and economics. In this work, glutaraldehyde (GA)-assisted crosslinking strategy was developed to prepare the crosslinked regenerated cellulose (CRC) films, and the effects of different crosslinking methods, including crosslinking steps, concentration of GA solution and crosslinking time, on dielectric and mechanical properties of the CRC films were systematically investigated. Microstructure and morphology characterizations show that compared with the common RC films, the CRC films show apparently reduced defects and enhanced intermolecular interaction. At GA concentration of 6 vol% and crosslinking time of 30 min, the CRC film shows the lowest dielectric loss (0.03 at 1000 Hz, 92.3% smaller than RC film) and the highest breakdown strength (336.55 MV m−1, 364.3% higher than RC film), and simultaneously, the film shows the high tensile strength of 76.8 MPa and excellent tensile modulus of 6.08 GPa, about 240.9% and 104% higher than those of the RC film, respectively. This work provides new insight in tailoring the dielectric and mechanical properties of the cellulose films through constructing the crosslinking structure, which is of great significance for the fabrication of the high-performance cellulose-based dielectric materials.Graphical abstract

Bio-Based Polymeric Substrates for Printed Hybrid Electronics

Printed flexible hybrid electronics (FHE) is finding an increasing number of applications in the fields of displays, sensors, actuators and in energy harvesting and storage. The technology involves the printing of conductive and insulating patterns as well as mounting electronic devices and circuits on flexible substrate materials. Typical plastic substrates in use are, for example, non-renewable-based poly(ethylene terephthalate) (PET) or poly(imides) (PI) with high thermal and dimensional stability, solvent resistance and mechanical strength. The aim of this study was to assess whether renewable-based plastic materials can be applied on sheet-to-sheet (S2S) screen-printing of conductive silver patterns. The selected materials were biaxially oriented (BO) bio-based PET (Bio-PET BO), poly(lactic acid) (PLA BO), cellulose acetate propionate (CAP BO) and regenerated cellulose film, NatureFlex™ (Natureflex). The biaxial orientation and annealing improved the mechanical strength of Bio-PET and PLA to the same level as the reference PET (Ref-PET). All renewable-based substrates showed a transparency comparable to the Ref-PET. The printability of silver ink was good with all renewable-based substrates and printed pattern resistance on the same level as Ref-PET. The formation of the printed pattern to the cellulose-based substrates, CAP BO and Natureflex, was very good, showing 10% to 18% lower resistance compared to Ref-PET and obtained among the bio-based substrates the smallest machine and transverse direction deviation in the S2S printing process. The results will open new application possibilities for renewable-based substrates, and also potentially biodegradable solutions enabled by the regenerated cellulose film and PLA.

Identification and prioritisation for risk assessment of phthalates, structurally similar substances and replacement substances potentially used as plasticisers in materials and articles intended to come into contact with food

The EFSA Panel on Food Contact Materials, Enzymes and Processing Aids was requested by the European Commission to re‐evaluate the risks to public health related to the presence of plasticisers such as phthalates, structurally similar substances and replacement substances, as a consequence of migration from food contact materials (FCMs). As the first part of the two‐part mandate, EFSA was tasked with identifying and prioritising those plasticisers used in FCMs that may warrant further data collection and eventual risk assessment. Close collaboration with the European Chemicals Agency (ECHA) was requested in the mandate. Substances potentially used as plasticisers were identified using Annex II of the mandate, ECHA’s PLASI inventory, the Plastics Regulation and the Regenerated Cellulose Film Directive, the ECHA database, the ECHA grouping approach, and consultation with the Member States. Only substances authorised for FCMs at EU or at national level were prioritised. Five substances classified either as carcinogenic, mutagenic, toxic to reproduction Cat. 1 (under CLP) or as endocrine disruptors, persistent, bioaccumulative and toxic, very persistent/very bioaccumulative (under REACH) were placed into an ‘exclusion group’. Prioritisation was based on the date of the most recent risk assessment in the context of FCM, with substances assessed before 2001 being placed in the high‐priority group, substances assessed between 2001 and 2011 in the medium‐priority group and substances assessed after 2011 in the low‐priority group. For the EU stream, the 76 substances were split into 59 high‐, 14 medium‐ and 3 low‐priority substances. For the nationally authorised stream, the split of the 72 substances is 66, 3 and 3, respectively. The outcome of follow‐up calls for data in support of the exposure assessment will be used for a final ranking.

Dissolving pulp from eucalyptus sawdust for regenerated cellulose products

This study assesses the possibility of obtaining regenerated cellulose products (beads and films) from eucalyptus sawdust dissolving pulps produced by non-conventional processes, compared with a commercial dissolving pulp as a reference. Eucalyptus sawdust dissolving pulps were obtained by soda pulping followed by two TCF sequential bleaching processes OOpZ, and OOp, followed by a cold soda extraction. The characterization of dissolving pulps involved alpha-, beta- and gamma-cellulose content, alkali solubility with 10 wt% (S10), and 18 wt% NaOH (S18) aqueous solutions, and degree of polymerization. Fock´s method was used to measure cellulose reactivity and the alkali solubility in a 9 wt% NaOH aqueous solution at − 5 °C to evaluate the pulps dissolving capacity. Dissolving pulps presented high cellulose content (> 93%, expressed as α-cellulose) and good reactivity (almost 8%). The dissolving pulps were adequate raw materials for regenerated cellulose products (beads and films) from two cellulose dissolution methods: direct dissolution in NaOH/urea and cellulose carbamate solution. The sequence OOpE (where E is an alkaline extraction) was more economically feasible and straightforward to produce dissolving pulp than OOpZE. The experimental pulps showed the expected characteristics of the dissolving pulp to obtain regenerated cellulose products. However, it is necessary to deepen the study of producing regenerated cellulose films with enhanced mechanical properties from experimental dissolving pulps, solvents, coagulation, and regeneration conditions.