Properties of polyvinyl alcohol films reinforced by citric acid modified cellulose nanocrystals and silica aerogels

Chen J., Zheng M., Tan K.B., Lin J., Chen M., Zhu Y.

Polyvinyl alcohol (PVA)-xanthan gum (XG) composite films with good degradation properties were prepared by casting method. The effects of XG amount on thickness, moisture content, water solubility, water vapor transmission (WVP), transmittance and mechanical properties of the composite film were investigated. All composite films produced uniform and transparent films and Fourier transform infrared (FT-IR) spectroscopy, as well as X-ray diffraction (XRD) had proven the formation of hydrogen bonds and subsequently compatibility of the two polymers. In general, addition of XG in PVA was able to decrease moisture content, water solubility and WVP more than the pure PVA films, with sample PX30 demonstrated the best performance. This sample also had the best mechanical properties. It also demonstrated food packaging and capability better than that of commercial plastic bag. More importantly, our sample can be fully decomposed in soil and water within 12 h, which was not only significantly shorter than commercial plastic bag, but also other biodegradable materials. Therefore, PVA/XG-based food packaging material has demonstrated huge potential to be commercialized and replaces commercial plastic bag as an alternative packing material which is renewable, sustainable and environmentally friendly.

Wu Z., Li Y., Tang J., Lin D., Qin W., Loy D.A., Zhang Q., Chen H., Li S.

In this study, chitosan(CS), nano-silicon aerogels(nSA) and tea polyphenols(TP) were used as film-forming materials and processed with ultrasonication to form films using the tape-casting method. The effects of ultrasonication time, temperature and frequency on the properties of CS/nSA/TP film were explored via material property testing. The results of response surface showed that the maximum tensile strength of the film was 4.036 MPa at ultrasonication time(57.97 min), temperature(37.26 °C) and frequency(30 kHz). The maximum elongation at break of the film was 279.42 % at ultrasonication time(60.88 min), temperature(39.93 °C) and frequency(30 kHz). Due to cavitation and super-mixing effects, ultrasonication may make the surface of the film smoother and easier to degrade. After ultrasonication, TPs were protected by the 3D network structure composed of CS and nSA. Ultrasonication improved the antioxidant and antibacterial properties of the film. These results show that ultrasonication is an effective method to improve the properties of films.

Lin D., Xiao L., Qin W., Loy D.A., Wu Z., Chen H., Zhang Q.

In this work, chitosan/lignosulfonate composite micelles (CS-LS) were successfully prepared through polyelectrolyte self-assembly. Curcumin was encapsulated in CS-LS to obtain CUR-CS-LS. The results showed that the average diameter of CS-LS and CUR-CS-LS were 239 nm and 286 nm, respectively. The results show that the aromatic rings of lignosulfonate are assembled into the hydrophobic core of micelles through π-π interactions, and chitosan binds outside the hydrophobic core as a hydrophilic shell through electrostatic interactions. Curcumin is encapsulated in the hydrophobic core through hydrophobic interactions. Encapsulation improves the thermal stability and pH stability of curcumin. Compared with free curcumin, the retention efficiency of curcumin in CUR-CS-LS increased by approximately 6.66 and 6.46 times under the same heat treatment and pH conditions, respectively. Encapsulation also increases the antioxidant activity of curcumin in aqueous solution. In addition, the release mechanism of curcumin is diffusion and matrix swelling. These findings explain that CS-LS may be an effective promising delivery system for encapsulating hydrophobic biologically active substances.

Abd Halim Z.A., Ahmad N., Yajid M.A., Hamdan H.

Silica aerogel (SA) is considered one of the most promising thermal insulation materials due to its nano-size open pore structure. In this study, one part room temperature vulcanized silicone rubber (RTV-SiR) composite with improved thermal performance has been produced simply by incorporating SA as filler. Hydrophobic SA particles of 0.5 mm with a surface area of ∼700 m 2 /g and density of 0.07 g/cm 3 were prepared from rice husk ash via ambient pressure drying. The RTV-SiR composite of 5.0 mm thickness was prepared by blending with 9 wt% of SA particles using a mechanical mixer and kept for vulcanization at room temperature. The properties of the RTV-SiR composite were systematically investigated using scanning electron microscopy (SEM), tensile test, surface roughness, water contact angle measurement, Fourier transform infrared spectroscopy (FTIR), hot-disk thermal conductivity analyzer, thermogravimetric analysis (TGA) and flame penetration test. Compared to pristine RTV-SiR, composite reinforced with SA particles demonstrates low density, high strength and specific modulus, low thermal conductivity, high surface hydrophobicity and excellent resistance to flame penetration test. The composite can withstand the penetration of the butane flame torch for more than 800 s and keep the unexposed side temperature (plateau of 100 °C) below the decomposition temperature of the SiR. The results suggest that the thermal performance of the composite is strongly influenced by the physical properties of the SA and the structural integrity of the SA in the composite. The SA reinforced SiR composite has a potential application prospect in building insulation and fire protection. • Hydrophobic SA (0.035 W/mK) was produced from RHA via ambient drying. • Incorporation of SA in RTV-SiR had significant effects on specific strength and thermal conductivity. • The composite demonstrates self-cleaning capability and excellent resistance to flame penetration test. • The SA filler acts as barrier for heat and mass transport depending on its structural integrity in the composite. • This proof-of-concept broadens the potential of SA based composites in thermal insulation application.

Tan R., Li F., Zhang Y., Yuan Z., Feng X., Zhang W., Liang T., Cao J., De Hoop C.F., Peng X., Huang X.

Polyvinyl alcohol (PVA) has been widely applied in industries for its low cost, nontoxicity, biodegradability, and renewable advantages. However, its unstable structure may not meet some strong physical and mechanical needs. In order to enhance the performances of the PVA film, cellulose nanocrystals (CNCs), tannic acid (TA), and chitosan (CS), working as a reinforcer, a crosslinker, and an antimicrobial agent, respectively, were introduced into the PVA matrix. The results indicated that CNCs, TA, and CS were evenly distributed and cohesively incorporated within the PVA matrix, which contributed to the good mechanical properties and thermal stabilities of biocomposite PVA films. Besides, the addition of TA remarkably improved the antiultraviolet and antioxidant capabilities of PVA films, although the light transmittance declined slightly. It was also observed that the pure PVA film and PVA reinforced with CNCs were incapable of protecting against bacteria, while the ones with CS had prominent antibacterial properties to Escherichia coli and Staphylococcus aureus. Overall, the resulting film presented a high potential utilization as a food packaging material for its outstanding physical and mechanical performances.

Carnicer V., Cañas E., Orts M.J., Sánchez E.

This study aims to demonstrate the feasibility of developing zirconia ceramic coatings with the incorporation of silica aerogel particles, which exhibit outstanding insulating properties. Thus, the research aims to find a suitable methodology to disperse aerogel particles, which are strongly hydrophobic, in an aqueous medium. In the study, a double rheological characterisation was carried out, firstly, to adapt the dispersion of the aerogel particles and, secondly, to characterise the different suspensions made up of silica aerogel and zirconia to be atomised. Aerogel additions ranging from 2% to 98% in volume were addressed. Spray-dried powders were characterised in terms of flowability. Finally, coatings microstructure was examined, and their thermal conductivity determined. The results showed that it is possible to disperse aerogel particles in an aqueous medium and to obtain stable suspensions together with the addition of zirconia. Suitable spray-dried powders were then produced in all the cases. On the other hand, coatings obtained by atmospheric plasma spraying showed appreciable microstructural differences with the addition of aerogel particles and their insulating effect is evident in the thermal tests, with their improved (decreased) thermal conductivity.

Zhang X., Li Z., Ji R., Li K., Zhang W.

Biodegradable composite films based on pullulan/carboxymethyl cellulose/nano-TiO2 were prepared using a solution casting method. In this study, the composite films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), and their physical, mechanical and antimicrobial properties were investigated. FTIR and XRD results confirmed that the presence of nano-TiO2 could enhance the interaction between the film matrix. SEM analysis revealed that the composite films had a homogeneous network structure, and good particle dispersion could be obtained when the nano-TiO2 particle content was low. DSC results indicated that the composite films possessed good thermal stability. The incorporation of nano-TiO2 increased the thickness and contact angle while significantly decreasing the water solubility (p < 0.05). As the content of nano-TiO2 increased, the water vapor and ultraviolet visible (UV–Vis) light barrier properties of composite films were significantly improved (p < 0.05). Mechanical analysis demonstrated that the tensile strength of the composite films first increased and then decreased, whereas the elongation at break decreased significantly (p < 0.05). In addition, the composite films exhibited excellent activity against Escherichia coli and Staphylococcus aureus mainly due to the inactivation of bacteria by nano-TiO2 photocatalysis. Preservation experiments showed that the composite films could decrease the weight loss significantly and maintain the firmness, titratable acidity, vitamin c and skin color of strawberries, thereby improving the overall quality of strawberries and extending their shelf life. This finding suggested that pullulan/carboxymethyl cellulose/nano-TiO2 composite films possessed excellent potential for application in food packaging.

Chen H., Zhang M., Rao Z.

Li J., Liu Y., Sun B., Zhang R.

Nuruddin M., Korani D.M., Jo H., Chowdhury R.A., Montes F.J., Howarter J.A., Youngblood J.P.

Cellulose Nanocrystals (CNCs) are promising materials for the packaging industry due to their non-toxicity, abundance in nature, biodegradability and high gas barrier properties. Unfortunately, CNC...

Zhou Y., Zhu X., Zhang C., Chai W.S., Chew K.W., Du A., Show P.L.

In this current study, whey protein isolate (WPI)/pectin biowaste composite film properties was investigated with addition of Streptomyces coelicolor-derived small laccase (SLAC). It was found that different SLAC concentrations has insignificant effect on the film color while best film transparency obtained with 4 U/100 mL SLAC. Optimum mechanical properties were obtained with 6 U/100 mL SLAC indicating best crosslinking effect on the WPI-pectin film. Lowest moisture content (MC), water vapor transmittance (WVP) and oxygen transmittance ( O 2 P) of the film obtained with 6 U/100 mL SLAC, while 4 U/100 mL SLAC resulted in lowest carbon dioxide transmittance (CO2P). Maximum increase in phase transition temperature and absorption peak shift according to DSC and FTIR results, respectively, indicated largest improvement in heat resistance and chemical bond strength of the film with 6 U/100 mL SLAC addition. The XRD results showed that the addition of SLAC was insignificant towards the film crystallinity. The work presents the development of new degradable composite film that can be derived from biowaste compounds for utilization in food processing application.

Gasti T., Dixit S., Sataraddi S.P., Hiremani V.D., Masti S.P., Chougale R.B., Malabadi R.B.

In this work, composite films for food packaging were prepared from chitosan (CS) and polyvinyl alcohol (PVA) incorporated with extracts of edible Solanum nigrum L. (SN) leaves by solvent casting method. The effect of water (SW), ethanol (SE), and methanolic (SM) extracts of SN leaves on the mechanical, physical, barrier, optical, soil degradability, antimicrobial, and antioxidant properties of the films were studied. The composite films have smooth homogeneous surface morphology and showed enhanced UV blocking properties. Incorporation of SN leaves extract greatly enhances the tensile strength. The water vapor transmission rate also improved by the influence of SN extracts. The surface wettability of the composite films significantly (p < 0.005) enhanced. The soil degradability of the film samples was improved by 50%. All the composite films have an overall migration rate within the permitted limit. Besides, the SN leaves incorporated CS/PVA films showed enhanced antibacterial activity towards Staphylococcus aureus and Escherichia coli bacteria and samples did not show significant antifungal activity towards Candida albicans. All SN extracts incorporated samples showed enhanced antioxidant activity by DPPH scavenging assay. These results suggest that all three SN leaves extract induced CS/PVA composite films can be used for food packaging applications.

Cui X., Ozaki A., Asoh T., Uyama H.

As the most extensively researched thermoplastic aliphatic polyester, poly (lactic acid) (PLA) derived from renewable resources has shown it tremendous potential at replacing the petroleum-based polymers in many fields. The greatest challenge hindering the use of PLA is considered as its poor toughness. In terms of reproducible processes and products, cellulose has been applied to the PLA matrix as reinforcing fillers but the poor compatibility due to the inherent hydrophilicity of cellulose and hydrophobic nature of PLA is troubling. To solve this issue, we carried out an effective water-based method to render the cellulose surface with high carboxylic group content through the esterification of hydroxyl groups with citric acid in a solid phase reaction to strengthen the hydrogen bonding interaction with PLA. Consequently, the modified cellulose showed good dispersion in PLA matrix. The resulting flexural properties of PLA composites incorporated by the citric acid-modified cellulose and its fibrillated form as fillers were improved compared to those of the pristine PLA resin. The potential nucleating function of the modified cellulose was discussed and the filler proportion in the composite was optimized. Because of the well-established processing technique, we believe that citric acid-modified cellulose has an immense potential as a sustainable and cost-effective reinforcing filler for PLA, as a representative of bio-based polyesters. • Citric acid-modified cellulose (CAC) used as reinforcing fillers for PLA composite. • CAC dispersed into the PLA matrix with good compatibility. • CAC reinforced the flexural property of PLA.

Rashtchian M., Hivechi A., Bahrami S.H., Milan P.B., Simorgh S.

In this research, cellulose nanocrystal (CNC) was synthesized from cotton waste using controlled hydrolysis against 64 % (w/w) sulfuric acid solution. The produced nanoparticles were then characterized using FTIR, XRD, TGA, and DLS analyses. Biaxial electrospinning technique was used to produce CNC incorporated PCL-PVA/NaAlg nanofibers. The sodium alginate portion was then crosslinked via submerging the samples in calcium chloride aqueous solution. The CNC incorporated and crosslinked sample was characterized using SEM, FTIR, and TGA techniques. Results confirmed the presence of CNC nanoparticles and alginate crosslinking reaction. Mechanical studies showed that CNC incorporation increases the tensile modulus by 65 %. Also, the crosslinked samples exhibited an increase in elongation at break. Water contact angle studies suggested that CNC incorporation and crosslinking improves nanofiber hydrophilicity. Cell viability of more than 90 % was observed in CNC incorporated PCL-CaAlg nanofibers. Also, SEM images of cells on nanofiber scaffolds showed better cell growth and attachment in PCL-CaAlg-CNC samples.

Le Gars M., Roger P., Belgacem N., Bras J.

The recent emergence of bio-based nanocomposites makes perfect sense from a technical and environmental point of view. Cellulose nanocrystals (CNCs) are novel bio-based nanomaterials with a wide range of beneficial properties. Their biodegradability, crystallinity, high surface area, and mechanical strength, as well as their highly reactive surface, make them ideal materials as nanofillers in polymeric matrices. However, most the bio-based polymers are hydrophobic, and the hydrophilicity of CNC is therefore a challenge to their incorporation in such matrices. In this study, a new procedure for surface modification of CNC with long aliphatic chains [lauric acid (12 carbons) and stearic acid (18 carbons)] was developed that limits the use of petro-chemicals and facilitates their potential recycling. A study of the dispersion state of CNC in acetone was performed first. Then, grafting efficiency was highlighted by several techniques and quantification of the amount of grafted fatty chains was investigated. Degrees of substitution on the bulk and on the surface of the CNC were calculated between 0.1 and 0.3, which provided enough grafted functions to confer hydrophobic behavior to modified CNCs, as highlighted by the increasing of contact angle from 65° for neat CNC to 80° after modification. Finally, conservation of CNC crystalline structure and morphology was proved by both X-ray diffraction and transmission electron microscopy analyses. Modified CNCs exhibit a crystallinity index close to 86% and length of approximately 350 nm. Thus, crystalline hydrophobic cellulosic nanomaterials were prepared using a more environmentally friendly procedure than those classically found in the literature.

Duan Y., Wu J., Qiao A., Guo X., Ge X., Qi W., Penkova A., Su R.

Zhu C., Tian M., Zhang D., Yang Q., Wang D., Fan S., Li X., Yang W., Hou C.

ABSTRACTIn this study, the surface of cellulose nanocrystals was first modified with citric acid, and the resultant modified cellulose nanocrystals (MCNC) were subsequently utilized as a reinforcement phase for polylactic acid (PLA). Findings indicated that MCNC interacted with PLA through hydrogen bonding, resulting in improved thermal stability, mechanical properties, and surface hydrophobicity of PLA nanofiber films. Specifically, the thermal degradation temperature, tensile strength, elongation at break, and contact angle of the nanofiber films increased by 19°C, 30.04%, 49.11%, and 11.22°, respectively, with a 3% addition of MCNC. Subsequently, utilizing PLA/MCNC as the base material and kaempferol as the active ingredient, a preliminary exploration into its potential as an active packaging material was carried out. When the addition amount of kaempferol was 10%, the DPPH and ABTS free radical scavenging ability of the nanofiber film reached more than 90%, demonstrating its application potential as an active packaging material. These results offer a promising strategy for the effective dispersion of CNC within PLA matrices, thereby expanding the potential applications of PLA in the field of active packaging.

Mavila B., Pradeep H., Suresh S., Cheroor Konathodi N., Adukkadan A., Monika M., Periyat P.

Singh A.K., Itkor P., Lee M., Choi S., Lee Y.S.

Shi S., Wang J., Wang W., Chen H., Bai L., Yang H., Yang L., Wei D., Yin K.

Cheng S., Yin C., Li K., Liu Z., Pan Q., Zuo X., Guo A., Ma H.

Films with excellent mechanical properties and antimicrobial activity have potential applications in food preservation. The antimicrobial film was prepared by blending probiotic Bacillus velezensis 906 metabolites (906), potassium sorbate (PS), and polyvinyl alcohol (PVA). The film was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermal stability analysis. The mechanical, barrier, and antimicrobial properties of the film were tested. The results of the physicochemical analysis indicated that, compared to the pure PVA film, the film's mechanical properties decreased, while its barrier properties and hydrophobicity increased with the addition of PS and 906, respectively. The results of the antimicrobial tests revealed that the blend film exhibited significant antimicrobial activity against Vibrio parahaemolyticus, Psychrobacter maritimus, Oceanobacillus kimchii, Pseudomonas aeruginosa, and Listeria monocytogenes. SEM demonstrated good fusion between the components of the PVA/PS/906 film, resulting in a dense and crack-free structure. FTIR suggested that PS and 906 enhance molecular interactions within the film matrix. XRD revealed that the film was crystallized, with 906 increasing the crystallinity of the bonds between the film components. Thermal analysis indicated the thermal stability of the films was enhanced. Consequently, the PVA/PS/906 blend film shows significant potential for application in the preservation of aquatic products.

Zhang D., Du K., Shi P., Wu X., Zhang S.

Aerogels have garnered extensive attention as crucial materials in the field of engineering. In this study, 2,2,6,6-tetramethylpiperidinyl-1-oxid (TEMPO)-oxidized bamboo cellulose nanofibril (TOCNF) was introduced as a critical component into the crosslinking network of polyvinyl alcohol (PVA) using glutaraldehyde (GA) as a bridge to obtain aerogel with enhanced pore structures and mechanical properties. The properties of composite aerogels with different TOCNF additions were investigated. The results showed that the aerogels exhibit low density, excellent pore structure, outstanding thermal stability and mechanical properties. The compressive strength and modulus of elasticity of the aerogel with 1.5% TOCNF had significantly increased by 260% and 150%, respectively, compared with blank sample. Furthermore, the aerogel displayed robust stability in liquids due to the interaction between TOCNF and PVA forming a crosslinked network structure. This work demonstrates a bamboo cellulose nanofibril enhanced aerogel that can be widely applied in the fields of energy, adsorption, construction, thermal insulation, and so on.

Zhang J., Han Y., Zhang L., Li Z., Yang H., Zhang X., Zhang J.

Silica aerogel (SA) has shown great promise in constructing thermal insulation composites in various forms. However, it is still challenging to disperse a huge amount of SA particles into other matrices for fabricating superior thermal insulation materials or highly filled masterbatch, owing to its high specific surface area and ultra-low density. Herein, inspired by high internal phase emulsion (HIPE), we successfully prepare processable SA/polyvinyl alcohol (PVA) composites (SA-PVA dough) with over 74 vol% dispersed SA, using a PVA aqueous solution as a binder. This is achieved by gradually mixing a large amount of hydrophobic SA filler into a small amount of PVA aqueous solution. The resulting SA-PVA dough exhibits an internal structure resembling that of HIPEs, with hydrophobic SA particles stabilized in the water phase by amphiphilic PVA chains, tightly packed within the thin continuous PVA aqueous phase. Benefiting from such a HIPE structure, the SA-PVA dough can be easily shaped into various forms and exhibits good applicability in further processing. The dried dough inherits the excellent properties of SA, including ultra-low density, superhydrophobicity (water contact angle: 153°), thermal insulation (thermal conductivity: 0.03 W m−1 K−1), and flame resistance. Moreover, the continuous PVA network structure, combined with the nanoscale pore structure of SA, provides the dough with excellent gas barrier properties, greatly expanding the application scope of SA-based composites.

Wu C., Wang S., Wu D., Ke C.

The challenge of global climate change has drawn people's attention to the issue of carbon emissions. Reducing the use of petroleum-derived materials and increasing the use of biodegradable materials is a current focus of research, especially in the packaging materials industry. This study focused on the use of environmentally friendly plastics and waste paper as the main materials for packaging films. Poly(butylene succinate-co-lactate) (PBSL) was modified with maleic anhydride (MA) to form a biobased compatibilizer (MPBSL), which was then blended with a mixture (WPS) of waste-paper powder (WP) and silica aerogel powder (SP) to form the designed composite (MPBSL/WPS). The modification of PBSL with MA improved interfacial adhesion between PBSL and WPS. The structure, thermal, and mechanical properties, water vapor/oxygen barrier, toxicity, freshness, and biodegradability of MPBSL/WPS films were evaluated. Compared with the PBSL/WP film, the MPBSL/WPS film exhibited increased tensile strength at break of 4-13.5 MPa, increased initial decomposition loss at 5 wt% of 14-35 °C, and decreased water/oxygen permeabilities of 18-105 cm3/m2·d·Pa. In the water absorption test, the MPBSL/WPS film displayed about 2-6 % lower water absorption than that of the PBSL/WP film. In the cytocompatibility test, both MPBSL/WPS and PBSL/WP membrane were nontoxic. In addition, compared with PBSL/WP film and the control, the MPBSL/WPS film significantly reduced moisture loss, extended the shelf life, and prevented microbial growth in vegetable and meat preservation tests. Both MPBSL/WPS and PBSL/WP films were biodegradable in a 60-day soil biodegradation test; the degradation rate was 50 % when the WP or WPS content was 40 wt%. Our findings indicate that the composites would be suitable for environmentally sustainable packaging materials.

Meng L., Xi J., Ye W., Xu K., Gai X., Xu Z., Xiao H., Wu W.

Using the semi-crystalline poly(vinyl alcohol) (PVA) as the polymer matrix and silica nanoparticles (SNPs) as the reinforcing filler, composite films with excellent water vapor barrier, high tensile strength, visible light transmission and ultraviolet (UV) shielding performances were constructed via a simple heat treatment process, during which the films underwent dehydration cross-linking and isothermal recrystallization to form a "spherical crystal interlocking structure". Both the dosage and average particle size of SNPs significantly affected the barrier property, and the optimal values were 7 wt% and 15 nm, respectively. The heat treatment further improved the water resistance, mechanical strength, and barrier property to a great extent. Moreover, different theoretical models including Guggenheim Anderson de Boer (GAB), Brunauer Emmett and Teller (BET), Hailwood-Horribon (H-H) model, crystallinity model and Fick's law model were successfully used to explain the water vapor barrier mechanism. The water vapor permeability (WVP) of the optimized composite film was reduced to 2.20 × 10−12 g·m/(m2·Pa·s) at 37°C and 65% RH, while the tensile strength was increased up to 116.8 MPa. In addition, the absorption rate of ultraviolet of the film after heat treatment increased from 13% to 92.0%, while the transmittance of visible light remained above 78%.

Wang H., Liu X., Wu M., Huang Y.

Polyvinyl alcohol (PVA) film, a promising alternative to non-biodegradable plastic packaging films for food and medical packaging, is limited by poor water resistance. In this work, a simple solvent evaporation self-assembly was used to construct a nanophase separation structure to establish dense interfacial hydrogen bonding, covalent bonding and iron metal ion coordination interactions between lignin-containing cellulose nanofibers (LCNFs) and PVA matrix to improve the interfacial force and solve the problem of poor compatibility of LCNFs in PVA. The iron ion (Fe3+) coordination tended to combine with the more active lignin phenolic hydroxyl group to construct the nanophase separation structure. Covalent crosslinking of glutaraldehyde (GA) improved the interfacial compatibility of PVA/LCNF films, enhanced the interfacial bonding and formed a homogeneous structure. The multi-nanophase structures improved the strength and elastic modulus of the PVA/LCNF film and provided the films with extremely low water absorption, water vapor transmission rate and excellent UV-shielding. Compared with pure PVA film, PVA-10L-5Fe-3GA film had about 106.9 % higher tensile strength, 93.9 % lower water absorption and 93.4 % lower mass loss, 69.8 % lower water vapor transmission coefficient, and was able to shield UV at 200-400 nm, which is highly expected to be used in packaging films.

Zhang X., Qiu H., Ismail B.B., He Q., Yang Z., Zou Z., Xiao G., Xu Y., Ye X., Liu D., Guo M.

The significant threat of foodborne pathogens contamination has continuously promoted the development of efficient antimicrobial food packaging materials. Here, an antimicrobial film was prepared with gallic acid-grafted-chitosan (CS/GA) that obtained by a two-step ultrasound method. The resultant films exhibited good transparency, improved UV barrier performance, and enhanced mechanical strength. Specifically, with the grafting of 1.2 % GA, the UV blocking ability of CS/GA film at 400 nm was significantly increased by 19.7 % and the tensile strength was nearly two times higher than that of CS film. Moreover, the CS/GA films exhibited an inspiring photoactivated bactericidal ability under 400 nm UVA light irradiation that eradicated almost 99.9 % of Staphylococcus aureus (S. aureus) cells within 60 min. To gain more insights into the antibacterial mechanism, the treated S. aureus cells were further investigated by visualizing bacterial ultrastructure and analyzing membrane properties. The results pointed to the peptidoglycan layer as the primary action target when bacteria come into contact with CS/GA films. Afterward, the intracellular oxidative lesions, disrupted bacterial integrity, and disordered membrane functional properties collectively resulted in eventual cell death. The findings revealed the unique peptidoglycan targeting and membrane disruptive mechanisms of CS/GA films, confirming the application values in controlling foodborne pathogens.

Niu Z., Wang Q., Lu J., Hu Y., Huang J., Zhao W., Liu Y., Long Y., Han G.

AbstractThe technical synergy between flexible sensing paper and triboelectric nanogenerator (TENG) in the next stage of artificial intelligence Internet of Things engineering makes the development of intelligent sensing paper with triboelectric function very attractive. Therefore, it is extremely urgent to explore functional papers that are more suitable for triboelectric sensing. Here, a cellulose nanocrystals (CNCs) reinforced PVDF hybrid paper (CPHP) is developed by electrospinning technology. Benefitting from the unique effects of CNCs, CPHP forms a solid cross‐linked network among fibers and obtains a high‐strength (25 MPa) paper‐like state and high surface roughness. Meanwhile, CNCs also improve the triboelectrification effect of CPHP by assisting the PVDF matrix to form more electroactive phases (96% share) and a higher relative permittivity (17.9). The CPHP‐based TENG with single electrode configuration demonstrates good output performance (open‐circuit voltage of 116 V, short‐circuit current of 2.2 µA and power density of 91 mW m−2) and ultrahigh pressure‐sensitivity response (3.95 mV Pa−1), which endows CPHP with reliable power supply and sensing capability. More importantly, the CPHP‐based flexible self‐powered tactile sensor with TENG array exhibits multifunctional applications in imitation Morse code compilation, tactile track recognition, and game character control, showing great prospects in the intelligent inductive device and human–machine interaction.

Oprică G.M., Panaitescu D.M., Lixandru B.E., Uşurelu C.D., Gabor A.R., Nicolae C., Fierascu R.C., Frone A.N.

The medical sector is one of the biggest consumers of single-use materials, and while the insurance of sterile media is non-negotiable, the environmental aspect is a chronic problem. Nanocellulose (NC) is one of the safest and most promising materials that can be used in medical applications due to its valuable properties like biocompatibility and biodegradability, along with its good mechanical properties and high water uptake capacity. However, NC has no bactericidal activity, which is a critical need for the effective prevention of infections in chronic diabetic wound dressing applications. Therefore, in this work, a natural product, propolis extract (PE), was used as an antibacterial agent, in different amounts, together with NC to obtain sponge-like structures (NC/PE). The scanning electron microscope (SEM) images showed well-impregnated cellulose fibers and a more compact structure with the addition of PE. According to the thermogravimetric analysis (TGA), the samples containing PE underwent thermal degradation before the unmodified NC due to the presence of volatile compounds in the extract. However, the peak degradation temperature in the first derivative thermogravimetric curves was higher for all the sponges containing PE when compared to the unmodified NC. The antibacterial efficacy of the samples was tested against Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, as well as on two clinically resistant isolates. The samples completely inhibited the development of Staphylococcus aureus, and Pseudomonas aeruginosa was partially inhibited, while Escherichia coli was resistant to the PE action. Considering the physical and biological properties along with the environmental and economic benefits, the development of an NC/PE wound dressing seems promising.

Wang S., Hyun D.Y., Park D.S., Park J., Lee S., Heo D., Min K., Kim M., Kim J., Jin Y.J., Na M.H., Cho K.H., Sim D.S., Tae G., Jeong M.H., et. al.

Hyaluronic acid (HA)-based nanofibers have been widely used for various biomedical applications such as cosmetics, wound dressing, and tissue engineering scaffolds owing to their large active surface areas and high water retention capability. However, HA-only solutions are relatively difficult to handle for electrospinning because of their limited stability and/or solvent toxicity, while the selection of a carrier polymer is not straightforward due to poor electrospinnability. Herein, we report on the optimization of the precursor solution composition for reliable electrospinning of polymer blend nanofibers with high HA contents. Polyvinyl alcohol (PVA) was selected as a carrier polymer due to its higher solubility in water, while citric acid (CA) was introduced as crosslinker to maintain the water stability of the resultant nanofibers. Thermally induced esterification was performed to interconnect PVA, HA and CA without additional catalysts and the average diameter and swelling ratio of crosslinked PVA-CA-HA nanofibers were systematically studied. To optimize electrospinnability, a mixture of water and DMF was employed as co-solvent considering that the addition of DMF increases the viscosity of the precursor solution, leading to the uniform formation of PVA-CA-HA blend nanofibers, particularly, with high HA contents (~ 16%). Finally, PVA-CA-HA nanofiber membranes were tested for cell viability and anti-coagulation characteristic to demonstrate the versatility of PVA-CA-HA nanofibers in various biomedical research fields.