Effect of microcrystalline and nanocrystals cellulose fillers in materials based on PLA matrix

The aim of this work was to compare the effects of microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC) addition on the properties of PLA matrix. The CNC were obtained by acid hydrolysis of the MCC. Both MCC and CNC were separately incorporated in PLA at ratios of 3, 5 and 7 wt%. In some compositions, organophilic silica (R972) was added to improve the cellulose-matrix compatibility. The properties of the materials were evaluated by FTIR, XRD, NMR and mechanical tests. Functional groups and crystalline structure of MCC and CNC were determined by FTIR and XRD, respectively. NMR T₁H values showed that films containing CNC presented better interfacial interaction than those containing MCC, and indicated that R972 acts as compatibilizer. MCC and CNC acted as nucleating agents for PLA crystallization and there was an improvement in the mechanical performance of materials with the addition of CNC.     

Thermal characterization and electrical properties of Fe-modified cellulose long fibers and micro crystalline cellulose

Thermal properties of polylactic acid (PLA) filled with Fe-modified cellulose long fibers (CLF) and microcrystalline cellulose (MCC) were studied using thermo gravimetric analysis (TG), differential scanning calorimetry, and dynamic mechanical analysis (DMA). The Fe-modified CLFs and MCCs were compared with unmodified samples to study the effect of modification with Fe on electrical conductivity. Results from TG showed that the degradation temperature was higher for all composites when compared to the pure PLA and that the PLA composites filled with unmodified celluloses resulted in the best thermal stability. No comparable difference was found in glass transition temperature (T _g) and melting temperature (T _m) between pure PLA and Fe-modified and unmodified CLF- and MCC-based PLA biocomposites. DMA results showed that the storage modulus in glassy state was increased for the biocomposites when compared to pure PLA. The results obtained from a femtostat showed that electrical conductivity of Fe-modified CLF and MCC samples were higher than that of unmodified samples, thus indicating that the prepared biocomposites have potential uses where conductive biopolymers are needed. These modified fibers can also be tailored for fiber orientation in a matrix when subjected to a magnetic field.     

Development of biopolymer/cellulose/silica nanostructured hybrid materials and their characterization by NMR relaxometry

The objective of this study was to investigate the preparation and properties of hybrid materials composed of poly(lactic acid) (PLA) and poly(lactic acid)/poly(lactic-co-glycolic acid) (PLA/PLGA) blends employing cellulose nanocrystals (CNCs) and/or organophilic silica (R972) as nanoparticles. The CNCs were obtained by acid hydrolysis of commercially available microcrystalline cellulose (MCC). The materials were produced in film form by solution casting. Organophilic silica was incorporated at a ratio of 3 wt.%, and CNCs were added at ratios of 3 wt.% and 5 wt.% in relation to the weight of the polymer matrix. Two series of films were obtained. The first was prepared using only PLA as the matrix, and the second was obtained using blends of PLA and PLGA. The properties of the films were evaluated by X-ray diffractometry, nuclear magnetic resonance, Fourier-transform infrared spectroscopy and measurement of mechanical properties. The results revealed that each nanoparticle, whether added individually or combined with the other type of nanoparticle, induced different final material properties. Cellulose nanocrystals can act as nucleating agents for the crystallization of PLA. There was an improvement in the mechanical performance of films with the addition of CNCs. Further, the incorporation of silica combined with CNCs resulted in the generation of films with the strongest mechanical properties. The results of this study indicate that silica decreases the surface tension between PLA-cellulose and PLA/PLGA-cellulose.     

Thermal properties of microcrystalline cellulose-filled PET–PTT blend polymer composites

Polymer composite materials were prepared from poly(ethylene terephthalate)–poly(trimethylene terephthalate) blends as the matrix and different microcrystalline cellulose (MCC) filler levels (0–40 wt%) using melt compounding followed by compression molding. The composites were analyzed using dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The DSC results indicated that there is no consistent or significant influence of the MCC addition on the glass transition (T _g), melting (T _m), and crystallization temperature of the composites. With increasing MCC content, dynamic mechanical properties improved because of the reinforcing effect of the MCC. The tan δ peak values from the DMTA were not significantly changed as the MCC content increased. TG indicated that the onset temperature of rapid thermal degradation decreased with increasing MCC content. It was also found that the thermal stability of the composites slightly decreased as the MCC content increased.     

Enhanced properties of poly(lactic acid) with silica nanoparticles

The objective of this article is to fabricate poly(lactic acid) (PLA) and nano silica (SiO₂) composites and investigate effect of SiO₂ on the properties of PLA composites. Surface‐grafting modification was used in this study by grafting 3‐Glycidoxypropyltrimethoxysilane (KH‐560) onto the surface of silica nanoparticles. The surface‐grafting reaction was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. Then the hydrophilic silica nanoparticles became hydrophobic and dispersed homogeneously in PLA matrix. Scanning electron microscope and Dynamic thermomechanical analysis (DMA) results revealed that the compatibility between PLA and SiO₂ was improved. Differential scanning calorimetry and polarized optical microscope tests showed that nano‐silica had a good effect on crystallization of PLA. The transparency analysis showed an increase in transparency of PLA, which had great benefit for the application of PLA. The thermal stability, fire resistance, and mechanical properties were also enhanced because of the addition of nano silica particles. Copyright © 2016 John Wiley & Sons, Ltd.     

Ultrasonic assisted synthesis of nanocrystalline cellulose as support and reducing agent for Ag nanoparticles: green synthesis and novel effective nanocatalyst for degradation of organic dyes

In this study, nanocrystalline cellulose (NCC) prepared from microcrystalline cellulose using high‐intensity ultrasonication as mechanical method without any chemical treatment. The obtained NCC with around 30–50 nm diameters, utilized as support, reducing and stabilizing agent for in‐situ green and eco‐friendly synthesis of silver nanoparticles (Ag NPs). The catalytic activity of composite was examined for degradation of environmental pollutants. The structure of as‐synthesized composite (Ag@NCC) was characterized by ultraviolet–visible spectroscopy (UV–vis), field emission scanning electron microscopy (FE‐SEM); Transmission electron microscopy (TEM); Energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA). The results of the catalytic reaction experiments showed that spherically shaped silver nanoparticles of around 20 nm distributed on the surface of nanocellulose demonstrated high catalytic efficiency towards the removal of methyl orange (MO) and 4‐nitrophenol (4‐NP).     

Electrostatic assembly of Ag nanoparticles onto nanofibrillated cellulose for antibacterial paper products

Nanofibrillated cellulose offers new technological solutions for the development of paper products. Here, composites of nanofibrillated cellulose (NFC) and Ag nanoparticles (NP) were prepared for the first time via the electrostatic assembly of Ag NP (aqueous colloids) onto NFC. Distinct polyelectrolytes have been investigated as macromolecular linkers in order to evaluate their effects on the building-up of Ag modified NFC and also on the final properties of the NFC/Ag composite materials. The NFC/Ag nanocomposites were first investigated for their antibacterial properties towards S. aureus and K. pneumoniae microorganisms as compared to NFC modified by polyelectrolytes linkers without Ag. Subsequently, the antibacterial NFC/Ag nanocomposites were used as fillers in starch based coating formulations for Eucalyptus globulus-based paper sheets. The potential of this approach to produce antimicrobial paper products will be discussed on the basis of complementary optical, air barrier and mechanical data.     

Design and preparation of poly(lactic acid) hydroxyapatite nanocomposites reinforced with phosphorus‐based organic additive: Thermal,combustion, and mechanical properties studies

A new phosphorus‐based organic additive (PDA) was designed and successfully synthesized using a three‐component reaction for improvement of the thermal and combustion resistance of polylactic acid (PLA). For compensate for mechanical properties of PLA, hydroxyapatite nanoparticles was modified via in situ surface modification with PDA and was used for preparation of PLA nanocomposites. The structure and morphology as well as thermal, combustion, and mechanical properties of the all PLA systems were investigated. The X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FE‐SEM) results indicated that the presence of PDA as surface modifier has been necessary for a desirable dispersion of hydroxyapatite (HA) nanoparticles in the PLA matrix. The thermal, combustion, and mechanical properties of the PLA system films were investigated using thermogravimetric analysis (TGA), microscale combustion calorimeter (MCC), and tensile test, respectively. The initial decomposition temperature and char residue of PLA containing 6 mass% of PDA along with 2 mass% HA nanoparticles were increased 20°C and 12% respectively, compared with that of the neat PLA. The peak of heat release rate was decreased from 566 W/g for the neat PLA to 412 W/g for PLA containing 2 mass% of PDA along with 6 mass% HA nanoparticles. By incorporation of only 2 mass% HA nanoparticles and 6 mass% of PDA, the tensile strength was obtained 51 MPa higher than that of the neat PLA.     

Coupled acid and enzyme mediated production of microcrystalline cellulose from corn cob and cotton gin waste

Microcrystalline cellulose has applications in food, pharmaceuticals, and other industries. Most microcrystalline cellulose (MCC) is produced from dissolving pulp using concentrated acids. We investigated steam explosion treatment of corn cobs and cotton gin waste for the production of microcrystalline cellulose. The corn cob was converted into a coarse brown powder after steam explosion and the lignin and residual hemicellulose fractions were extracted respectively with sodium hydroxide solution and water. The residual cellulose was readily bleached with hydrogen peroxide and converted to microcrystalline cellulose using hydrochloric acid, sulfuric acid and cellulase enzyme preparation. The resulting microcrystalline cellulose samples had properties that were similar to commercial microcrystalline cellulose. Similarly, cotton gin waste was steam exploded and converted into microcrystalline cellulose, but this material was more difficult to bleach using hydrogen peroxide. The degree of polymerization for the MCC samples ranged from 188.6 to 549.8 compared to 427.4 for Avicel PH101 MCC.     

Deposition of silver nanoparticles on cellulosic fibers via stabilization of carboxymethyl groups

The stabilizing role of carboxymethyl groups on the conformal deposition of Ag NPs over cellulosic fibers was elucidated while developing a method for the deposition of silver nanoparticles (NPs) on cellulose acetate (CA), cellulose and partially carboxymethylated cellulose (CMC) electrospun fibers. CMC fibers were prepared through judicious anionization of deacetylated cellulose acetate fibers. Ag NPs were chemically reduced from silver nitrate using sodium borohydride and further stabilized using citrate. Ag NPs were directly deposited onto CA, cellulose and CMC electrospun fibers at pH conditions ranging from 2.5 to 9.0. The resulting composites of Ag/fiber were characterized by field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX). The results revealed that the amount of Ag agglomerates and NPs deposited on CMC fibers was higher than that deposited on cellulose fibers at similar pH conditions, and that barely any Ag agglomerates or NPs were deposited on the CA fibers. These results implied that functional groups on the cellulose backbone played two important roles in the deposition of NPs as follows: (1) Hydrogen bonding was the main driving force for agglomeration of NPs when the medium pH was below 4.4, which corresponds to the pKa of carboxylic acid groups; (2) Carboxymethyl groups could replace citrate groups as stabilizers allowing the fabrication of a uniform and evenly distributed Ag NPs layer over CMC fibers at higher pH values. This report also highlights the importance of the substrate’s surface charge and that of the pH of the medium used, on the deposition of NPs. The composite of Ag NPs on CMC electrospun fibers appears to be a promising candidate for wound dressing applications due to its superior antibacterial properties originated by the uniform and even distribution of Ag NPs on the surface of the fibers and the wound healing aptness of the CMC fibers.     

Biodegradable electrospun poly(l-lactide) fibers containing antibacterial silver nanoparticles

Biodegradable poly(l-lactide) (PLA) ultrafine fibers containing nanosilver particles were prepared via electrospinning. Morphology of the Ag/PLA fibers and distribution of the silver nanoparticles were characterized. The release of silver ions from the Ag/PLA fibers and their antibacterial activities were investigated. These fibers showed antibacterial activities (microorganism reduction) of 98.5% and 94.2% against Staphylococcus aureus and Escherichia coli, respectively, because of the presence of the silver nanoparticles.     

Cellulose/silver nanoparticles composite microspheres: eco-friendly synthesis and catalytic application

Cellulose/silver nanoparticles (Ag NPs) composites were prepared and their catalytic performance was evaluated. Porous cellulose microspheres, fabricated from NaOH/thiourea aqueous solution by a sol–gel transition processing, were served as supports for Ag NPs synthesis by an eco-friendly hydrothermal method. The regenerated cellulose microspheres were designed as reducing reagent for hydrothermal reduction and also micro-reactors for controlling growth of Ag NPs. The structure and properties of obtained composite microspheres were characterized by Optical microscopy, UV–visible spectroscopy, WXRD, SEM, TEM and TG. The results indicated that Ag NPs were integrated successfully and dispersed uniformly in the cellulose matrix. Their size (8.3–18.6?nm), size distribution (3.4–7.7?nm), and content (1.1–4.9?wt%) were tunable by tailoring of the initial concentration of AgNO₃. Moreover, the shape, integrity and thermal stability were firmly preserved for the obtained composite microspheres. The catalytic performance of the as-prepared cellulose/Ag composite microspheres was examined through a model reaction of 4-nitrophenol reduction in the presence of NaBH₄. The composites microspheres exhibited good catalytic activity, which is much high than that of hydrogel/Ag NPs composites and comparable with polymer core–shell particles loading Ag NPs.     

The effect of halloysite nanotubes and N,N'- ethylenebis (stearamide) on the properties of polylactide nanocomposites with amorphous matrix

Amorphous polylactide/halloysite nanotube (PLA/HNT) nanocomposites were prepared and examined. Neat HNT and HNT treated with N,N'- ethylenebis(stearamide) (EBS) were used as nanofillers. The role of HNT and/or EBS content on the cold crystallization of amorphous PLA matrix, HNT dispersion, as well as on the dynamic mechanical and optical properties of the materials was determined.The PLA/HNT-based nanocomposites contained well-distributed nanotubes and occasionally micron-sized aggregates, especially at high loading. HNT, EBS treated HNT and EBS influenced the cold crystallization of PLA, therefore the formation of the disorder α′ and the order α crystallographic forms of PLA.The nanocomposites exhibited increased stiffness and decreased transparency compared to the neat PLA. Due to the reinforcing effect and additional specific features of HNT, the addition of the nanofiller allows tuning of the properties of the nanocomposites with amorphous PLA matrix.     

Nano cellulose particles covered with block copolymer of cellulose and methyl methacrylate produced by solid mechano chemical polymerization

Nano cellulose particles covered with a block copolymer of microcrystalline cellulose and poly(methyl methacrylate) (MCC-block-PMMA) were produced by a solid mechano-chemical polymerization. The polymerization of methyl methacrylate was initiated by chain-end-type microcrystalline cellulose (MCC) radicals (i.e., MCC mechano radicals) on the surface of MCC that were induced by mechanical fracture of β-1,4 glycosidic linkages. The chemically modified cellulose particles with MCC-block-PMMA were fractionated by Soxhlet extraction with chloroform, and resulted in MCC-block-PMMA residue from residue on the filter and MCC-block-PMMA filtrate from filtrate solution. The surface of the MCC particles chemically modified with MCC-block-PMMA in MCC-block-PMMA residue was partially covered with PMMA chains of the MCC-block-PMMA. In contrast, the surfaces of the MCC nanoparticles chemically modified with MCC-block-PMMA in MCC-block-PMMA filtrate were fully covered with PMMA chains of the MCC-block-PMMA. A dispersion of the chemically fully modified MCC nanoparticles in chloroform was optically transparent. The average diameter of the chemically fully modified MCC nanoparticles in chloroform was estimated to be 52 nm. These were confirmed by electron spin resonance, Fourier transform infrared, and ¹H nuclear magnetic resonance spectroscopy, by gel permeation chromatography and dynamic light scattering.     

Preparation and characterization of Ag‐deposited aminosilane‐modified silicate by chemical reduction method

Nanocomposites based on silver (Ag) and organically modified silicate (Ormosil) were prepared by an in situ reduction method, in which silver nitrate, tetraethoxysilane and N‐[3‐(trimethoxysilyl)propyl]diethylenetriamine (ATS) acted as precursor, linker, and colloidal suspension stabilizer, respectively. The objective of the study was to produce silver nanoparticles through AgNO₃ chemical reduction in a continuous media, in which aminosilanes act as superficial modifiers of Ag nanoparticles, inhibiting their growth and preventing aggregation. The physical properties of the Ormosil/Ag composites were examined using NMR, electron spin resonance, scanning electron microscope, transmission electron microscope, and thermal gravimetric analysis spectroscopy, the results of which indicated that Ag was incorporated in the Ormosil matrix after impregnation. The Ag content and surface morphology of the Ormosil/Ag composites depended on the initial concentration of AgNO₃. The antibacterial effects of the Ormosil/Ag composites were assessed by the zone of inhibition and plate‐counting methods, and an excellent antibacterial performance was discovered. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Mechanisms of Diffusion-Reduction Interaction of Microcrystalline Cellulose and Silver Ions

The preparation of microcrystalline cellulose samples containing intercalated silver(0) particles includes two main stages: diffusion of silver ions from aqueous AgNO₃ into the microcrystalline cellulose matrix, followed by reduction of the silver ions bound to cellulose macromolecules to Ag(0) and growth of Ag(0) particles inside the cellulose matrix and on its surface. Mechanisms of interaction of silver ions with cellulose as reducer and with other reducers and ligands are considered.     

Efficient barrier properties of mechanically enhanced agro-extracted cellulosic biocomposites

The objective of this work was to prepare the mechanically stable hydrophobic biocomposites by incorporating the cellulose fibers into the polymer matrices for their applications in biomedical and food packaging. Herein, two different types of biocomposites were prepared by mixing polylactic acid (PLA) and polyhydroxybutyrate (PHB) with the agro-extracted cellulose, separately at 170 °C. The influence of the cellulose fibers on the thermal, mechanical, and barrier properties of polymer matrices (PLA and PHB) was observed. With an increase in the cellulose content in PLA and PHB, the tensile strength of the biocomposite materials significantly improved with the enhancement of 24.45% and 32.08%, respectively, compared with the pure PLA and PHB. Furthermore, a decrease of 74.16% and 73.49% in the water vapor transmission rate and oxygen transmission rate, respectively, was observed for cellulose/PHB biocomposites. This study highlights that adding cellulose fibers significantly improves the mechanical and the barrier properties of PLA and PHB, suggesting their biocomposites for use in biodegradable polymer industries.     

Green fabrication of thermally-stable oxidized cellulose nanocrystals by evolved Fenton reaction and in-situ nanoreinforced thermoplastic starch

Cellulose - High performance fibers and improved interfacial interaction can enhance the properties of polymer composites. Herein, microcrystalline cellulose (MCC) was oxidized by H2O2/CuSO4, a new...     

One-pot synthesis of biofoams from castor oil and cellulose microfibers for energy absorption impact materials

The use of renewable feedstocks in foam technology has created a worldwide demand for more sustainable materials. Castor oil is a vegetable oil, composed mainly of triricinoglycerol, a natural polyol, suitable for polyurethane foam production. In this study, castor oil and variable amounts of microcrystalline cellulose (MCC) fibers were used in a straightforward one-pot synthesis approach for the preparation of novel biofoams. The ensuing biofoams were characterized by several techniques, including attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis, and their mechanical performance was evaluated by compression mechanical testing and by dynamic mechanical thermal analysis. They were (semi-) flexible, with a cell-like morphology and reinforced toughness due to the use of MCC. They had a Young’s modulus varying between 0.188 and 1.06 MPa depending on the amount of MCC used and were thermally stable up to 267 °C. The properties of these novel biofoams enable them to be strong candidates for use as tough, energy-absorbing foams, advantageously prepared using renewable-based resources.     

On the use of plant cellulose nanowhiskers to enhance the barrier properties of polylactic acid

Polylactic acid (PLA) nanocomposites were prepared using cellulose nanowhiskers (CNW) as a reinforcing element in order to asses the value of this filler to reduce the gas and vapour permeability of the biopolyester matrix. The nanocomposites were prepared by incorporating 1, 2, 3 and 5 wt% of the CNW into the PLA matrix by a chloroform solution casting method. The morphology, thermal and mechanical behaviour and permeability of the films were investigated. The CNW prepared by acid hydrolysis of highly purified alpha cellulose microfibers, resulted in nanofibers of 60–160 nm in length and of 10–20 nm in thickness. The results indicated that the nanofiller was well dispersed in the PLA matrix, did not impair the thermal stability of this but induced the formation of some crystallinity, most likely transcrystallinity. CNW prepared by freeze drying exhibited in the nanocomposites better morphology and properties than their solvent exchanged counterparts. Interestingly, the water permeability of nanocomposites of PLA decreased with the addition of CNW prepared by freeze drying by up to 82% and the oxygen permeability by up to 90%. Optimum barrier enhancement was found for composites containing loadings of CNW below 3 wt%. Typical modelling of barrier and mechanical properties failed to describe the behaviour of the composites and appropriate discussion regarding this aspect was also carried out. From the results, CNW exhibit novel significant potential in coatings, membranes and food agrobased packaging applications.