The Effects of the Deacetylation of Chitin Nanowhiskers on the Performance of PCL/PLA Bio-Nanocomposites.

The multiple roles of organic nanofillers in biodegradable nanocomposites (NC) with a blend-based matrix is not yet fully understood. This work highlights combination of reinforcing and structure-directing effects of chitin nanowhiskers (CNW) with different degrees of deacetylation (DA), i.e., content of primary or secondary amines on their surface, in the nanocomposite with the PCL/PLA 1:1 matrix. Of importance is the fact that aminolysis with CNW leading to chain scission of both polyesters, especially of PLA, is practically independent of DA. DA also does not influence thermal stability. At the same time, the more marked chain scission/CNW grafting for PLA in comparison to PCL, causing changes in rheological parameters of components and related structural alterations, has crucial effects on mechanical properties in systems with a bicontinuous structure. Favourable combinations of multiple effects of CNW leads to enhanced mechanical performance at low 1% content only, whereas negative effects of structural changes, particularly of changed continuity, may eliminate the reinforcing effects of CNW at higher contents. The explanation of both synergistic and antagonistic effects of structures formed is based on the correspondence of experimental results with respective basic model calculations.

Preparation and performance of bionanocomposites based on grafted chitosan, GO and TiO2-NPs for removal of lead ions and basic-red 46.

Wastewater rich in heavy metals and organic compounds represents one of the essential environmental pollutants. Therefore, a practical approach is to fabricate eco-friendly polymer-based systems with a high ability to absorb pollutants. Herein, bionanocomposites consisting of chitosan (Cs) grafted by various monomers, such as acrylamide (Am), acrylic acid (AA), and 4-styrene sulfonic acid (SSA), and hybrid nanoparticles of graphene oxide/titanium dioxide nanoparticles (GO@TiO2-NPs) were fabricated. The prepared nanomaterials and bionanocomposites characterized via various tools. The data illustrated that the prepared GO had a thickness of 10 nm and TiO2-NPs had a diameter of 25 nm. In addition, the grafted chitosan (gCs) using Am and SSA had the largest surface area (gCs2; 22.89 nm) and its bionanocomposite (NC5; 104.79 nm). In addition, the sorption ability of the 0.15 g of prepared bionanocomposites to the (100 mg/L) of lead ions (Pb2+) and (25 mg/L) of basic-red 46 (BR46) under various conditions has been studied. The results showed that gCs3 and NC5 had the highest adsorption of Pb2+ (79.54 %) and BR46 (79.98 %), respectively. The kinetic study results of the sorbents obeyed the Pseudo second-order model. In contrast, the isothermal study followed the Freundlich adsorption model for Pb2+ and the Langmuir adsorption model for BR46.

Effect of Polydopamine Coating of Cellulose Nanocrystals on Performance of PCL/PLA Bio-Nanocomposites.

In bio-nanocomposites with a poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) matrix with neat and polydopamine (PDA)-coated cellulose nanocrystals (CNCd), the use of different mixing protocols with masterbatches prepared by solution casting led to marked variation of localization, as well as reinforcing and structure-directing effects, of cellulose nanocrystals (CNC). The most balanced mechanical properties were found with an 80/20 PLA/PCL ratio, and complex PCL/CNC structures were formed. In the nanocomposites with a bicontinuous structure (60/40 and 40/60 PLA/PCL ratios), pre-blending the CNC and CNCd/PLA caused a marked increase in the continuity of mechanically stronger PLA and an improvement in related parameters of the system. On the other hand, improved continuity of the PCL phase when using a PCL masterbatch may lead to the reduction in or elimination of reinforcing effects. The PDA coating of CNC significantly changed its behavior. In particular, a higher affinity to PCL and ordering of PLA led to dissimilar structures and interface transformations, while also having antagonistic effects on mechanical properties. The negligible differences in bulk crystallinity indicate that alteration of mechanical properties may have originated from differences in crystallinity at the interface, also influenced by presence of CNC in this area. The complex effect of CNC on bio-nanocomposites, including the potential of PDA coating to increase thermal stability, is worthy of further study.

Carboxymethyl cellulose-hydrogel embedded with modified magnetite nanoparticles and porous carbon: Effective environmental adsorbent.

Adsorption is the most efficient technique for the removal of metal ions and organic dyes from water. This stimulates demand for the preparation of eco-friendly adsorbents. In this study, magnetic hydrogels based on a crosslinked carboxymethyl cellulose grafted acrylamide (CMC-g-AM) embedded with porous carbon (PC) and citric acid-modified magnetite were prepared. PC was synthesized via single-step oxidation of bagasse under muffled atmosphere condition. The magnetite (Fe3O4) nanoparticles were synthesized using the co-precipitation method (Fe2+/Fe3+) and citric acid modification (CFe). Functionality and parameters of adsorbent were characterized by infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray. The magnetic hydrogels have a highly effective performance for Pb-ions and methylene blue dye (MB) removal from water due to the unique role of crosslinked CMC matrix in supporting synergy between embedded PC and CFe. Adsorption testing using time intervals (5-120 min) and Pb-ions and MB concentrations (5-500 mg/L) indicate that CMC-g-AM containing equal content of PC and CFe has substantially higher removal efficiency; 70.8 and 96.1 % against 47.8 and 30.2 % (without PC and CFe) for Pb-ions and MB adsorption respectively for CMC-g-AM. The equilibrium time and the maximum sorption capacity (qm) from the adsorption studies were found to be 60 and 30 min and 294.1 and 222.2 mg/g for Pb-ions and MB respectively. The kinetics and isotherms were studied to highlight the adsorption rate and mechanism of the adsorption process.

Synergistic effects in Methylcellulose/Hydroxyethylcellulose blend: Influence of components ratio and graphene oxide.

A specific feature of water-soluble polysaccharides is formation of organized structures in solutions. This study deals with an unexpected effect of 2-hydroxyethylcellulose (HEC) on structure and mechanical performance of methylcellulose (MC) films. The values of modulus with 5 and 10 % HEC content exceed those of the linear model, which indicates synergistic effect consisting in formation of ordered structures. However, higher content of HEC leads to worse properties corresponding to contribution of its lower parameters. The structural transformations are confirmed by XRD and polarized-light microscopy. Ability of HEC to support formation of ordered structures in MC solutions is indicated by rheology. Important fact is that low graphene oxide (GO) content has a high reinforcing effect on neat MC or HEC, but its presence in blends is accompanied by elimination of HEC-induced structural transformations. The results confirm complex effect of blending and GO on structure and properties of the MC/HEC system.

Nano-modified epoxy: the effect of GO-based complex structures on mechanical performance.

The application of nanofillers (NFs) in multicomponent polymer systems is accompanied by important structure-directing effects that are more marked in partially miscible systems, such as polymer-modified epoxy. This study deals with rubber-modified epoxy using different combinations of GO and amine-terminated butadiene-acrylonitrile copolymer (ATBN), including in situ and pre-made grafting. Moreover, GO grafted via planar epoxy groups or solely edge-localized carboxyls was used. It is shown that the grafted ATBN chains promote the assembly of GO-g-ATBN into nacre-mimicking lamellar structures instead of usual exfoliation in thermoplastics. This complex structure of elastically embedded GO leads to the best mechanical performance. It is obvious that a small concentration of the grafted polymer exceeds the contribution of a higher concentration of separately added ATBN. The results highlight the important effect of the degree of grafted chains and geometry of the internal structure of the self-assembled arrays and their effect on the mechanical performance.

Facile preparation of biocompatible poly (lactic acid)-reinforced poly(ε-caprolactone) fibers via graphite nanoplatelets -aided melt spinning.

Addition of high-aspect-ratio (AR) nanofillers can markedly influence flow behavior of polymer systems. As a result, application of graphite nanoplatelets (GNP) allows preparation of microfibrillar composites (MFC) based on PCL matrix reinforced with in-situ generated PLA fibrils. This work deals, for the first time, with preparation of analogous melt-drawn fibers. Unlike other blend-based fibers, the spinning and melt drawing leads to structure of deformed inclusions due to unfavorable ratio of rheological parameters of components. Subsequent moderate cold drawing of the system with dissimilar deformability of components causes strengthening with PLA fibrils. Unexpectedly, high velocity and extent of cold drawing leads to structure with low-AR inclusions, similar to the original melt-drawn blend. Extensive fast deformation of the soft PCL matrix does not allow sufficient stress transfer to rigid PLA. In spite of peculiarities found, the GNP-aided melt spinning allows facile preparation of biodegradable biocompatible fibers with wide range of diameters (80-400 µm) and parameters (2.35-18 cN/tex).

Graphite nanoplatelets-modified PLA/PCL: Effect of blend ratio and nanofiller localization on structure and properties.

Structure and properties of poly(lactic acid) (PLA)/poly (ɛ-caprolactone) (PCL) influenced by graphite nanoplatelets (GNP) were studied in dependence on blend composition. Electron microscopy indicates predominant localization of GNP in PCL. GNP-induced changes in viscosity hinder refinement of PCL inclusions, support PCL continuity in the co-continuous system, and lead to reduction of PLA inclusions size without GNP being present at the interface in the PCL-matrix blend. Negligible differences in crystallinity of both phases indicate that mechanical behaviour is mainly influenced by reinforcement and GNP-induced changes in morphology. Addition of 5 parts of GNP leads to ~40% and ~25% increase of stiffness in the PCL- and PLA-matrix systems, respectively, whereas the reinforcing effect is practically eliminated in the co-continuous systems due to GNP-induced lower continuity of PLA which enhances toughness. Impact resistance of the 80/20 blend shows increase with 5 parts content due to synergistic effect of PCL/GNP stacks, whereas minor increase in the blend of the ductile PCL matrix with brittle PLA inclusions is caused by GNP-modification of the component parameters. Results indicate high potential of GNP in preparing biocompatible systems with wide range of structure and properties.

Composite films prepared from agricultural by-products.

In our study we used holocelluloses from sugar beet and bagasse for film preparation. Films from sugar beet holocellulose have better mechanical properties than from bagasse holocellulose. By subsequent carboxymethylation of bagasse holocellulose, films with better properties were produced. Specimens prepared from combined sugar beet and bagasse carboxymethylated holocellulose had the best mechanical properties. The results could be explained by the ratios of cellulose, arabinan, polygalacturonan and xylan content in individual films, based on the elemental analysis data. The use of microwaves to prepare holocellulose film speed up the process, but negatively affected the mechanical properties. Lignin content of the sugar beet holocellulose and bagasse samples was low and did not affect the mechanical properties. Both types of agricultural by-products could be used for preparation of composite film with high strength and stiffness suitable for broad range of applications.

Cationization of heparin for film applications.

Trimethylammonium-2-hydroxypropyl-(TMAHP) spacer was introduced into heparin (H) and the prepared films were characterized by elemental analysis, NMR, SEC-MALS, TG/DTG/DTA, AFM and mechanical tester. When quaternized at the ratio of H/NaOH/alkylating agent/H2O=0.1-1/0-2/0.1-1/50-500 mmol, H was substituted at A6 and A3 positions. The formation of double-substituted structures by substitution of free hydroxyl group of the previously introduced TMAHP substituent is evident. In the absence of NaOH (H/GTMAC/H2O=1:1:500) the most drastic decrease of M(n) to 8.639 kg/mol and M(w)/M(n) at 1.48 was observed in comparison to H (Mn=9532 g/mol with M(w)/M(n)=1.38). The film mechanical properties were better on H (E=4030 MPa; σ(b)=65 MPa; ɛ(b)=4.6%) than on quaternized specimens (E=2500-3340 MPa; σ(b)=25-40 MPa; ɛ(b)=1.7-1.8%). The AFM images did not prove relation between mechanical properties and surface shape.

Carboxymethylated-, hydroxypropylsulfonated- and quaternized xylan derivative films.

Under alkaline/water conditions carboxymethyl, 2-hydroxypropylsulfonate and trimethylammonium-2-hydroxypropyl groups were introduced into xylan in one step with the goal to prepare film specimens. The materials were characterized by NMR, SEC-MALS, TG/DTG/DTA, AFM and mechanical testing. The properties of triple, double and mono-substituted materials were compared. The numerical molar masses of the specimens were from 12.3 to 17.6 kg/mol with Mw/Mn from 1.27 to 1.34. The elastic modulus values are decreasing in order: xylan (X; 7354 MPa)>carboxymethyl xylan (CX; 6090MPa)>2-hydroxypropylsulfonate xylan (SX; 6000 MPa)>carboxymethyl/2-hydroxypropylsulfonate xylan (CSX; 4490 MPa)>quaternized xylan (QX; 3600 MPa)>carboxymethyl/quaternary/2-hydroxypropylsulfonate xylan (CQSX; 3380 MPa)>carboxymethyl/quaternary xylan (CQX; 2805 MPa). The onset temperatures of SX (214°C), CQSX (212°C), QSX (211°C) and CQX (207°C) were higher than for X (205°C). The roughness values of the film surfaces (3.634-18.667 nm) are higher on top than on the bottom of the specimen.

Quaternized and sulfated xylan derivative films.

Xylan quaternized sulfate films were prepared from beech xylan (X) and compared with fully sulfated xylan films (XS). When quaternized xylan (QX) was prepared in the first step (DS(Q)=0.55), than by sulfation of QX in the second step the fully substituted ampholytic derivative (QXS; DS(Q)=0.33; DS(S)=1.67) could be obtained. By sulfation in first step, xylan sulphate (SX, DS(S)=0.70) was obtained and by subsequent quaternization, SXQ film with DSQ=0.55 and DSS=0.33 which contained partially unsubstituted hydroxyls. The molar masses (M(n)) of the film's soluble parts were increasing in order X