Crystallization kinetics and morphology of small concentrations of cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) melt-compounded into poly(lactic acid) (PLA) with plasticizer

Enhancement of PLA crystallization, transparency, and strength by adding the long aliphatic chains grafted CNC

The combination of crystallization, transparency, and strength is still a challenge for broadening the application of polylactic acid (PLA) films, while it is also difficult to balance. In this work, the long aliphatic chains of octadecylamine (ODA) were grafted onto the surface of cellulose nanocrystal (CNC) by tannic acid oxidation self-polymerization and Michael addition/Schiff base reaction between polytannic acid and ODA. Furthermore, the ODA grafted CNC (g-CNC) was used as green reinforcement for the PLA matrix and a series of PLA/g-CNC nanocomposite films were prepared by the casting method. The DSC, WAXD, POM, UV-vis and stretching test were employed to examine the effect of g-CNC on the properties of the as-prepared PLA/g-CNC nanocomposite films. It shows that the g-CNC is effective to improve the melt crystallization rate of PLA from 11 min to 7.3 min. Most importantly, the crystal size of the PLA spherulites was significantly reduced due to the well dispersion in the amorphous PLA matrix, which would effectively improve the transmittance of the PLA films and synchronously realize the combination of crystallization (62 %) and transparency (80.6 %). Moreover, the improved crystallization could also enhance the heat deformation performance of the PLA films since the heat resistance is closely associated with the crystallinity. Besides, the grafted ODA long chains improve the compatibility between CNC and PLA, leading to the reinforcement of PLA matrix, where the tensile strength reaches 65.05 MPa from 44.31 MPa. Compared with the pristine CNC, the addition of g-CNC makes more comprehensive improvement in the properties of the PLA films.

In-situ self-reinforcement of amorphous polylactide (PLA) through induced crystallites network and its highly ductile and toughened PLA/poly(butylene adipate-co-terephthalate) (PBAT) blends

Crystallites of a semicrystalline polylactide (cPLA) were induced in an amorphous PLA (aPLA) and its blends with poly(butylene adipate-co-terephthalate) (PBAT) to achieve in-situ self-reinforced PLA based structures. The approach involved the melt blending of cPLA as a minor phase with aPLA and its blends with PBAT at processing temperatures below the crystal melting peak of cPLA. An injection molding (IM) process was first adopted to obtain self-reinforced PLA (SR-PLA) structures at aPLA/cPLA weight ratios of 100/0, 95/5, 90/10, 85/15, and 80/20. IM barrel and mold temperatures revealed crucial impacts on preserving the cPLA crystallites and thereby enhancing the final mechanical performance of SR-PLA (i.e., aPLA/cPLA) samples. SR-PLA samples at various aPLA/cPLA weight ratios of 100/0, 90/10, 80/20, and 70/30 were then melt blended with PBAT to produce SR-PLA/PBAT at a given ratio of 85/15. These blends were first prepared in an internal melt mixer (MM) to evaluate the rheological properties. The rheological analysis confirmed the significance of cPLA reinforcing efficiency within SR-PLA and its corresponding blends with PBAT. Similar SR-PLA/PBAT blends were also prepared using the IM process to explore their thermal and mechanical characteristics. The effect of cPLA concentrations in blends was distinctive, leading to significant enhancements in stain at break and toughness values. This was due to the increased crystallite network within the matrix, further refining PBAT droplets. Morphological analysis of the melt-processed blends through MM and IM also revealed that the PBAT droplets were further refined when the IM process was applied. The induced shear during the molding could have further elongated the cPLA crystallites towards a fiberlike structure, which could additionally cause the matrix viscosity to increase and refine the PBAT droplets.

Cellulose-Reinforced Polylactic Acid Composites for Three-Dimensional Printing Using Polyethylene Glycol as an Additive: A Comprehensive Review

Growing concerns about environmental issues and global warming have garnered increased attention in recent decades. Consequently, the use of materials sourced from renewable and biodegradable origins, produced sustainably, has piqued the interest of scientific researchers. Biodegradable and naturally derived polymers, such as cellulose and polylactic acid (PLA), have consistently been the focus of scientific investigation. The objective is to develop novel materials that could potentially replace conventional petroleum-based polymers, offering specific properties tailored for diverse applications while upholding principles of sustainability and technology as well as economic viability. Against this backdrop, the aim of this review is to provide a comprehensive overview of recent advancements in research concerning the use of polylactic acid (PLA) and the incorporation of cellulose as a reinforcing agent within this polymeric matrix, alongside the application of 3D printing technology. Additionally, a pivotal additive in the combination of PLA and cellulose, polyethylene glycol (PEG), is explored. A systematic review of the existing literature related to the combination of these materials (PLA, cellulose, and PEG) and 3D printing was conducted using the Web of Science and Scopus databases. The outcomes of this search are presented through a comparative analysis of diverse studies, encompassing aspects such as the scale and cellulose amount added into the PLA matrix, modifications applied to cellulose surfaces, the incorporation of additives or compatibilizing agents, variations in molecular weight and in the quantity of PEG introduced into the PLA/cellulose (nano)composites, and the resulting impact of these variables on the properties of these materials.

Investigation on Nanocomposites of Polysulfone and Different Ratios of Graphene Oxide with Structural Defects Repaired by Cellulose Nanocrystals

In this manuscript, nanofillers of graphene oxide (GO) and cellulose nanocrystal (CNC) with different weight ratios (G/C ratios), named GC 2:1, GC 4:1, GC 8:1, GC 16:1, and GC 32:1, were successfully prepared. Characterization methods such as Raman spectroscopy, X-ray photoelectron spectrometry (XPS), and thermogravimetric analysis (TGA) were performed. Additionally, the effects of these samples on the thermal stability, mechanical properties, and gas barrier properties of polysulfone (PSF) nanocomposites were investigated. A hydrophilic interaction took place between CNC and GO; as a consequence, CNCs were modified on the surface of GO, thus repairing the structural defects of GO. With the increase in G/C ratios, the repair effect of insufficient CNCs on the defects of GO decreased. The G/C ratio had a great influence on the improvement of mechanical properties, thermal stability, and gas barrier properties of nanocomposites. Compared with PSF/GC 2:1 and PSF/GC 32:1, the differences in the growth rates of tensile strength, elongation at break, and Young's modulus were 30.0%, 39.4%, and 15.9%, respectively; the difference in Td 3% was 7 °C; the difference in decline rate of O2 permeability was 40.0%.

Probing into the nucleation and reinforcing effects of poly (vinyl acetate) grafted cellulose nanocrystals in melt-processed poly (lactic acid) nanocomposites

Blending poly (lactic acid) (PLA) with cellulose nanocrystals (CNCs) to fabricate nanocomposites is a valuable strategy to improve the properties of PLA without sacrificing its biodegradability. However, the nucleation and reinforcing mechanisms of CNCs for semi-crystalline PLA matrix are still elusive in melt-processed PLA/CNC nanocomposites. Herein, poly (vinyl acetate) (PVAc) chains were grafted onto the surface of CNCs via an efficient radical polymerization in an aqueous medium, making CNCs suitable for conventional melting processing techniques. It is found that the dispersion state of CNCs in the PLA matrix and the interface interaction between PLA and CNCs can be tailored by varying the PVAc grafting density. Further studies show that well-dispersed CNCs play a positive role in reinforcing PLA. But unexpectedly, the nucleation effect is suppressed even though the homogeneous dispersion of CNCs is achieved with higher PVAc grafting density because the rich PVAc chains at the interface dilute the PLA chains, thus hindering the nucleation and spherulite growth of PLA. This research sheds light on the nucleation and reinforcing mechanisms of polymer grafted CNCs, and will provide theoretical guidance for the industrialization of high-performance bio-based nanocomposites.

Improved thermal insulation and compressive property of bimodal poly (lactic acid)/cellulose nanocomposite foams

In this work, an innovative PLA/CNF nanocomposite foam with a bimodal cell structure is prepared by a simple one-step depressurization foaming process using only supercritical carbon dioxide (ScCO₂) as the foaming agent. Only at a specific foaming temperature, PLA/CNF nanocomposites foam with a bimodal cell structure could be obtained. According to the different crystallization kinetics and nucleation efficiency of samples, it was inferred that the crystallization rate and phase interface would affect the cell structure. The prepared PLA/CNF nanocomposite foam with a bimodal cell structure had an expansion ratio as high as 20 times and thermal conductivity of 0.041 w m^-1 k^-1, which exhibited low density and excellent thermal-insulation property. Meanwhile, the PLA/CNF nanocomposite foam exhibited excellent compression performance due to the presence of CNFs, which showed promising application in packaging and construction materials.

Biobased nucleation agents for poly-L-(lactic acid) - Effect on crystallization, rheological and mechanical properties

In the present work, the nucleating aptitude for poly-L-(lactic acid) (PLLA) of several biobased nanoparticles (NPs) with different morphologies and surface properties, including cellulose nanofibrils with and without lignin (LCNFs and CNFs) as well as cellulose, chitin and starch nanocrystals (CNCs, ChNCs and SNCs), was investigated. A single melt-processing step using a small amount of poly(ethylene glycol) (PEG) as carrier for the NPs was adopted to prepare films with the same nanofiller content of 1 wt%. The nucleation efficiency was investigated by differential scanning calorimetry using Avrami's and Lauritzen-Hoffman's secondary nucleation theory. The crystallization half-time was found to change considerably according to the morphology and surface properties of the NPs, with the lowest time observed for CNFs and CNCs, followed by ChNCs, SNCs and LCNFs. Comparing the surface energy components of the different nucleating agents, it was found that the nanofiller with the highest γ^p had the lowest t_1/2 and demonstrated the most effective nucleating aptitude. The evolution of the melt rheological properties of the different compositions, and the mechanical and optical properties of the films with and without a short annealing treatment were also studied.

Compositional Influence on the Morphology and Thermal Properties of Woven Non-Woven Mats of PLA/OLA/MgO Electrospun Fibers

In the present work, a statistical study of the morphology and thermal behavior of poly(lactic acid) (PLA)/oligomer(lactic acid) (OLA)/magnesium oxide nanoparticles (MgO), electrospun fibers (efibers) has been carried out. The addition of both, OLA and MgO, is expected to modify the final properties of the electrospun PLA-based nanocomposites for their potential use in biomedical applications. Looking for the compositional optimization of these materials, a Box−Wilson design of experiment was used, taking as dependent variables the average fiber diameter as the representative of the fiber morphologies, as well as the glass transition temperature (Tg) and the degree of crystallinity (Xc) as their thermal response. The results show <r2> values of 73.76% (diameter), 88.59% (Tg) and 75.61% (Xc) for each polynomial fit, indicating a good correlation between both OLA and MgO, along with the morphological as well as the thermal behavior of the PLA-based efibers in the experimental space scanned.

Self-healable nanocellulose composite hydrogels combining multiple dynamic bonds for drug delivery

Herein, we developed two nanocomposite polysaccharide hydrogels TPP-CNC and TPP-CNF via simple mixing method, which were constructed with multiple dynamic bonds. The microstructural features, mechanical properties, rheological properties, healable ability and biocompatibility of the complex hydrogels were evaluated. The TPP-CNC and TPP-CNF complex hydrogels exhibited higher tensile strength than pure polysaccharide hydrogel, from ~259 KPa to ~890 KPa and ~910 KPa, respectively, that was attributed to the contribution of ionic crosslinked network and hydrogen bonds. In addition, the hydrogels indicated superior fatigue resistance and high energy dissipation ratio during loading-unloading tests because of the physical sacrifice bonds, which also decreased the self-healing time at room temperature (~15 min). More importantly, the drug loaded nanocomposite hydrogels showed sustained release, reduction burst release, increased release under acidic environment, and the drug release kinetics belonged to Fickian diffusion mechanism. Therefore, the nanocellulose polysaccharide hydrogels have the highly promising to explore as biomaterials for drug delivery.

Recent Developments in Cellulose Nanomaterial Composites

Cellulose nanomaterials (CNMs) are a class of materials that have recently garnered attention in fields as varied as structural materials, biomaterials, rheology modifiers, construction, paper enhancement, and others. As the principal structural reinforcement of biomass giving wood its mechanical properties, CNM is strong and stiff, but also nontoxic, biodegradable, and sustainable with a very large (Gton yr^-1 ) source. Unfortunately, due to the relatively young nature of the field and inherent incompatibility of CNM with most man-made materials in use today, research has tended to be more basic-science oriented rather than commercially applicable, so there are few CNM-enabled products on the market today. Herein, efforts are presented for preparing and forming cellulose nanomaterial nanocomposites. The focus is on recent efforts attempting to mitigate common impediments to practical commercialization but is also placed in context with traditional efforts. The work is presented in terms of the progress made, and still to be made, on solving the most pressing challenges-getting properties that are competitive with currently used materials, removing organic solvent, solving the inherent incompatibility between CNM and polymers of interest, and incorporation into commonly used industrial processing techniques.

Effect of Cellulose and Cellulose Nanocrystal Contents on the Biodegradation, under Composting Conditions, of Hierarchical PLA Biocomposites

In this work, the effect of microfibrillated cellulose (MFC) and cellulose nanocrystals (CNCs) on the biodegradation, under composting conditions, of hierarchical PLA biocomposites (HBCs) was studied using a full 2² factorial experimental design. The HBCs were prepared by extrusion processing and were composted for 180 days. At certain time intervals, the specimens were removed from the compost for their chemical, thermal and morphological characterizations. An ANOVA analysis was carried out at different composting times to study MFC and CNCs’ effects on biodegradation. The specimen’s mass loss and molecular weight loss were selected as independent variables. The results show that the presence of MFC enhances the PLA biodegradation, while with CNCs it decreases. However, when both cellulosic fibers are present, a synergistic effect was evident—i.e., in the presence of the MFC, the inclusion of the CNCs accelerates the HBCs biodegradation. Analysis of the ANOVA results confirms the relevance of the synergistic role between both cellulosic fibers over the HBC biodegradation under composting conditions. The results also suggest that during the first 90 days of incubation, the hydrolytic PLA degradation prevails, whereas, beyond that, the enzymatic microbial biodegradation dominates. The SEM results show MFC’s presence enhances the surface biodeterioration to a greater extent than the CNCs and that their simultaneous presence enhances PLA biodegradation. The SEM results also indicate that the biodegradation process begins from hydrophilic cellulosic fibers and promotes PLA biodegradation.

Structure-Property Relationship of Cellulose Nanocrystal-Polyvinyl Alcohol Thin Films for High Barrier Coating Applications

CO₂ and O₂ gas permeability are paramount concerns in food packaging. Here, the permeability of cellulose nanocrystals (CNCs) and polyvinyl alcohol (PVA) coatings was explored as it relates to varied CNC content. Specifically, this work focuses on the role of PVA in rheology and barrier performance of the CNC films. Results show that shear-casted CNC films are transparent and have a high-order parameter, which is attributed to the shear-thinning behavior of the CNCs. The barrier performance of the CNC films improved because of the synergistic effect of having both alignment of CNCs and a lower free volume. The CNC-PVA films exhibited excellent barrier performance as compared to traditional engineered polymers, even much higher than high barrier ethylene-vinyl alcohol copolymer films. Furthermore, the moisture sensitivity of the films was greatly diminished with the addition of PVA. Overall, the results show applicability of CNC-PVA coating formulations for high barrier packaging applications.

Biodegradable Poly(Lactic Acid) Nanocomposites for Fused Deposition Modeling 3D Printing

3D printing by fused deposition modelling (FDM) enables rapid prototyping and fabrication of parts with complex geometries. Unfortunately, most materials suitable for FDM 3D printing are non-degradable, petroleum-based polymers. The current ecological crisis caused by plastic waste has produced great interest in biodegradable materials for many applications, including 3D printing. Poly(lactic acid) (PLA), in particular, has been extensively investigated for FDM applications. However, most biodegradable polymers, including PLA, have insufficient mechanical properties for many applications. One approach to overcoming this challenge is to introduce additives that enhance the mechanical properties of PLA while maintaining FDM 3D printability. This review focuses on PLA-based nanocomposites with cellulose, metal-based nanoparticles, continuous fibers, carbon-based nanoparticles, or other additives. These additives impact both the physical properties and printability of the resulting nanocomposites. We also detail the optimal conditions for using these materials in FDM 3D printing. These approaches demonstrate the promise of developing nanocomposites that are both biodegradable and mechanically robust.

Influence of Free Volume Determined by Positron Annihilation Lifetime Spectroscopy (PALS) on Gas Permeability of Cellulose Nanocrystal Films

Cellulose nanocrystals (CNCs) are of increasing interest for packaging applications because of their biodegradability, low cost, high crystallinity, and high aspect ratio. The objective of this study was to use positron annihilation lifetime spectroscopy (PALS) to investigate the free volume of CNC films with different structural arrangements (chiral nematic vs shear-oriented CNC films) and relate this information to gas barrier performance. It was found that sheared CNC films with higher CNC alignment have lower free volume and hence have more tortuosity than chiral nematic self-assembled films, which lowers gas diffusion throughout the films. The overall barrier performance of the aligned CNC film obtained in this study has a higher barrier performance than high barrier polymer films like PVOH and EVOH. Furthermore, a modified model was developed for single-component CNC films to predict the gas permeability with variation of CNC alignment with validation by the data taken.