Comparison of polyolefin biocomposites prepared with waste cardboard, microcrystalline cellulose, and cellulose nanocrystals via solid-state shear pulverization

Polylactic Acid Chemical Foaming Assisted by Solid-State Processing: Solid-State Shear Pulverization and Cryogenic Milling

A chemical foaming process of polylactic acid (PLA) was developed via the solid-state processing methods of solid-state shear pulverization (SSSP) and cryogenic milling. Based on the ability of solid-state processing to enhance the crystallization kinetics of PLA, chemical foaming agents (CFA) are first compounded before foaming via compression molding. Specifically, the effects of the pre-foaming solid-state processing method and CFA concentration were investigated. Density reduction, mechanical properties, thermal behavior, and cell density of PLA foams are characterized. Solid-state processing of PLA before foaming greatly increases the extent of PLA foaming by achieving void fractions approximately twice that of the control foams. PLA's improved ability to crystallize is displayed through both dynamic mechanical analysis and differential scanning calorimetry. The solid-state-processed foams display superior mechanical robustness and undergo low stress relaxation. The cell density of the PLA foams also increases with solid-state processing, especially through SSSP. Additionally, crosslinking of PLA during the pre-foaming processing step is found to result in the greatest enhancement of crystallization but decreased void fraction and foam effectiveness. Overall, SSSP and cryogenic milling show significant promise in improving chemical foaming in alternative biopolymers.

Effect of Microwave Plasma Pre-Treatment on Cotton Cellulose Dissolution

The utilization of cellulose to its full potential is constrained by its recalcitrance to dissolution resulting from the rigidity of polymeric chains, high crystallinity, high molecular weight, and extensive intra- and intermolecular hydrogen bonding network. Therefore, pretreatment of cellulose is usually considered as a step that can help facilitate its dissolution. We investigated the use of microwave oxygen plasma as a pre-treatment strategy to enhance the dissolution of cotton fibers in aqueous NaOH/Urea solution, which is considered to be a greener solvent system compared to others. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, and Powder X-ray Diffraction analyses revealed that plasma pretreatment of cotton cellulose leads to physicochemical changes of cotton fibers. Pretreatment of cotton cellulose with oxygen plasma for 20 and 40 min resulted in the reduction of the molecular weight of cellulose by 36% and 60% and crystallinity by 16% and 25%, respectively. This reduction in molecular weight and crystallinity led to a 34% and 68% increase in the dissolution of 1% (w/v) cotton cellulose in NaOH/Urea solvent system. Thus, treating cotton cellulose with microwave oxygen plasma alters its physicochemical properties and enhanced its dissolution.

Fabrication of branching poly (butylene succinate)/cellulose nanocrystal foams with exceptional thermal insulation

Branching poly (butylene succinate) (BPBS) nanocomposite foams incorporated with cellulose nanocrystals (CNCs) were prepared by supercritical CO₂. Surface modification of CNCs by acetylation was achieved through replacing hydrophilic hydroxyl groups with hydrophobic acetyl groups, which improved the dispersibility of CNCs significantly. The crystallite sizes of CNCs and acetylated CNCs were calculated by Scherrer's formula as 25 and 19 nm, respectively. The initial crystallization temperature of diverse poly (butylene succinate) (PBS) specimens, a crucial factor for regulating cell nucleation type, increased remarkably by 11.8 °C as well as their storage modulus increased by 2 orders of magnitudes, due to branching reaction and bio-filler addition. BPBS/CNCs foam possessed a high volume expansion ratio as 37.1 times and displayed an exceptional thermal conductivity as 0.021 W(m K)^-1. This study provided a promising potential strategy to develop exceptional thermal-insulation polymer foams for composite structures, energy conservation and environment protection.

Recycled Cellulose Polypropylene Composite Feedstocks for Material Extrusion Additive Manufacturing

Many types of consumer-grade packaging can be used in material extrusion additive manufacturing processes, providing a high-value output for waste plastics. However, many of these plastics have reduced mechanical properties and increased warpage/shrinkage compared to those commonly used in three-dimensional (3D) printing. The addition of reinforcing materials can lead to stiffer parts with reduced distortion. This paper presents work in the reinforcement of recycled polypropylene using cellulose waste materials to generate a green composite feedstock for extrusion-based polymer additive manufacturing. Recycled polypropylene/waste paper, cardboard, and wood flour composites were made using a solid-state shear pulverization process. Fourier transform infrared and thermogravimetric analysis were utilized to qualitatively analyze the amount of filler incorporated into the 3D-printed materials. Recycled polymer composites had increased levels of filler incorporated in the printed parts compared to the virgin polymer composites based on the thermal gravimetric analysis. The dynamic mechanical analysis showed a ca. 20-30% increase in storage modulus with the addition of cellulose materials. Tensile strength was not significantly increased with the addition of 10 wt % cellulose, but the elastic modulus increased 38% in virgin polypropylene. The analysis of fracture surfaces revealed that failure initiates at the interface, suggesting that the interfacial strength is weaker than the filler strength.

New approach to recycle office waste paper: Reinforcement for polyurethane with nano cellulose crystals extracted from waste paper

New approach to recycle office waste paper was purposed in this paper, i.e., cellulose nanocrystal (CNC) was extracted from waste paper and then used CNC as the organic filler to reinforce polyurethane elastomer (PUE) in thermal properties. A series of CNC/PUE nanocomposites was prepared in situ using a two-step process in solvent N,N-dimethylformamide solution by changing the content of CNC from 0.5, 1, 2, 3, 4 to 5 wt%. The results showed that CNC was covalently bonded to PUE, and specifically concerned with the hard segments of PUE resulting from the strong hydrogen bonding. The interactions between CNC and PUE caused the increased thermal and thermo-mechanical properties, and decreased water absorption of nanocomposites. Importantly, the initial degradation temperature of PUE with 2 wt% content CNC (CNC/PUE2) increased by 21 °C. CNC/PUE2 had the better comprehensive properties with the worse water absorption, which made CNC/PUE2 appealing in load bearing and outdoor applications. Hence, this work not only provided a new recycling method of waste paper but also provided a thermolstable PUE with lower cost.

Effect on Mechanical and Thermal Properties of Random Copolymer Polypropylene/Microcrystalline Cellulose Composites Using T-ZnOw as an Additive

Four-needle zinc oxide whisker (T-ZnOw) incorporated into microcrystalline cellulose/maleic anhydride grafted polypropylene/random copolymer polypropylene (MCC/PP-g-MA/rPP) composite was prepared by melt blending. 5 wt% PP-g-MA was used as a coupling agent to improve the interfacial compatibility between fillers and rPP. The effect of T-ZnOw on MCC/PP-g-MA/rPP composite was investigated by mechanical testing, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Addition of T-ZnOw enhanced the mechanical properties of composites with tensile and flexural strengths increasing by 10% and 6%, respectively. SEM studies showed an improvement in the compatibility of fracture surfaces, which was evident from the absence of gaps between fillers and rPP. Additionally, initial thermal decomposition temperature and maximum weight loss temperature of T-ZnOw/MCC/PP-g-MA/rPP composite were both higher than those of MCC/PP-g-MA/rPP composite. Thermal degradation kinetics suggested that T-ZnOw has a weak catalytic effect on MCC, resulting in the early degradation of MCC and adhesion to the surface of rPP. Because of the presence of inorganic whiskers, the remaining weight percent was more than that of other composites at the end of the reaction. Crystallization temperature of the T-ZnOw/MCC/PP-g-MA/rPP composite was almost 3~5°C higher than that of MCC/PP-g-MA/rPP composite and close to the crystallization temperature of pure rPP.

Mechanically strong polystyrene nanocomposites by peroxide-induced grafting of styrene monomers within nanoporous cellulose gels

Nanocellulose is a promising candidate as a "green" reinforcing nanofiller for polymer nanocomposites. Three-dimensionally nanoporous cellulose gels (NCGs) have been demonstrated to exhibit significant dispersibility and compatibilization with hydrophobic polymers. We report a simple and versatile process for the fabrication of NCG/polystyrene (PS) nanocomposites by the in situ free radical polymerization of styrene monomers within the NCG. The volume fraction of the NCG in the NCG/PS nanocomposites could be controlled from 10% to 60%. The interconnected nanofibrillar cellulose networks of the NCG were finely distributed and well preserved in the PS matrix after polymerization. Dynamic mechanical analysis revealed a remarkable reinforcement in the tensile storage modulus of the NCG/PS nanocomposites, especially above the glass transition temperature (T_g) of the PS matrix. The modified percolation model was in good agreement with the mechanical properties of the NCG/PS nanocomposites. The introduction of the NCG into the PS matrix significantly improved the flexural and tension properties of the NCG/PS nanocomposites.

Polyurethane elastomer composites reinforced with waste natural cellulosic fibers from office paper in thermal properties

Polyurethane elastomer (PUE) composites were synthesized with a low additive content of waste natural cellulosic fibers from office paper. A new technology combining prepolymer method with physical blending and modification was adopted. The results showed that cellulosic fibers were covalently bonded to polyurethane molecular chains and served as a cross-linking agent making the degree of phase separation decrease. Even so, the lowest additive content of cellulosic fibers (1 wt%) in this work could make polyurethane still hold a certain degree of phase separation. Besides, thermal stability of polyurethane was improved from 288 to around 300 °C even at the low cellulosic fibers content. PUE with 3% cellulosic fibers had the better interfacial compatibility between cellulosic fibers and polyurethane causing the greater thermal reinforcement. PUE with 4% and 5% cellulosic fibers had the worse interfacial compatibility generating the better damping capacity indicating that cellulosic fibers could improve damping performance of polyurethane, especially polyurethane with 5 wt% fibers. It meant that cellulosic fibers had a potential application in damping materials.

Influence of particle size of isotactic polypropylene (iPP) on barrier property against agglomeration of homogenized microcrystalline cellulose (HMCC) in iPP/HMCC composites

Isotactic polypropylene (iPP) powders were treated by a colloid mill for different times to obtain a series of particle sizes ranging from 682 μm to 89 μm. The relative crystallinity degree index (Xc, %) calculated by X-ray diffraction, and the initial degradation temperature measured by thermogravimetry, were all reduced after the milling process, which revealed that the structure of iPP molecular chains was destroyed during the powerful shearing and friction action. Furthermore, the increasing melt flow rate (MFR) index indicated that the molecular weight of iPP had reduced during the mechanical treatment. Scanning electron micrographs showed the inevitable agglomeration of homogenized microcrystalline cellulose (HMCC) fibers after being dried directly without iPP powders. However, the addition of achieved superfine iPP powders presented a good barrier property against the agglomeration phenomenon and consequent improvement in mechanical performance of the iPP/HMCC composites.

Preparation of cellulose-based fluorescent carbon nanoparticles and their application in trace detection of Pb(ii)

Nanocrystalline cellulose (NCC) with a particle size of 23.80 ± 0.33 nm was prepared from microcrystalline cellulose by a mixed treatment with acids and ultrasound.

Influence of Cellulose on the Mechanical and Thermal Stability of ABS Plastic Composites

Microcrystalline cellulose was explored as possible biodegradable fillers in the fabrication of ABS plastic composites. TGA indicates that upon inclusion of cellulose microcrystals the thermal stability of the ABS plastics was improved significantly when compared to the neat ABS plastic counterparts. Furthermore, inclusion of extracted cellulose from plant biomass showed a higher thermal stability with maximum decomposition temperatures around 131.95°C and 124.19°C for cellulose from cotton andHibiscus sabdariffa, respectively, when compared to that of the purchased cellulose. In addition, TMA revealed that the average CTE value for the neat ABS and 1 : 1 ratio of cellulose to ABS fabricated in this study was significantly lower than the reported CTE (ca. 73.8 μm/m°C).