Temperature-dependent mechanical properties of wood-adhesive bondline evaluated by nanoindentation

Phenol formaldehyde (PF) and urea formaldehyde (UF) were used to prepare wood-adhesive bonds, respectively. The reduced elastic modulus (E_r) and hardness (H) of the control wood cell wall, the adhesive, and the cell wall penetrated with an adhesive (CW-adhesive) at the wood-adhesive bondline were measured within a certain temperature range from 20 to 160°C using high-temperature nanoindentation (NI). The results indicated that the wood-PF bondline showed a strong dependence on elevated temperatures, while the wood-UF bondline presented better mechanical stability. A reduction of carbohydrates and increment of lignin in wood resulting from heat treatment at a temperature above 140°C were beneficial to increase the micromechanics of wood cell walls at the bondline. Furthermore, the possible post cross-linking reactions between the wood cell walls and PF adhesive molecules during the long heating period at high temperature made a major contribution to a significant increase in E_r and H of the bondline. However, the significant difference in the mechanics of the PF adhesive and CW-PF in bondline after heat treatment negatively affects the interfacial adhesion properties of wood panels.     

Irradiation effects on electrical properties of cellulose nitrate

Cellulose nitrate (CA-80-15) films were exposed to UV and neutron irradiations. An increase of the electrical conductivity was observed. The values of the activation energy diminish with irradiation from 0.42 to 0.15 eV for UV and to 0.31 eV for neutron irradiation. A sharp increase in the current was observed after exposing CA-80-15 samples to fission neutron fluences of 1*10⁷ n/cm². The electrical conduction in cellulose nitrate is governed by the Shottky mechanism. The value of the electron affinity of the polymer used is 4.46 eV. This value is increased after both types of irradiation. The dielectric permittivity (ε′) of the above samples together with the dielectric loss factor (ε″) were measured over a range of temperatures (293–403 K) at fixed frequencies (1*10³, 1*10⁴, and 1*10⁵Hz). Three neutron exposures (? = 1*10⁵, 1*10⁶, and 1*10⁷ n/cm²) were used. The obtained results made it possible to determine a complete set of conduction parameters including dielectric susceptibility χ, ac conductivity α_ac, and temperature coefficient of permittivity TC. © 1995 John Wiley & Sons, Inc.     

Dynamic mechanical properties of bacterial cellulose nanofibres

In this work, dynamic mechanical properties of the grown bacterial cellulose (BC) nanofibers were investigated. BC pellicles were fabricated using bacterial fermentation (Gluconacetobacter xylinus). The morphology results confirmed that the dried BC at ambient conditions could be categorized as a xerogel. The thermal dynamic mechanical analysis results indicated that the bound water in bacterial cellulose structure had a very significant effect on thermal and dynamic mechanical properties of BC pellicles. The results of dehydration kinetics study showed that the main mechanism governing water loss of BC was Fickian diffusion. The glass transition temperatures (T_g) of the BC dried at 25 °C (ambient temperature) and 105 °C were estimated ??33 and ??18 °C, respectively. This discrepancy can be attributed to the plasticizing effect of the bound water of BC dried at ambient temperature. Furthermore, the results indicated that its modulus drop smaller than one order of magnitude can be attributed to its high crystalline nature. The storage modulus versus frequency increased due to the limitation of the relaxation process of the polymer chains. Moreover, the relaxation time distribution was achieved from the slope of the modulus master curve versus logarithmic frequency. As a result, BC exhibited a solid-like behavior.     

Poly(methyl methacrylate)–cellulose nitrate copolymers. II. Physical and mechanical properties

Poly(methyl methacrylate)–cellulose nitrate copolymers were prepared by bulk polymerization using benzoyl peroxide as initiator. Cellulose nitrates of two different nitrogen contents (11.4 and 12.2%) were used. The prepared copolymers were γ-irradiated for specified periods of up to 11.83 Mrad. Their physical and mechanical properties were measured before and after irradiation. The title copolymers showed lower modulus, tensile strength, and elongation at break than poly(methyl methacrylate) itself, but they showed better hardness and abrasion. Irradiation to up to 6.57 Mrad improved the modulus of the copolymers. Hardness and abrasion were improved by increasing cellulose nitrate content. The prepared copolymers that contained cellulose nitrate of 11.4% nitrogen showed secondary transition points. The increase of cellulose nitrate concentration shifted both first and second transition points to relatively higher values.     

Thermal and dynamic mechanical properties of hydroxypropyl cellulose films

Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to characterize the morphology of solvent cast hydroxypropyl cellulose (HPC) films. DSC results were indicative of a semicrystalline material with a melt at 220°C and a glass transition at 19°C (T₁), although an additional event was suggested by a baseline inflection at about 80°C (T₂). Corresponding relaxations were found by DMTA. A secondary relaxation at ?55°C was attributed to the interaction between hydroxyl groups of the polymer and residual diluent. The tan δ peak at T₂ was found to arise from an organized phase, presumably from a liquid-crystal mesophase formed while in solution. Crosslinking with a diisocyanate increased the peak temperature of the two primary relaxations, and resulted in a more clearly defined peak for the T₂ transition. From this behavior it was concluded that both T₁ and T₂ are similar to glass transitions (T_g's) associated with an amorphous component and a more highly ordered phase (due to a residual liquid crystal superstructure) in the HPC bulk.     

Influence of mechanical treatments on the properties of cellulose nanofibers isolated from microcrystalline cellulose

The possibility of preparing cellulose whiskers-like materials by mechanical treatment of commercially available microcrystalline cellulose (MCC) was explored. High shear homogenization, grinding with a supermass colloider, and hammer-milling were the processes selected to disintegrate the MCC, which yielded F-MCC, G-MCC and H-MCC, respectively. Processing aqueous dispersions with high solid content allowed for the production of cellulose particles with greatly reduced dimensions. Morphological characterization revealed that homogenization and grinding reduced the particle size more effectively than hammer-milling, although the disintegration was incomplete in all cases. The reinforcing potential of the materials was evaluated against commercially available whiskers by using the various particles as fillers to mechanically reinforce hydroxypropylcellulose. Nanocomposite films containing 5, 10, or 20 wt.% of the filler were prepared and the mechanical properties were characterized. The results show that H-MCCs are just slightly better than the original MCC, whereas F-MCC and G-MCC performed similar to whiskers at 10 wt.% loading, despite the presence of a fraction of micrometer-sized particles. It is therefore reasonable to envision the use of the more easily produced F-MCC and G-MCC as replacement of cellulose whiskers in some applications.     

Preparation and mechanical properties of green epoxy nanocomposites with cellulose nanocrystals

Epoxy resin is widely used to make composites, electronic and electric parts, adhesives, and coating materials because it has excellent thermal, electrical, and mechanical properties. Using natural materials in making epoxy composites and nanocomposites would make the final products greener. Therefore, in this study, epoxidized soybean oil (ESO) and cellulose nanocrystals (CNCs) were used to make green epoxy nanocomposites. ESO was prepared by epoxidation of soybean oil with peroxyacetic acid and it was confirmed by Fourier transform infrared spectroscopy. The ESO was mixed with diglycidyl ether of bisphenol A at different weight ratios (10%–50%) and the stoichiometric amount of ethylene diamine was used for curing. CNC content in the nanocomposites was changed from 0.125 to 1 phr. Mechanical properties of the epoxy samples and the nanocomposites were investigated by universal testing machine and izod impact tester. The epoxy sample showed best mechanical properties at ESO 30%. The nanocomposite with CNC 0.25 phr showed best mechanical properties. Fracture surfaces of the epoxy sample and the nanocomposites were investigated by scanning electronic microscope. POLYM. ENG. SCI., 60:439–445, 2020. © 2019 Society of Plastics Engineers     

纤维素/海藻酸钠共混膜的制备及力学性能

将纤维素和海藻酸钠分别溶于氢氧化钠/尿素/硫脲体系,制得纤维素膜和纤维素/海藻酸钠共混膜,通过正交实验和单因素实验法分析,确定制备纤维素膜的最佳工艺条件,在此基础上研究了纤维素/海藻酸钠共混膜的制备工艺。结果表明:质量分数为4.5%的纤维素溶液所制得的膜在25℃的5%的硫酸溶液中凝固15 min,20%的甘油溶液中塑化30 min,其膜的拉伸强度较佳为5.2 MPa;纤维素/海藻酸钠共混膜的较佳工艺:质量分数分别为4.5%的纤维素溶液和3%的海藻酸钠溶液按质量比100/5共混后先浸入5%硫酸溶液中反应15 min,再放入10%氯化钙溶液中凝固10 min,用15%甘油溶液塑化15 min后,共混膜的拉伸强度达到3.50 MPa。     

Enhanced mechanical properties of epoxy composites using cellulose micro- and nano-crystals

Epoxy polymers are commonly utilized in structural applications due to their high bearing capacity and excellent chemical resistance. However, their inherent brittleness poses a significant challenge for their use in high shock and fracture strength products. To address this shortcoming, fillers can be incorporated into the polymer during preparation. In this study, we aimed to investigate the effect of incorporating cellulose-based fillers, namely cellulose nanocrystals (CNCs) and microcrystalline cellulose (MCC), on the mechanical properties of epoxy polymer composites. The study evaluated the impact of various factors, including filler concentration, particle size, and moisture content, on the mechanical properties of the composites. The results demonstrated that the incorporation of CNC or MCC powders at concentrations below 5% could enhance the mechanical properties of the resulting epoxy composites without adversely affecting their surface and thermal properties. The maximum tensile strength and fracture toughness of the filler-based epoxy composites were achieved at 2 and 4 wt% for CNCs and MCC, respectively. CNCs with a smaller particle size distribution were found to be much more effective than MCC in improving the mechanical properties of the epoxy composites. Furthermore, utilizing dried fillers resulted in a higher improvement in tensile strength, which was achieved at lower filler concentrations.     

硝酸铵发射药力学性能的研究

研究硝酸铵对发射药力学性能的影响。采用拉伸实验方法,测定不同硝酸铵含量、粒径下发射药的拉伸强度、伸长率、应力-应变曲线。结果表明,随着硝酸铵含量的升高,发射药的拉伸强度、伸长率、回弹模量、韧性模量先降低、再升高、后降低;在硝酸铵含量较低时,随着硝酸铵粒径的减小,发射药的拉伸强度升高;硝酸铵在发射药中形成次级结构,使其粒...     

Preparation and mechanical properties of composite of fibrous cellulose and maleated polyethylene

Fibrous cellulose and maleated polyethylene (FC–MPE) composites were prepared under melt mixing by maleation of polyethylene (PE) to obtain maleic anhydride (MA) grafted PE (MPE) and successive compounding of the resultant MPE with fibrous cellulose (FC). When increasing the content of added MA to 2 wt %, the grafting efficiency of MA decreases gradually to 84% and the grafted MA chains become longer. Scanning electron microscopy (SEM) reveals strong adhesion of MPE to FC in the FC–MPE composite, which is probably due to the increased compatibility between MPE and FC, in contrast to no adhesion of unmaleated PE (UPE) to FC in the FC–UPE composite. This difference in interfacial structure between the FC–MPE and FC–UPE composites results in quite different mechanical properties for them. With an increase in the FC content to 60 wt %, the tensile strength of the FC–MPE composite increases significantly and reaches 125% that of pure PE. Furthermore, the larger Young's modulus, larger bending elastic modulus, and smaller elongation of the FC–MPE composite strongly indicate effective transfer of the high tensile strength and elasticity of FC to the MPE matrix through the strong adhesion between FC and MPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1971–1980, 2002; DOI 10.1002/app.10428     

Effect of gamma irradiation on optical and chemical properties of cellulose nitrate thin films

In this work, cellulose nitrate films were irradiated with different doses of gamma irradiations. The gamma irradiation doses were 25, 55, 120, and 170 kGy. The compositional transformation, optical properties, and morphological changes resulted from the gamma irradiation were obtained using different spectroscopic methods. These methods were Fourier transform infrared spectrometry, UV/visible spectrometry, and scanning electron microscope. The surface roughness, as well, for pristine and gamma-irradiated polymer films was determined. The obtained results exhibit changes in the absorbance intensities of the function groups of the irradiated cellulose nitrate films. An induced increase in the UV/visible absorption spectra with increase in the gamma irradiation was observed. A noticeable shifting in the UV/visible spectra toward higher wavelength and decrease in the optical band gap were observed as the gamma irradiation increases. As well, the number of carbon clusters and the activation energy were discussed. The morphological investigation indicates the decrease in the roughness surface with increasing of gamma irradiation.     

包覆硝酸铵发射药界面力学性能研究

研究包覆硝酸铵发射药的界面力学性能。采用拉伸剪切和压缩的方法测定在不同硝酸铵含量、不同硝酸铵粒径、不同温度下包覆硝酸铵发射药的界面剪切强度。实验结果表明,随着硝酸铵含量的升高,发射药的界面剪切强度先上升再下降;随着硝酸铵粒径的降低,发射药的界面剪切强度不断下降;随着温度的升高,发射药的界面剪切强度先升高再降低。     

Mechanical and dynamical mechanical properties of chloroprene rubber and cellulose II composites

Vulcanized composites of chloroprene rubber (CR) with cellulose II (Cel II) as a filler were investigated. Cel II, obtained by the coagulation of cellulose xanthate, was incorporated in the rubber by the traditional method. The filler content varied from 0 to 30 phr. For comparison purposes, carbon black (CB)–CR composites were also studied. The CB amount varied from 0 to 45 phr. The mechanical and dynamic mechanical properties were determined, and the CR composite containing 20 phr of Cel II showed the best set of properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2425–2430, 2004     

Effect of chitosan penetration on physico-chemical and mechanical properties of bacterial cellulose

Bacterial cellulose-chitosan composites (BC-Ch) were prepared in order to obtain the BC-Ch composites with improved physico-mechanical characteristics. BC sheets were immersed in a Ch solution hoping that the Ch penetrates into the BC sheet. Ch penetration was observed according to variations in temperature, operation mode and treatment time. The morphological changes due to enhanced penetration were observed through FE-SEM, FT-IR and XRD analysis. FE-SEM analyses confirmed the formation of three dimensional multilayered structures in BC-Ch, whose thickness increased with Ch penetration. The FT-IR analysis showed intermolecular hydrogen bonding interaction between the BC and Ch molecules. XRD results revealed a slight decrease in the crystallinity index of the BC-Ch composites compared to pure BC. The mechanical properties, water holding capacity (WHC) and water release rate (WRR) of the BC-Ch composites were significantly improved compared to pure BC. The superior mechanical properties, WHC and water release rate would make the BC-Ch composites suitable for wound dressing and other biomedical applications.     

Size exclusion chromatography of cellulose nitrate

Summary There had been studied the calibration conditions on the system cellulose nitrate (sharp fractions) -THF--Styragel by comparing the viscosity averages of DP obtained from the elution curves of GPC with the corresponding viscosimetrically determined ones. Deriving the elution volumes from the integral elution curves and applying adjustment of the calibration by means of adequate iterations, a very good coincidence between DP_n(visc.) and DP_n(GPC) can be reached. The molecular weight distribution curves obtained by GPC and by precipitation fractionation agree within the limits of error of both methods. It appears, however, that if in the calibration only one kind of average value of the master samples had been involved, only the same type of average can be determined with satisfying exactness.     

Structure and mechanical properties of cellulose derivatives/soy protein isolate blends

Biodegradable and biocompatible composites based on soy protein isolate (SPI) and various cellulose derivatives have been prepared, and the dependence of structures and mechanical properties on the content and species of cellulose derivatives for the composites were investigated by X‐ray diffraction, differential scanning calorimetry, scanning electron microscope, and tensile test. The selected cellulose derivatives, such as methyl cellulose (MC), hydroxyethyl cellulose (HEC), and hydroxypropyl cellulose, were miscible with SPI when the content of cellulose derivatives was low, and then the isolated crystalline domains, shown as the structures of network and great aggregate, formed with an increase of cellulose derivative content. The miscible blends could produce the higher strength, and even result in the simultaneous enhancement of strength and elongation for the HEC/SPI and MC/SPI blends. Meanwhile, the moderate content of great MC domains also reinforced the materials. However, the damage of original ordered structure in SPI gave the decreased modulus. Since all the components, i.e., cellulose derivatives and soy protein, are biocompatible, the resultant composites are not only used as environment‐friendly material, but the biomedical application can be expected, especially for the tissue engineering scaffold. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Construction of porous cellulose tubes and the evaluations of mechanical properties and cytocompatibility

In this work, regenerated cellulose (RC) tubes with the porous structure were successfully fabricated for constructing the non-invasive detection platform of vascular microenvironment. Polyethylene oxide (PEO) as a porogen was applied to induce porous structure of cellulose tubes. Tensile and burst pressure tests were carried out to evaluate the effects of PEO molecular weight and amount on the mechanical properties of cellulose tubes. The results showed that tensile strength of RC tubes was increased with increasing PEO molecular weight. The compliance of cellulose tubes decreased with increasing the PEO content. When 120 kDa PEO was applied, the average tensile strength of RC tubes could reach 1.27 MPa. The maximum burst pressure and compliance of RC tubes could reach 488.25 ± 35 mmHg and 7.50 ± 3.7%/100 mmHg, respectively. Human umbilical vein endothelia cells (HUVECs) exhibited obvious proliferation on cellulose tubes, and the collagen coating further improve the biocompatibility. The incorporated collagen further improved adhesion of the cells and growth on cellulose tubes. This work provided a kind of cellulose-based tube material with potential application for the construction of the vitro vascular microenvironment.