Soybean-oil-based waterborne polyurethane dispersions: effects of polyol functionality and hard segment content on properties

The environmentally friendly vegetable-oil-based waterborne polyurethane dispersions with very promising properties have been successfully synthesized without difficulty from a series of methoxylated soybean oil polyols (MSOLs) with different hydroxyl functionalities ranging from 2.4 to as high as 4.0. The resulting soybean-oil-based waterborne polyurethane (SPU) dispersions exhibit a uniform particle size, which increases from about 12 to 130 nm diameter with an increase in the OH functionality of the MSOL from 2.4 to 4.0 and decreases with increasing content of the hard segments. The structure and thermophysical and mechanical properties of the resulting SPU films, which contain 50-60 wt % MSOL as renewable resources, have been studied by Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, transmission electron microscopy, and mechanical testing. The experimental results reveal that the functionality of the MSOLs and the hard segment content play a key role in controlling the structure and the thermophysical and mechanical properties of the SPU films. These novel films exhibit tensile stress-strain behavior ranging from elastomeric polymers to rigid plastics and possess Young's moduli ranging from 8 to 720 MPa, ultimate tensile strengths ranging from 4.2 to 21.5 MPa, and percent elongation at break values ranging from 16 to 280%. This work has addressed concerns regarding gelation and higher cross-linking caused by the high functionality of vegetable-oil-based polyols. This article reports novel environmentally friendly biobased SPU materials with promising applications as decorative and protective coatings.     

Multi-scale characterization of swine femoral cortical bone

Multi-scale experimental work was carried out to characterize cortical bone as a heterogeneous material with hierarchical structure, which spans from nanoscale (mineralized collagen fibril), sub-microscale (single lamella), microscale (lamellar structures), to mesoscale (cortical bone) levels. Sections from femoral cortical bone from 6, 12, and 42 months old swine were studied to quantify the age-related changes in bone structure, chemical composition, and mechanical properties. The structural changes with age from sub-microscale to mesoscale levels were investigated with scanning electron microscopy and micro-computed tomography. The chemical compositions at mesoscale were studied by ash content method and dual energy X-ray absorptiometry, and at microscale by Fourier transform infrared microspectroscopy. The mechanical properties at mesoscale were measured by tensile testing, and elastic modulus and hardness at sub-microscale were obtained using nanoindentation. The experimental results showed age-related changes in the structure and chemical composition of cortical bone. Lamellar bone was a prevalent structure in 6 months and 12 months old animals, resorption sites were most pronounced in 6 months old animals, while secondary osteons were the dominant features in 42 months old animals. Mineral content and mineral-to-organic ratio increased with age. The structural and chemical changes with age corresponded to an increase in local elastic modulus, and overall elastic modulus and ultimate tensile strength as bone matured.     

Silicone fouling-release coatings: effects of the molecular weight of poly(dimethylsiloxane) and tetraethyl orthosilicate on the magnitude of pseudobarnacle adhesion strength

A series of poly(dimethyl siloxane) (PDMS)/silica nanocomposites were synthesized utilizing a sol gel method. The samples were evaluated using pseudobarnacle adhesion and tensile strength tests. The effects of the molecular weight of the PDMS and the size and structure of the silica domains on biofouling release and the mechanical behavior of the PDMS/silica materials were investigated. Three different molecular weights (18,000, 49,000 and 79,000 g mol(-1)) of hydroxyl-terminated PDMS (HT-PDMS) were used to prepare the nanocomposites with three different weight ratios (1:1, 3:1 and 5:1) of HT-PDMS to tetraethyl orthosilicate (TEOS). TEOS served as a crosslinker to form PDMS networks and as a precursor to form silica domains. Two different variants of TEOS with regard to its degree of polymerization (n) (monomeric type: n ≈= 1 and oligomeric type: n ≈= 5) were used for in situ formation of silica particles via the sol-gel process. The mechanical properties of the composites were characterized using stress-strain isotherms. All the mechanical properties evaluated (Young's modulus, tensile strength, energy required for rupture, elongation at break) improved with increases in the molecular weight of the HT-PDMS and the silica content. The pseudobarnacle adhesion test was used to examine the fouling- release (FR) properties of coatings applied on aluminum plates. The rupture energy and tensile strength increased substantially when oligomeric TEOS was employed in the PDMS/silica composites. Scanning electron microscopy (SEM) was used to investigate the structure of the silica domains. It was found that the use of oligomeric TEOS in higher molecular weight PDMS samples with higher PDMS/TEOS weight ratios led to low pseudobarnacle adhesion strengths of ≈ 0.3 MPa, which is in the range of commercial FR coatings.     

Mechanical properties of polyurethane foams prepared from liquefied corn stover with PAPI

Corn stover was liquefied by using ethylene carbonate (EC) as liquefying solvent and 97% sulfur acid as catalyst at 170 degrees C for 90 min. Polyurethane (PU) foams were prepared from liquefied corn stover (LCS) with variable amount of polymethylene polyphenylisocyanate (PAPI) by one-shot method, with water as blowing agent, silicone as surfactant and triethylamine and dibutyltine dilaurate as co-catalyst. The mechanical properties of LCS-PU foam with different [NCO]/[OH] ratio were studied on a universal tensile tester. With the increase of [NCO]/[OH] ratio from 0.4 to 1.0, the tensile strength and Young's modulus of the LCS-PU foam first raised, reached their maximum values at [NCO]/[OH] ratio of 0.8, and then declined; while the elongation at break decreased from 117% to 3.6%. The results indicated that by changing the [NCO]/[OH] ratio, mechanical properties of LCS-PU foams could be adjusted for various end uses.     

Mechanical properties and failure of Streptococcus mutans biofilms, studied using a microindentation device

Knowledge of mechanical properties and failure mechanisms of biofilms is needed to determine how biofilms react on mechanical stress. Methods currently available cannot be used to determine mechanical properties of biofilms on a small scale with high accuracy. A novel microindentation apparatus in combination with a confocal microscope was used to determine the viscoelastic properties of Streptococcus mutans biofilms. The apparatus comprises a small glass indenter and a highly sensitive force transducer. It was shown that the present biofilm, grown under still conditions, behaves as a viscoelastic solid with a storage modulus of 1-8 kPa and a loss modulus of 5-10 kPa at a strain of 10%. Biofilm failure was investigated visually through a confocal microscope by dragging the indenter through the biofilm. It was shown that the tensile strength of the biofilm is predominantly determined by the tensile strength of the extracellular polysaccharide matrix. The combination of microindentation and confocal microscopy is a promising technique to determine and characterize the mechanical properties of soft materials in various fields of microbiology.     

Novel silicon-containing polyurethanes from vegetable oils as renewable resources. Synthesis and properties

Hydrosilylation of methyl 10-undecenoate (UDM) with phenyl tris(dimethylsiloxy)silane (PTDS) followed by a reduction of carboxylate groups was used to obtain a silicon-containing polyol with terminal primary hydroxyl groups (PSi194). Biobased silicon-containing polyurethanes, with a silicon content between 1.7% and 9.0%, were prepared from epoxidized methyl oleate-based polyether polyol (P184), PSi194, and 4,4'-methylenebis(phenyl isocyanate) (MDI). The thermal, mechanical, and flame-retardant properties of these materials were examined. The most notable change resulting from the incorporation of PSi194 is the appearance of melting endotherms of variable enthalpy and position and a downward shift in the T(g). The incorporation of silicon does not change the thermal stability but enhances the stability of the char under air atmosphere. Polyurethanes with higher silicon content no longer burn in ambient air without complementary oxygen, which suggests that these biobased materials are very interesting for applications that require fire resistance.     

Growth-related changes in the mechanical properties of collagen fascicles from rabbit patellar tendons

Growth-related changes in the mechanical properties of collagen fascicles (approximately 300 microm in diameter) were studied using patellar tendons obtained from skeletally immature 1 and 2 months old and matured 6 months old rabbits. Tensile properties were determined using a specially designed micro-tensile tester. In each age group, there were no significant differences in the properties among cross-sectional locations in the tendon. Tangent modulus and tensile strength significantly increased with age; the rates of their increases between 1 and 2 months were higher than those between 2 and 6 months. The tangent modulus and tensile strength were positively correlated with the body weight of animals. However, growth-related changes in the mechanical properties were different between collagen fascicles and bulk patellar tendons, which may be attributable to such non-collagenous components as ground substances and also to mechanical interactions between collagen fascicles.     

High Molecular Weight Poly(butylene succinate-co-butylene furandicarboxylate) Copolyesters: From Catalyzed Polycondensation Reaction to Thermomechanical Properties

Novel potentially biobased aliphatic-aromatic copolyesters poly(butylene succinate-co-butylene furandicarboxylate) (PBSFs) in full composition range were successfully synthesized from 2,5-furandicarboxylic acid (FA), succinic acid (SA), and 1,4-butanediol (BDO) via an esterification and polycondensation process using tetrabutyl titanate (TBT) or TBT/La(acac)(3) as catalyst. The copolyesters were characterized by size exclusion chromatography (SEC), Fourier transform infrared (FTIR), (1)H NMR, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and their tensile properties were also evaluated. The weight average molecular weight (M(w)) ranges from 39?000 to 89?000 g/mol. The copolyesters are random copolymers whose composition is well controlled by the feed ratio of the diacid monomers. PBSFs have excellent thermal stability. The glass transition temperature (T(g)) increases continuously with ?(BF) and agrees well with the Fox equation. The crystallizability and T(m) decrease with increasing butylene furandicarboxylate (BF) unit content (?(BF)) from 0 to 40 mol %, but rise again at ?(BF) of 50-100 mol %. Consequently, the tensile modulus and strength decrease, and the elongation at break increases with ?(BF) in the range of 0-40 mol %. At higher ?(BF), the modulus and strength increase and the ultimate elongation decreases. Thus, depending on ?(BF), the structure and properties of PBSFs can be tuned ranging from crystalline polymers possessing good tensile modulus (360-1800 MPa) and strength (20-35 MPa) to nearly amorphous polymer of low T(g) and high elongation (～600%), and therefore they may find applications in thermoplastics as well as elastomers or impact modifiers.     

The role of mineral content in determining the micromechanical properties of discrete trabecular bone remodeling packets

In trabecular bone, each remodeling event results in the resorption and/or formation of discrete structural units called ‘packets’. These remodeling packets represent a fundamental level of bone’s structural hierarchy at which to investigate composition and mechanical behaviors. The objective of this study was to apply the complementary techniques of quantitative backscattered electron microscopy (qBSEM) and nanoindentation to investigate inter-relationships between packet mineralization, elastic modulus, contact hardness and plastic deformation resistance. Indentation arrays were performed across nine trabecular spicules from 3 human donors; these spicules were then imaged using qBSEM, and discretized into their composite remodeling packets (127 in total). Packets were classified spatially as peripheral or central, and mean contact hardness, plastic deformation resistance, elastic modulus and calcium content calculated for each. Inter-relationships between measured parameters were analysed using linear regression analyses, and dependence on location assessed using Student’s t-tests. Significant positive correlations were found between all mechanical parameters and calcium content. Elastic modulus and contact hardness were significantly correlated, however elastic modulus and plastic deformation resistance were not. Calcium content, contact hardness and elastic modulus were all significantly higher for central packets than for peripheral, confirming that packet mineral content contributes to micromechanical heterogeneity within individual trabecular spicules. Plastic deformation resistance, however, showed no such regional dependence, indicating that the plastic deformation properties in particular, are determined not only by mineral content, but also by the organic matrix and interactions between these two components.     

Changes in the molecular orientation and tensile properties of uniaxially drawn cellulose films

Cellulose films were prepared by dissolving lyocell fibers in LiCl/N,N-dimethylacetamide solvent and subsequently coagulating and drying them under ambient conditions. To introduce preferred orientation, the films were uniaxially drawn under air-dry and rewetted conditions, respectively. Preferred orientation was determined by birefringence measurements and by wide-angle X-ray scattering. Mechanical properties were characterized by means of tensile tests with films conditioned to standard temperatures and humidity. Drawing resulted in the substantial reorientation of cellulose, whereby the molecular chains in the amorphous regions exhibited clearly stronger reorientation than the crystalline fraction. The average degree of orientation was comparable to orientation achieved in spun cellulose fibers. Wet-drawing resulted in improved tensile strength and modulus of elasticity but reduced elongation at break. The mechanical properties of wet-drawn films are competitive with regard to cellophane and melt-blown cellulose films, particularly considering their high modulus of elasticity of up to 26 GPa, which is also comparable to values obtained for industrially produced cellulose fibers.     

Collagen fibril diameter distribution does not reflect changes in the mechanical properties of in vitro stress-deprived tendons

The purpose of this study was to determine if an association exists between the tensile properties and the collagen fibril diameter distribution in in vitro stress-deprived rat tail tendons. Rat tail tendons were paired into two groups of 21 day stress-deprived and 0 time controls and compared using transmission electron microscopy (n = 6) to measure collagen fibril diameter distribution and density, and mechanical testing (n =6) to determine ultimate stress and tensile modulus. There was a statistically significant decrease in both ultimate tensile strength (control: 17.95+/-3.99 MPa, stress-deprived: 6.79+/-3.91 MPa) and tensile modulus (control: 312.8+/-89.5 MPa, stress-deprived: 176.0+/-52.7 MPa) in the in vitro stress-deprived tendons compared to controls. However, there was no significant difference between control and stress-deprived tendons in the number of fibrils per tendon counted, mean fibril diameter, mean fibril density, or fibril size distribution. The results of this study demonstrate that the decrease in mechanical properties observed in in vitro stress-deprived rat tail tendons is not correlated with the collagen fibril diameter distribution and, therefore, the collagen fibril diameter distribution does not, by itself, dictate the decrease in mechanical properties observed in in vitro stress-deprived rat tail tendons.     

All-cellulose composite prepared by selective dissolving of fiber surface

An all-cellulose composite was prepared from conventional filter paper by converting a selective dissolved fiber surface into a matrix. The structure and mechanical, thermal, and optical properties of this composite were investigated using X-ray diffraction, a scanning electron microscope, an optical microscope, a tensile test, and dynamic viscoelastic analyses. After optimizing the immersion condition of the filter paper in a solvent, the fibers, with selectively dissolved surfaces, were unified by compression followed by drying. The tensile strength of the composite reached 211 MPa at 25 degrees C, isotropically. This value was comparable or even higher than those of conventional glass-fiber-mat-reinforced composites. The composites possessed a high storage modulus of more than 20 GPa at -150 degrees C, and a storage modulus of the GPa order was maintained up to around 250 degrees C. The good interface is considered to bring optical transparency to this composite. In addition, this composite is composed of sustainable resources and is biodegradable after service, which gives it advantages with regard to disposal, composting, and incineration.     

Biomechanical properties across trabeculae from the proximal femur of normal and ovariectomised sheep

The elastic behaviour of trabecular bone is a function not only of bone volume and architecture, but also of tissue material properties. Variation in tissue modulus can have a substantial effect on the biomechanical properties of trabecular bone. However, the nature of tissue property variation within a single trabecula is poorly understood. This study uses nanoindentation to determine the mechanical properties of bone tissue in individual trabeculae. Using an ovariectomised ovine model, the modulus and hardness distribution across trabeculae were measured. In both normal and ovariectomised bone, the modulus and hardness were found to increase towards the core of the trabeculae. Across the width of the trabeculae, the modulus was significantly less in the ovariectomised bone than in the control bone. However, in contrast to this hardness was found not to differ significantly between the two groups. This study provides valuable information on the variation of mechanical material properties in healthy and diseased trabecular bone tissue. The results of the current study will be useful in finite element modelling where more accurate values of trabecular bone modulus will enable the prediction of the macroscale behaviour of trabecular bone.     

A Quantitative Study of the Relationship between the Distribution of Different Types of Collagen and the Mechanical Behavior of Rabbit Medial Collateral Ligaments

The mechanical properties of ligaments are key contributors to the stability and function of musculoskeletal joints. Ligaments are generally composed of ground substance, collagen (mainly type I and III collagen), and minimal elastin fibers. However, no consensus has been reached about whether the distribution of different types of collagen correlates with the mechanical behaviors of ligaments. The main objective of this study was to determine whether the collagen type distribution is correlated with the mechanical properties of ligaments. Using axial tensile tests and picrosirius red staining-polarization observations, the mechanical behaviors and the ratios of the various types of collagen were investigated for twenty-four rabbit medial collateral ligaments from twenty-four rabbits of different ages, respectively. One-way analysis of variance was used in the comparison of the Young''s modulus in the linear region of the stress-strain curves and the ratios of type I and III collagen for the specimens (the mid-substance specimens of the ligaments) with different ages. A multiple linear regression was performed using the collagen contents (the ratios of type I and III collagen) and the Young''s modulus of the specimens. During the maturation of the ligaments, the type I collagen content increased, and the type III collagen content decreased. A significant and strong correlation () was identified by multiple linear regression between the collagen contents (i.e., the ratios of type I and type III collagen) and the mechanical properties of the specimens. The collagen content of ligaments might provide a new perspective for evaluating the linear modulus of global stress-strain curves for ligaments and open a new door for studying the mechanical behaviors and functions of connective tissues.     

In vivo characterization of mechanical tissue properties of internal organs using endoscopic microscopy and inverse finite element analysis

Knowledge about mechanical tissue properties is required for functional modelling and simulating of tissue and organ responses to external mechanical stress. To get the right properties especially for functional modelling of organs, tissue properties have to be determined in vivo. There are only few described methods for characterization of internal organ's tissue mechanics that can be applied in vivo. We introduce and evaluate a method to determine mechanical tissue properties, especially those of lung tissue, endoscopically. Inverse finite element analysis (utilizing a Neo-Hookean model for hyperelastic materials) and image processing algorithms are used to determine the shear modulus of a soft tissue. The resulting values for shear moduli were normally distributed. The shear modulus of the artificial tissue sample was determined with a relative error of 0.47% compared to the value obtained by uniaxial tensile test.     

Carboxymethylcellulose-montmorillonite nanocomposite films activated with murta (Ugni molinae Turcz) leaves extract

The functionality of nanocomposite films based on carboxymethylcellulose (CMC) and montmorillonite (MMT) activated with murta (Ugni molinae Turcz) leaves extract was studied. Films were prepared by casting from film-forming dispersions containing CMC, glycerol (used as plasticizer) and different concentrations of MMT, using water or murta extract as solvent. The addition of MMT increased the tensile strength and the elasticity modulus of the films, and decreased their permeabilities to water vapor, oxygen and carbon dioxide. Besides the antioxidants properties provided to the films, the addition of murta leaves extract changed the gas permeability in different forms according to the MMT content, and plasticized the nanocomposite matrix.     

Nanoindentation study of human premolars subjected to bleaching agent

Bleaching of teeth is gaining popularity due to cosmetic reasons. However, the effect it has on teeth is still largely unknown. This paper seeks to evaluate the effect of a bleaching agent, 30% hydrogen peroxide, on the nanomechanical properties of dentin and enamel using the nanoindentation technique. The Young's modulus and hardness obtained from nanoindentation before and after bleaching were compared. Five newly extracted human premolars were used. Nanoindentation was first done on the sliced enamel and dentin regions to determine their mechanical properties. One batch of samples was kept in Hank's balanced salt solution as control while the other was bleached in 30% hydrogen peroxide for 24h. The same number of nanoindentations was then done near the previously indented regions for both the control and bleached samples and the results compared. Using paired sample t-tests with alpha=0.05, it was found that there were no significant differences in both the Young's modulus and hardness of dentin and enamel kept in control. However, the mechanical properties of the bleached dentin were significantly decreased. For intertubular dentin, the mean hardness decreased by 29-55% and the mean Young's modulus decreased by 19-43%. For enamel, the mean hardness decreased by 13-32% while the mean Young's modulus decreased by 18-32%. The exact mechanism by which hydrogen peroxide affects the dentin and enamel has yet to be fully elucidated. However, it is observed to have an undermining effect on the nanomechanical properties of teeth.     

Structure–properties relationship in cross-linked high amylose starch cast films

Cross-linked high amylose starch cast films were prepared to study the effect of cross-linking degree on various properties in normal environmental conditions. Mechanical tensile properties (Young's modulus, elongation at break, tensile strength), water vapour transmission rate (WVTR) and oxygen permeability coefficients of cast films were determined as a function of cross-linking degree and percentage of free humidity. Cross-linking degree and degree of crystallinity are closely related and seem to have non-negligible opposite effect on the properties of interest. By using increased amounts of cross-linking agents, the effect of cross-linking degree tends to reduce the degree of crystallinity modulating thus mechanical properties, water vapour permeability and oxygen permeability coefficients. Yield strength, tensile strength at break, WVTR versus cross-linking degree showed a non-monotonous behaviour. Maximal values for these properties were reached for moderate cross-linking degree. Optimal crystalline/amorphous ratio in the films may induce interactions and balanced effects, which would be responsible for the non-linear behaviour of some of the investigated properties. By cross-linking with epichlorohydrin in the range 1–10 g crosslinker/100 g polymer, the mechanical properties of films are still related to water content and water vapour permeability remains high compared to some synthetic polymeric materials.     

Prediction on elastic properties of Nb-doped Ni systems

On the basis of first-principles simulation, the structure, formation enthalpy and mechanical properties (elastic constant, bulk and shear modulus and hardness) of five Nb-doped Ni systems are systematically studied. The calculated equilibrium volume increases with the Nb concentration increasing. The computational elastic constants and formation enthalpy indicate that all Nb-doped Ni systems are mechanically and thermodynamically stable in our research. The hardness of these systems was predicted after the bulk modulus and shear modulus had been accurately calculated. The results show that the hardness increases with the Nb concentration increasing when the Nb concentration was below 4.9%, beyond which the hardness will decrease; this is within the scope of our study.     

Surface modification of natural fibers using bacteria: depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites

Triggered biodegradable composites made entirely from renewable resources are urgently sought after to improve material recyclability or be able to divert materials from waste streams. Many biobased polymers and natural fibers usually display poor interfacial adhesion when combined in a composite material. Here we propose a way to modify the surfaces of natural fibers by utilizing bacteria ( Acetobacter xylinum) to deposit nanosized bacterial cellulose around natural fibers, which enhances their adhesion to renewable polymers. This paper describes the process of modifying large quantities of natural fibers with bacterial cellulose through their use as substrates for bacteria during fermentation. The modified fibers were characterized by scanning electron microscopy, single fiber tensile tests, X-ray photoelectron spectroscopy, and inverse gas chromatography to determine their surface and mechanical properties. The practical adhesion between the modified fibers and the renewable polymers cellulose acetate butyrate and poly(L-lactic acid) was quantified using the single fiber pullout test.