Wet Tensile Strength Research Articles

Performance of Micro- and Nano-Modified Asphalt Mixtures Through Flow Number and Moisture Susceptibility Evaluations

Abstract The objective of this study was to utilize micro- and nano-materials to improve the overall performance of asphalt mixtures through flow number and moisture susceptibility evaluations. The materials included non-modified nanoclay and polymer modified nanoclay, carbon microfiber, nanomer material, and nanosilica. These materials were mixed with the control asphalt to prepare the modified asphalt, and then, the modified asphalt was mixed with the aggregates to compact the modified asphalt mixtures. The Superpave performance tests were employed to evaluate the resistance to permanent deformation and moisture susceptibility of asphalt mixtures, including the flow number and indirect tensile strength tests. The microstructures of modified asphalt were examined by the field emission scanning electron microscope (FE-SEM) and the images helped to understand the modification mechanism. Statistical analysis was used to analyze the levels of impact of these modifiers on the improvement in performance. Based on the results of test data processing, (1) the flow number values of modified asphalt mixtures improved significantly, and it indicated that the rutting performance of modified mixtures was enhanced after the addition of these modifiers; the statistical analysis data revealed that all modifiers had a significant influence on the improvement in performance; (2) the dry and wet tensile strengths increased in most of the modified mixtures, and the statistical analysis results implied that most of the modifiers can greatly impact the moisture susceptibility of asphalt mixtures.

Preparation and Characterization of Resorbable Bacterial Cellulose Membranes Treated by Electron Beam Irradiation for Guided Bone Regeneration.

Bacterial cellulose (BC) is an excellent biomaterial with many medical applications. In this study, resorbable BC membranes were prepared for guided bone regeneration (GBR) using an irradiation technique for applications in the dental field. Electron beam irradiation (EI) increases biodegradation by severing the glucose bonds of BC. BC membranes irradiated at 100 kGy or 300 kGy were used to determine optimal electron beam doses. Electron beam irradiated BC membranes (EI-BCMs) were evaluated by scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, thermal gravimetric analysis (TGA), and using wet tensile strength measurements. In addition, in vitro cell studies were conducted in order to confirm the cytocompatibility of EI-BCMs. Cell viabilities of NIH3T3 cells on 100k and 300k EI-BCMs (100 kGy and 300 kGy irradiated BC membranes) were significantly greater than on NI-BCMs after 3 and 7 days (p < 0.05). Bone regeneration by EI-BCMs and their biodegradabilities were also evaluated using in vivo rat calvarial defect models for 4 and 8 weeks. Histometric results showed 100k EI-BCMs exhibited significantly larger new bone area (NBA; %) than 300k EI-BCMs at 8 weeks after implantation (p < 0.05). Mechanical, chemical, and biological analyses showed EI-BCMs effectively interacted with cells and promoted bone regeneration.

The Efficacy of Electron Beam Irradiated Bacterial Cellulose Membranes as Compared with Collagen Membranes on Guided Bone Regeneration in Peri-Implant Bone Defects.

Bacterial cellulose (BC) is a natural polysaccharide produced by some bacteria, and consists of a linear polymer linked by β-(1,4) glycosidic bonds. BC has been developed as a material for tissue regeneration purposes. This study was conducted to evaluate the efficacy of resorbable electron beam irradiated BC membranes (EI-BCMs) for guided bone regeneration (GBR). The electron beam irradiation (EI) was introduced to control the biodegradability of BC for dental applications. EI-BCMs had higher porosity than collagen membranes (CMs), and had similar wet tensile strengths to CMs. NIH3T3 cell adhesion and proliferation on EI-BCMs were not significantly different from those on CMs (p > 0.05). Micro-computed tomography (μCT) and histometric analysis in peri-implant dehiscence defects of beagle dogs showed that EI-BCMs were non-significantly different from CMs in terms of new bone area (NBA; %), remaining bone substitute volume (RBA; %) and bone-to-implant contact (BIC; %) (p > 0.05). These results suggest resorbable EI-BCMs can be used as an alternative biomaterial for bone tissue regeneration.

Chemically modified cellulose micro- and nanofibrils as paper-strength additives

Chemically modified cellulose micro- and nanofibrils were successfully used as paper strength additives. Three different kinds of cellulose nanofibrils (CNFs) were studied: carboxymethylated CNFs, periodate-oxidised carboxymethylated CNFs and dopamine-grafted carboxymethylated CNFs, all prepared from bleached chemical fibres of dissolving grade, and one microfibrillated cellulose from unbleached kraft fibres. In addition to mechanical characterization of the final paper sheets the fibril retention, sheet density and sheet morphology were also studied as a function of addition of the four different cellulose fibrils. In general, the cellulose fibrils, when used as additives, significantly increased the tensile strength, Young’s modulus and strain-at-break of the paper sheets. The effects of the different fibrils on these properties were compared and evaluated and used to analyse the underlying mechanisms behind the strengthening effect. The strength-enhancing effect was most pronounced for the periodate-oxidised CNFs when they were added together with polyvinyl amine (PVAm) or poly(dimethyldiallylammonium chloride) (pDADMAC). The addition of periodate-oxidised CNFs, with pDADMAC as retention aid, resulted in a 37% increase in tensile strength at a 2 wt% addition and an 89% increase at a 15 wt% addition (from 67 to 92 and 125 kNm/kg, respectively) compared to a reference with only pDADMAC. Wet-strong sheets with a wet tensile index of 30 kNm/kg were also obtained when periodate-oxidised CNFs and PVAm were combined. This significant increase in wet strength is suggested to be the result of a formation of cross-links between the aldehyde groups, introduced by the periodate oxidation, and hydroxyl groups on the lignocellulosic fibres and the primary amines of PVAm. Even though less significant, there was also an increase in wet tensile strength when pDADMAC was used together with periodate-oxidised fibrils which shows that the aldehyde groups are able to increase the wet strength without the presence of the primary amines of the PVAm. As an alternative method to strengthen the fibre network, carboxymethylated CNFs grafted with dopamine, by an ethyl dimethylaminopropyl carbodiimide coupling, were used as a strength additive. When used as an additive, these CNFs showed a strong propensity to form films on and around the fibres and significantly increased the mechanical properties of the sheets. Their addition resulted in an increase in the Young´s modulus by 41%, from 5.1 to 7.2 GPa, and an increase in the tensile strength index of 98% (from 53 to 105 kNm/kg) with 5 wt% retained dopamine-grafted CNFs.

The Strength of Moulding Sand Consisting of a Mixture of Bentonite, Tapioca Flour, and Sago Flour as a New Binder Formula to Improve the Quality of Al-Si Cast Alloy

The major factors determining the quality of sand casting products are the base sand and the composition of the sand mould and the binding material. In the foundry industry, the most commonly used binder for creating sand moulds is bentonite. However, the price of bentonite is likely to keep rising. This study aimed at discovering a new binder formula associated with the effect of binder composition i.e. bentonite, tapioca flour, and sago flour on the basis of its mechanical and physical properties. The new formula was expected to be a better binder in the production of sand moulds, resulting in high-quality casting products with minimal defects. Moreover, it is probable to be much more economical than bentonite. This research focused on testing the moulding sand composition with a number of different binders, i.e. bentonite, tapioca flour, and sago flour, each in a different proportion. The mixture of the moulding sand with each of the three binders will be tested in terms of its mechanical properties including compressive, shear, and tensile strength. Based on the test results, sago flour has the highest dry compressive strength of 28.6 N/cm2, whereas bentonite has the highest wet compressive strength, i.e. 11.83 N/cm2 and the highest wet shear strength i.e. 3.16 N/cm2. The binder with the highest dry shear strength is tapioca flour with 18.16 N/cm2. Regarding the tensile strength value, bentonite has the highest wet tensile strength of 0.85 N/cm2, while sago flour has the highest dry tensile strength of 1.73 N/cm2.

Filaments with Affinity Binding and Wet Strength Can Be Achieved by Spinning Bifunctional Cellulose Nanofibrils.

We demonstrate benzophenone (BP) conjugation via amine-reactive esters onto oxidized cellulosic fibers that were used as precursors, after microfluidization, of photoactive cellulose nanofibrils (CNF). From these fibrils, cellulose I filaments were synthesized by hydrogel spinning in an antisolvent followed by fast biradical UV cross-linking. As a result, the wet BP-CNF filaments retained extensively the original dry strength (a remarkable ∼80% retention). Thus, the principal limitation of these emerging materials was overcome (the wet tensile strength is typically <0.5% of the value measured in dry conditions). Subsequently, antihuman hemoglobin (anti-Hb) antibodies were conjugated onto residual surface carboxyl groups, making the filaments bifunctional for their active groups and properties (wet strength and bioactivity). Optical (surface plasmon resonance) and electroacoustic (quartz crystal microgravimetry) measurements conducted with the bifunctional CNF indicated effective anti-Hb conjugation (2.4 mg m-2), endowing an excellent sensitivity toward Hb targets (1.7 ± 0.12 mg m-2) and negligible nonspecific binding. Thus, the anti-Hb biointerface was deployed on filaments that captured Hb efficiently from aqueous matrices (confocal laser microscopy of FITC-labeled antibodies). Significantly, the anti-Hb biointerface was suitable for regeneration, while its sensitivity and selectivity in affinity binding can be tailored by application of blocking copolymers. The developed bifunctional filaments based on nanocellulose offer great promise in detection and affinity binding built upon 1D systems, which can be engineered into other structures for rational use of material and space.

The Strength of Moulding Sand Consisting of a Mixture of Bentonite, Tapioca Flour, and Sago Flour as a New Binder Formula to Improve the Quality of Al-Si Cast Alloy

The major factors determining the quality of sand casting products are the base sand and the composition of the sand mould and the binding material. In the foundry industry, the most commonly used binder for creating sand moulds is bentonite. However, the price of bentonite is likely to keep rising. This study aimed at discovering a new binder formula associated with the effect of binder composition i.e. bentonite, tapioca flour, and sago flour on the basis of its mechanical and physical properties. The new formula was expected to be a better binder in the production of sand moulds, resulting in high-quality casting products with minimal defects. Moreover, it is probable to be much more economical than bentonite. This research focused on testing the moulding sand composition with a number of different binders, i.e. bentonite, tapioca flour, and sago flour, each in a different proportion. The mixture of the moulding sand with each of the three binders will be tested in terms of its mechanical properties including compressive, shear, and tensile strength. Based on the test results, sago flour has the highest dry compressive strength of 28.6 N/cm2, whereas bentonite has the highest wet compressive strength, i.e. 11.83 N/cm2 and the highest wet shear strength i.e. 3.16 N/cm2. The binder with the highest dry shear strength is tapioca flour with 18.16 N/cm2. Regarding the tensile strength value, bentonite has the highest wet tensile strength of 0.85 N/cm2, while sago flour has the highest dry tensile strength of 1.73 N/cm2.

Influence of TEMPO-oxidised cellulose nanofibrils on the properties of filler-containing papers

In this work, cellulose nanofibrils (CNF) were produced from a Eucalyptus globulus bleached kraft pulp by TEMPO-mediated oxidation and mechanical homogenisation, and their effects in papermaking, namely filler flocculation and retention, dry and wet-web strength and structural properties, were studied in detail. Cellulose nanofibrils possessing 0.6 mmol/g carboxyl groups and a degree of polymerisation (DP) of ca. 550 were found to promote filler flocculation and retention in the fibre mat, whereas the same amount (3 wt%) of CNF having 1.5 mmol/g of carboxyl groups, a DP of ca. 200 and a similar mean diameter exhibited the opposite effect. These results were interpreted with the help of flocculation studies of precipitated calcium carbonate (PCC) in the presence of CNF carried out by laser diffraction spectrometry. In addition, the mechanical and structural properties of the handsheets were analysed, revealing that the less charged CNF led to more closed matrices and, even increasing the filler retention, had a positive role on the tensile strength. A bonding mechanism among eucalypt fibres, PCC, CNF and a linear cationic polyacrylamide is proposed, consistent with the flocculation, retention and paper strength and structural property results. It is concluded that, to be used in papermaking, the CNF must not have a high charge (or a small length) to be able to flocculate the filler particles and, at the same time, to increase the filler-to-cellulosic fibres bonding. A complementary study on the wet-web resistance of handsheets produced with the less charged CNF was conducted for moisture contents between 10 and 70%, showing that these CNF can significantly improve the handsheet wet tensile strength (nearly 100%) even for water contents above 50%. The use of CNF in the paper machine may thus contribute, through the higher wet-web tensile resistance, to reducing breaks and increasing the operating speeds and, through the higher filler retention, to important fibre and cost savings.

Cellulose oxidation by Laccase-TEMPO treatments

In this work, laccase-TEMPO (Lac-T) treatments were applied to bleached commercial dissolving pulp in order to introduce carbonyl and carboxyl groups, which were found to improve dry and wet strength-related properties. Also the solubility behavior towards xanthate reactions was assessed. The effect of a refining step (R) before the oxidative treatment, the absence or presence of oxygen pressure, TEMPO dose (2 or 8% oven dried pulp) and reaction time (8 or 20h) were thoroughly examined. Treatments conducted in the presence of oxygen pressure exhibited greater amount of functional groups. Introducing a pre-refining treatment resulted in similar functional groups but higher wet strength was achieved. Specifically, a high W/D strength ratio was observed, indicating that wet strength-related property was satisfactorily developed. Besides the fact that all Lac-T treatments caused severe cellulose degradation, no fiber strength loss was detected. In fact, all oxidized samples presented higher Wet Zero-Span Tensile Strength, mainly in R+ Lac-T (O2) sample, which suggested the formation of hemiacetal linkages between the new introduced aldehyde groups and available free hydroxyl groups resulting from fibrillation.

Compressive, diametral tensile and biaxial flexural strength of cutting-edge calcium phosphate cements

Calcium phosphate cements (CPCs) are widely used in bone repair. Currently there are two main types of CPCs, brushite and apatite. The aim of this project was to evaluate the mechanical properties of particularly promising experimental brushite and apatite formulations in comparison to commercially available brushite- and apatite-based cements (chronOS™ Inject and Norian® SRS®, respectively), and in particular evaluate the diametral tensile strength and biaxial flexural strength of these cements in both wet and dry conditions for the first time. The cements׳ porosity and their compressive, diametral tensile and biaxial flexural strength were tested in wet (or moist) and dry conditions. The surface morphology was characterized by scanning electron microscopy. Phase composition was assessed with X-ray diffraction. It was found that the novel experimental cements showed better mechanical properties than the commercially available cements, in all loading scenarios. The highest compressive strength (57.2±6.5MPa before drying and 69.5±6.0MPa after drying) was found for the experimental brushite cement. This cement also showed the highest wet diametral tensile strength (10.0±0.8MPa) and wet biaxial flexural strength (30.7±1.8MPa). It was also the cement that presented the lowest porosity (approx. 12%). The influence of water content was found to depend on cement type, with some cements showing higher mechanical properties after drying and some no difference after drying.

A paper-based in vitro model for on-chip investigation of the human respiratory system.

Culturing cells at the air-liquid interface (ALI) is essential for creating functional in vitro models of lung tissues. We present the use of direct-patterned laser-treated hydrophobic paper as an effective semi-permeable membrane, ideal for ALI cell culture. The surface properties of the paper are modified through a selective CO2 laser-assisted treatment to create a unique porous substrate with hydrophilic regions that regulate fluid diffusion and cell attachment. To select the appropriate model, four promising hydrophobic films were compared with each other in terms of gas permeability and long-term strength in an aqueous environment (wet-strength). Among the investigated substrates, parchment paper showed the fastest rate of oxygen permeability (3 times more than conventional transwell cell culture membranes), with the least variation in its dry and wet tensile strengths (124 MPa and 58 MPa, remaining unchanged after 7 days of submersion in PBS).The final paper-based platform provides an ideal, robust, and inexpensive device for generating monolayers of lung epithelial cells on-chip in a high-throughput fashion for disease modelling and in vitro drug testing.

Micro-computed tomography: a tool to study the fracture behaviour of calcium phosphate cements

Event Abstract Back to Event Micro-computed tomography: a tool to study the fracture behaviour of calcium phosphate cements Sara Gallinetti1 and Caroline Öhman Mägi1 1 Uppsala University, Division of Applied Materials Science, Department of Engineering Sciences, Sweden Introduction: Due to its ability of non-destructive 3D imaging at high resolution, the use of micro-computed tomography (or micro-CT) in bone microstructure analysis has increased over the last decays. This technique can also be applied to implants or materials for bone augmentation e.g., calcium phosphate cements (CPCs). Despite many advantages[1], CPCs are brittle materials and are commonly not used alone, nor approved for use alone, in load-bearing applications. Nevertheless, it would be of importance to understand their fracture behaviour under different loading conditions. The aim of this study was to investigate the possibility to use micro-CT imaging to study the fracture behaviour of CPCs during compression and diametral tensile tests and to study possible correlations between mechanical and structural properties. Materials and Methods: Brushite cement were prepared by mixing monocalcium phosphate monohydrate (sieved to < 75 μm) and β-tricalcium phosphate powders at a molar ratio of 45:55 (each containing 1 wt % of disodium dihydrogen pyrophosphate) with 0.5 M citric acid at different liquid to powder ratios (L/P). Samples were let to set in PBS for 24 hours. Porosity was measured with a solvent exchange method[2] and samples were scanned with a micro-CT (Skyscann 1172, Bruker), using a source voltage of 100 kV, a current of 100 μA and an aluminium and cupper filter. Wet compressive strength (CS) and diametral tensile strength (DTS) were measured. Thereafter the samples were rescanned to visualise the fracture in 3D. dCS and dDTS samples were tested and scanned using an in situ loading stage in displacement control at increasing steps of 0.01 mm. Reconstruction, 3D visualisation and analysis of the micro-CT images were performed using respectively the softwares NRecon, CTvox and CTAn (Skyscan, Bruker). Details about samples and tests are reported in Table 1. SEM was used to investigate the microstructure of CPCs. Results and Discussion: Porosity increased linearly with L/P. Average CS decreased exponentially with L/P and the dimensions of the biggest defect (the latter calculated with CTAn). Average CS decreased with porosity but no model fitted the data. In fact, it was observed that the microstructure and the entanglement of the crystals played an important role in the CS. Materials with similar porosity but smaller crystals showed a significantly higher CS. Micro-CT imaging exposed several cracks in the samples after compression, which can be clearly visualized with this technique (Fig 1a). Similarly, DTS decreased with increased L/P and porosity. The post-scans also showed several cracks. Dynamic tests revealed that in both dCS and dDTS samples the failure did not occur at the first crack (Fig 1). Analogous results have been obtained in Portland cements[3]. Figure 1 - Micro CT reconstructions of: a) a section of the CPC before compression (left), the first crack (mid) and the sample after failure (right); b) a section of the DTS sample before testing (left), the first cracks (mid) and the sample after failure (right). The load at each step is displayed at the bottom of each image. Conclusions: Mechanical properties were found to be correlated to different structural parameters. Micro-CT imaging seems to be a promising method to study crack propagation and fracture behaviour of CPCs in different loading conditions. Carl Tryggers Stiftelse (CTS 13:533); Stiftelsen Lars Hiertas Minne (FO2014-0504)

Flame Retardation Modification of Paper-Based PVC Wallcoverings

The flame-retarded paper-based polyvinyl chloride (PVC) wallcoverings were successfully prepared, using plant fiber paper as base material and adding inorganic flame retardants and flame-retarded plasticizer as additives. Flame retardancy, thermostability, smoke suppression and mechanical properties were tested regarding to the prepared wallcoverings. The results showed that 2ZnO·3B 2 O 3 ·3.5H 2 O could improve flame retardancy and thermostability of paper-based PVC wallcoverings; plasticizer tricresyl phosphate increased flame retardancy of the prepared materials auxiliarily. Also, flame-retarded paper-based PVC wallcoverings with higher flame retardancy, smoke suppression and mechanical property was prepared using plant fiber paper with fix quantity of 90 g/m 3 as base material, using 2ZnO·3B 2 O 3 ·3.5H 2 O as inorganic flame retardant, and using tricresyl phosphate as plasticizer. For the flame-retarded paper-based PVC wallcoverings in this study, the limit oxygen index (LOI) reaches 32.3, maximal smoke density is 16.91 %, and the horizontal and longitudinal wet tensile strength reaches 1.38 kN·m −1 and 1.51 kN·m −1 respectively. Meanwhile, its flame retardancy meets the requirements about flame retardancy for material Class B 1 listed in Chinese National Standards GB 8624-2012, Classification for burning behavior of building materials and products . This research creates an effective path to prepare paper-based PVC wallcoverings with high flame retardancy.

Modelling the properties of pigment‐printed polypropylene nonwoven fabric using the Box–Behnken technique

The aim of this study was to develop statistical models for the effect of binder concentration and curing temperature and time on the air permeability, tear strength, tensile strength, and crocking fastness of pigment‐printed nonwoven polypropylene fabric. The design and analysis of the experimental work were carried out using Minitab® statistical software according to the Box–Behnken design of response surface methodology. Models were successfully developed. It was found that binder concentration improves the wet crocking and tensile strength while having a negative impact on all other responses. Increase in curing temperature and time affects the fabric tear strength negatively but has a positive effect on wet crocking fastness and fabric tensile strength. It could be concluded that pigment prints of good dry crocking fastness may be obtained on polypropylene nonwovens without deterioration in the mechanical strength and air permeability to a commercially unacceptable level. However, further work is required to improve the wet crocking fastness properties.

Evaluation of Moisture Susceptibility Minimization Strategies for Warm-Mix Asphalt: Case Study

AbstractWarm-mix asphalt (WMA) technologies aid in reducing mixing and compaction temperatures for asphalt concrete mixtures, allowing for savings in fuel consumption and extending haul distances and construction season. The reduced temperatures also provide a greener technology as emissions are lowered at the plant and the construction site. Engineering and environmental benefits promoted the rapid implementation of WMA technologies, but concerns remain regarding the difference in mixture performance of WMA versus hot-mix asphalt (HMA) because of the changes in the production process, specifically in terms of moisture susceptibility. This case study evaluates moisture susceptibility through the use of laboratory tests including the wet indirect tensile (IDT) strength test, the tensile strength ratio (TSR), and the Hamburg wheel tracking test (HWTT) analyzed with a novel methodology. The performance of two WMA technologies (Evotherm DAT and foaming) versus a control HMA is analyzed with and without antist...

Evaluation of foamed sulfur asphalt stabilized soils for road applications

This paper summarizes the research carried out to evaluate and compare the performance of marginal soils, namely marl, sabkha and dune sand treated with foamed sulfur asphalt (FSA) with the mixes of the same soils treated with conventional foamed asphalt (FA) for the construction of road bases. FSA and FA mixes were designed for the three soils utilizing low percentage of Portland cement (2%) and were optimized to meet dry and wet indirect tensile strength (ITS) requirements. Designed mixes were evaluated for Marshall stability, static triaxial (shear strength) and dynamic resilient modulus at 22°C.Results indicate that properly designed FSA mixes displayed a significant improvement in ITS (17% for marl and 9.4% for sand soils), Marshall stability (14% for marl and sand soils) and shear strength (135%, 76% and 250% for marl, sabkha and sand soils, respectively) as compared with those of conventional FA mixes. Resilient modulus testing indicated that FSA has marginally reduced the resilient modulus of soils compared with FA. Foamed sulfur asphalt technology can be used successfully to construct road bases from available marginal soils.

Structure and Properties of Chitin Whisker Reinforced Papers for Food Packaging Application

In recent years, concerns about environmental waste caused by petroleum-derived chemicals as well as the consumer's demand for high quality food products, have prompted people to pay more attention to developing biodegradable food packaging materials using natural resources such as cellulose fibers and chitin derivatives. In this study, chitin whiskers have been successfully generated by hydrolyzing the α-chitin sample. Then the synthesized nano-sized chitin whiskers were used at ratios from 0.1% to 2% (wt%) for improving strength properties of paper sheets by the dip-coating method. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) were used to investigate the morphology of chitin whiskers and cellulose fiber compounds. The results showed that coating with chitin whiskers brought about an increase in tear strength, burst strength, and wet and dry tensile strength, with a decrease in Zeta-potential value.

A preparation method of cellulose fiber networks reinforced by glutaraldehyde-treated chitosan

An eco-friendly polymeric additive was developed to increase the dry and wet strengths of cellulose fiber networks. Biopolymer chitosan was firstly treated with glutaraldehyde (GA) and then mixed with cellulose fibers in pulp suspension. GA-treated chitosan was deposited onto cellulose fibers by adjusting pH. Increases of 140 and 930 % were achieved for dry and wet tensile strength, respectively, at 2 wt% dosage which were much higher than that for the chitosan-treated samples (50 and 180 %, respectively). The surface morphology of cellulose fibers deposited with GA-treated chitosan was examined by scanning electron microscopy. The effects of GA-chitosan treatment on tear resistance and color properties were also investigated.

Effect of interfibrillar PVA bridging on water stability and mechanical properties of TEMPO/NaClO2 oxidized cellulosic nanofibril films

TEMPO/NaClO2 oxidized cellulosic nanofibrils (TCNF) were covalently bonded with poly(vinyl alcohol) (PVA) to render water stable films. Pure TCNF films and TCNF–PVA films in dry state showed similar humidity dependent behavior in the elastic region. However, in wet films PVA had a significant effect on stability and mechanical characteristics of the films. When soaked in water, pure TCNF films exhibited strong swelling behavior and poor wet strength, whereas covalently bridged TCNF–PVA composite films remained intact and could easily be handled even after 24h of soaking. Wet tensile strength of the films was considerably enhanced with only 10wt% PVA addition. At 25% PVA concentration wet tensile strengths were decreased and films were more yielding. This behavior is attributed to the ability of PVA to reinforce and plasticize TCNF-based films. The developed approach is a simple and straightforward method to produce TCNF films that are stable in wet conditions.

Surface modification of natural fibers by plasma for improving strength properties of paper sheets

Abstract Fibers of aspen chemi-thermomechanical pulp (CTMP), spruce CTMP, bleached kraft pulp (BKP), and kraft pulp were treated by low-temperature plasma (air) aiming at the detection of the relationship between chemical components on the surface and the properties of sheets. The effects of plasma treatment were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The results show that the strength properties of sheets, especially the wet-tensile strength, were significantly improved, while optical properties were scarcely affected. Aspen and spruce CTMPs with abundant lignin and extractives were sensitive to plasma treatment in that the O/C ratio increased and lignin or extractive contents decreased. However, the crystallinity of BKP evidently decreased after plasma treatment owing to carbohydrate enrichment on the surface. Compared to the partial removal of noncarbohydrates through a laccase/mediator system, plasma treatment did not remove them in large amounts but created more carboxyl and hydroxyl groups, which improved the strength properties of paper sheets.