High PVA Research Articles

Facile strategy of Fe3+ rich collagen-based composite hydrogel for antibacterial, electricity harvesting and sensing applications

Conventional hydrogels have poor conductivity and low stretchability, limiting their practical applications for different purposes. Herein, collagen (CL) based, poly(vinyl alcohol) (PVA) and glutaraldehyde (GT) cross-linked ferric ion (Fe3+) rich highly conductive CL/GT/PVA/Fe hydrogel was developed. The presence of high CL, PVA and Fe3+ ions, together with the effective Fe3+ complexes formation, delivers the hydrogel with some particular assigns, such as high ionic conductivity (3.44 S.m−1) and antibacterial activity; furthermore, a very high stretchability. The CL/GT/PVA/Fe hydrogel demonstrated excellent mechanical properties, where the highest tensile strength of the hydrogels was ∼204.5 kPa at an elongation of 674 %, and the highest compressive strength was ∼0.39 MPa, with the highest stretchability of 81.67 %. The strengths are enhanced significantly by the incorporation of Fe3+ ions because of the formation of effective complexation of Fe3+ with rich hydroxyl and carboxyl groups of PVA and CL. As a flexible strain sensor, the CL/GT/PVA/Fe hydrogel with excellent conductivity manifests high sensitivity in human motion monitor. The hydrogels’ sufficient –OH and –COOH groups play a key role in imparting moist-induce electricity supply and the highest 173 mV of open circuit voltage (Voc) generated during moisture spray.

High Ion-Conducting PVA Nanocomposite Hydrogel-Based Wearable Piezoelectric and Triboelectric Sensors for Harsh Environments.

Traditional hydrogel-based wearable sensors with flexibility, biocompatibility, and mechanical compliance exhibit potential applications in flexible wearable electronics. However, the low sensitivity and poor environmental resistance of traditional hydrogels severely limit their practical application. Herein, high-ion-conducting poly(vinyl alcohol) (PVA) nanocomposite hydrogels were fabricated and applied for harsh environments. MXene ion-conducting microchannels and poly(sodium 4-styrenesulfonate) ion sources contributed to the directional transport of abundant free ions in the hydrogel, which significantly improved the sensitivity and mechanical-electric conversion of the nanocomposite hydrogel-based piezoelectric and triboelectric sensors. More importantly, the glycerol as an antifreezing agent enabled the hydrogel-based sensors to function in harsh environments. Therefore, the nanocomposite hydrogel exhibited high gauge factor (GF) at -20 °C (GF = 3.37) and 60 °C (GF = 3.62), enabling the hydrogel-based sensor to distinguish different writing letters and sounding words. Meanwhile, the hydrogel-based piezoelectric and triboelectric generators showed excellent mechanical-electric conversion performance regardless of low- (-20 °C) or high- (60 °C) temperature environments, which can be applied as a visual feedback system for information transmission without external power sources. This work provides self-powered nanocomposite hydrogel-based sensors that exhibit potential applications in flexible wearable electronics under harsh environmental conditions.

Lignin/PVA hydrogel with enhanced structural stability for cationic dye removal

In this study, a lignin-based hydrogel for wastewater treatment was prepared by incorporating kraft lignin (KL) into a poly (vinyl alcohol) (PVA) matrix. The underwater structural stability of the KL-PVA hydrogel was guaranteed through physicochemical crosslinking, involving freeze–thaw process and chemical crosslinking reaction. The KL-PVA hydrogel displayed superior compressive characteristics compared to the original PVA hydrogel. This improvement was attributed to the chemical crosslinking and the reinforcing effect of the incorporated KL microparticles. The incorporation of anionic KL microparticles into the PVA three-dimensional network structure enhanced the cationic methylene blue (MB) and crystal violet (CV) adsorption efficiency of the prepared KL-PVA hydrogel. The MB adsorption results were well explained by pseudo-2nd order kinetics model and Langmuir isotherm model. Electrostatic forces, hydrogen bonding and π-π stacking interactions were the main adsorption mechanisms between cationic dyes and KL surfaces, indicating the potential of KL-PVA hydrogel as an effective adsorption material. Moreover, regulating the molecular weight of PVA not only prevented lignin leakage from the KL-PVA hydrogel but also elevated the KL content within the hydrogel, consequently improving its dye removal performance. For KL-PVA hydrogel with high molecular weight PVA, the MB and CV adsorption capacities were 193.8 mg/g and 190.0 mg/g, respectively.

Novel Antibacterial and Biocompatible Nanostructured Gels Based on One-step Synthesis as a Potential Disinfectant for Endodontic Infection Control

AimThe objective of this study was to develop nanostructured gels as biocompatible intracanal disinfectants by one-step microwave radiation-assisted synthesis. MethodsPolyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) were used as a support network, and polyethylene glycol (PEG) was used as a reducing agent. The gels were characterized by measuring the swelling ratio (SR) and rheological properties and by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The antibacterial effects of each gel were evaluated against the endodontic clinical strain Enterococcus faecalis. Then, the viability of the 21-day mature multispecies bacterial biofilm was assessed using confocal microscopy in an ex vivo model, where the biofilm was exposed to the mix of nanogels. The cell proliferation, viability, and morphology of human periodontal ligament (HPDL) cells were quantified using a real-time IncuCyte® S3 Live-Cell System. Viability was measured by confocal microscopy using an ex vivo model exposing a 21-day mature multispecies bacterial biofilm to the mix of nanogels. ResultsThe antibacterial activity of the gels coincided with the superficial characterization and the solubility of the gel in the growth medium. Gels with higher viscosity (327.85-980.58 Pa s), higher dissolution (42-70%SR), and lower porosity (no porosity and 611.63 nm) showed excellent antibacterial activity against E. faecalis. Despite their physicochemical characteristics, CuNPs gels showed greater effectiveness against E. faecalis.These nanostructured gels with high PVA concentrations promote HPDL cells proliferation while still exerting antibacterial properties. Mix of nanogels showed an increase non-viable cells biomass from at of application. ConclusionsThe use of biocompatible polymers influences the physicochemical, bactericidal, and cytotoxic response, making these materials potential disinfectant agents against resistant bacteria with good biocompatibility and improved HPDL cells proliferation.

Enhancing Polyantimonic-Based Materials’ Moisture Response with Binder Content Tuning

Humidity sensors are of huge importance in diverse domains. Several types of materials present a moisture-sensing capacity; however, frequently, their electrical response does not display time stability. Due to its high thermal stability, high ionic conductivity, and different conduction mechanism contributing to its overall conductivity, polyantimonic acid (PAA) is seen as a promising material for humidity-sensing devices. In the present work, crystalline PAA was obtained via a simple and safe hydrolysis technique using SbCl3 as a precursor. Bulky sensor samples were produced using different amounts of polyvinyl alcohol (10–20 wt.% PVA) as a binder. The obtained PAA solid sensors were tested at room temperature (RT) in order to evaluate their moisture detection/measuring ability in the relative humidity range 0–100%; the evaluation was carried out with electrical impedance spectroscopy. The sample’s structure and morphology were studied using diverse experimental techniques (porosimetry, scanning electron microscopy, X-ray diffraction analysis, and thermogravimetry analysis, etc.). The sensors’ electrical response was in line with the found structural and morphological features. The slope of the resistance variation with an RH percentage concentration between 1 kΩ and 1.5 kΩ was noted for all sensors (showing no changes with time) in the interval between 30 and 100% RH. A good repeatability and reproducibility of the evaluated sensors’ electrical response was observed: the ones that displayed a higher sensitivity were the ones with a high PVA binder content, higher than previously published results for PAA, as well as a very good time stability along the time and low hysteresis.

Preparation and characterization of high strength and high modulus PVA-La fiber with synthesized syndiotacticity-rich high polymerization degree PVA polymers as raw materials

Preparation and characterization of high strength and high modulus PVA-La fiber with synthesized syndiotacticity-rich high polymerization degree PVA polymers as raw materials

Amphiphilic Poly(vinyl alcohol) Membranes Leaving Out Chemical Cross-Linkers: Design, Synthesis, and Function of Tailor-Made Poly(vinyl alcohol)-b-poly(styrene) Copolymers.

Tailor-made poly(vinyl alcohol)-b-poly(styrene) copolymers (PVA-b-PS) for separation membranes are synthesized by the combination of reversible-deactivation radical polymerization techniques. The special features of these di-block copolymers are the high molecular weight (>70kDa), the high PVA content (>80wt%), and the good film-forming property. They are soluble only in hot dimethyl sulfoxide, but by the "solvent-switch" technique, they self-assemble in aqueous media to form micelles. When the self-assembled micelles are cast on a porous substrate, thin-film membranes with higher water permeance than that of PVA homopolymer are obtained. Thus, by using these tailor-made PVA-b-PS copolymers, it is demonstrated that chemical cross-linkers and acid catalysts can no longer be needed to produce PVA membranes, since the PS nanodomains within the PVA matrix act as cross-linking points. Lastly, subsequent thermal annealing of the thin film enhances the membrane selectivity due to the improved microphase separation.

Preparation of well-defined Poly(Vinyl alcohol) by hydrolysis of Poly(Vinyl acetate) synthesized by RAFT suspension polymerization

Poly(vinyl alcohol) (PVA) is a widely used synthetic polymer that is made by hydrolysis of poly(vinyl acetate) (PVAc). A significant challenge in the production of well-defined PVA arises due to the high frequency of chain transfer reactions that occur in the radical polymerization of PVAc, which limits the molecular weight and leads to branching. Upon hydrolysis of PVAc, both acetate groups and branch points can be hydrolyzed, resulting in a PVA with a significantly lower molecular weight than the parent PVAc, making control over the molecular weight distribution of PVA difficult. In this work we demonstrate the production of PVAc with a well-defined and linear structure by reversible addition-fragmentation chain transfer (RAFT) polymerization under conditions in which chain transfer is reduced. PVAc samples were prepared by suspension polymerization using both conventional free-radical polymerization and RAFT polymerization at 50 °C. When using RAFT polymerization, upon hydrolysis there was a minimal decrease of the degree of polymerization and high molecular weight PVA of low dispersity was obtained. These results demonstrate the synthesis of well-defined PVA and offers a potential route to the production of PVAc and PVA products with uniform properties.

Synthesis of poly(vinyl alcohol) by blue light bismuth oxide photocatalysed RAFT. Evaluation of the impact of freeze/thaw cycling on ice recrystallisation inhibition.

Poly(vinyl alcohol), PVA, is the most potent polymeric ice recrystallisation inhibitor (IRI), mimicking a complex function of ice binding proteins. The IRI activity of PVA scales with its molecular weight and hence broad molecular weight distributions in free radical-derived PVAs lead to activity measurements dominated by small amounts of heavier fractions. Well-defined PVA can be prepared by thermally initiated RAFT/MADIX polymerization using xanthates by the polymerization of the less activated monomer vinyl acetate. The low conversions and molecular weights obtained during this approach, often requires feeding of additional initiator and bulk polymerization. Here we employ bismuth oxide photo-RAFT in solution, using blue light (450 nm), rather than previously reported white light, to obtain a library of PVA's. The use of blue light enabled quantitative conversion and acceptable dispersities. Purple light (380 nm) was also used, but asymmetric molecular weight distributions were obtained in some cases. High concentrations of high molecular weight PVA is known to form cryogels during freeze/thaw which has led to speculation this might limit the use of PVA in environments where the temperature cycles e.g. the construction industry. After 4 freeze/thaw cycles there was only small changes in observable IRI for all synthesised PVAs and two commercial standards. In an extended test, activity was retained after 100 freeze/thaw cycles, mitigating concerns that PVA could not be used in situations where freeze/thaw cycles occur. This work presents a convenient method to obtain well-defined PVAs for cryoscience studies compared to conventional thermal-RAFT and indicates that cryogelation concerns may not prevent their use.

Environmentally friendly, flexible and high performance PVA dielectric layer fabricated by solution method and its application in IGZO-TFT

At present, Poly (Vinyl Alcohol) (PVA)is often used as the dielectric layer of thin film transistors (TFT)because of its good insulation and environmental protection. However, because of the hydroxyl groups on the surface, PVA films have poor contact with electrodes and semiconductors. Therefore, in this paper, we proposed an effective way to make PVA molecules curled up by applying dual solvent system with water and ethanol. As a result, the leakage current density is reduced from 1.2 × 10 −4 A/cm [2]@0.5 mV/cm to 6.2 × 10 −6 A/cm [2]@0.5 mV/cm. Moreover, we adjusted the molecular morphology of PVA in the solution by optimizing the configuration sequence of the precursor solution, so as to obtain a PVA film with better performance, with a leakage current density of only 5.9 × 10 −7 A/cm [2]@0.5 mV/cm. The change in molecular morphology can be seen from the solution viscosity and surface tension measurements. Finally, we prepared IGZO-TFT devices for comparison, and it is proved that the PVA films prepared after changing the configuration sequence have better application in TFT, with a mobility of 8.19 cm 2 V −1 s −1 and a switching ratio of 2.76 × 10 6 . ∙ A dual solvent system is used to change the morphology of the polymer to improve its properties ∙Form better PVA films with a leakage current density of only 5.9 × 10 −7 A/cm [2]@0.5 mV/cm and it is better applied in TFT with a mobility of 8.19 cm 2 V −1 s −1 and a switching ratio of 2.76 × 10 6 ∙The materials used in the whole experiment are environmentally friendly and low-priced

Study on carrier dyeing for high strength high modulus PVA fiber

High strength high modulus PVA fiber or PVA high-fiber has excellent performances, such as high strength, high modulus, heat resistance, corrosion resistance, UV resistance, excellent impact resistance and adhesion. With the expansion of the application range of PVA high-fiber and the demand for color, it is pressing to study on the dyeing of PVA high-fiber. In this paper, dyeing process on PVA high-fiber had been deeply researched. PVA high-fiber has compact structure and high crystallinity, so carrier dyeing was selected here. Meanwhile, the types of dyes (Direct dyes, Reactive dyes, Cationic dyes, Disperse dyes) and carriers (type: anion, amphoteric ion, non-ion), the carrier concentration, the dyeing temperature and dyeing holding time were all selected and optimized. In the end, the most suitable dye, the most suitable carrier and the most optimal dyeing process were all identified. It was found that Direct dyes were the most suitable for PVA high-fiber dyeing, and non-ionic carrier had the most obvious dyeing effect. Under Direct dye and carrier N-25 conditions, the dye uptake was higher up to 68.6%, and wash fastness could reach grade 4. In addition, the optimal pretreatment time and power of low temperature plasma was identified. However, it was found that the pretreatment was little effective to promote PVA fiber dyeing. Considering that the carrier may reduce PVA high-fiber performance, x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), single fiber strength test were used. Finally it was concluded that the break strength of the dyed PVA high-fiber was slightly decreased and the crystal structure was barely changed.

Synthesis of syndiotacticity-rich high polymerization degree PVA polymers with VAc and VPa, fabrication of PVA fibers with superior mechanical properties by wet spinning

Synthesis of syndiotacticity-rich high polymerization degree PVA polymers with VAc and VPa, fabrication of PVA fibers with superior mechanical properties by wet spinning

Patient\u2013ventilator asynchrony, impact on clinical outcomes and effectiveness of interventions: a systematic review and meta-analysis

BackgroundPatient–ventilator asynchrony (PVA) is a common problem in patients undergoing invasive mechanical ventilation (MV) in the intensive care unit (ICU), and may accelerate lung injury and diaphragm mis-contraction. The impact of PVA on clinical outcomes has not been systematically evaluated. Effective interventions (except for closed-loop ventilation) for reducing PVA are not well established.MethodsWe performed a systematic review and meta-analysis to investigate the impact of PVA on clinical outcomes in patients undergoing MV (Part A) and the effectiveness of interventions for patients undergoing MV except for closed-loop ventilation (Part B). We searched the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, ClinicalTrials.gov, and WHO-ICTRP until August 2020. In Part A, we defined asynchrony index (AI) ≥ 10 or ineffective triggering index (ITI) ≥ 10 as high PVA. We compared patients having high PVA with those having low PVA.ResultsEight studies in Part A and eight trials in Part B fulfilled the eligibility criteria. In Part A, five studies were related to the AI and three studies were related to the ITI. High PVA may be associated with longer duration of mechanical ventilation (mean difference, 5.16 days; 95% confidence interval [CI], 2.38 to 7.94; n = 8; certainty of evidence [CoE], low), higher ICU mortality (odds ratio [OR], 2.73; 95% CI 1.76 to 4.24; n = 6; CoE, low), and higher hospital mortality (OR, 1.94; 95% CI 1.14 to 3.30; n = 5; CoE, low). In Part B, interventions involving MV mode, tidal volume, and pressure-support level were associated with reduced PVA. Sedation protocol, sedation depth, and sedation with dexmedetomidine rather than propofol were also associated with reduced PVA.ConclusionsPVA may be associated with longer MV duration, higher ICU mortality, and higher hospital mortality. Physicians may consider monitoring PVA and adjusting ventilator settings and sedatives to reduce PVA. Further studies with adjustment for confounding factors are warranted to determine the impact of PVA on clinical outcomes.Trial registration protocols.io (URL: https://www.protocols.io/view/the-impact-of-patient-ventilator-asynchrony-in-adu-bsqtndwn, 08/27/2020).

Branched/Hyperbranched Copolyesters from Poly(vinyl alcohol) and Citric Acid as Delivery Agents and Tissue Regeneration Scaffolds

AbstractMultifunctional branched/hyperbranched copolymers from poly(vinyl alcohol) (PVA) and citric acid (CA) are synthesized by varying the mole compositions of PVA and CA and are used as a prospective vehicle for encapsulation and release of bioactive molecules and as a potential scaffold for cell adhesion and growth. The branched architecture is established from spectroscopy and rheological measurements. All the copolymers have shown a lower hydrodynamic size and viscosity than the linear, high molecular weight PVA because of spherical and more compact architecture. Importantly, the size of the highly branched copolymer is found independent of pH which proved that the branch ends are capped with OH groups. Lower viscosity at equivalent solid content, biocompatibility, high antibacterial property, and presence of adequate macromolecular voids make the branched/hyperbranched copolymers a potential platform for encapsulation and release of gentamicin and other bioactive molecules. The macromolecular voids and chain end functionality also promote adhesion and growth of differentiated primary cells as well as undifferentiated stem cells implying that the copolyester can also be used as a potential 2D/3D scaffold for tissue engineering applications.

Results of CoALL 07-03 study childhood ALL based on combined risk assessment by in vivo and in vitro pharmacosensitivity

AbstractWe conducted a clinical trial and report the long-term outcome of 773 children with acute lymphoblastic leukemia upon risk-adapted therapy accrued in trial CoALL 07-03 (from the Cooperative Study Group for Childhood Acute Lymphoblastic Leukemia). In a 2-step stratification, patients were allocated to receive either low- or high-risk treatment, based on initial white blood cell count, age, and immunophenotype. A second stratification was performed according to the results of in vitro pharmacosensitivity toward prednisolone, vincristine, and asparaginase (PVA score) and in vivo response after induction therapy (minimal residual disease [MRD]). Therapy was reduced for both risk groups in patients with a low PVA score or negative MRD result, and intensified in patients with a high PVA score. Overall outcome improved significantly compared with the predecessor CoALL 06-97 trial, with identical therapy backbone despite treatment reduction in 15.8% of patients (10-year probability of event-free survival, 83.5% vs 73.9%; overall survival, 90.7% vs 83.8%). Outcome for patients in the reduced treatment arms was superior to that of patients in the standard arms, associated with a profound reduction in frequency and severity of infectious complications. Importantly, we observed a lack of correlation between in vitro and in vivo drug response, as well as a lower predictive value of in vitro drug testing, reflecting an intrinsic limitation of this methodology that prevents its use for treatment stratification in future trials. In conclusion, it might be possible to reduce chemotherapy in children with acute lymphoblastic leukemia selected by stringent in vivo measurement of MRD without jeopardizing overall outcome.

Computational Predictability of Microsponge Properties Using Different Multivariate Models.

The capabilities of principal component regression (PCR) and multiple linear regression (MLR) were evaluated to decipher and predict the impact of formulation and process parameters on the modeled metronidazole benzoate (MB)-ethyl cellulose (EC) microsponge (MBECM) properties. MBECM were prepared by a quasi-emulsion solvent diffusion method. A minimum experimentation was designed using Box-Behnken approach with one center point after initial screening experiments. Data was modeled by principal component analysis (PCA), PCR, and MLR. Two distinct groupings of developed MBECM was observed in initial qualitative PCA as a function of their respective formulation and processing parameters. Group A formulations with low dichloromethane, high PVA, and low stirring speed exhibited larger particle size, lower entrapment efficiency (EE), and lower actual drug content (ADC) than Group B formulations. Optimized quantitative PCR and MLR models demonstrated a linear dependence of particle size and quadratic dependence of EE and ADC on the studied formulation and process parameters. Interestingly, MLR models showed relatively better predictability of the selected MBECM formulation properties when compared with PCR. MBECM were amorphous in nature and spherical shaped. Carbopol® 940 NF based hydrogel of selected MBECM formulation exhibited a prolonged MB release than the commercial MB gel (Metrogyl®), showing no signs of necrosis in the goat mucosa. Thus, a properly designed minimum experimentation coupled with multivariate modeling generated a knowledge-rich target space, which enabled to understand and predict the performance of developed MBECM within a prescribed design space.

Solution properties and electrospinning of poly(galacturonic acid) nanofibers

Poly(galacturonic acid) (PGuA) is an important natural biopolymer, however its potential has not been realized due to its anionic nature and rigid structure, which limits its processability into fine films and fibres. This study aims at modifying the solution properties of PGuA in alkaline medium (aq. sodium hydroxide) to enable their conversion into electrospun nanofibers. Addition of anionic surfactants was found to play an important role in individualizing the PGuA chains that lead to formation of small spindle shaped fibers of length ranging from 2 to 10 μm and diameter from 287 to 997 nm. However, continuous fibers were not formed even at concentrations higher than the critical concentration. Addition of small amount (10–30%) of high molecular weight PVA resulted in formation of continuous fibers. Correlation of fiber diameters of PGuA/PVA with the rheological properties suggested a strong dependence of diameter with the elasticity of the blend solutions. Such PGuA based fibers may be utilized in various biomedical applications.

Pervaporation Dehydration of Azeotropic Water/Acetonitrile Mixture Using High Water Affinity PVA–PVAm Blended Membrane

Acetonitrile and water forms an azeotropic mixture having a boiling point of 76.5 °C and containing approximately 82.2 wt % acetonitrile under atmospheric pressure. Accordingly for their separation, heterogeneous distillation, extractive distillation, and solvent extraction have been used. The recovery of solvent and solute from the extract phase can usually be done by additional distillation processes, which ultimately lead to a less economical and energy intensive pathway. The hydrophilic polymers, poly(vinyl alcohol) and poly(vinyl amine) were used to prepared blended membrane and crosslinked them using glutaraldehyde as crosslinking agent. The FTIR, XRD, DSC, SEM, and swelling studies techniques were used to characterize all the blended membranes and applied for pervaporation separation of water/acetonitrile feed mixtures. Comparison of pervaporation data with water–acetonitrile vapor–liquid equilibrium data confirmed that the membrane acted as a third phase to effectively break azeotropes.

PVA-gelatin hydrogels formed using combined theta-gel and cryo-gel fabrication techniques

Poly(vinyl alcohol) (PVA) is a synthetic, biocompatible polymer that has been widely studied for use in bioengineered tissue scaffolds due to its relatively high strength, creep resistance, water retention, and porous structure. However, PVA hydrogels traditionally exhibit low percent elongation and energy dissipation. PVA material and mechanical properties can be fine-tuned by controlling the physical, non-covalent crosslinks during hydrogel formation through various techniques; PVA scaffolds were modified with gelatin, a natural collagen derivative also capable of forming reversible hydrogen bonds. Blending in gelatin and poly(ethylene glycol) (PEG) with PVA prior to solidification formed a highly organized hydrogel with improved toughness and dynamic elasticity. Theta-gels were formed from the solidification of warm solutions and the phase separation of high molecular weight gelatin and PVA from a low molecular PEG porogen upon cooling. While PVA-gelatin hydrogels can be synthesized in this manner, the hydrogels exhibited low toughness with increased elasticity. Thus, theta-gels were additionally processed using cryo-gel fabrication techniques, which involved freezing theta-gels, lyophilizing and re-hydrating. The result was a stronger, more resilient material. We hypothesized that the increased formation of physical hydrogen bonds between the PVA and gelatin allowed for the combination of a stiffer material with energy dissipation characteristics. Rheological data suggested significant changes in the storage moduli of the new PVA-gelatin theta-cryo-gels. Elastic modulus, strain to failure, hysteresis and resilience were studied through uniaxial tension and dynamic mechanical analysis in compression.

Experimental tests on the underwater abrasion of Engineered Cementitious Composites

The abrasion of Engineered Cementitious Composites (ECC) due to waterborne materials in hydraulic structures was investigated using the ASTM C1138 abrasion test method. The test specimens were divided into two groups, the first was directed to study the effect of the PVA fiber content, while the second investigated the effect of the ECC covering layer thickness. The tests were conducted at ages of 3, 7 and 28 days. The test results showed that the abrasion resistance increases as PVA content increase. At an age of 28 days, incorporating low PVA contents (0.5% and 1.0%) increased the abrasion resistance by approximately 20%, while the inclusion of high PVA contents (1.5% and 2.0%) improved the abrasion resistance significantly with percentage improvements ranging from 50 to 95%. The percentage abrasion weight losses after 72 testing hours at this age were 7.6, 5.9, 4.7, 3.6 and 2.4% for fiber contents of 0, 0.5, 1.0, 1.5 and 2.0%, respectively. The test results also showed that covering of normal concrete with 1 cm layer of ECC is not effective during the early age of this material, while a layer of 3 cm thickness showed good abrasion resistance at early and mature ages.