Chemical degradation of polyacrylamide by advanced oxidation processes

Study on synergistic catalytic degradation of wastewater containing polyacrylamide catalyzed by low-temperature plasma-H2O2

The degradation behavior of polyacrylamide (PAM) solution by low-temperature plasma was investigated, and the effect of some factors that might affect the degradation process was further examined. The PAM solution was treated with low-temperature plasma generated by dielectric barrier discharge (DBD) combined with H2O2 and a Mn + Cu/AC composite catalyst. The optimal conditions for the oxidation degradation of a PAM solution using low-temperature plasma-H2O2-Mn + Cu/AC were determined as follows: initial concentration of 1000 mg/L, discharge voltage of 18 kV, H2O2 addition of 2%, and catalyst addition of 810 mg. The results indicated that the degradation rate increased with the increase of the catalyst dosage at the same discharge time. The degradation rate of 180 min increases from 90 to 97.6% with an increase in voltage from 16 to 18 kV, and the molecular weight decreases from 2,720,204.23 to 1,370,815.54. The degradation effect caused by the change of H2O2 addition was considerable compared with other factors. When the discharge time was 180 min, the degradation rate increased 26.3% with the increase of 1.6% H2O2 addition. Under the optimal process conditions, the addition of the catalyst resulted in a more rapid initial decrease in the pH value of the solution compared to the system without the catalyst.

Water-Soluble Synthetic Polymers: Their Environmental Emission Relevant Usage, Transport and Transformation, Persistence, and Toxicity

Water-soluble synthetic polymers (WSPs) are distinct from insoluble plastic particles, which are both critical components of synthetic polymers. In the history of human-made macromolecules, WSPs have consistently portrayed a crucial role and served as the ingredients of a variety of products (e.g., flocculants, thickeners, solubilizers, surfactants, etc.) commonly used in human society. However, the environmental exposures and risks of WSPs with different functions remain poorly understood. This paper provides a critical review of the usage, environmental fate, environmental persistence, and biological consequences of multiple types of WSPs in commercial and industrial production. Investigations have identified a wide market of applications and potential environmental threats of various types of WSPs, but we still lack the suitable assessment tools. The effects of physicochemical properties and environmental factors on the environmental distribution as well as the transport and transformation of WSPs are further summarized. Evidence regarding the degradation of WSPs, including mechanical, thermal, hydrolytic, photoinduced, and biological degradation is summarized, and their environmental persistence is discussed. The toxicity data show that some WSPs can cause adverse effects on aquatic species and microbial communities through intrinsic toxicity and physical hazards. This review may serve as a guide for environmental risk assessment to help develop a sustainable path for WSP management.

Study on low temperature plasma combined with AC/Mn + TiO2-Al2O3 catalytic treatment of sewage-containing polyacrylamide

With the introduction of tertiary oil recovery technology, polymer oil drive technology has effectively improved the recovery rate of crude oil, but the resulting oilfield wastewater-containing polyacrylamide (PAM) is viscous and complex in composition, which brings difficulties to wastewater treatment. The treatment of this kind of wastewater has become an urgent problem to be solved, and the removal of PAM is the key. In this paper, a dielectric barrier discharge (DBD) co-catalyst was used to treat PAM-containing solutions to investigate the effect of different catalytic reaction systems on the degradation of PAM. The morphological changes of the PAM solution before and after the reaction were also studied by the environmental electron microscope scanner (ESEM), and the information of the functional groups in the solution before and after the reaction was studied by infrared spectroscopy analysis of the PAM solution. The degradation rate rose by 26.3% in comparison to that without discharge when AC/Mn + TiO₂ and Al₂O₃ were combined and catalyzed at a mass ratio of 2:1 and a discharge period of 300 min. The degradation rate rose by 19.3 and 6.8%, respectively, in comparison to AC/Mn + TiO₂ and Al₂O₃-catalyzed alone. It demonstrates that this catalytic system has the optimum catalytic effect.

Detection and treatment of organic matters in hydraulic fracturing wastewater from shale gas extraction: A critical review

Although shale gas has shown promising potential to alleviate energy crisis as a clean energy resource, more attention has been paid to the harmful environmental impacts during exploitation. It is a critical issue for the management of shale gas wastewater (SGW), especially the organic compounds. This review focuses on analytical methods and corresponding treatment technologies targeting organic matters in SGW. Firstly, detailed information about specific shale-derived organics and related organic compounds in SGW were overviewed. Secondly, the state-of-the art analytical methods for detecting organics in SGW were summarized. The gas chromatography paired with mass spectrometry was the most commonly used technique. Thirdly, relevant treatment technologies for SGW organic matters were systematically explored. Forward osmosis and membrane distillation ranked the top two most frequently used treatment processes. Moreover, quantitative analyses on the removal of general and single organic compounds by treatment technologies were conducted. Finally, challenges for the analytical methods and treatment technologies of organic matters in SGW were addressed. The lack of effective trace organic detection techniques and high cost of treatment technologies are the urgent problems to be solved. Advances in the extraction, detection, identification and disposal of trace organic matters are critical to address the issues.

Clearance of methylene blue by CdS enhanced composite hydrogel materials

Hydrogel material is considered to be one of the effective adsorbents widely used to remove organic pollutants. However, the poor mechanical properties of some hydrogels limit their applications. Herein, we prepared composite hydrogels, for which acrylic acid (AA) and acrylamide (AM) were cross-linked and polymerised as the main substrate with adsorption function, while CdS nanoparticles were mainly used as reinforced material. Scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), two-dimensional infrared vibrational echo spectroscopy (2D-IR), and thermal gravimetric analyzer (TGA) were used to determine the physical and chemical structures of the hydrogels. The effects of the composition of AA, AM, and CdS on the mechanical properties and adsorption behaviours of the hydrogels were investigated. Besides, based on the great potential photocatalytic application value for wastewater remediation under the sunlight of CdS, the influence of the CdS doping amount on the photocatalytic property was also studied. As a result, when the mass ratio of AA to AM was 5:5, the hydrogel showed the best mechanical properties, and along with increasing the amount of CdS, the mechanical strength of the hydrogel was significantly enhanced from 0.445 MPa to 1.014 MPa. Besides, the composite hydrogels showed high adsorption and photocatalytic degradation synergistic clearance effect on methylene blue. Thus, the introduction of CdS photocatalytic nanoparticles may be an efficient and economical approach towards bifunctional hydrogel materials with enhanced mechanical property and photocatalytic degradation for wastewater remediation.

Efficient degradation of polyacrylamide using a 3-dimensional ultra-thin SnO2-Sb coated electrode

Polyacrylamide (PAM) is widely used in polymer flooding processes to increase oil recovery while the byproduct of PAM-containing wastewater is a serious environmental issue. In this study, electrochemical oxidation process (EAOP) was applied for treating PAM wastewater using a new type of 3-dimensional ultra-thin SnO₂-Sb electrode. Nano-sized catalysts were evenly dispersed both on the surface and inside of a porous Ti filter forming nano-thickness catalytic layer that enhances the utilization and bonding of catalysts. This porous Ti electrode showed 20% improved OH· production and 16.3 times increased accelerated service life than the planar Ti electrode. Using this electrode to treat 100 mg L^-1 PAM, the TOC removal efficiency reached over 99% within 3 h under current density of 20 mA cm^-2. The EAOP could fastly break the long-chain PAM molecules into small molecular intermediates. With the porous electrode treating 5 g L^-1 PAM under current density of 30 mA cm^-2, EAOP reduced 94.2% of average molecular weight in 1 h and 92.0% of solution viscosity in 0.5 h. Moreover, the biodegradability of PAM solution was significantly improved as the solution BOD₅/COD ratio raised from 0.05 to 0.41 after 4 h treatment. The degradation pathway of PAM was also investigated.

Toxicity of acrylamide after degradation by conjugated (UV/H2O2) photolysis in microalgae

Acrylamide (AA) is routinely used in laboratories and industries, and its disposal is always a problem; consequently, offering an alternative for their treatment contributes to conducting research in a responsible way. Therefore, in this work, acrylamide solutions were degraded by ultraviolet radiation and hydrogen peroxide (H₂O₂), and their toxicity was evaluated using a Desmodesmus quadricauda microalgae growth assay. The AA solutions were exposed to different dosages of H₂O₂ and different exposure times to UV radiation. The degradation was evaluated by liquid chromatography, which allowed the identification of the acrylamide peak and subsequent by-product peaks. A 100% degradation of the 1.5 mg L^-1 AA solution with UV/H₂O₂ (0.034 g L^-1) was achieved in just 10 min. The by-products formed did not inhibit the growth of D. quadricauda microalgae. The number of D. quadricauda individuals that grew in acrylamide solutions exposed to 20 and 30 min of UV radiation, with 0.034 g L^-1 of H₂O₂, was very similar to the number of individuals that grew in the control solution. Thus, the treatment proposed in this work using H₂O₂ combined with ultraviolet radiation degraded acrylamide into by-products with reduced toxicity.

Synergetic activation of persulfate by heat and Fe(II)-complexes for hydrolyzed polyacrylamide degradation at high pH condition: Kinetics, mechanism, and application potential for filter cake removal during cementing in CO2 storage wells

The long-term integrity of the interface between cement and formation rock in CO₂-capture and storage wells is crucial to avoid leakage of CO₂ in/along wells. However, the interface can be easily damaged by the filter cake, which is a compressed composite of bentonite, polymers such as hydrolyzed polyacrylamide (HPAM), and barite, on the wellbore rock. Therefore, removing the filter cake during the cementing process by degrading HPAM in an efficient way is essential. In this study, chelated-Fe²⁺ activated potassium persulfate (KPS) was used for HPAM degradation and filter-cake removal. Ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA-2Na) and diethylenetriaminepentaacetic acid (DTPA) were adopted to control the precipitation of Fe²⁺/Fe³⁺. A mixture of 0.4 mM Fe²⁺, 0.8 mM DTPA, and 4 mM KPS at a pH of 10.0 at 70 °C reduced the molecular weight of HPAM significantly from 3.0 × 10⁶ to (3.6-10) × 10⁴ Da. Electron paramagnetic resonance (EPR) analysis suggested that HO was the dominant radical and that SO₄^- and O₂^- were responsible for the degradation. The reactions conformed to continuous distribution kinetics with an activation energy of 38.36 kJ mol^-1. A possible degradation pathway was proposed based on analyses via infrared spectroscopy (IR) and time-of-flight liquid chromatography-mass spectrometry (TOF-LC/MS). >90 wt% of the filter cake was removed by the system. The results suggest that the proposed DTPA-Fe²⁺ activated KPS system exhibits promising potential for in situ degradation of high molecular weight HPAM and for the removal of filter cake in downhole wells.

Rapid removal of polyacrylamide from wastewater by plasma in the gas-liquid interface

Due to the severe restrictions imposed by legislative frameworks, the removal of polyacrylamide (PAM) rapidly and effectively from produced wastewater in offshore oilfields before discharge is becoming an urgent challenge. In this study, a novel advanced oxidation process based on plasma operated in the gas-liquid interface was used to rapidly decompose PAM, and multiple methods including viscometry, flow field-flow fractionation multi-angle light scattering, UV-visible spectroscopy, and attenuated total reflectance-Fourier transform infrared spectroscopy were used to characterize the changes of PAM. Under a discharge voltage of 25 kV and pH 7.0, the PAM concentration decreased from 100 to 0 mg/L within 20 min and the total organic carbon (TOC) decreased from 49.57 to 1.23 mg/L within 240 min, following zero-order reaction kinetics. Even in the presence of background TOC as high as 152.2 mg/L, complete removal of PAM (100 mg/L) was also achieved within 30 min. The biodegradability of PAM improved following plasma treatment for 120 min. Active species (such as O₃ and H₂O₂) were produced in the plasma. Hydroxyl radical was demonstrated to play an important role in the degradation of PAM due to the inhibitory effect observed after the addition of an ·OH scavenger, Na₂CO₃. Meanwhile, the release of ammonia and nitrate nitrogen confirmed the cleavage of the acylamino group. The results of this study demonstrated that plasma, with its high efficiency and chemical-free features, is a promising technology for the rapid removal of PAM.

Investigation of a novel pyrolusite particle electrode effects in the chlorine-containing wastewater

Research on three-dimensional electrode system mainly focuses on the material of plate electrode and catalytic activity, and minimal attention is provided to particle electrode. Pyrolusite was prepared as a novel particle electrode with high active chlorine (ACl) yield. The particle electrode was characterised by scanning electrode microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and electrochemical properties. Results show that the intended pyrolusite particle electrode was prepared successfully. These pyrolusite particle electrodes were applied to degrade sulphonated phenolic resin in chlorine-containing wastewater and displayed an excellent catalytic activity. A total of 68.76 mg/L ACl was produced, and the COD_Cr removal rate was 49.55%. These results indicated that pyrolusite particle electrode is much more effective than the reference material, that is, granular activated carbon. Furthermore, the product of electrolytic process was characterised by gas chromatography-mass spectrometry (GC-MS) and ultraviolet visible spectrometry (UV-vis). The enhanced mechanism was proposed that the high degradation efficiency could be ascribed to the increase of ACl.

Chemical Degradation of Polyacrylamide during Hydraulic Fracturing

Polyacrylamide (PAM) based friction reducers are a primary ingredient of slickwater hydraulic fracturing fluids. Little is known regarding the fate of these polymers under downhole conditions, which could have important environmental impacts including decisions on strategies for reuse or treatment of flowback water. The objective of this study was to evaluate the chemical degradation of high molecular weight PAM, including the effects of shale, oxygen, temperature, pressure, and salinity. Data were obtained with a slickwater fracturing fluid exposed to both a shale sample collected from a Marcellus outcrop and to Marcellus core samples at high pressures/temperatures (HPT) simulating downhole conditions. Based on size exclusion chromatography analyses, the peak molecular weight of the PAM was reduced by 2 orders of magnitude, from roughly 10 MDa to 200 kDa under typical HPT fracturing conditions. The rate of degradation was independent of pressure and salinity but increased significantly at high temperatures and in the presence of oxygen dissolved in fracturing fluids. Results were consistent with a free radical chain scission mechanism, supported by measurements of sub-μM hydroxyl radical concentrations. The shale sample adsorbed some PAM (∼30%), but importantly it catalyzed the chemical degradation of PAM, likely due to dissolution of Fe²⁺ at low pH. These results provide the first evidence of radical-induced degradation of PAM under HPT hydraulic fracturing conditions without additional oxidative breaker.

The flocculation mechanism and treatment of oily wastewater by flocculation

In the present study, the performance of compound flocculants composed of different concentrations of polyaluminum chloride (PAC) and cationic polyacrylamide (CPAM), the influencing mechanism of the flocculation process and the effects of temperature, settling time, and speed and time of stirring were investigated. The results show that the poor water quality with high concentrations of oil, suspended solids (SS) and polymer greatly increases the oily wastewater emulsion stability and the difficulty of the flocculation treatment process. The compound flocculant in oily wastewater treatment can achieve best results at optimum conditions of temperature 45 °C, settling time 60 min, and two stirring stages, 250 r·min^-1 for 3 min followed by 100 r·min^-1 for 7 min. At the PAC dosage of 80 mg·L^-1 and the CPAM dosage of 0.8 mg·L^-1, the turbidity of oily wastewater is reduced from 153.8 NTU to 11.2 NTU, and the turbidity removal rate reaches 92.69%. Through further measurements, oil content and SS content are less than 10 mg·L^-1, which meets the requirement of the Daqing oilfield re-injection standard.

Characterization of the chemicals used in hydraulic fracturing fluids for wells located in the Marcellus Shale Play

Hydraulic fracturing, coupled with the advances in horizontal drilling, has been used for recovering oil and natural gas from shale formations and has aided in increasing the production of these energy resources. The large volumes of hydraulic fracturing fluids used in this technology contain chemical additives, which may be toxic organics or produce toxic degradation byproducts. This paper investigated the chemicals introduced into the hydraulic fracturing fluids for completed wells located in Pennsylvania and West Virginia from data provided by the well operators. The results showed a total of 5071 wells, with average water volumes of 5,383,743 ± 2,789,077 gal (mean ± standard deviation). A total of 517 chemicals was introduced into the formulated hydraulic fracturing fluids. Of the 517 chemicals listed by the operators, 96 were inorganic compounds, 358 chemicals were organic species, and the remaining 63 cannot be identified. Many toxic organics were used in the hydraulic fracturing fluids. Some of them are carcinogenic, including formaldehyde, naphthalene, and acrylamide. The degradation of alkylphenol ethoxylates would produce more toxic, persistent, and estrogenic intermediates. Acrylamide monomer as a primary degradation intermediate of polyacrylamides is carcinogenic. Most of the chemicals appearing in the hydraulic fracturing fluids can be removed when adopting the appropriate treatments.

Physical-chemical evaluation of hydraulic fracturing chemicals in the context of produced water treatment

Produced water is a significant waste stream that can be treated and reused; however, the removal of production chemicals-such as those added in hydraulic fracturing-must be addressed. One motivation for treating and reusing produced water is that current disposal methods-typically consisting of deep well injection and percolation in infiltration pits-are being limited. Furthermore, oil and gas production often occurs in arid regions where there is demand for new water sources. In this paper, hydraulic fracturing chemical additive data from California are used as a case study where physical-chemical and biodegradation data are summarized and used to screen for appropriate produced water treatment technologies. The data indicate that hydraulic fracturing chemicals are largely treatable; however, data are missing for 24 of the 193 chemical additives identified. More than one-third of organic chemicals have data indicating biodegradability, suggesting biological treatment would be effective. Adsorption-based methods and partitioning of chemicals into oil for subsequent separation is expected to be effective for approximately one-third of chemicals. Volatilization-based treatment methods (e.g. air stripping) will only be effective for approximately 10% of chemicals. Reverse osmosis is a good catch-all with over 70% of organic chemicals expected to be removed efficiently. Other technologies such as electrocoagulation and advanced oxidation are promising but lack demonstration. Chemicals of most concern due to prevalence, toxicity, and lack of data include propargyl alcohol, 2-mercaptoethyl alcohol, tetrakis hydroxymethyl-phosphonium sulfate, thioglycolic acid, 2-bromo-3-nitrilopropionamide, formaldehyde polymers, polymers of acrylic acid, quaternary ammonium compounds, and surfactants (e.g. ethoxylated alcohols). Future studies should examine the fate of hydraulic fracturing chemicals in produced water treatment trains to demonstrate removal and clarify interactions between upstream and downstream processes.

Intensification of depolymerization of polyacrylic acid solution using different approaches based on ultrasound and solar irradiation with intensification studies

Depolymerization of polyacrylic acid (PAA) as sodium salt has been investigated using ultrasonic and solar irradiations with process intensification studies based on combination with hydrogen peroxide (H2O2) and ozone (O3). Effect of solar intensity, ozone flow and ultrasonic power dissipation on the extent of viscosity reduction has been investigated for individual treatment approaches. The combined approaches such as US+solar, solar+O3, solar+H2O2, US+H2O2 and US+O3 have been subsequently investigated under optimum conditions and established to be more efficient as compared to individual approaches. Approach based on US (60W)+solar+H2O2 (0.01%) resulted in the maximum extent of viscosity reduction as 98.97% in 35min whereas operation of solar+H2O2 (0.01%), US (60W), H2O2 (0.3%) and solar irradiation resulted in about 98.08%, 90.13%, 8.91% and 90.77% intrinsic viscosity reduction in 60min respectively. Approach of US (60W)+solar+ozone (400mg/h flow rate) resulted in extent of viscosity reduction as 99.47% in 35min whereas only ozone (400mg/h flow rate), ozone (400mg/h flow rate)+US (60W) and ozone (400mg/h flow rate)+solar resulted in 69.04%, 98.97% and 98.51% reduction in 60min, 55min and 55min respectively. The chemical identity of the treated polymer using combined approaches was also characterized using FTIR (Fourier transform infrared) spectra and it was established that no significant structural changes were obtained during the treatment. Overall, it can be said that the combination technique based on US and solar irradiations in the presence of hydrogen peroxide is the best approach for the depolymerization of PAA solution.

Intensified depolymerization of aqueous polyacrylamide solution using combined processes based on hydrodynamic cavitation, ozone, ultraviolet light and hydrogen peroxide

The present work deals with intensification of depolymerization of polyacrylamide (PAM) solution using hydrodynamic cavitation (HC) reactors based on a combination with hydrogen peroxide (H2O2), ozone (O3) and ultraviolet (UV) irradiation. Effect of inlet pressure in hydrodynamic cavitation reactor and power dissipation in the case of UV irradiation on the extent of viscosity reduction has been investigated. The combined approaches such as HC+UV, HC+O3, HC+H2O2, UV+H2O2 and UV+O3 have been subsequently investigated and found to be more efficient as compared to individual approaches. For the approach based on HC+UV+H2O2, the extent of viscosity reduction under the optimized conditions of HC (3 bar inlet pressure)+UV (8 W power)+H2O2 (0.2% loading) was 97.27% in 180 min whereas individual operations of HC (3 bar inlet pressure) and UV (8 W power) resulted in about 35.38% and 40.83% intrinsic viscosity reduction in 180 min respectively. In the case of HC (3 bar inlet pressure)+UV (8 W power)+ozone (400 mg/h flow rate) approach, the extent of viscosity reduction was 89.06% whereas individual processes of only ozone (400 mg/h flow rate), ozone (400 mg/h flow rate)+HC (3 bar inlet pressure) and ozone (400 mg/h flow rate)+UV (8 W power) resulted in lower extent of viscosity reduction as 50.34%, 60.65% and 75.31% respectively. The chemical structure of the treated PAM by all approaches was also characterized using FTIR (Fourier transform infrared) spectra and it was established that no significant chemical structure changes were obtained during the treatment. Overall, it can be said that the combination of HC+UV+H2O2 is an efficient approach for the depolymerization of PAM solution.

Hydrolyzed polyacrylamide biodegradation and mechanism in sequencing batch biofilm reactor

An investigation was performed to study the performance of a sequencing batch biofilm reactor (SBBR) to treat hydrolyzed polyacrylamides (HPAMs) and to determine the mechanisms of HPAM biodegradation. The mechanisms for the optimized parameters that significantly improved the degradation efficiency of the HPAMs were investigated by a synergistic effect of the co-metabolism in the sludge and the enzyme activities. The HPAM and TOC removal ratio reached 54.69% and 70.14%. A significant decrease in the total nitrogen concentration was measured. The carbon backbone of the HPAMs could be degraded after the separation of the amide group according to the data analysis. The HPLC results indicated that the HPAMs could be converted to polymer fragments without the generation of the acrylamide monomer intermediate. The results from high-throughput sequencing analysis revealed proteobacterias, bacteroidetes and planctomycetes were the key microorganisms involved in the degradation.

Oil-water separation property of polymer-contained wastewater from polymer-flooding oilfields in Bohai Bay, China

In this study, the effects of gravitational settling time, temperature, speed and time of centrifugation, flocculant type and dosage, bubble size and gas amount were investigated. The results show that the simple increase in settling time and temperature is of no use for oil-water separation of the three wastewater samples. As far as oil-water separation efficiency is concerned, increasing centrifugal speed and centrifugal time is highly effective for L sample, and has a certain effect on J sample, but is not valid for S sample. The flocculants are highly effective for S and L samples, and the oil-water separation efficiency increases with an increase in the concentration of inorganic cationic flocculants. There exist critical reagent concentrations for the organic cationic and the nonionic flocculants, wherein a higher or lower concentration of flocculant would cause a decrease in the treatment efficiency. Flotation is an effective approach for oil-water separation of polymer-contained wastewater from the three oilfields. The oil-water separation efficiency can be enhanced by increasing floatation agent concentration, flotation time and gas amount, and by decreasing bubble size.

Performance and biocompatibility of extremely tough alginate/polyacrylamide hydrogels

Although hydrogels now see widespread use in a host of applications, low fracture toughness and brittleness have limited their more broad use. As a recently described interpenetrating network (IPN) of alginate and polyacrylamide demonstrated a fracture toughness of ≈ 9000 J/m(2), we sought to explore the biocompatibility and maintenance of mechanical properties of these hydrogels in cell culture and in vivo conditions. These hydrogels can sustain a compressive strain of over 90% with minimal loss of Young's Modulus as well as minimal swelling for up to 50 days of soaking in culture conditions. Mouse mesenchymal stem cells exposed to the IPN gel-conditioned media maintain high viability, and although cells exposed to conditioned media demonstrate slight reductions in proliferation and metabolic activity (WST assay), these effects are abrogated in a dose-dependent manner. Implantation of these IPN hydrogels into subcutaneous tissue of rats for 8 weeks led to mild fibrotic encapsulation and minimal inflammatory response. These results suggest the further exploration of extremely tough alginate/PAAM IPN hydrogels as biomaterials.