High Intrinsic Viscosity Research Articles

Cationic starch: an effective flocculant for separating algal biomass from wastewater RO concentrate treated by microalgae

Microalgae can remove nutrients and organic contaminants from municipal wastewater reverse osmosis concentrate (ROC) and enable resource recovery via biomass production. Two cationic starch flocculants (starch-graft-poly cationic moiety 2-methacryloyloxyethyl trimethyl ammonium chloride (St-g-PDMC) and starch-graft-poly cationic moiety 2,3-epoxypropyl trimethyl ammonium chloride (St-GTA)) were synthesized and tested as potential greener and lower cost alternatives to conventional chemical flocculants for harvesting Chlorella vulgaris and Nannochloropsis salina from the algae-treated ROC. St-GTA achieved up to 97% separation (based on optical density) for both algal species at the dosage of 5–10 mg g−1 dry cell weight (DWC) compared to alum (69% at 10 mg g−1 DWC) and PolyDADMAC (93% at 35 mg g−1 DWC). The overall better performance of St-GTA was attributed to its higher intrinsic viscosity, positive surface charge, and solubility. The harvesting efficiency was influenced by algal growth phases, which led to differences in the levels of negative charge and functional groups on the algal surfaces. The effectiveness of the flocculants was primarily associated with their respective level of positive surface charge (R2 = 0.87) that facilitated charge neutralization as indicated by apparent surface charge of the algal flocs (R2 = 0.97). Flocculation using St-GTA removed 40% TP, 25% TN, and 20% DOC from the residual contaminants of the algae-treated ROC. Overall, the study indicated that cationic starch could be an environmentally benign and cost-effective approach for harvesting microalgae from the treated ROC, and beneficial to the subsequent utilization of the harvested biomass.

Exploring interactions between pectins and procyanidins: Structure-function relationships

During fruit and vegetable processing, procyanidins interact with cell walls and form complexes, which further impact their potential health effects. Among cell wall polysaccharides, pectins have the highest affinity for procyanidins. Binding of two procyanidin fractions with twelve pectins of different linearity and size was investigated by ITC, UV–Visible spectrophotometry and HPSEC-MALLS. Pectins interacted preferentially with highly polymerized procyanidins except beet pectins probably because of steric hindrance due to abundant feruloylated arabinans. Linear pectins had higher affinity for procyanidins: this was verified both for comparison between botanical origins (kiwifruit > apple > beet pectins) and between extraction conditions. Debranched pectins, extracted at pH 2.0, had higher affinity and aggregation capacities with procyanidins than those extracted at other pHs. However, the factors affecting pectins of different origins seemed to be different. High molar mass, intrinsic viscosity and hydrodynamic radius contributed more to increased adsorption of procyanidins by apple and beet pectins. Highly linear kiwifruit pectins, with high homogalacturonan content and lower branching ratio bound preferentially to procyanidins. The enthalpy/entropy proportion of the interaction between kiwifruit pectins and procyanidins was higher than that of apple and beet pectins, which suggested more hydrogen bonding. Predominance of homogalacturonan regions and high degree of methylation thus appeared key structural features of pectins for high affinity for procyanidins, while high degree of branching was detrimental. These findings provide the structural foundation for selectivity of interactions in molecular-level.

Low‐crystallinity to highly amorphous copolyesters with high glass transition temperatures based on rigid carbohydrate‐derived building blocks

AbstractThe current trend of developing novel biobased polymeric materials is focused more on utilizing the unique structural/physical properties of renewable building blocks towards niche market applications. In this work, with the aim of developing low‐crystallinity to amorphous polyesters with enhanced thermal properties, a series of copolyesters based on rigid and structurally asymmetric carbohydrate‐derived building blocks, namely furan‐2,5‐dicarboxylic acid and isosorbide, and 1,4‐butanediol were successfully synthesized using melt polycondensation. The copolyesters were obtained with varied chemical compositions and rather high molecular weights (Mn = 24 000–31 000 g mol−1) and intrinsic viscosities ([η] = 0.56–0.72 dL g−1). Incorporation of both building blocks significantly enhances the glass transition temperatures (Tg = 38–107 °C) of polyesters, and also efficiently inhibits the crystallization of the copolyesters. A low content of isosorbide (ca 10 mol%) leads to complete transition of the homopolyester to nearly fully amorphous materials. Detailed characterizations of the chemical structures and thermal properties of the synthesized copolyesters were conducted using various analytical techniques. In addition, hydrolytic and enzymatic degradations of the copolymers in the presence of porcine pancreatic lipase and cutinase were also investigated. © 2020 Society of Industrial Chemistry

Effect of dissolution pathways of polyacrylonitrile on the solution homogeneity: Thermodynamic- or kinetic-controlled dissolution

Dissolution behavior of polyacrylontrile (PAN) in N,N-dimethylformamide (DMF) and dimethylsulfoxide (DMSO) is investigated in terms of dipole-dipole interactions at polymer-solvent interface. Fourier-transformed infrared (FTIR) imaging of polymer-solvent interface under static dissolution condition at 25 °C and 60 °C exhibits the gel-like swollen layer in the early stage of dissolution for both solvents. This layer readily disappears in PAN-DMSO and DMSO molecules penetrate deep into the polymer phase, whereas that in PAN-DMF is still observed until 12 h even at 60 °C. The better dissolving ability of DMSO is interpreted by higher intrinsic viscosity and lower Huggins’ constant. The solubility (solution homogeneity) is also evaluated by rheological analysis in a wide concentration range of 8–20 wt%. At above 15 wt%, DMSO produces homogeneous solution at 60 °C even without stirring, showing the lower Newtonian flow region. On the other hand, it is necessary to apply vigorous stirring and heating for PAN-DMF system in order to prepare concentrated solution. DMSO provides greater slope of the Cole-Cole plot by rheological measurement than DMF, indicating better solution homogeneity in PAN-DMSO. The FTIR spectra and 2D correlation analysis show that both DMSO and DMF dissolve PAN in a way of sequential contributions of enthalpic and entropic factors. However, DMSO exhibits predominant contribution by enthalpic factor, suggesting that enthalpy change of mixing is a driving force of PAN dissolution in DMSO, whereas dissolution of PAN-DMF is governed by kinetic control.

Modification of poly(ethylene 2,5-furandicarboxylate) with aliphatic polycarbonate diols: 1. Randomnized copolymers with significantly improved ductility and high CO2 barrier performance

Poly(ethylene 2,5-furandicarboxylate) (PEF) is a very promising biobased polymer possessing very high mechanical strength, rigidity and gas barrier performance. But its poor ductility and toughness may limit its applications. In this study, PEF-based copolymers with high intrinsic viscosity were successfully synthesized via melt polycondensation of dimethyl 2,5-furandicarboxylate (DMFD) and ethylene glycol in the presence of a copolycarbonate diol (PPeHC diol) as produced from 1,5-pentylene diol (PeDO), 1,6-hexylene diol (HDO) and dimethyl carbonate, and characterized with 1H NMR, 13C NMR, DSC, TGA, tensile, impact and gas barrier testing. The products were “randomnized” as a result of ester-carbonate exchange reaction occurring along melt polycondensation, and therefore became amorphous copolymers possessing composition-dependent physico-mechanical properties which can be tunable from rigid-to-ductile thermoplastics to thermoplastic elastomers. Particularily, the copolymers with φPPeHC of 25 wt% and 30 wt% are thermoplastics possessing greatly improved ductility (elongation at break up to 194%) and CO2 barrier performance higher than poly(ethylene terephthalate) (PET; BIFCO2 3.6–2.8), and retaining high tensile modulus (2.2–1.9 GPa) and yielding strength (69–58 MPa) comparable to the bottle-grade PET. In comparison, the copolymer with φPPeHC of 40 wt% behaves as a high performance thermoplastic elastomer with excellent gas barrier performance as well as high tensile strength (23 MPa).

Efficient separation of functional xylooligosaccharide, cellulose and lignin from poplar via thermal acetic acid/sodium acetate hydrolysis and subsequent kraft pulping

Thermal acetic acid/sodium acetate hydrolysis (ASH) on poplar wood chips were carried out to obtain functional xylooligosaccharide, then the hydrolyzed wood chips were subjected to kraft pulping (KP) to fractionate cellulose and lignin. The separated three fractions were extensively characterized for further utilization in view of the integral biorefinery concept. The extraction efficiency of hemicelluloses by ASH strongly depends on the buffer ratio of the acetic acid/sodium acetate buffer solution. The ASH facilitated producing a high ratio of xylooligosaccharides with high molecular weight, while prevented further degradation of the saccharides, and simultaneously inhibited the condensation of lignin facilitating the subsequent kraft delignification. The obtained cellulose pulps had higher intrinsic viscosities as compared with the traditional autohydrolysis-KP process. Moreover, the ASH-KP process delivered a high purity of lignin with relatively high molecular weight. Therefore, the proposed integrated fractionation strategy is conducive to convert the lignocellulosic components into bio-based functional materials.

Fabrication and Application of Cationic Polyacrylamide

Abstract Cationic polyacrylamide (CPAM) was prepared in aqueous solution by free radical polymerization of methacryloyloxy ethyl trimethylammonium chloride (DMC) and acrylamide (AM). A redox initiator system was used. The structure of CPAM was characterized by IR and 1H NMR. The intrinsic viscosity and cationicity of CPAM were measured by an Ubbelohde viscometer and titration experiments, respectively. It was found that at the same concentration, the intrinsic viscosity decreases as the cationicity increases. The antistatic properties of CPAM on polyester fabric, the combability of hair, the flocculation on diatomaceous earth in a simulated sewage system and the thickening effect in solution were investigated. The results show that the higher the concentration, cationicity and intrinsic viscosity of CPAM, the better the thickening effect and the better the combability, the antistatic and flocculation properties. Therefore, the production of CPAM with high intrinsic viscosity and cationicity is important for an enhanced application performance.

Effect of recycled content and rPET quality on the properties of PET bottles, part I: Optical and mechanical properties

The effect of recycled content and type of recycled poly (ethylene terephthalate) (rPET) on the haziness; colour parameters L*, a*, and b*; total colour change; ultraviolet‐visual spectrum (UV‐VIS) absorption; and environmental stress cracking (ESC) of PET bottles was studied. Three series of PET bottles were made at a small scale production facility with same type of virgin PET and three different types of rPET with recycled contents of 25%, 50%, 75%, and 100%. Also, the particle contamination of the produced PET bottles was studied by dissolving bottle fragments and counting the insoluble particles. A linear relationship was found between the haziness of PET bottles and the particle contamination, with a coefficient of determination of 0.96. Linear relationships were also found between the colour parameters L* and b* and the particle contamination of the PET bottles, but the slope differed for each type of rPET. The origin of rPET (mono‐collection or cocollection) seems to be the crucial factor determining particle contamination and colour of the produced bottles. No correlation was found between the recycled content and the incidence of ESC. However, PET bottles in which high intrinsic viscosity (IV) values were measured showed lower chances of ESC than PET bottles with low IV values

Synthesis of super high molecular weight copolymer of AM/NaA/AMPS by oxidation\u2013reduction and controlled radical polymerization

Super high molecular weight copolymers of AM/NaA/AMPS were prepared by oxidation–reduction [OR-P(AM/NaA/AMPS)] and controlled radical polymerization [CR-P(AM/NaA/AMPS)]. The resulting copolymers were fully characterized, and the reaction conditions for their preparation were optimized. OR-P(AM/NaA/AMPS), CR-P(AM/NaA/AMPS), and conventional partially hydrolyzed polyacrylamide (HPAM) in brine solution were comprehensively characterized by thermogravimetric analysis, scanning electron microscopy, atomic force microscopy, and dynamic light scattering. OR-P(AM/NaA/AMPS) and CR-P(AM/NaA/AMPS) containing AMPS monomer showed better salt resistance, temperature tolerance, and viscosification property than the conventional HPAM polymer, making them more promising for enhanced oil recovery. Through comprehensive comparison and analysis, it was found that OR-P(AM/NaA/AMPS) was more conducive for high-temperature condition due to the existence of xanthone in OR-P(AM/NaA/AMPS). On the other hand, CR-P(AM/NaA/AMPS) was more suitable for high-mineral atmosphere, which could be attributed to its higher intrinsic viscosity.

Fabricating a hydrophobic modified flocculant through UVC irradiation initiation for metalworking wastewater treatment

In this work, a hydrophobically modified cationic polyacrylamide (CPAC) flocculant was polymerized by short-wave ultraviolet (UVC) initiation with acrylamide, acryloyloxyethyl trimethylammonium chloride, and coconut diethanolamide (CDEA) as monomers to enhance the destabilization and separation efficiency of emulsified oil and particles/colloids from metalworking fluids wastewater (MWFs). The parameters for flocculant polymerization were optimized, and the features of UVC-initiated polymerization were studied. Moreover, the structural and morphological characteristics of the polymers were explored, and the flocculation performance of CPAC in MWFs treatment was evaluated. The characterization results suggested that flocculants with a multilayer, loose-sheet morphology and intrinsic viscosity of 11.32dLg−1 could be successfully polymerized by UVC-initiated polymerization. Compared with traditional UV, UVC irradiation initiation promoted the copolymerization of flocculants with a high monomer conversion rate and intrinsic viscosity. We observed the low dosage requirement and acid resistance of the flocculant synthesized by UVC-initiated polymerization, which produced the lowest residual turbidity, highest chemical oxygen demand, and most efficient oil removal during MWFs treatment among the samples studied. Besides charge neutralization and bridging effects, the adsorption effect between hydrophobic CDEA blocks and nonpolar oil/colloids facilitated the formation of microflocs and improved the flocculation efficiency of the flocculant.

Fractionation of Acacia seyal gum by ion exchange chromatography

Acacia gum is a complex gum exudate from trees of selected Acacia species (i.e. A. senegal and A. seyal). It is a continuum of molecular species showing diverse, sugar and protein composition, molar mass and charge density. Numerous studies have been conducted on several aspects of Acacia senegal gum (Asen), including its fractionation. Acacia seyal gum (Asey) has been less studied, although it has recently been gaining importance. Certain gum characteristics, such as the protein and polysaccharide composition and the molecular parameters, play a key role in the Acacia gums functionality and, hence, in their uses by food, pharmaceutical or materials industries. Our main objective is to obtain a fraction from Asey gum with high molar mass and high protein content, allowing future research works and industrial applications. Asey gum has been separated by ion exchange chromatography (IEC) into two different fractions, IEC-F1 and IEC-F2, which have been thoroughly characterized. Thus, we have succeeded to recover a protein-rich fraction with high molar mass and high intrinsic viscosity, the fraction IEC-F1. The Mark-Houwink-Sakurada analysis further indicated that fraction IEC-F1 presents more anisotropic conformation compared to fraction IEC-F2. From the partial specific volume (vs°) and the partial specific adiabatic compressibility (βs°) coefficients, a more flexible and less hydrated structure in the fraction IEC-F1 compared to Asey gum was suggested.

Haemorheology in dilute, semi-dilute and dense suspensions of red blood cells

We present a numerical analysis of the rheology of a suspension of red blood cells (RBCs) in a wall-bounded shear flow. The flow is assumed as almost inertialess. The suspension of RBCs, modelled as biconcave capsules whose membrane follows the Skalak constitutive law, is simulated for a wide range of viscosity ratios between the cytoplasm and plasma,$\unicode[STIX]{x1D706}=0.1$–10, for volume fractions up to$\unicode[STIX]{x1D719}=0.41$and for different capillary numbers ($Ca$). Our numerical results show that an RBC at low$Ca$tends to orient to the shear plane and exhibits so-called rolling motion, a stable mode with higher intrinsic viscosity than the so-called tumbling motion. As$Ca$increases, the mode shifts from the rolling to the swinging motion. Hydrodynamic interactions (higher volume fraction) also allow RBCs to exhibit tumbling or swinging motions resulting in a drop of the intrinsic viscosity for dilute and semi-dilute suspensions. Because of this mode change, conventional ways of modelling the relative viscosity as a polynomial function of$\unicode[STIX]{x1D719}$cannot be simply applied in suspensions of RBCs at low volume fractions. The relative viscosity for high volume fractions, however, can be well described as a function of an effective volume fraction, defined by the volume of spheres of radius equal to the semi-middle axis of a deformed RBC. We find that the relative viscosity successfully collapses on a single nonlinear curve independently of$\unicode[STIX]{x1D706}$except for the case with$Ca\geqslant 0.4$, where the fit works only in the case of low/moderate volume fraction, and fails in the case of a fully dense suspension.

Hydrophobic modification of cationic microblocked polyacrylamide and its enhanced flocculation performance for oily wastewater treatment

In this study, a novel amphiphilic flocculant TP-ADL was synthesized using acrylamide, methacryloxyethyltrimethyl ammonium chloride and lauryl acrylate as monomers through UV-light-initiating template copolymerization technology. Copolymerization conditions were optimized towards higher intrinsic viscosity and conversion rate. The Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy (NMR) analysis confirms the functional groups composition in TP-ADL, and the thermogravimetric (TGA) analysis indicates its good thermal stability. Furthermore, the detailed 1H NMR and TGA analysis confirms the microblock structure in polymer chain. The amphiphilic rheological characteristics of copolymer were detected according to apparent viscosity. TP-ADL displayed superior flocculation efficiency towards oily wastewater in terms of oil and turbidity removal rate, and zeta potential. The median floc size (d50) and fractal dimension (Df) results indicate a large and compact floc structure. The synergistic effect between cationic microblock structure and inter-molecular hydrophobic association is the main reason for the better treatment efficiency.

Biobased 1,5-pentanediol derived aliphatic-aromatic copolyesters: Synthesis and thermo-mechanical properties of poly(pentylene succinate-co-terephthalate)s and poly(pentylene adipate-co-terephthalate)s

1,5-Pentanediol (PeDO) is a biobased but less studied diol monomer for polyester synthesis. As one of a series of studies on PeDO-derived polyesters, two aliphatic-aromatic copolyesters, poly(pentylene succinate-co-terephthalate) (PPeST) and poly(pentylene adipate-co-terephthalate) (PPeAT), were synthesized through melt copolycondensation of biobased PeDO, SA (or AA) and TPA. The chemical structure was characterized by 1H NMR, and the thermo-mechanical properties were assessed by DSC, WAXD, TGA and tensile test. The 1H NMR results demonstrated random structure and controllable copolymer composition. PPeATs showed two-stage thermal decomposition as the PeA units were clearly less stable than the PeT units at high temperature. In comparison, PPeSTs exhibited better thermal stability which was improved with increasing PeT unit content. Due to the difference in thermal stability, high intrinsic viscosity (0.78–1.4 dL/g) was facilely reached in synthesizing PPeSTs with melt copolycondensation, but medium intrinsic viscosity (0.58–0.66 dL/g) for PPeATs. Both kinds of copolyesters showed isodimorphism behavior and composition-dependent weak crystallizability. The PeT-rich copolyesters like PPeST85 and PPeAT85 showed reasonably good tensile properties because of higher crystallizability and stronger chain interaction.

New poly(ether imide)s with pendant di-tert-butyl groups: Synthesis, characterization and gas transport properties

Polymers with bulky substituents are of pronounced interest in membrane based separation applications. In this direction, the present work reports the synthesis and characterization of a series pendant di-tert-butyl and trifluorometyl groups containing new poly(ether imide)s (PEIs). The PEIs were prepared by thermal imidization of polyamic acid which is derived by the reaction of a diamine monomer, namely 1,4-bis-[{2′-trifluoromethyl 4′-(4″-aminophenyl)phenoxy}] 2,5-di-t-butylbenzene (FMTBDA) with four different commercially available aromatic dianhydrides, i.e. BPADA, 6FDA, ODPA, and BTDA. The PEIs are soluble in many organic solvents and show reasonably high intrinsic viscosity (0.87 to 1.10 dL/g in NMP) and weight average molecular mass as high as 371,900 g/mol with a polydispersity index of 3.8. The proton NMR and FTIR spectroscopic investigation are in accordance with the respective polymer repeating unit structures. The physical properties of the polymers like thermal and mechanical stability are investigated thoroughly to assess their suitability for membrane based application. The polymers are thermally stable up to 474 °C with 10% weight loss temperature in air environment and have a glass transition temperature as high as 253 °C. The polymer membranes have satisfactory mechanical strength with stress at break value up to 95 MPa. The gas permeability coefficients of the PEIs are somewhat higher than those of other polyimides prepared from the same dianhydrides.

Molecular Engineering of Superplasticizers for Metakaolin‐Portland Cement Blends with Hierarchical Machine Learning

AbstractBlending metakaolin (MK), a calcined clay, into portland cement (PC) improves resulting concrete material properties, ranging from strength to durability, as well as reducing embodied CO2 and energy. However, superplasticizers developed for PC can be inefficient or ineffective for improving the dispersion of PC‐MK blends. Here, a novel machine algorithm is applied to tailor a superplasticizer to address poor flowability characteristic of 15/85 blends of MK‐PC. A hierarchical machine learning (HML) system is trained on a library of seven superplasticizers using a middle layer, which represents underlying physical interactions that determine system responses, based on polymer contributions to physicochemical forces in both the pore solution and particle surface. Following reparameterization of the response surface by polymer composition, the trained algorithm predicted that a novel styrene sulfonate‐methacrylic acid‐poly(ethylene glycol) methacrylate copolymer would maximize slump of the MK‐PC paste. Synthesis of the algorithm prediction resulted in a water‐soluble polymer with an extremely high intrinsic viscosity that nevertheless increased the slump flow of the MK‐PC paste but did not plasticize pure PC paste. The results from this study demonstrate the importance of HML as a design tool for the molecular engineering of complex material systems.

Diffusion of Rodlike Polymers: Pulsed Gradient Spin Echo NMR of Poly(γ-stearyl-α,l-glutamate) Solutions and the Importance of Helix Stability.

Many natural and synthetic polymers and particles have a rodlike shape, leading to important and intriguing solution behavior, such as high intrinsic viscosities and liquid crystalline phases. Much of what is known about suspensions of rods has been learned by studying helical polypeptides, even though such molecules are not perfectly rigid, smooth cylinders. Previous optical tracer self-diffusion studies of poly(γ-benzyl-α,l-glutamate) (PBLG) revealed that the molecule initially resists topological constraints imposed by neighboring molecules, but diffusion strongly decreases as concentration rises beyond a certain number density. In contrast, the tracer self-diffusion coefficient of truly rigid tobacco mosaic virus begins decreasing immediately with concentration. We used pulsed gradient spin echo NMR to measure another polypeptide, poly(γ-stearyl-α,l-glutamate) (PSLG), to gain physical insight into the question of polypeptide diffusion in crowded isotropic solutions. The PSLG molecule, with long alkyl sidechains, is semiflexible like PBLG but does not exhibit the same ability to evade topological constraints. Instead, PSLG follows a simple exponential decay, D/ DKR = A e(-κν/ν*) + B, where DKR is the Kirkwood-Riseman expectation for rod diffusion, ν is the number density of rods, ν* is the Onsager expectation for the number density at the onset of liquid crystal formation, A = 1 ± 0.1, B = 0.1 ± 0.01, and κ = 4.5 ± 0.5. The results emphasize the importance of helix stability when choosing rodlike polypeptides as model systems, particularly with regard to the chain ends.

Preparation, Characterization, and Sludge Conditioning of Cationic Polyacrylamide Synthesized by a Novel UVA-Initiated System

Controlling the concentration of free radicals in polymerization systems is advantageous for preparing cationic polyacrylamide (CPAM) with a high molecular weight and acceptable dissolvability. In this study, a novel ultraviolet (UVA)-initiated system characterized by an adjustable light intensity and a redox-azo complex initiator was used to synthesize a CPAM flocculant named NP. Comparatively, another CPAM flocculant named SP with a stable UVA light intensity and a single initiator was prepared. Their chemical structure, morphology, and thermal stability were analyzed through instrumental analysis. 1H NMR indicated that NP was successfully prepared, and a small fraction of a cationic homopolymer was mixed in the product. Polymerization conditions of NP were optimized, and polymerization mechanism was determined by investigating the effects of various parameters on intrinsic viscosity, conversion, and dissolvability. Results showed that the best performance was obtained at indices of 0.45 wt‰ redox initiator concentration, 0.2 wt‰ azo initiator concentration, 40.0 wt% cationic monomer, 3 wt‰ urea, and first- and second-stage light intensities of 8.5 and 13 mW/cm2, respectively. The sludge conditioning performances of NP and SP were comparatively evaluated, and the mechanism was determined by examining sedimentation behavior and floc size distribution. High intrinsic viscosity, porous morphology structure, and mixed NP cationic homopolymer contributed to the improvement of sludge conditioning performance.

Physicochemical and rheological properties of cross-linked inulin with different degree of polymerization

Long-chain inulin (L-In) and short-chain inulin (S-In) from native inulin was separated through the method of alcohol precipitation. Cross-linked inulin with two different degree of polymerization (average DP = 6.88 and 15.10) were prepared in aqueous solutions by using the L-In and S-In respectively as raw material and sodium hexametaphosphate as cross-linker. Structural characteristics of cross-linked inulin were determined by Fourier-transform infrared spectroscopy and scanning electron microscopy. Compared with native L-In and S-In, cross-linked inulin had a higher intrinsic viscosity, stronger stability and moisture absorption capability, but lower water solubility. Only 1% reducing sugar produced when cross-linked inulin was heated within 100 °C, and inulin hydrolysis occurred in acidic environment (pH < 6). Rheological properties of inulin dispersions with different degree of polymerization were investigated and compared. The viscoelastic properties of steady shear measurements indicated that cross-linked inulin dispersions presented shear-thinning behaviors, which could be described by a power law model with determination coefficients (R2 = 0.9312–0.9926). The viscoelastic properties of dynamic frequency sweep measurements indicated that cross-linked inulin dispersion showed more solid viscoelastic properties than corresponding native inulin dispersions.

An Effective Flocculation Method to the Kaolin Wastewater Treatment by a Cationic Polyacrylamide (CPAM): Preparation, Characterization, and Flocculation Performance

P(AM-DMC) (PAD) was synthesized by ultraviolet- (UV-) initiated copolymerization with methacryloxyethyl trimethyl ammonium chloride (DMC) and acrylamide (AM) as the monomers and initiator 2,2-azobis [2-(2-imidazolin-2-yl) propane] dihydrochloride (VA-044) as the photoinitiator. Parameters that affect the molecular weight were reviewed by using the single-factor approach. The results showed that the molecular weight (MW) of PAD could come to 7.88 × 106 Da with the optimum polymerization conditions as follows: monomer concentration of 30%, monomer mass ratio m(AM) : m(DMC) of 3 : 1, initiator concentration of 0.6‰, illumination time of 80 min, solution pH value of 4.5, and incident light intensity of 1000 μW cm−2. The PAD was represented by several instruments. The results of FTIR and 1H NMR showed that PAD was indeed polymerized by AM and DMC. The results of TGA showed that PAD was very stable at room temperature while the result of SEM revealed that PAD had a porous structure and rough surface. For PAD used as flocculant in kaolin wastewater treatment, the results confirmed that, at optimal conditions, the turbidity and the floc size d50 could reach to 5.9 NTU and 565.936 μm, respectively, at the optimal conditions (pH = 7.0 and dosage = 2 mg l−1). Kaolin wastewater flocculation test outcome reveals that the PAD with high cationic degree and intrinsic viscosity could boost the charge neutralization and bridging capability. Consequently, the result is an excellent flocculation performance of treating kaolin wastewater.