Maximum Grafting Degree Research Articles

Mechanistic insights into the interaction of Lycium barbarum polysaccharide with whey protein isolate: Functional and structural characterization

Protein-polysaccharide interactions are crucial for food system structure and stability. This study investigates the interaction of Lycium barbarum polysaccharide (LBP) at 0–2.00 % concentrations with whey protein isolate (WPI), focusing on functionality and structural changes. LBP covalently grafted onto WPI, as confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), forming WPI-LBP complexes with a maximum degree of grafting (DG) of 44.58 % at 2.00 % LBP. This grafting reduced WPI's surface hydrophobicity (H0) and improved solubility, emulsifying properties, and digestibility under certain conditions, with optimal antioxidant activity at 1.00 % LBP. Multispectral analysis and microscopy showed LBP grafting alters WPI's secondary, tertiary, crystalline, and micro/nanostructures. The comprehensive analysis indicates that the interaction between LBP and WPI involves covalent bonding, hydrogen bonding, hydrophobic interactions, and electrostatic forces, as supported by zeta potential and chemical forces results. These findings suggest LBP-protein complexes as promising food materials for enhancing functionality and stability in the food industry.

Direct observation of radiation-induced graft polymerization on a polyethylene film

Radiation-induced graft polymerization is widely used in the synthesis of polymeric materials with various functionalities; however, the details of the reaction mechanism are still unresolved. Herein, the initial stage of the graft polymerization reaction was investigated through atomic force microscopy (AFM). We used glycidyl methacrylate (GMA) in methanol (monomer solution) and a high-density polyethylene (HDPE) film with a well-ordered lamellar structure as the substrate. Using polymer film surfaces with a maximum grafting degree of 0.5%, AFM can distinguish between crystalline and amorphous polyethylene (PE) phases as well as a grafted polymer GMA (PGMA) phase. The graft polymerization reaction started from the interface between the crystalline and amorphous PE phases. As the reaction proceeded, the PGMA covered the crystalline PE phase: i.e., the entire surface of the PE film were covered by the PGMA. Further, the crystalline lamellae of the PE film eventually became a scaffold for the formation of aggregates comprising grafted polymer chains alone. The graft polymerization reaction mechanism was explained by comparing the solubility parameters of the monomer solution, substrate, and grafted polymer chains. Understanding the reaction mechanism at a low grafting degree obtained in this study may contribute to enhancing the efficiency of the graft polymerization reaction on any polymeric material.

МЕХАНИЧЕСКИЕ СВОЙСТВА БИОРАЗЛАГАЕМЫХ КОМПОЗИТОВ НА ОСНОВЕ ПОЛИЭТИЛЕНА И ЖЕЛАТИНА

As a result of this study, we have obtained polymer blends that are based on linear low-density polyethylene (LLDPE) and gelatin, and received data on biodegradation, mechanical properties, and amounts of compounds produced from blending of graft copolymer and free gelatin. It was found that as the amount of maleic groups in the polyethylene macromolecule increases, the amount of graft copolymer grows, and an increase in the content of gelatin in the blend leads to a noticeable rise in the elastic modulus, tensile strength, and a decrease in elongation at break. It was also found that the rate of biodegradability increases with a growth of the content of gelatin in the blend, biological degradation was observed in the first 10 days at 54 %, up to a maximum of 58 %. It was maintained that maximum degree of grafting LLDPE-g-MA and gelatin to each other depends on the amount of maleic anhydride in the graft copolymer; maximum degree of grafting appeared to be higher with increased amount of maleic anhydride in the composites.

Mechanical and Thermal Properties of Biodegradable Composites Based on graft copolymer LLDPE-g-MA/Gelatin

The uncontrolled development of morphology at the stage of formation of biodegradable compositions based on synthetic and natural polymers limits the possibility of achieving satisfactory physical and mechanical and operational characteristics. In the present work, to achieve finely dispersed mixture morphology, an approach was proposed for reactive mixing of functionalized polyethylene with gelatin to form a linear low density polyethylene-grafted-maleic anhydride and gelatin (LLDPE-g-MA/GEL) graft copolymer. Using the selective extraction of the mixture components, we determined amount of graft copolymer LLDPE-g-MA/GEL, free gelatin, mechanical and thermal properties, as well as biodegradability data. It was found that as the amount of maleic groups in the polyethylene macromolecule increased, the amount of graft copolymer increased, and an increase in the content of gelatin in the blend led to a noticeable increase in the elastic modulus, tensile strength, and a decrease in elongation at break. Due to the degradation of gelatin, the thermal stability of the composite (initial temperature) decreased with increasing gelatin content. The maximum rate of destruction of the graft copolymer in the temperature range of 400–500 ºC increased markedly with an increase in the content of gelatin. It was found that the rate of biodegradability would increase with an increase in the content of gelatin in the blend; the maximum level of degradation was observed during the first 10 days and was more than 50 %. It was found that the maximum degree of grafting LLDPE-g-MA and gelatin to each other depended on the amount of maleic anhydride in the graft copolymer. The maximum degree of grafting was ob-served to be higher with increasing amount of maleic anhydride in the composites.

THE INFLUENCE OF OLEIC ACID AND BENZOYL PEROXIDE AGAINST OLEIC ACID GRAFTED ONTO LLDPE

In this study, the graft copolymerization of oleic acid (OA) onto linear low-density polyethylene (LLDPE) was successfully prepared by free radical reaction using benzoyl peroxide (BPO) initiator in the molten state. The study aims to determine the influence of OA monomer and BPO initiator on the grafting degree (GD) percentage of LLDPE-g-OA and its characteristics. LLDPE, OA, and BPO were mixed in an internal mixer, purified using acetone and methanol to separate from the unreacted OA and the OA homopolymer. The results showed that the addition of 12 wt% of OA monomer and 5 wt% of BPO initiator achieved the maximum GD percentage. The presence of a small band at 1707.1 cm-1, which is the OA carbonyl group, indicated that OA had been grafted onto LLDPE. LLDPE-g-OA also displayed better thermal stability than neat LLDPE and has a melting point of 123 °C. There were significant morphological changes and increased mass percentage of elemental carbon after the OA monomer grafting onto LLDPE.

Controllable Wetting Modification of Polypropylene Fibrous Mats

In this study, polypropylene (PP) fibrous mats are modified by plasma treatment, following by chemical grafting. Initially, the as-prepared PP fibrous mats are treated by plasma at different oxygen (O2) and argon (Ar) ratios. Then, the PP fibrous mats are modified by grafting dopamine onto polar groups for in situ polymerizations, resulting in a polydopamine (PDA) coating on the substrate's surface. Time-sensitive wettability is thereby converted into permanent wettability in PP fibers. The morphology, chemical performance, and relative wettability of the modified PP fibers are then characterized. The experimental results show, using an O2/Ar ratio of 3:7 during plasma treatment, that the water contact angle was decreased from 114.2° to 0°, and the maximum grafting degree was 0.79%.

Hydrodynamic alignment and self-assembly of cationic lignin polymers made of architecturally altered monomers

Cationic kraft lignin (CKL) polymers with different degrees of grafting (35.2–125.5 mol%) were synthesized via polymerizing kraft lignin (KL) and [2-(acryloyloxy)ethyl]trimethylammonium chloride (ATAC) or [2 (methacryloyloxy)ethyl]trimethylammonium methyl sulfate (METAM) to investigate the impact of the chain extension of the polymers on the physicochemical behavior of CKL in an aqueous solution. It was observed that, at the same grafting ratio, the structural difference of CKLs influenced their hydrophilicity, in which the contact angle of KL-METAM and KL-ATAC solution (1 g/L) reached 9.4° and 11.8° on a glass slide, respectively, at the maximum degree of grafting of ~125 mol%. KL-METAM had a more three-dimensional and flexible structure than KL-ATAC in solution, which promoted its self-assembly (with the aggregate diameter of 235–532 nm) and sedimentation (with the TSI value of 16.8). The rheological studies confirmed the more elasticity of KL-METAM than KL-ATAC with the elastic modulus of 9.3 and 8 Pa at the highest frequency. Quartz crystal microbalance (QCM) adsorption studies illustrated that KL-METAM adsorbed more greatly and generated a bulkier and more viscoelastic adlayer than KL-ATAC did on a rigid surface, below saturation (ΔD/Δf slope of 0.13–0.45) and at equilibrium (ΔD/Δf slope of 0.02–0.17). For the deposited adlayer, the alterations in the slope of dissipation/frequency (ΔD/Δf) between the early and late stages of adsorption were claimed to be related to the conformational changes of CKLs upon adsorption. The findings of this study showed that the architecture of cationic monomers could affect the structure of CKLs so significantly that the lignin polymers would have different chain conformations and flexibility in solution, varied rheological properties, and adsorption performance on a solid surface. The significance of the monomer architecture on the properties and performance of CKLs was more observable at a higher grafting ratio.

Synthesis and Water Absorbing Properties of KGM-g-P(AA-AM-(DMAEA-EB)) via Grafting Polymerization Method

In this study, a novel KGM-based superabsorbent polymer KGM-g-poly-(acrylic acid-co-acrylamide-co-N,N'-dimethyl-N-ethylmethacryloxylethylammoniumbromide) (KAAD) was prepared, which was obtained by the free radical grafting solution polymerization of acrylamide (AM), acrylic acid (AA) and N,N'-dimethyl-N-ethylethacryloxylethylammonium bromide (DMAEA-EB) onto konjac glucomannan (KGM) with of potassium persulfate (K2S2O8) as initiator and N,N'-methylenebisacrylamide (MBA) as crosslinker. The groups of AA, AM and DMAEA-EB grafted on KGM were detected by infrared spectroscopy (FTIR). The effects of the reaction conditions (including an initiator dosage, AA and AM mass ratio, and a reaction temperature, etc.) on the grafting degree and grafting efficiency were investigated by a gravimetric method. The maximum grafting degree and grafting efficiency of the obtained graft polymer in the experiment were 71.51 and 89.90%, respectively. The effects of crosslinking agent and GD on water absorption were explored. And all of the experimental data show that the water absorption ratio of the KAAD resin exceeds 527.00 g/g under each optimal reaction conditions. Therefore, KAAD can be widely used as a functional material in pharmaceutics, textiles, construction and other fields due to its excellent superabsorbent properties.

Structural elucidation and biological aptitude of modified hydroxyethylcellulose-polydimethyl siloxane based polyurethanes

The main aim of this research work was to incorporate modified hydroxyethylcellulose (HEC) into PDMS based polyurethanes. In the first part, modification of hydroxyethylcellulose was carried out by polymerizing lactic acid (LA) with HEC using ammonia water to prepare poly(lactic acid) grafted hydroxyethylcellulose (HEC-g-PLA). The maximum degree of grafting (59.5%) was achieved at: 1:9 mole ratio of HEC/LA, 2 h, 80 °C (for activation) and 4 h, 90 °C (for reaction) with 0.74 degree of substitution. In the second part, hydroxyl terminated polybutadiene (HTPB) was reacted with isophorone diisocyanate to produce NCO-terminated polyurethane prepolymer which in turn extended by chain extender to synthesize polydimethyl siloxane hydroxyl terminated (PDMS) based polyurethanes. Effect of incorporation of HEC-g-PLA as a chain extender was studied by varying its mole ratio in PDMS based PUs. Characterization of HEC-g-PLA and all PDMS/HEC-g-PLA based polyurethane samples was carried out by using Fourier Transform Infrared (FTIR) and proton solid-state NMR (1H SS NMR). Biological behavior of synthesized samples was also tested by various biological activities and results indicated that incorporation of HEC-g-PLA in to PDMS based polyurethanes leads to improvement in antibacterial activity, anti-biofilm inhibition, biocompatibility and non-mutagenicity. Therefore, HEC-g-PLA/PDMS blended polyurethanes are promising biomaterials that have potential for various biomedical applications.

Preparation and electrical properties of 4-acetoxystyrene grafted polypropylene for HVDC cable insulation

Polypropylene (PP) is considered to be a potential eco-friendly cable insulation material. However, space charge accumulation in PP under high electric stress limits its application for HVDC cable. In this paper, PP was modified with 4-acetoxystyrene (AOS) by melt grafting to improve electric properties. The molecular structure of the polypropylene-graft-4-acetoxystyrene (PP-g-AOS) was characterized by means of Fourier Transform Infrared Spectroscopy (FT-IR). The effects of temperature, screw speed, time, initiator content and monomer content on grafting degree of PP-g-AOS were investigated. Furthermore, the influence of grafting degree of PP-g-AOS on space charge suppression, volume resistivity and dc breakdown field strength was investigated. The FT-IR result showed that AOS was successfully grafted onto PP. It was found that under the proper grafting conditions, the obtained PP-g-AOS exhibited a maximum grafting degree of 1.31%. Moreover, PP-g-AOS with grafting degree of 1.14% can suppress space charge efficiently, and increase both volume resistivity and dc breakdown strength. This provides a new idea for the study of polypropylene HVDC cable insulation.

Structural changes in HDPE produced by in-line plasma-pretreated reactive extrusion

Structure of high density poly ethylene (HDPE) was changed after Plasma-induced graft polymerization of methyl methacrylate (MMA) monomer onto HDPE. Continuous polymerization of monomer wetted HDPE pellets was carried out sequentially via in-line plasma pretreatment followed by reactive extrusion. It was influenced by plasma pretreatment times between 15 s and 120 s on degree of grafting and molecular structure of the extrudate. Maximum degree of grafting was limited to 6% after 30 s plasma pretreatment. The addition of dicumyl peroxide (DCP) increased the degree of grafting to 10% after 15 s of plasma treatment. Gel formation to levels in the range 3–5% was detected, increasing with plasma pretreatment time. The formation of long chain branched (LCB) architecture, of the extruded PMMA-g-HDPE, was confirmed by rheological test in oscillatory shear, which results in increases in low frequency storage and loss moduli and melt viscosity than that of neat HDPE, especially after DCP addition. Finally, formation of a fully crosslinked structure was observed after annealing at 210 °C for 1 h as evidenced by a change in rheological properties at lowest frequencies to solid-like behaviour. Such extensive crosslinking could be useful in producing high strength adhesive joints between HDPE and other materials.

Influence of pH to Increase Grafting Degree into Fluoropolymers

Poly(ethylene-alt-tetra-fluoroethylene (ETFE) and poly(tetrafluoroethylene-cohexafluoropropylene) (FEP) were pre-irradiated under air using a Co60 gamma source to graft styrene at low pH. Grafting copolymers were tuned by study of different parameters (monomer, reaction time, temperature, and pH with addition of sulfuric acid (H2SO4)). The maximum degree of grafting was 80% and 40% for ETFE and FEP respectively at dose 2 kGy. Influence of low pH in grafting degree by adding sulfuric acid was studied. Grafting degree was examined by infrared (FTIR-ATR), differential scanning calorimetry (DSC) and swelling behavior analysis after sulfonation process.

Preparation and characterization of hydrophilicity fibers based on 2-(dimethyamino)ethyl mathacrylate grafted polypropylene by UV- irradiation for removal of Cr(VI) and as(V)

The hydrophilic fibers based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) which could remove Cr(VI) ions rapidly were prepared by UV-irradiation induced grafting of DMAEMA through pre-coating photoinitiator on the fibers and modifying with bromoethane(BE). The FTIR, FESEM, XPS, TG-DTG and contact angle spectra manifested that DMAEMA was grafted onto the surface of PP fibers and subsequently was quaternized. The maximum grafting degree (22.9 %) and exchange capacity of DMAEMA (1.2 mmol g−1) was obtained when PP fibers was immersed in BP concentration of 0.3 % for 4 h, irradiated with the DMAEMA concentration of 100 % and irradiation time of 20 min, and then was modified with BE. The modified fibers of PP-g-DMAEMA with bromoethane were proved to remove Cr(VI) and As(V) with removal rate of 97.3 % and 96.2 % within 10 min, respectively. The prepared fibers have potential application for the removal of Cr(VI) and As(V) from wastewater highly and rapidly.

Effects of modified LDPE on physico-mechanical properties of HDPE/CaCO3 composites

HDPE/CaCO3/LDPE-g-MA composites of high density polyethylene (HDPE) and calcium carbonate (CaCO3) with maleic anhydride grafted low density polyethylene (LDPE-g-MA) as a compatibilizer were prepared by melt mixing. LDPE-g-MA was prepared using a solution process. The maximum grafting degree was obtained at 6 wt% maleic anhydride (MA) and 0.2 wt% dicumyl peroxide (DCP) at 120 °C and 240 min. Functional groups not found in pure LDPE were observed with the formation of LDPE-g-MA. The successful dispersion of CaCO3 particles in the HDPE matrix using LDPE-g-MA was revealed. The crystallite size of the composites was a little higher than that of CaCO3. The mechanical properties of the HDPE/CaCO3/LDPE-g-MA composites increased with decreasing CaCO3 content. Thermogravimetric analysis (TGA) revealed a higher thermal stability for the HDPE/CaCO3/LDPE-g-MA composites than for pure HDPE. Differential scanning calorimetry (DSC) revealed that the crystallization conditions were not substantially different. However, melting enthalpy and crystallinity increased with decreasing CaCO3 content. The thermal stability was greatly improved compared to that previously reported for nano CaCO3.

The effect of epoxy and tetramethyl thiuram disulfide on melt‐grafting of maleic anhydride onto polypropylene by reactive extrusion

ABSTRACTIn this report, melt grafting of maleic anhydride (MAH) and epoxy resin onto polypropylene (PP) by peroxide‐initiated reactive extrusion has been investigated. As evidenced by Fourier transform infrared spectroscopy, both MAH and epoxy resin were successfully grafted onto PP through the reactions of MAH with PP and epoxy resin with MAH. It was found that tetramethyl thiuram disulfide could promote the grafting of MAH and inhibit the degradation of PP, as revealed by chemical titration and melt flow experiments, through prolonging the lifetime of the macroradical; meanwhile, epoxy resin could reduce the sublimation of MAH and the maximum grafting degree of MAH. Furthermore, the introduction of grafted products was found to enhance the mechanical properties of PP/glass fiber composites, and this influence was very significant at high grafting degrees with a high content of epoxy resin, which could be interpreted in terms of improved compatibility and adhesion at the interface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43422.

Homogeneous dielectric elastomers with dramatically improved actuated strain by grafting dipoles onto SBS using thiol–ene click chemistry

Herein, we report an approach to the preparation of a homogeneous styrene–butadiene–styrene triblock copolymer (SBS) dielectric elastomer (DE) with dramatically improved actuated strain by using a photochemical thiol–ene click reaction. The stock SBS was grafted with dipoles (ester groups) to increase the polarizability of SBS. The grafting degree of dipoles on SBS can be controlled by irradiation time to control its electromechanical properties. The grafting degree of modified SBS increases with the increase of irradiation time, and a maximum grafting degree of 81% can be achieved at a radiation time of 40 min. After modification, the phase mixing of PB and PS blocks occurs and the size of PS domains largely decreases, leading to the obvious decrease in the tensile strength and elastic modulus (Y). However, the modified SBS still shows good tensile strength (>3 MPa). More importantly, the dielectric constant (k) largely increases for the modified SBS. The simultaneous increase in k and decrease in Y result in a large increase in electromechanical sensitivity, and thus a large increase in maximum actuated strain and the actuated strain at low electric fields (e.g. 15 kV mm−1). In addition, the modified SBS shows consistently low dielectric loss. Our study provides a simple, effective and controllable chemical method to prepare a homogeneous DE with a high k, large actuated strain at a low electric field, good mechanical strength, easy processibility, and recyclability.

Preparation of PMMA grafted calcium carbonate whiskers and its reinforcement effect in PVC

In this study, calcium carbonate (CaCO3) whiskers were grafted with poly(methyl methacrylate) (PMMA) by in situ emulsion polymerization using γ‐methacryloxy propyl trimethoxyl silane (γ‐MPS) as a coupling agent, and the properties of resultant whisker were determined using Fourier transform infrared (FTIR) spectroscopy, energy dispersive spectroscopy (EDS), X‐ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The results show that PMMA has been successfully grafted onto the surface of CaCO3 whiskers and the maximum grafting degree (Gd) is 3.75%. The scanning electron microscopy (SEM) micrographs of the tensile‐fractured surfaces show that modified CaCO3 whiskers have strong interfacial adhesion to the poly(vinyl chloride) (PVC) matrix. The tensile strength increases from 44.0 MPa for PVC composite with unmodified whisker to 49.5 MPa for that with grafted whisker. The dynamic mechanical analysis (DMA) and TGA results indicate that the composites reinforced by modified CaCO3 whiskers have much higher modulus, glass transition temperature, and better thermal stability than their counterparts reinforced by unmodified CaCO3 whiskers. POLYM. COMPOS., 38:2753–2761, 2017. © 2015 Society of Plastics Engineers

Novel concept of polymer electrolyte membranes for high-temperature fuel cells based on ETFE grafted with neutral acrylic monomers

High temperature proton exchange membranes were synthesized via electron beam treatment of commercial poly(ethylene-alt-tetraflouroethylene) (ETFE) films and subsequent graft radical copolymerizations with 2-hydroxyethyl methacrylate (HEMA) and 2-hydroxyethyl acrylate (HEA). The maximum degree of grafting achieved was 193%. Both grafted monomers are hydrophilic and lead to high membrane affinity to phosphoric acid. Doping with phosphoric acid resulted in a maximum doping level of 310%. The grafted membranes combine stable ETFE backbone polymer with hydrophilic side chains. As indicated by stress–strain curves the graft copolymer membranes show good mechanical stability. In addition, the polymer–acid-composites are thermally stable up to around 210°C. The polymer–acid-composite materials were tested in H2/O2 fuel cells at 120°C. Power densities of up to 108mWcm‒2 were obtained at a current density of 200mAcm‒2. It is shown that the alternate concept of polymer–acid composites without any basic units is also suitable for the application in high temperature fuel cells.

The optimized synthesis of starch-g-lactic acid copolymer with high grafting degree catalyzed by sulfuric acid

The starch-g-lactic acid copolymer was synthesized with catalysis of sulfuric acid by onestep process, and the structure of starch-g-lactic acid copolymer was characterized by means of IR, 13C-NMR, HMBC, XRD, and SEM. The experimental results show that the maximum grafting degree of starch can reach 75% when the starch-g-lactic acid copolymer is activated at 80 °C for 2 h and reacted with lactic acid at 90 °C for 4 h in vacuum.

Controlled graft copolymerization of lactic acid onto starch in a supercritical carbon dioxide medium

This work presents a new approach for the synthesis of a starch-g-poly L-lactic acid (St-g-PLA) copolymer via the graft copolymerization of LA onto starch using stannous 2-ethyl hexanoate (Sn(Oct)2) as a catalyst in a supercritical carbon dioxide (scCO2) medium. The effects of several process parameters, including the pressure, temperature, scCO2 flow rate and reaction time, on the polymerization yield and grafting degree were studied. Amorphous graft St-g-PLA copolymers with increased thermal stability and processability were produced with a high efficiency. The maximum grafting degree (i.e., 52% PLA) was achieved with the following reaction conditions: 6h, 100°C, 200bar and a 1:3 (w/w) ratio of St/LA. It was concluded that these low cost biobased graft biopolymers are potential candidates for several environment-friendly applications.