Influences of the grafting percentage of natural rubber‐graft‐poly(2‐hydroxyethyl acrylate) on properties of its vulcanizates

The graft copolymerization of 2‐hydroxyethyl acrylate (HEA) monomer onto natural rubber (NR) latex was successful using cumene hydroperoxide and tetraethylene pentamine as redox initiators. The grafting of poly(2‐hydroxyethyl acrylate) (PHEA) on the NR particles was confirmed by Fourier transform infrared spectroscopy, ¹H NMR spectroscopy and TEM. The NR‐g‐PHEA with various grafting percentages (0%, 8.7%, 14.3% and 18.7%) was compounded on a two‐roll mill with a sulfur vulcanization system. The effects of grafting percentage on the cure characteristics, dielectric properties, thermal properties and physical properties of NR‐g‐PHEA vulcanizates were investigated. It was found that increased grafting caused NR‐g‐PHEA vulcanizates to have reduced water contact angle, scorch time and cure time, while the dielectric constant and dissipation factor increased. The NR‐g‐PHEA vulcanizate with 8.7% grafting exhibited the highest delta torque (M_H ? M_L), crosslink density, tensile strength, moduli at 100%, 200% and 300% strains, and hardness, with insignificant loss of elongation at break in comparison to the other cases. © 2018 Society of Chemical Industry     

Synthesis of polyethylene‐graft‐poly(styrene‐co‐maleic anhydride) and its compatibilizing effects on polyethylene/starch blends

Low density polyethylene (LDPE) was reacted with benzoyl peroxide (BPO) and 2,2,6,6‐tetramethyl‐l‐piperidinyloxy (TEMPO) to prepare a latent macroinitiator, PE–TEMPO. Little polymer was synthesized when maleic anhydride (MAH) was bulk polymerized in the presence of the PE–TEMPO. However, addition of styrene accelerated the polymerization rate and PE‐grafted‐poly(styrene‐co‐maleic anhyride) [PE‐g‐P(ST‐co‐MAH)] was produced to a high yield. Chemical reaction between MAH units and hydroxyl groups of starch was nearly undetectable in the PE/PE‐g‐P(ST‐co‐MAH)/starch blend system, and the tensile properties of the blend were not enhanced significantly. However, addition of tetrabutyl titanate (TNBT) during the blending procedure improved the tensile properties significantly through an increased interfacial adhesion between the components in the blend system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2434–2438, 2003     

Rheological and curing behavior of reactive blending. I. Maleated natural rubber–cassava starch

Maleated natural rubber (MNR) was prepared and used as a blending composition and a compatibilizer for blending of natural rubber (STR 5L) and cassava starch. The melt rheological behavior in terms of Mooney viscosity, apparent shear stress, and shear viscosity at 100°C were quantified. We found that the pure MNR gave the lower apparent shear stress, shear viscosity than did those of the blends with cassava starch. The rheological data of the MNR blends increased with increasing quantity of cassava starch. The highest value was observed for the blend of MNR. The rheological value was as follows: MNR > STR 5L with MNR (as the compatibilizer) > STR 5L compounds. Furthermore, rheological properties increased with increasing the levels of compatibilizer (MNR). The rheological results were described in terms of intermolecular interaction between the polar groups in the natural rubber and cassava starch molecules. Each rubber blend was compounded, and their curing characteristics were studied. The pure MNR compounds exhibited a long delayed onset of vulcanization for approximately 10 min. The retardation was found, because the accelerator (MBT) reacted with the anhydrides in the compound instead of acting as an accelerator. The retardation was not observed for the compound with the cassava starch. The curing curves for all MNRs were not in equilibrium at a maximum torque, while the pure STR 5L compound gave a curing curve with a maximum torque and a slight reversion. The curing curve for the compound with MNR as the compatibilizer was a combination of the curing curves of MNR and STR 5L. That is, the curve was in equilibrium at the maximum torque and the short delayed action. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2803–2813, 2001     

Stress‐relaxation behavior of natural rubber/polystyrene and natural rubber/polystyrene/natural rubber‐graft‐polystyrene blends

We studied the stress‐relaxation behavior of natural rubber (NR)/polystyrene (PS) blends in tension. The effects of strain level, composition, compatibilizer loading, and aging on the stress‐relaxation behavior were investigated in detail. The dispersed/matrix phase morphology always showed a two‐stage mechanism. On the other hand, the cocontinuos morphology showed a single‐stage mechanism. The addition of a compatibilizer (NR‐g‐PS) into 50/50 blends changed the blend morphology to a matrix/dispersed phase structure. As a result, a two‐step relaxation mechanism was found in the compatibilized blends. A three‐stage mechanism was observed at very high loadings of the compatibilizer (above the critical micelle concentration), where the compatibilizer formed micelles in the continuous phase. The aged samples showed a two‐stage relaxation mechanism. The rate of relaxation increased with strain levels. The aging produced interesting effects on the relaxation pattern. The rate of relaxation increased with temperature due to the degradation of the samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of starch nanocrystal‐graft‐polycaprolactone on mechanical properties of waterborne polyurethane‐based nanocomposites

Based on a “graft from” strategy, the surface of starch nanocrystals (StN) were functionalized by grafting with polycaprolactone (PCL) chains via microwave assisted ring‐opening polymerization (ROP). The modified natural nanoparticles were then compounded into a PCL‐based waterborne polyurethane as matrix. The structural and mechanical properties of the WPU/StN‐g‐PCL nanocomposites were characterized by XRD, FTIR, SEM, DSC, DMA, and tensile testing. It was interesting to note that a loading‐level of 5 wt % StN‐g‐PCL resulted in a simultaneous enhancement of tensile strength and elongation at break, both of which were higher than those of neat WPU. This enhancement was attributed to the uniform dispersion of StN‐g‐PCL because of its nano‐scale size, the increased entanglements mediated with grafted PCL chains, and the reinforcing function of rigid StN. Increasing the StN‐g‐PCL content however caused the StN‐g‐PCL to self‐aggregate as crystalline domains, which impeded improvement in tensile strength and elongation at break, but significantly enhanced Young's modulus. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Investigation of sensing effects of polystyrene‐graft‐polyaniline for cyanide compounds

Polyaniline and its derivatives have high antioxidative stability and are considered to belong to the most useful conductive polymers for practical application. In this work, we have linked 1,4‐phenylenediamine to poly(styrene‐co‐chloromethylstyrene) and prepared poly(styrene‐co‐p‐aminoanilinemethylstyrene), poly(S‐co‐PAAMS). Polystyrene‐graft‐polyaniline, (PS‐g‐PANi), has been synthesized by adding solution of ammonium persulfate and p‐toluenesufonic acid in water. The conductivity of these polymers was measured by the four‐point probe method. The copolymers produced exhibit electrical conductivity comparable to that of polyaniline. PS‐g‐PANi was also exposed to some cyanide compounds such as hydrocyanic acid (Hydrogen cyanide‐HC), ethanedinitrile (Cyanogen‐CY), cyanogen chloride (Chlorocyan‐CC), and cyanogen bromide (Bromocyan‐BC). The cyanide compounds are classified as blood agents groups, in terms of chemical warfare agents standards. First, we prepared different concentration of blood agents at 50, 100, and 150 ppm and exposed them on PS‐g‐PANi for 2 min. Second, we have drawing conductivity change curves versus time and produced optimum conductivity versus time taken. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3920–3926, 2006     

Chitosan graft copolymers‐HA/DBM biocomposites: Preparation,characterization, and in vitro evaluation

The combination of biopolymer with a bioactive component takes advantage of the osteoconductivity and osteoinductivity properties. The studies on composites containing hydroxyapatite (HA), demineralized bone matrix (DBM) fillers and chitosan biopolymer are still conducted. In the present study, the bioactive fillers were loaded onto p(HEMA‐MMA) grafted chitosan copolymer to produce a novel biocomposites having osteoinductive and osteoconductive properties. The produced composites were assessed by TGA, XRD, FTIR, and SEM techniques to prove the interaction between both matrices. In vitro behavior of these composites was performed in SBF to verify the formation of apatite layer onto their surfaces and its enhancement. The results confirmed the formation of thick apatite layer containing carbonate ions onto the surface of biocomposites especially these containing HA‐DBM mixture and pMMA having bone cement formation in their structure. These a novel biocomposites have unique bioactivity properties can be applied in bone implants and tissue engineering applications as scaffolds in future. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Rheological,thermal, and curing properties of natural rubber‐g‐poly(methyl methacrylate)

Graft copolymers of NR and PMMA (i.e., NR‐g‐PMMA) were prepared with the bipolar redox initiation system, using various percentages of molar ratios of NR/MMA at 95/5, 90/10, 80/20, 70/30, and 60/40. It was found that the Mooney viscosity, shear stress, and shear viscosity of the NR‐g‐PMMA increased with an increase in the molar ratio of MMA used in the graft copolymerization. This may be attributed to an increasing trend of the chemical interaction between polar functional groups within the grafted PMMA molecules. Furthermore, a decreasing trend of storage moduli was observed with increasing molar ratios of MMA. The glass transition temperature was obtained from the tan δ curves. We found a slightly increasing trend of the T_g's with an increase in molar ratios of MMA used in the grafting reaction. The NR‐g‐PMMA was later compounded using TBBS as an accelerator. With an increase in molar ratios of MMA in the grafting reaction, we observed an increasing trend of minimum torque, maximum torque, cure time, and scorch time, but quite similar levels of torque difference and crosslink density. Furthermore, the tensile strength of the NR‐g‐PMMA gum vulcanizate increased with an increase in molar ratios of MMA, whereas the elongation at break decreased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1600–1614, 2006     

Synthesis of graft copolymer polyethylene‐ graft‐poly(ethylene oxide) by a new anionic graft‐from polymerization

A series of amphiphilic graft copolymers, PE‐graft‐PEO, containing hydrophobic polyethylene (PE) as the backbone and hydrophilic poly(ethylene oxide) (PEO) as the side‐chain, have been synthesized by a novel route. The graft structure and the molecular weight, as well as the molecular weight distribution of the graft copolymer can easily be controlled. The molecular weight of the side‐chain PEO is proportional to the reaction time and the monomer concentration, which indicates the ‘living’ character of the anionic polymerization of ethylene oxide. The produced copolymers PE‐graft‐PEO were characterized by ¹H NMR and DSC measurements. Copyright © 2004 Society of Chemical Industry     

Optimization of synthesis and characterization of cassava starch‐graft‐poly(acrylonitrile) using response surface methodology

Graft copolymerization of poly(acrylonitrile) onto cassava starch was carried out with potassium persulphate (PPS) as the free radical initiator using a response surface Box–Behnken design. Different levels of monomer concentration, initiator concentration, and temperature were used, and regression models were generated in terms of these factors, which can be used to predict the grafting level and efficiency at a given level of the factors. The grafted starches were characterized by FTIR, XRD, and SEM analyses and determination of %grafting (%G), N‐content, thermal properties, water and saline solution retention, and rheological properties. Under the conditions used, %G was found to depend only on the temperature used for the reaction. The maximum %G of 120.1 was obtained for the sample synthesized under the following conditions: weight of AN = 0.753 mol/10 g starch, weight of PPS = 0.284 g and temperature = 55°C, and the grafting efficiency was 30.03%. The absorption bands at 2243 cm^?1 for the nitrile group (? CN) in the FTIR spectra of the products confirmed the grafting reaction. There was a decrease in crystallinity and disappearance of the granular structure after grafting of the starch. The melting temperatures of the graft copolymers determined by differential scanning calorimetry analysis were higher than that of the native starch. The grafted starches exhibited very high thermal stability as observed from the thermogravimetric analysis. The superabsorbent polymer prepared from the grafted starch by alkali saponification exhibited a maximum water absorbency of 636 g/g. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study of the effect of natural rubber‐graft‐o‐aminophenol on the thermal stability and mechanical properties of nitrile rubber

The grafting copolymerization of natural rubber and o‐aminophenol was carried out by using two‐roll mill machine. The prepared grafted antioxidant, NR‐graft‐o‐AP, analyzed by using Infrared and ¹H‐NMR Spectroscopy techniques. The thermal stability, mechanical properties, and ultrasonic attenuation coefficient were evaluated for NBR vulcanizates containing the commercial antioxidant, PBN, and the prepared grafted antioxidant, NR‐graft‐o‐AP, and the control vulcanizate. Results of the thermal stability indicate that the prepared NR‐graft‐o‐AP can protect NBR vulcanizate against thermal treatment much better than the commercial antioxidant, PBN, and control mix, respectively. The prepared grafted antioxidant improves the mechanical properties of NBR vulcanizate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

木薯双醛淀粉制备木材用胶粘剂的研究

以木薯淀粉为原料、高碘酸钠为氧化剂,在一定条件下制得双醛淀粉(DAS);然后以过硫酸铵(APS)为引发剂、聚乙烯醇(PVA)为保护胶体和醋酸乙烯酯(VAc)为DAS的接枝单体,再配合其他助剂制得双醛接枝淀粉基木材用胶粘剂。结果表明:当w(DAS中醛基)=20%、m(DAS)∶m(VAc)=1∶2.5、w(PVA)=75%、VAc为25 mL、接枝反应温度为65℃和反应时间为3 h时,胶粘剂的干、湿强度分别为3.0、2.4 MPa。     

Thermal and flame resistance properties of natural rubber‐g‐poly‐(dimethyl(methacryloyloxymethyl)phosphonate)

Natural rubber grafted with poly(dimethyl(methacryloyloxymethyl)phosphonate) (i.e., NR‐g‐PDMMMP) was prepared in latex medium via photopolymerization. Thermal and flame resistance properties of the NR‐g‐PDMMMP prepared with various levels of grafted PDMMMP or grafting rate (GR) were investigated. Thermal behaviors were investigated by thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). It was found that the graft copolymer exhibited phase separation with double T_g values. A shift of T_gs toward each other was observed with increasing GR, which indicated tendency to become a single phase material. Increasing GRs also caused increasing heat and flame resistance with increasing degradation temperature and level of char residue. Furthermore, increasing level of limited oxygen index (LOI) and decreasing burning rate were observed with increasing the GR. This is attributed to increasing content of char residue of the phosphorus compound, which acted as the thermal insulation and a barrier of oxygen to transfer to the burning materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Graft copolymerization of acrylic acid onto cocoyam starch by ceric ion in the presence of N,N′‐dimethylacetamide

Grafting of acrylic acid onto cocoyam starch, Xanthosoma sagittitolium was initiated by ceric ion—N,N′‐dimethylacetamide redox pair in aqueous media. The reaction was characterized by high graft yields of up to 676%, and infrared spectroscopy affirmed the presence of grafted polymer. Graft yield was enhanced by N,N′‐dimethylacetamide (DMAc) in the concentration range, 9.0–36.0 × 10^?4M but lower concentrations were more favorable with the ratio of percentage graft, P_g/P_g0, in the presence and absence of DMAc respectively, of up to 1.34 at 9.0 × 10^?4M of the latter. Ceric ion was nonterminating of the graft reaction and a 10‐fold increase in its concentration of 4.16 × 10^?3M resulted in high efficiency of graft of 50.2% in monomer conversion to grafted polymer. Enhanced homopolymer formation and low efficiency of graft were observed at monomer concentration greater than 0.69M. Long reaction time, greater than 30 min, was unfavorable to the graft reaction and the latter showed negative dependence on temperature in the range, 30–50°C. At 30‐min reaction time, the graft yield at 50°C was not more than 70% of the corresponding value at 30°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Use of natural rubber‐g‐polystyrene as a compatibilizer in casting natural rubber/polystyrene blend films

Natural rubber/polystyrene (NR/PS) blend films with weight ratios of 70/30, 60/40, and 50/50 were prepared using polystyrene grafted natural rubber copolymers (NR‐g‐PS) as the compatibilizer. Copolymers with molar ratios of 90/10, 80/20, and 70/30 were synthesized via emulsion copolymerization using tert‐butyl hydroperoxide/tetraethylene pentamine as an initiator. The copolymers were subsequently added into the blends at 0, 5, 10, 15, 20, 25, and 30 phr. The mixtures were cast into films by the solution‐casting method using toluene as the casting solvent. Mechanical and morphological properties of the prepared films were investigated. The film prepared from 80/20 NR‐g‐PS showed higher tensile and tear strength, as well as finer domain size of the dispersed phase, than those prepared from 90/10 and 70/30 NR‐g‐PS. However, the mechanical properties of the films were decreased at high loading of the copolymers. In addition, themogravimetric analysis revealed that weight loss was decreased upon introduction of the compatibilizer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 826–831, 2005     

Thermoforming starch‐graft‐polycaprolactone biocomposites via one‐pot microwave assisted ring opening polymerization

A thermoformable starch‐graft‐polycaprolactone biocomposite was prepared by initiating ring‐open polymerization of caprolactone monomer onto starch under microwave irradiation. In this case, the thermoplastic and hydrophobic modification of starch could be realized by one‐pot grafting PCL, where the grafted PCL chains acted as the “plasticizing” tails of thermoforming and as the hydrophobic species of water‐resistance. The resultant biocomposites were injection‐molded as the sheets and their structure and properties were investigated by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, differential scanning calorimetry, dynamic mechanical analysis, contact angle measurement, and tensile testing. In this case, the grafted PCL chains entangled each other, and hence contributed to the strength and elongation of biocomposites. This work provided a simple strategy of one‐pot thermoplastic and hydrophobic modification of starch, and may be applied in a continuous process of modification, compounding, and molding. Meanwhile, the resultant biocomposites containing starch are believed to have a great potential application as an environment‐friendly and/or biomedical material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological and curing behavior of reactive blending. II. Natural rubber‐g‐poly(methyl methacrylate)–cassava starch

Graft copolymers of natural rubber (NR) and methyl methacrylate (MMA) were prepared using cumene hydroperoxide and tetraethylene pentamine as redox initiators via the semibatch emulsion polymerization technique. Various molar percentage ratios of NR/MMA were studied in the grafting reaction (i.e., 95/5, 90/10, 80/20, 70/30, and 60/40). The graft copolymer with a 70/30 molar ratio was selected and used to prepare rubber blends with cassava starch. The starch was used at levels of 0, 20, 40, and 60 phr. Another set of rubber blends was prepared for comparison purposes. The NR‐g‐poly(MMA) (PMMA, 75 phr) was blended with 25 phr of NR air dried sheets (ADS) and a given level of the cassava starch. We found that the Mooney viscosity, shear stress, and shear viscosity increased with an increasing concentration of cassava starch. This may be attributed to the chemical interactions between the polar groups of the NR‐g‐PMMA and the cassava starch. The blends were later compounded using a compounding formulation according to ASTM D 3184‐89. A similar short delay onset of vulcanization (i.e., approximately 1 min) was observed for the whole set of compounds under study. However, different curing characteristics were observed for the blends of NR‐g‐PMMA–cassava starch and NR‐g‐PMMA–ADS–cassava starch. The NR‐g‐PMMA–cassava starch compounds exhibited two‐stage curing characteristics. The curing curve had a slight reversion at a testing time of approximately 8 min. The shear modulus then abruptly increased with an increasing testing time in the range of 20–60 min. The curing curves for NR‐g‐PMMA–ADS–cassava starch blends exhibited a single curing stage with a shear modulus that increased slightly with the testing time was increased from 20 to 60 min. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1453–1463, 2003     

Modified chitosan. I. Optimized cerium ammonium nitrate‐induced synthesis of chitosan‐graft‐polyacrylonitrile

Chitin was extracted from shrimp shells and then deacetylated to obtain chitosan. The degree of deacetylation of the chitosan was determined to be 0.76 using pH‐metric titration. A large number of cyanide functional groups were introduced onto chitosan by grafting with polyacrylonitrile as an efficient way of modification. The graft copolymerization reactions were carried out under argon atmosphere in a homogeneous aqueous phase (containing a small portion of acetic acid) by using ceric ammonium nitrate as an initiator. Evidence of grafting was obtained by comparing FTIR spectra of chitosan and the graft copolymer as well as solubility characteristics of the products. The synthetic conditions were systematically optimized through studying the influential factors, including temperature and concentrations of the initiator, acrylonitrile monomer (AN), acetic acid, and chitosan. The effect of individual factors was investigated by calculating and monitoring the variations of the grafting parameters [i.e., grafting ratio (Gr), grafting efficiency (Ge), add‐on value (Ad), homopolymer content (Hp), and total conversion (Ct)]. Under optimum conditions, the grafting parameters were achieved as 535, 98, 81, 2, and 102%, respectively. A mechanism for the free‐radical grafting was proposed. As empirical rates of polymerization and graft copolymerization were plotted against [AN] and [Ce⁴⁺]^1/2, the experimental kinetic data displayed a good match to a reported rate statement. The overall activation energy for the graft copolymerization was determined to be 44.9 kJ/mol. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2048–2054, 2003     

Microwave‐assisted green approach for graft copolymerization of l‐lactic acid onto starch

Poly l ‐lactic acid grafted starch (St‐g‐PLA) copolymers were directly synthesized under microwave irradiation by using sodium hydroxide (NaOH) and stannous 2‐ethyl hexanoate acting as a catalyst, without the use of toxic solvents. The product were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (¹³C CP/MAS NMR), X‐ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA‐DTG). SEM analysis indicated that microwave heating had a considerable effect on the interfacial adhesion between PLA and starch. Thermogravimetric analysis (TGA‐DTG) revealed that copolymers exhibited better thermal stability. Maximum PLA grafting was achieved with the following reaction conditions: 450W microwave power, monomer ratio of 1:5 and 0.4M of NaOH. This study demonstrates that it is possible to obtain St‐g‐PLA copolymers with better processing characteristics and smaller sizes via microwave‐assisted synthesis. The applied procedure is an interesting “green” synthesis method for the production of biodegradable materials used in a diverse range of applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42937.     

Synthesis of starch‐graft‐polyacrylonitrile hydrolyzate and its characterization

The graft copolymerization of three vinyl monomer species, acrylonitrile (AN), acrylamide (AAm), and acrylic acid (AA), onto starch was carried out with ceric salt (Ce salt) as an initiator. With 3 mmol/L Ce salt, the monomer activity onto starch decreased in the following order: AN > AAm > AA. Grafting efficiency with AN as the grafting monomer was greater than 90%, but with AA and AAm, it was less than 50%. Starch‐graft‐polyacrylonitrile was hydrolyzed to introduce amide and carboxyl groups into starch. The hydrolyzates were analyzed with infrared spectroscopy. The hydrolysis reaction was accelerated with increasing alkali concentration, reaction temperature, and time. The water absorbancy of the hydrolyzate increased with an increasing carboxyl molar fraction in the polymer, and it dissolved in water above a 0.6 molar fraction. The absorbancy of water was 2 times higher than that of a NaCl aqueous solution. The copper‐ion‐exchange capacity of the sample was greater in graft copolymers with higher carboxyl group contents. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1437–1443, 2001