Uncrosslinked Blend Research Articles

Radiation crosslinked Polyolefinic blends: exploring thermally tuned dual Shape Memory character

Shape memory behavior of thermally triggered polymeric materials based on ethylene octene copolymer (EOC) and ethylene propylene diene rubber (EPDM) has been studied in details. Investigation of the shape memory behavior of uncrosslinked EOC–EPDM and electron beam crosslinked EOC–EPDM blends have been pursued thoroughly. Shape memory study has been carried out at 60°C, which shows that with the effect of electron beam radiation shape fixity behavior of the crosslinked blends becomes poor as compared with its uncrosslinked blend system whereas the improvement in shape recovery behavior takes place after the exposure to electron beam radiation. Morphology study by Atomic Force Microscopy (AFM) and crystallinity study by X-ray diffraction analysis also give the clear idea regarding the formation of crosslinked network structure. Improvement in gel content with increasing radiation dose supports the formation of network structure. Even after the crosslinking in presence of electron beam radiation also, it has been found that crosslinked EPDM rich blends is superior in terms of shape memory behavior point of view. Lower decay of stress value coupled with lower relaxation ratio of crosslinked EPDM rich blend support its superior shape memory behavior. Copyright © 2016 John Wiley & Sons, Ltd.

Study on the toughening mechanism of PP/EVA dynamically crosslinked blend

ABSTRACTThe toughening mechanism of polypropylene (PP)/ethylene-co-vinyl acetate (EVA) dynamically crosslinked blend was investigated. The results indicated that dynamical crosslinking technology not only improved the interfacial adhesion between PP and EVA, but also increased the mechanical properties of PP/EVA blend. The quantitative and qualitative analysis of scanning electron microscopy (SEM) micrographs demonstrated that dynamical crosslinking technology could refine EVA particles in PP/EVA blend and promote the size distribution of EVA particles. The critical matrix ligament thickness of dynamically crosslinked and uncrosslinked blend was about 0.55 μm and 0.6 μm, respectively, indicating that the brittle-ductile transition occurred. Dynamic mechanical analysis (DMA) results illustrated that the tan δ peak of PP component in the dynamically crosslinked blend moved toward lower temperature compared with that of pure PP and the PP component in uncrosslinked blend; and the tan δ value of the dynamically crosslinked blend was higher than that of the uncrosslinked blend, which interpreted the toughening mechanism of dynamical crosslinking technology from the dynamic mechanical property of the blend.

Super thermoplastic vulcanizates based on carboxylated acrylonitrile butadiene rubber (XNBR) and polyamide (PA12)

Thermoplastic vulcanizates (TPVs) are special classes of thermoplastic elastomers, in which dynamic vulcanization of the rubber phase takes place during melt mixing with a semi-crystalline thermoplastic matrix phase at elevated temperature. TPV is characterized by processing behaviour like thermoplastic at elevated temperature and performance properties of vulcanized rubber at ambient temperature. High performance TPVs or super TPVs are new generation TPVs which exhibit high heat resistance as well as excellent oil resistance property suitable for automotive under-the-hood applications. In the present work, a new super TPV based on carboxylated acrylonitrile butadiene rubber (XNBR) and polyamide (PA12) has been developed. (XNBR:PA12) TPVs of different blend ratios have been prepared by using a fixed concentration of novel cyclic monofunctional peroxide. Final morphology of TPVs varies from either a co-continuous to a dispersed one depending on the blend ratio. TPV of 50:50 XNBR-PA12 shows the highest mechanical properties as well as superior thermal stability among all other TPVs. From differential scanning calorimetric (DSC) study, it can be clearly seen that the glass transition temperature (Tg) of XNBR has shifted to high temperature range in case of all TPVs as compared to that of uncrosslinked blend system. Dynamic mechanical analysis (DMA) also demonstrates that tanδ values of all the TPVs are lower and the storage moduli are higher than the uncrosslinked blend system. Lowest tanδ peak of TPV of 50:50 blend ratio of XNBR:PA12 indicates the highest degree of crosslinking and this is also supported by the swelling studies. The highest level of mechanical properties and superior thermal stability support that phenomenon. Heat aging and oil resistance study have also been carried out in details to understand the performance behaviour of these super TPVs at service condition.

Viscoelastic and Rheological Properties of Carboxymethyl Cellulose /Starch/Graphite Oxide as Superabsorbent Hydrogel Nano Composites (SHNCs)

Uncross-linked carboxymethyl cellulose (CMC) / starch blend used to prepare two hydrogels; the first is cross-linked CMC / starch with aluminum sulfate octadecahydrate cross-linker and the second is SHNCs manufactured from incorporation of 0.3wt% nano graphite oxide (GO) in the above cross-linked blend. Viscoelastic and rheological properties of these two hydrogels were studied and compared with the uncross-linked blend. Results showed that the cross-linking process increases the blend miscibility and converted it to miscible blend. The SHNCs hydrogel has the higher Tg and the uncross-linked blend has the higher Tan δ. GO addition causes increment in some viscoelastic parameters such as G*, G', and G, and decrement in damping parameters and make the damping behavior more stable at lower frequencies, and causes increment for all rheological parameters (η* , ηo, ηf , and GNo). GO addition leads, also, to the absence of the shear thickening behavior and increases both the entanglement density and the molecular weight average. Both hydrogels exhibited broad molecular weight distribution (MWD) and highly cross-linking degree and their elastic behavior predominates; makes them rigid specially at higher frequencies.

Effects of plasticizer/cross-linker on the mechanical and thermal properties of starch/PVA blends

Biodegradable blends of potato starch and polyvinyl alcohol were prepared by solution casting method. Citric acid was employed to introduce the plasticizing effect into the starch materials. Glutaraldehyde as cross-linker was used to enhance the properties of the blend films. Cross-linking is a common method to improve the strength and stability of starch products. The effects of citric acid and glutaraldehyde on the mechanical properties, thermal properties and swelling degree were investigated. The prepared films were measured for their antibacterial activities and biodegradability. The blend samples were characterized by the thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and FTIR analysis techniques. From the mechanical properties study, it was analyzed that the blend films showed improvement in their tensile strength after cross-linking with glutaraldehyde. The SEM micrographs indicated that the blend films were smooth without any cracks, pores and were well cross-linked. The TGA curves showed that there was an increase in the thermal stability of the blend films after cross-linking as compared to uncross-linked blend films. The prepared films showed good antibacterial properties against Gam-positive and Gram-negative bacteria. The biodegradability of the blends was determined by placing the samples in compost soil for different time intervals and were found to be biodegradable in nature.

Preparation of Chitosan/Sericin Blend Membrane and the Characteristics of the Resulting Membrane

Physical properties of uncrosslinked and crosslinked by ethyleneglycoldiglycidyl (EGDE) or polyethyleneglycoldiglycidyl (PGDE) sericin-chitosan blend membranes were investigated. 1. The surface of chitosan membrane was very smooth even after the treatment with aqueous sodium hydroxide. Those of uncrosslinked and crosslinked blend membranes were relatively flat before washing, but they were extremely uneven after washing with an alkaline solution. 2. With increasing sericin mixing ratio tensile stress increased whereas tensile strain decreased for uncrosslinked blend membrane. For crosslinked blend membrane by EGDE, both of tensile stress and tensile strain decreased. Tensile stress increased but tensile strain decreased for crosslinked blend membrane by PGDE (n=4). Both values for crosslinked blend membrane by PGDE (n=9) were equal or over to those of chitosan membrane. 3. The diffusion coefficient and permeability coefficient for an anionic dye (CI Acid Orange 7) into the blend membrane greatly increased. Those for the blend membrane crosslinked by PGDE of n=4 decreased whereas those values for the crosslinked blend membrane by PGDE of n=9 increased, because of the increase in the porosity by cleaning with an aqueous sodium hydroxide.

Dynamic Vulcanization of Thermoplastic Elastomers Based on Poly(Epichlorohydrin-Co-Ethylene Oxide) and Polypropylene

Unvulcanized and dynamically vulcanized blends of poly(epichlorohydrin-co-ethylene oxide) elastomer and polypropylene have been prepared by melt mixing in an internal mixer. The solvent resistance, morphology, dynamic mechanical and mechanical properties of these blends were studied with special reference to the effect of the crosslinking agent content. The swelling behaviour shows that the blends, with and without dynamic vulcanization, present excellent resistance to solvents ASTM A, B, C and D, at room temperature. Morphology study by scanning electron microscopy of the cryofractured surface and analysis of the dynamic mechanical properties of the system indicate that the uncrosslinked blend is immiscible and form a two-phase structure, where the rubber phase was dispersed as domains in the continuous polypropylene matrix. The mechanical properties of the crosslinked blends do not improve by increasing the doses of crosslinking agent.

Thermal, viscoelastic, solution and membrane properties of sodium alginate/hydroxyethylcellulose blends

Solution and film blend compatibility of carbohydrate polymers, viz. sodium alginate and hydroxyethylcellulose have been studied. Blend solutions were prepared in water. Films of the individual polymers and their blends were prepared by solution casting and crosslinking with glutaraldehyde and urea–formaldehyde–sulfuric acid mixture. Compatibility of blends in solution was studied by density and viscosity, while blend compatibility in solid films was evaluated by differential scanning calorimetry, dynamic mechanical thermal analyzer and scanning electron microscopy. Solution density showed a linear trend with the blend composition. The glass transition of the blends lies in between the individual polymers. The glass transition temperature of sodium alginate was lowered with the addition of HEC in the blend. These results suggested the compatibility of sodium alginate and hydroxyethylcellulose blends. Storage modulus of sodium alginate film decreased after the addition of hydroxyethylcellulose. For the crosslinked blend films, storage modulus was higher than the respective uncrosslinked blend systems. A typical blend film was chosen for the pervaporation separation of water+tetrahydrofuran mixture, while the crosslinked sodium alginate film was tested for the pervaporation separation of water+1,4-dioxane mixture.

Synthesis and characterization of konjac glucomannan/poly(vinyl alcohol) interpenetrating polymer networks

AbstractNovel interpenetrating polymer networks (IPNs) coded as KP were synthesized successfully from poly(vinyl alcohol) (PVA) and konjac glucomannan (KGM) in the presence of glutaraldehyde as a crosslink agent. The transparent IPN films that were 40 μm thick were prepared by means of conventional solvent‐casting technique and dried at room temperature for 2 days. The structure and miscibility of the KP films were studied by Fourier transformed infrared spectra, scanning electron microscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction, and ultraviolet visible spectroscopy (UV–Vis). The results indicated that strong intermolecular interaction caused by crosslink bonding between PVA and KGM occurred in the IPN films, resulting in wonderful miscibility when the reaction time is 4 h. The tensile strength, elongation at break, and moisture uptake was much higher than that of the pure PVA film, KGM film, and uncrosslinked blend films. In other words, the structure of IPN endowed the films with excellent performance, so the new material has promising applications to food package film and agricultural film because of its biodegradability. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2775–2780, 2004

Mechanical properties, morphological structure, and thermal behavior of dynamically photocrosslinked PP/EPDM blends

AbstractA dynamically photocrosslinked polypropylene (PP)/ethylene–propylene–diene (EPDM) rubber thermoplastic elastomer was prepared by simultaneously exposing the elastomer to UV light while melt‐mixing in the presence of a photoinitiator as well as a crosslinking agent. The effects of dynamic photocrosslinking and blend composition on the mechanical properties, morphological structure, and thermal behavior of PP/EPDM blends were investigated. The results showed that after photocrosslinking, tensile strength, modulus of elasticity, and elongation at break were improved greatly. Moreover, the notched Izod impact strength was obviously enhanced compared with corresponding uncrosslinked blend. Scanning electron microscopy (SEM) morphological analysis showed that for uncrosslinked PP/EPDM blends, the cavitation of EPDM particles was the main toughening mechanism; whereas for dynamically photocrosslinked blends, shear yielding of matrix became the main energy absorption mechanism. The DSC curves showed that for each dynamically photocrosslinked PP/EPDM blend, there was a new smaller melting peak at about 152°C together with a main melting peak at about 166°C. Dynamic mechanical thermal analysis (DMTA) indicated that the compatibility between EPDM and PP was improved by dynamic photocrosslinking. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3371–3380, 2004

Properties of crosslinked casein/waterborne polyurethane composites

AbstractWaterborne polyurethane (WPU) and casein (1 : 1 by weight) were blended at 90°C for 30 min, and then were crosslinked by adding 1–10 wt % ethanedial to prepare a series of sheets. Their structure and properties were characterized by using infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis, and tensile testing. The results indicated that crosslinked blend sheets exhibited a certain degree of miscibility, and exhibited much higher tensile strength and water resistivity than did the WPU, casein, and the uncrosslinked blend from WPU and casein. When the ethanedial content was 2 wt %, the tensile strength and elongation at break of crosslinked sheets achieved 19.5 MPa and 148% in the dry state, and 5.0 MPa and 175% in the wet state, respectively. A 2 wt % content of ethanedial plays an important role in the enhancement of mechanical properties, thermal stability, and water resistivity of the blends of WPU and casein as a result of intermolecular crosslinking. This work provided a new protein plastic with good water resistivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 332–338, 2004

Improvement of physical properties of crosslinked alginate and carboxymethyl konjac glucomannan blend films

AbstractBlend films from carboxymethyl konjac glucomannan and sodium alginate in different ratios were prepared by blending 4 wt % sodium alginate aqueous solution with 2 wt % konjac glucomannan aqueous solution. After crosslinking with 5 wt % calcium chloride aqueous solution, the blend films formed a structure of semi‐interpenetrating networks. The structure and physical properties of both uncrosslinked and crosslinked films were characterized by Fourier transformed infrared spectra (FTIR), differential thermal analysis (DTA), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and tensile tests. The results indicated that the mechanical properties and the thermal stability of the films were improved by blending sodium alginate with carboxymethyl konjac glucomannan due to the intermolecular hydrogen bonds between sodium alginate and carboxymethyl konjac glucomannan. The crosslinked blend films with Ca2+, compared with uncrosslinked blend films, exhibited further improved physical properties due to the formation of a semi‐IPN structure. Furthermore, the degree of swelling of the crosslinked films was also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2554–2560, 2002

Transport and thermal properties of poly(ether imide)/acetylene-terminated monomer blends

Blends of an acetylene-terminated monomer (ATM) with a commercially available poly(etherimide) (PEI, Ultem™) were prepared, crosslinked, and characterized. Varying degrees of crosslinking were achieved through thermal treatment at 150–270°C. Incorporation of the uncrosslinked additive into the PEI resulted in reductions in the glass transition temperature, gas permeabilities and selectivities, and thermal stability. These behavior are consistent with antiplasticization of the polymer host by the ATM additive. Crosslinking of the actylene-terminated additive led to increases in thermal and chemical stability and improved gas selectivities as compared to the uncrosslinked blend. Gas transport properties are reported as a function of temperature. For the blend composition considered (9 wt% ATM in PEI), the fully crosslinked blend had transport properties which were essentially equivalent to the virgin PEI. Further, processing of the blend could be achieved in the same manner as for the virgin PEI. The resistance of the crosslinked blend to chemical dissolution or swelling was markedly improved as compared to PEI.

Studies on the effect of blend ratio and crosslinking system on thermal, X-ray and dynamic mechanical properties of blends of natural rubber and ethylene-vinyl acetate copolymer

Differential scanning calorimetry (d.s.c.), X-ray, dynamic mechanical and microscopy studies were carried out using a series of blends of natural rubber (NR) and ethylene-vinyl acetate copolymer (EVA) in the crosslinked and uncrosslinked states. The crosslinking system (sulfur, peroxide and mixed) and blend ratio do not influence significantly the melting temperature ( T m) of EVA. The decrease in percentage crystallinity of EVA with NR content is related to the incomplete crystallization, as indicated by the lower heat of fusion ( ΔH). The glass transition temperature ( T g) of NR in the uncrosslinked blend did not change substantially and this indicated incompatibility. However, in the case of crosslinked systems, depending on the type of crosslinking agents used, the T g of the NR phase in the blend was shifted to higher temperatures. This has been explained with reference to the predominant crosslinking of the NR phase. From X-ray diffraction patterns, the interplanar distances ( d values) were calculated. With the addition of NR there was a tendency for the d values to increase in all systems. The crystallinity was measured by X-ray and the results were in line with those of d.s.c. measurements. The dynamic mechanical properties such as tan δ, storage modulus and loss modulus of the blends were evaluated. The existence of separate T g values in dynamic mechanical thermal analyser studies indicates that the blends are incompatible. The morphology of the uncrosslinked blends has been studied by scanning electron microscopy.

Morphology of Elastomeric Alloys

Abstract The field of thermoplastic elastomers has shown an explosive growth with the successful commercialization of elastomeric alloys (EAs) in 1981, based on the original work of Coran, Das, and Patel on dynamic vulcanization and the discovery of preferred cure system by Abdou-Sabet and Fath. These discoveries have led to the development of commercial products having true elastomeric properties while maintaining excellent thermoplastic processing. The success of EAs in the marketplace has led to the introduction of new products by Monsanto and others at a rate of 60 products per year in the last half of the eighties. Elastomeric alloys have been characterized as compositions containing rubber particulate domains approximately 1–2 µm in diameter in a matrix of thermoplastic resin. Such dispersed phase morphology has not been widely accepted, especially when it came to explaining the true elastomeric properties of the soft elastomeric products, i.e. 64 and 55 Shore A hardness products. Interaction among the rubber particles leading to a network of vulcanized elastomer phase that gave the appearance of two continuous networks has been proposed. In this paper, the morphology of EPDM/polypropylene elastomeric alloys is examined with some detail, and evidence leading to dispersed phase morphology is provided. There are several variables to such an investigation which can be grouped under the following headings: 1. Molecular weight of EPDM and polypropylene (PP). 2. Ratio of EPDM to PP. 3. Crosslinked or uncrosslinked blend. 4. Degree of crosslinking. 5. Type of crosslinks. 6. Typical and commercial products. It is not the subject of this paper to review the morphology of different binary polymer blends, which have been extensively covered in the literature. It can be concluded that a variety of morphologies can be obtained, however, depending on the mixing conditions, polymer ratios, relative surface energies of the polymer pair, and viscosities and molecular weights of the two polymers. In this study, the mixing conditions were kept similar as much as possible to eliminate the possibility of morphological changes as a function of the applied mixing intensity as influenced by shear rate, mixing time, and temperature.