Influence of chain extension on the compatibilization and properties of recycled poly(ethylene terephthalate)/linear low density polyethylene blends

Polymeric methylene diphenyl diisocyanate (PMDI) was added as chain extender to a blend of recycled poly(ethylene terephthalate) (R-PET) and linear low density polyethylene (LLDPE) with compatibilizer of maleic anhydride-grafted poly(styrene-ethylene/butadiene-styrene) (SEBS-g-MA). Hydroxyl end groups of PET can react with both isocyanate groups of PMDI and maleic anhydride groups of SEBS-g-MA, which are competing reactions during reactive extrusion. The compatibility and properties of the blends with various contents of PMDI were systemically evaluated and investigated. WAXD results and SEM observations indicated that chain extension inhibits the reaction between PET and SEBS-g-MA. As the PMDI content increased, the morphology of dispersed phase changed from droplet dispersion to rodlike shape and then to an irregular structure. The DSC results showed that the crystallinity of PET decreased in the presence of PMDI, and the glass transition temperature (T_g) of PET increased with addition of 0-0.7 w% PMDI. The impact strength of the blend with 1.1 w% PMDI increased by 120% with respect to the blend without PMDI, accompanied by only an 8% tensile strength decrease. It was demonstrated that the chain extension of PET with PMDI in R-PET/LLDPE/SEBS-g-MA blends not only decreased the compatibilization effect of SEBS-g-MA but also hindered the crystallization of PET.     

Thermogravimetric Analysis and Thermal Ageing of Crosslinked Nitrile Rubber/Poly(ethylene-co-vinyl Acetate) Blends

The thermal behaviour of nitrile rubber (NBR)/poly(ethylene-co-vinyl acetate) (EVA) blends was studied by thermogravimetry. The effects of blend ratio, different crosslinking systems (sulphur, peroxide and mixed), various fillers (silica, clay and carbon black) and filler loading on the thermal properties were evaluated. It was found that the initial decomposition temperature increased with the addition of NBR to EVA. Among the various crosslinking systems studied, the peroxide cured system showed the highest initial decomposition temperature. This is associated with the high bond dissociation energy of C–C linkages. The addition of fillers improved the thermal stability of the blend. The mass loss at different temperatures and activation energy of degradation were also studied. The thermal ageing of these blends was carried out at 50 and 100°C for 72 h. It was seen that the properties are not affected by the mild ageing condition. Also, the peroxide cured system was found to exhibit better retention in properties, than other crosslinking systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nonisothermal crystallisation, melting behavior and wide angle X-ray scattering investigations on linear low density polyethylene (LLDPE)/ethylene vinyl acetate (EVA) blends: effects of compatibilisation and dynamic crosslinking

Crystallisation studies on LLDPE/EVA blends and the individual components were performed with wide angle X-ray scattering (WAXS) technique and differential scanning calorimetry (DSC) DSC was used to characterise the quiescent crystallisation behavior. The heat of fusion and crystallinity of the blends were reduced by the addition of EVA. The experimental and theoretical values of crystallinity of the blends were found to be mutually agreeing. Crystallisation of LLDPE remains impeded to some extent due to the presence of amorphous EVA. Compatibilisation does not affect crystallinity whereas crosslinking decreases crystallinity. Crosslinking and compatibilisation make no significant change in the melting temperature of the blends. X-ray diffraction studies were carried out on un-crosslinked and crosslinked LLDPE/EVA blends with a view to study the effect of blend composition and crosslinking on crystallinity and lattice distance. Studies revealed that LLDPE and EVA have orthorhombic unit cell. Blending with EVA did not affect the crystalline structure of LLDPE, but the crystallinity decreases with EVA content. At low concentrations of EVA the lattice parameters remain unchanged. Above 30% EVA content however, a linear increase has been observed. Dicumyl peroxide (DCP) crosslinked samples show considerable shift of (1 1 0), (2 0 0) and (0 2 0) crystalline peaks towards lower 2θ values indicating an increase of unit cell parameters of the orthorhombic unit cell of polyethylene. At lower EVA-concentrations (<50%) the crystalline structure remains unchanged. For EVA-contents of more than 70% however, increasing DCP-content reduces the crystallinity of the blends and increases the lattice distance. This indicates that DCP-crosslinking is more effective in EVA phase than in the LLDPE phase.     

Allylic monomers as reactive plasticizers of polyphenylene oxide. Part III – Rheological and mechanical properties

The chemorheology of blends of diallyl ortho-phthalate (DAOP) as reactive plasticizer of polyphenylene oxide (PPO) were monitored during their cure with either dicumyl peroxide (DCP) or tert-butyl hydroperoxide (TBHP), and their mechanical properties and morphology were studied. The steady shear and dynamic rheology behaviour was consistent with chemical gelation of DAOP in blends with low concentrations of PPO but the gelation behaviour at higher PPO concentrations was more complex. Dynamic mechanical thermal analysis of the blends of PPO:DAOP cured with either DCP or TBHP indicated a two phase structure. For PPO:DAOP/DCP, the lowest transition (between 150 °C and 200 °C) was attributed to a DAOP-rich phase and its T_g was higher than that for pure DAOP/DCP due to the presence of PPO in the DAOP-rich phase. The smaller damping shoulder near 250 °C was caused by a PPO-rich phase with a T_g that was lower than pristine PPO due to the presence of unpolymerized or polymerized DAOP. In contrast, the glass transition region of the PPO:DAOP/TBHP system was very broad due to an overlap of the transitions for DAOP-rich and PPO-rich phases caused by higher levels of unpolymerized DAOP. SEM observations of the blends revealed a two phase morphology with PPO-rich particles in a poly-DAOP matrix for blends with ?30 wt% PPO, a co-continuous morphology for blends with 40 wt% PPO, and a phase inverted morphology with more than 50 wt% PPO. These SEM observations agree with studies of the swelling, disintegration or dissolution of matrix of the blends in solvent.     

Thermal stability and ageing properties of sulphur and gamma radiation vulcanized natural rubber (NR) and carboxylated styrene butadiene rubber (XSBR) latices and their blends

The thermal stability of natural rubber (NR) and carboxylated styrene butadiene rubber (XSBR) latices and their blends was studied by thermogravimetric methods. Ageing characteristics of these latex blends were studied by applying hot air oven thermal ageing for seven days at 70 °C. The mechanical properties of the aged samples were studied. Thermal degradation and ageing properties of these individual latices and their blends were investigated with special reference to blend ratio and vulcanization techniques. As the XSBR content in the blends increased their thermal stability was also found to increase. Among sulphur and radiation-vulcanized samples, radiation cured possesses higher thermal stability due to the higher thermal stability of carbon-carbon crosslinks. DTG curves were used for the determination of different stages involved in the degradation. Activation energy for degradation was determined from Coats-Redfern plot. The properties of aged samples were found to decrease due to chain depletion. However, the moduli of XSBR and NR/XSBR blends were found to increase owing to the formation of crosslinks upon ageing.     

Synergistic effects of layered double hydroxide with hyperfine magnesium hydroxide in halogen-free flame retardant EVA/HFMH/LDH nanocomposites

The synergistic effects of layered double hydroxide (LDH) with hyperfine magnesium hydroxide (HFMH) in halogen-free flame retardant ethylene-vinyl acetate (EVA)/HFMH/LDH nanocomposites have been studied by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), thermogravimetric analysis (TGA), limiting oxygen index (LOI), mechanical properties' tests, and dynamic mechanical thermal analysis (DMTA). The XRD results show that the exfoliated EVA/HFMH/LDH can be obtained by controlling the LDH loading. The TEM images give the evidence that the organic-modified LDH (OM-LDH) can act as a disperser and help HFMH particles to disperse homogeneously in the EVA matrix. The TGA data demonstrate that the addition of LDH can raise 5-18 °C thermal degradation temperatures of EVA/HFMH/LDH nanocomposite samples with 5-15 phr OM-LDH compared with that of the control EVA/HFMH sample when 50% weight loss is selected as a point of comparison. The LOI and mechanical tests show that the LDH can act as flame retardant synergist and compatilizer to apparently increase the LOI and elongation at break values of EVA/HFMH/LDH nanocomposites. The DMTA data verify that the T_g value (−10 °C) of the EVA/HFMH/LDH nanocomposite sample with 15 phr LDH is much lower than that (T_g = −2 °C) of the control EVA/HFMH sample without LDH and approximates to the T_g value (−12 °C) of pure EVA, which indicates that the nanocomposites with LDH have more flexibility than that of the EVA/HFMH composites.     

Toughening of poly(2,6-dimethyl-1,4-phenylene oxide)/nylon 6 alloys with functionalized elastomers via reactive compatibilization: morphology, mechanical properties, and rheology

Blends of poly(2,6-dimethyl-1,4-phenylene oxide)/nylon 6 alloys based on ethylene-propylene-diene elastomer (EPDM) grafted with maleic anhydride (MA) (EPDM-g-MA), EPDM grafted with glycidyl methacrylate (EPDM-g-GMA), and styrene-ethylene-butadiene-styrene block copolymer grafted with MA (SEBS-g-MA) were prepared via melt extruction, and morphology, mechanical properties, and rheology were studied. The compatibilizing effects of functionalized elastomers on the PPO/nylon 6 alloys were proved by DSC analysis and confirmed by the significant improvement in the notched Izod impact strength. Toughening was resulted from the smaller particle size and finer dispersion of EPDM in the PPO/nylon 6 matrix as well as a novel network structure of SEBS-g-MA domain in matrix. The notched Izod impact strength of the blends exhibited an optimum value when the extent of MA or GMA graft ratio of EPDM varied, which was an order of magnitude higher than the non-toughened alloys. The morphology revealed that the size of EPDM particles decreased with an increase in graft ratio of MA or GMA onto EPDM. Rheology investigation indicated that the MA or GMA moieties on EPDM reacted with the amine groups of nylon 6, which increased the molecular weight and the degree of branching, and thus resulted in an increase in the viscosity of the blends. This proved the reactive compatibilization between functionalized EPDM and PPO/nylon 6 matrix.     

UV-curing behavior and adhesion performance of polymeric photoinitiators blended with hydrogenated rosin epoxy methacrylate for UV-crosslinkable acrylic pressure sensitive adhesives

UV-crosslinkable polyacrylates were synthesized for use as pressure sensitive adhesives (PSAs). These polyacrylates acted as polymeric photoinitiators due to the benzophenone incorporated into their backbones. Hydrogenated rosin epoxy methacrylate (HREM; based on hydrogenated rosin and glycidyl methacrylate) was also synthesized as a tackifier, and blended at different levels with the synthesized, UV-crosslinkable polyacrylates for use as PSAs. The effect of the new tackifier, HREM, on the properties of the UV-crosslinkable PSAs was examined in comparison with the properties exhibited by PSA/hydrogenated rosin blends. The characteristics of these PSA/tackifier blends were examined by Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and an advanced rheometric expansion system (ARES). In addition, the adhesion performance of the PSA blends was investigated using probe tack tests. DSC and ARES revealed all the PSA blends with HREM or hydrogenated rosin to be miscible at the molecular level. The glass transition temperature (T_g) of HREM was −25.6 °C, which is lower than that of other commercially available rosin tackifiers. FTIR revealed changes in the relative concentration of benzophenone groups in the PSAs at 1580 cm⁻¹, which demonstrated that the crosslinking efficiency is proportional to the benzophenone content and UV dose, but decreases with increasing hydrogenated rosin content. However, the reduced crosslinking reaction efficiency was improved in the PSA/HREM blends due to the low T_g of HREM which only slightly increased the T_g of the PSA blends. Moreover, the relative initial decrease in the probe tack of the PSA/HREM blends was lower than that of the PSA/hydrogenated rosin blends after UV irradiation.     

High Tg nematic thermosets: Synthesis, characterization and thermo-mechanical properties

In this paper the synthesis and characterization of a new family reactive nematic oligomers based on 4-hydroxybenzoic acid (4-HBA) will be presented. We modified the backbone using para- and meta-substituted aromatic monomers such as terephthalic acid (TA), isophthalic acid (IA), hydroquinone (HQ), resorcinol (RS), 4,4′-bisphenol (BP) and 3-hydroxybenzoic acid (3-HBA). All oligomers, with a target M_n of 5000 and 9000 g mol⁻¹, were end-capped with reactive phenylethynyl functionalities and synthesized using standard melt condensation techniques. Curing of the phenylethynyl reactive functionalities proceeds through chain extension and crosslinking, depending upon the temperature and time and can be carried out between 310 and 400 °C. Fully cured nematic thermosets could be obtained with glass-transition temperatures previously not accessible (T_g > 400 °C). The cured polymers exhibit excellent tensile properties, i.e. tensile strength (83 MPa) and elongation at break (9%). This approach allows us to prepare all-aromatic polymers with a combination of useful properties such as ease of processing, high T_g’s, and excellent mechanical properties.     

Dynamic mechanical behavior of acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) blends

The dynamic mechanical behavior of uncrosslinked (thermoplastic) and crosslinked (thermosetting) acrylonitrile butadiene rubber/poly(ethylene‐co‐vinyl acetate) (NBR/EVA) blends was studied with reference to the effect of blend ratio, crosslinking systems, frequency, and temperature. Different crosslinked systems were prepared using peroxide (DCP), sulfur, and mixed crosslink systems. The glass‐transition behavior of the blends was affected by the blend ratio, the nature of crosslinking, and frequency. sThe damping properties of the blends increased with NBR content. The variations in tan δ_max were in accordance with morphology changes in the blends. From tan δ values of peroxide‐cured NBR, EVA, and blends the crosslinking effect of DCP was more predominant in NBR. The morphology of the uncrosslinked blends was examined using scanning electron and optical microscopes. Cocontinuous morphology was observed between 40 and 60 wt % of NBR. The particle size distribution curve of the blends was also drawn. The Arrhenius relationship was used to calculate the activation energy for the glass transition of the blends, and it decreased with an increase in the NBR content. Various theoretical models were used to predict the modulus of the blends. From wide‐angle X‐ray scattering studies, the degree of crystallinity of the blends decreased with an increasing NBR content. The thermal behavior of the uncrosslinked and crosslinked systems of NBR/EVA blends was analyzed using a differential scanning calorimeter. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1556–1570, 2002     

Thermal and mechanical properties of in situ polymerized PS/EPDM blends

In situ polymerized PS/EPDM blends were prepared by dissolving poly(ethylene-co-propylene-co-2-ethylidene-5-norbornene) (EPDM) in styrene monomer, followed by bulk polymerization at 60 °C and 80 °C . EPDM has excellent resistance to such factors as weather, ozone and oxidation, attributed to its non-conjugated diene component, and it could be a good alternative for substituting polybutadiene-based rubbers in PS toughening. The in situ polymerized blends were characterized by dynamic mechanical analysis, thermogravimetric analysis, gel permeation chromatography, and tensile and Izod impact resistance tests. The PS/EPDM blends are immiscible and present two phases, a dispersed elastomeric phase (EPDM) in a rigid PS matrix whose phase behavior is strongly affected by the polymerization temperature. Mechanical properties of the blends are influenced by the increase in the average size of EPDM domains with the increase in the polymerization temperature and EPDM content. The blends polymerized at 60 °C containing 5 wt% of EPDM presents an increase in the impact resistance of 80% and containing 17 wt% of EPDM presents an increase in the strain at break of 170% in comparison with the value of PS. The blend polymerized at 80 °C containing 17 wt% of EPDM presents an increase in the strain at break of 480% and in impact resistance of 140% in comparison with the value of PS.     

Photochemical deterioration of poly(vinylbutyral) in the range of wavelengths from middle ultraviolet to the visible

Films of poly(vinylbutyral) (PVB) from two proprietary sources were tested for photochemical behavior upon exposure to UVB, UVA, BLB, and high-output “daylight” fluorescent (DLF) lamps. Discoloration and brittleness followed the buildup and subsequent decline of peroxide content. In the range of 60-89.9 °C, the onset of crosslinking and the loss of weight obeyed the Arrhenius relationship. At temperatures above the second-order-transition temperature, T_g, crosslinking predominated; at temperatures below T_g, chain breaking tended to prevail.     

Synergistic effect of SEBS-g-MA and epoxy on toughening of polyamide 6/glass fiber composites

Maleated styrene-ethylene-butylene-styrene block copolymer (SEBS-g-MA) and epoxy monomer, individually or in combination, are used to toughen polyamide 6/glass fiber composites. The epoxy monomer enhanced interaction between polyamide 6 and glass fiber. SEBS-g-MA rubber is uniformly dispersed in polyamide 6 matrix caused by the preferred compatibilizing reaction between the anhydride group of rubber and the amine terminal group of polyamide 6. The addition of epoxy does not affect the fine dispersion of SEBS-g-MA. Polyamide 6/glass fiber binary composites are brittle. The addition of epoxy monomer alone does not change their brittle features. Similarly, in the absence of epoxy monomer, adding 20 wt % of SEBS-g-MA to polyamide 6/glass fiber composites does not greatly increase the tensile ductility. Only when both SEBS-g-MA and epoxy monomer are present in some combination, do the polyamide 6/glass fiber composites show prominent ductile characteristics, such as stress-whitening and necking. This synergistic effect of epoxy monomer and SEBS-g-MA also imparts higher notched impact strengths to the ternary composites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1448–1458, 2007     

Phenylethynylnaphthalic endcapped imide oligomers with reduced cure temperatures

A series of 4-(2-phenylethynyl)-1,8-naphthalic anhydride (PENA) endcapped imide oligomers with different chemical backbones and calculated number average molecular weights (Calc’d M_n) were successfully synthesized and characterized. The PENA-endcapped imide oligomers were mixtures of mono- and double-endcapped imide oligomers with polymerization degree (P_n) of 1-5 and number average molecular weights (M_n) of 2515-3851 g/mol. determined by GPC. Study on effect of chemical structures on the curing behaviors of two model compounds: PENA-m based on PENA and PEPA-m derived from 4-phenylethynylphthalic anhydride (PEPA) revealed that PENA-m showed the cure temperature of 50 °C lower than PEPA-m and the activity energy of thermal curing reaction for PENA-m was also lower than that of PEPA-m. The PENA-endcapped imide oligomers could be melt at temperatures of >250 °C with the minimum melt viscosity of 1.2-230 Pa s at 275-301 °C and the widen melt processing windows, along with 10-40 °C lower cure temperature than the PEPA-endcapped analogue.The PENA-endcapped imide oligomers could be thermally cured at 350 °C/1 h to afford the thermally cured polyimides with good combined thermal and mechanical properties including T_g of 344-397 °C (DMA), T_d of 443-513 °C, tensile strength of as high as 54.7 MPa, flexural strength of as high as 126.1 MPa and modulus of as high as 2.3 GPa, respectively.     

Preparation and thermal properties of diglycidylether sulfone epoxy

A diglycidylether sulfone monomer (sulfone type epoxy monomer, SEP) was prepared from bis(4-hydroxyphenyl) sulfone (SDOL) and epichlorohydrin without any NaOH or KOH as basic catalyst. FT-IR, ¹H NMR, ¹³C NMR and mass spectroscopic instruments were utilized to determine the structure of the SEP monomer. The cured SEP epoxy material exhibited not only a higher T_g (163.81 °C) but also a higher T_g than pristine DGEBA (from 111.25 °C to 139.17 °C) when the SEP monomer moiety had been introduced into the DGEBA system. The thermal stability of cured epoxy herein was investigated by thermogravimetric analysis (TGA). The results demonstrated that the sulfone group of the cured SEP material decomposed at lower temperatures and formed thermally stable sulfate compounds, improving char yield and enhancing resistance against thermal oxidation. Additionally, the IPDT and char yield of the cured SEP epoxy (IPDT = 1455.75, char yield = 39.67%) exceeded those of conventional DGEBA epoxy (IPDT = 667.27, char yield = 16.25%).     

Poly(N-isopropylacrylamide) thermoresponsive cross-linked conjugates containing polymeric soybean oil and/or polypropylene glycol

Synthesis, characterization and solution properties of a new series of the PNIPAM-soybean oil and/or polypropylene glycol, PPG, conjugates (conjugates also referred to as co-networks) have been described. For this purpose free radical polymerization of NIPAM monomer was initiated by macroinitiators based on PSB and/or PPG in order to obtain PSB-g-PNIPAM, PPG-g-PNIPAM and PSB-g-PPG-g-PNIPAM cross-linked graft copolymers. The autooxidation of soybean oil under air at room temperature rendered waxy soluble polymeric soybean oil peroxide associated with cross-linked parts. The soluble polymeric oil macro-peroxide isolated from the cross-linked part was used to initiate the free radical polymerization of NIPAM to give PSB-g-PNIPAM cross-linked copolymer. To obtain PPG-macromonomeric initiator, PPG-MIM, PPG-bis amino propyl ether with Mn 400 (or 2000) Dalton was reacted with 4,4′-azo bis cyanopentanoyl chloride and methacryloyl chloride, respectively. PPG-MIM also initiated the free radical polymerization of NIPAM at 80 °C to yield PPG-g-PNIPAM cross-linked thermoresponsive product. In order to obtain PSB-g-PPG-g-PNIPAM cross-linked triblock copolymer, NIPAM was polymerized by using the mixture of two macroinitiators, PSB and PPG-MIM. PSB contents in the graft copolymers were calculated via elemental analysis of nitrogen in graft copolymers. Thermal analysis, SEM, FTIR and ¹H NMR techniques were used in the characterization of the products. The effect of polymeric soybean oil, PSB, and/or PPG on the thermal response rate of poly(N-isopropylacrylamide, PNIPAM, cross-linked-graft copolymers swollen in water has been investigated by means of swelling-deswelling and drug release behaviors against to temperature change. Lower critical solution temperatures (LCST) of the cross-linked PNIPAM conjugates (conjugates also referred to as co-networks) were determined from the curves of swelling degrees versus solution temperatures. The response temperature of the hydrophobically modified PNIPAM conjugates was reduced to 27 °C, 23 °C and 27 °C for PSB-g-PNIPAM, PPG-g-PNIPAM and PSB-g-PPG-g-PNIPAM, respectively. We have found that the graft copolymers were not pH-responsive. In addition, higher pH ranges cause the hydrolysis of the PSB ester linkages, quickly and makes the cross-linked graft copolymers soluble.The fastest shrinking of the gels was observed by loosing water between 65% and 98% at 50 °C.Methyl orange (MO), was used as a model drug, loaded into cross-linked graft copolymers to examine and compare the effects of controlled release at lower and higher temperatures of lower critical solution temperature (LCST).     

Characterization of irradiation-induced crosslink of epoxidised natural rubber/ethylene vinyl acetate (ENR-50/EVA) blend

The effect of irradiation on tensile, dynamic mechanical properties, thermal properties and morphology of ENR-50, EVA and ENR-50/EVA blend was investigated. All the samples were irradiated using a 3.0 MeV electron beam (EB) machine with doses ranging from 20 to 100 kGy. Results indicate that the gel fraction of ENR-50, EVA and ENR-50/EVA blend increases with irradiation dose. Concerning tensile properties, it can be seen that EB radiation increases the tensile strength of all the samples, increases the elongation at break of ENR-50 and ENR-50/EVA blend, reduces the elongation at break of EVA, increases M200 (modulus at 200% strain) of ENR-50 and EVA, while decreases M200 of the ENR-50/EVA blend. For dynamic mechanical studies, it was found that EB radiation increases the T_g of all the samples due to the effect of irradiation-induced crosslinking. The compatibility of ENR-50/EVA blend also found to be improving upon irradiation. In the case of thermal properties, it was detected that T_m, T_c and the degree of crystallinity of ENR-50/EVA blend increase with an increase in irradiation dose. This was due to the perfection in the crystal growth occurring upon radiation. Morphology changes play a major role in the changes of the properties of ENR-50/EVA blend. Finally, it can be concluded that ENR-50/EVA blend can be vulcanized by EB radiation.     

Mechanical properties and strain-rate effect of EVA/PMMA in situ polymerization blends

Transparent EVA/PMMA sheets are produced via in situ polymerization of MMA in this work. In the presence of the EVA-graft-PMMA (EVA-g-PMMA), which is synthesized by using tert-butyl peroctoate (t-BO) as initiator during MMA polymerization, EVA can be well dispersed in the PMMA matrix. Both tensile fracture energy and Izod impact strength of the EVA/PMMA blends are higher than those of the neat PMMA. SEM photos show that the grafted copolymer also prevents the dispersed EVA particles from being pulled out from the fracture surface. While the EVA/PMMA blends are investigated at room temperature over the strain rates of four decades (from 1.6 × 10⁻⁴ to 0.16 s⁻¹). It has an obvious transition, whereas the neat PMMA remains brittle over the entire range of strain rates.     

Morphology, thermal stability and visco-elastic properties of polystyrene-poly(vinyl chloride) blends

The morphology, thermal and mechanical properties of polystyrene (PS) blends with 2.5-20 wt% of poly(vinyl chloride) (PVC) have been studied. The measurement of the glass transition temperature (T_g) from the maxima of tan δ data using dynamic mechanical thermal analysis showed that the blends were incompatible and homogenously distributed only within a limited range of PVC contents in PS. The value of the storage modulus was found to increase initially but then decreased with further addition of PVC in the matrix. Distribution of the phases in the virgin and degraded blends was also studied through scanning electron microscopy. The thermogravimetric studies on these blends were carried out under inert atmosphere from ambient to 800 °C at different heating rates varying from 2.5 to 20 °C/min. The thermal decomposition temperatures of blends were found higher than that of pure PS which indicated the stabilizing effects of PVC on PS. The effect varies with the heating rates and the composition of the blends and the phenomenon has been explained due to changing morphology of the blends with composition and the degradation time which affect the interfacial interaction between the degrading products from the polymer components. The kinetic parameters of the degradation process calculated from a method described by Ozawa have been reported for these blends.     

Neodymium Ziegler-Natta catalysts: Evaluation of catalyst ageing effect on 1,3-butadiene polymerization

Catalysts constituted by neodymium versatate, diisobutylaluminium hydride and t-butyl chloride were used in this work. After their synthesis, they were aged at 40 °C for 48 h. Afterwards, they were maintained at 10 °C for more 5, 15, 40, 80, 160 and 250 days and finally the aged catalysts were evaluated in butadiene polymerization. The polybutadienes were characterized by size exclusion chromatography (SEC) to determine the molecular weight characteristics and by infrared spectroscopy (FTIR) to determine the microstructure. The aim of this work is to evaluate the effect of ageing time on 1,4 polymerization of butadiene. The results showed that the stereoselectivity of the active sites was not affected by the ageing conditions. However, the catalyst activity increased for long times of ageing.