Melt strength and fade resistance of a random propylene-ethylene copolymer (PEC) were enhanced by generating long-chain branched (LCB) structures using two amine-polyfunctional chain-linking agents (CAs). A maleic-anhydride-grafted copolymer (PECg) was first obtained as a precursor to the LCB polymers that were obtained by reactive melt mixing using various concentrations of m-xylylenediamine (XDA) and Basic Fuchsin (BF). The resulting changes in molecular structure were analyzed using FTIR and shear and extensional rheometry, while color characteristics and fastness were studied using UV-visible spectroscopy, colorimetry, and solvent extraction. The results demonstrate that both CAs react with PECg to form polymers with LCBs and complex molecular structures, being BF being less efficient than XDA. However, the simultaneous use of both CAs produces a significant synergistic effect. For example, the rate of change of the strain-hardening coefficient with CA concentration (SHIexp similar to 36.5 c(CA)) is greater than the value predicted by a Linear Mixing Rule based on Xi and Fi data (SHILMR similar to 27.8 c(CA)). All colored materials exhibit excellent fade resistance, as demonstrated by the color permanence of films exposure to solvents for 10 days. Altogether, the selected approach allows for the generation of dye-grafted polyolefins with improved melt strength and fade resistance.

Polypropylene (PP) and random propylene-ethylene copolymer (PEC) with long-chain branches (LCB) have been synthesized from linear polymers by sequential melt reactive processing. The process starts with the grafting of low concentrations of maleic anhydride using an organic peroxide as a radical initiator. Then, halfway through the processing time, the chain-linking agent, m-xylylenediamine (XDA), is added to the reactive medium to generate branched molecular structures. The occurrence of grafting and chain-linking reactions was confirmed by infrared spectroscopy, size exclusion chromatography, and dynamic and transient extensional rheology. Branched polymers with up to similar to 1 branch per 1000 monomer units were achieved without largely altering the average molecular weights of the original materials and their tensile mechanical properties. The amount of LCB obtained in PEC practically doubles that in the branched PP. Properties such as maximum tensile stress, elastic modulus, and tensile stress at yield were found to be primarily a function of the molecular weight and crystallinity level of the polymers, and not of their degree of LCB. Altogether, the results demonstrate that grafting low concentrations of maleic anhydride onto the polymer with the addition of the chain-linking agent at half processing time is an efficient and practical method to produce polymers with improved melt strength.

Nanocomposites (NC) of polypropylene (PP) and organophilic montmorillonite (oMt) are produced by reactive mixing with simultaneous grafting of maleic anhydride (MA) onto PP using organic peroxide as initiator. Five different strategies of incorporating reactants and clay into a laboratory mixer are used. The structure of composites is examined by FT-IR spectroscopy, x-ray diffraction and scanning electron microscopy. Rotational rheometry, thermogravimetry and oxygen permeability are used to evaluate properties. The preparation method has a remarkable influence on NC's structure. Simultaneous addition of peroxide and MA to molten PP followed by incorporation of clay 20 minutes later produces the best degree of clay exfoliation/disaggregation. The NCs obtained using this procedure are highly transparent and have very thin tactoids with interlayer spacing more than 50% larger than the original oMt. The incorporation of just 2 wt% of clay gives place to more than 30% reduction in PP oxygen permeability. Additionally, the temperature at the maximum thermal degradation rate in nitrogen reduces in about 60 degrees C while the temperature at which the thermal degradation process begins is not affected.

Reactive melt processing is a known technique used to produce long-chain branched polypropylene. It involves polyfunctional substances that act as chain-linking agents (CA). In this work, polyfunctional amine dyes are used as CA in a novel method for simultaneously improving melt strength and fade resistance of polypropylene. Colored long-chain branched polymer is synthesized by reactive processing of maleic anhydride grafted polypropylene (PPg) in the molten state using glycerol, basic fuchsin and disperse blue 1. Selected CA concentrations avoid gel-like structures and impart good color intensity. FT-IR spectroscopy confirms the reaction between PPg and the CAs while rheological characterization supports the synthesis of long-chain branched structures. Covalent bonding of dye molecules to PPg is confirmed by both UV-visible spectroscopy and colorimetry. A maximum total color difference, ?E*, of about 20 was measured after xylene purification. New materials show good color homogeneity and transparency with minimum bleeding after 48 hours exposure to water and ethanol.

Propylene-ethylene copolymer (PEC) is an important material used in the production of a large diversity of plastic goods. However, its low polarity and lack of functional groups make PEC challenging for dye coloring. A method to obtain colored PEC using the cationic dye Rhodamine 6G (RA) was investigated. It involves modifi-cation with very low concentrations of organophilic montmorillonite (o-Mt) and a propylene copolymer grafted with maleic anhydride by producing nanocomposites having very thin clay tactoids. Mixing was performed in molten state in a batch mixer considering 0.1 wt% of dye and up to 3 wt% of clay. FT-IR, XRD, SEM and rheology were used to analyze the effect of clay and dye on composite morphology while fade resistance to solvent and UV-radiation was analyzed by UV-visible spectroscopy and colorimetry. Neither structure nor properties of polymeric systems are affected by addition of RA. In fact, the degree of oxidation reached by the polymeric material after UV irradiation as well as its fade resistance is determined by clay concentration. The addition of just 1 wt% of o-Mt reduces in about one eighth the exposure time at which the polymer reaches a given value of total color difference, Delta E*.

Random propylene–ethylene copolymers (RPC) are a type of polyolefin in increasing demand, mainly for packaging, due to its high impact resistance, large durability as well as high transparency and flexibility. The present study aims to investigate the morphological and rheological properties, as well as the photo-oxidation by UV irradiation, of five different RPCs and their nanocomposites. Organophilic montmorillonite is used as filler and maleic anhydride grafted RPCs as compatibilizers. Aging was performed by exposing strips of materials to UVA radiation for a maximum period of 96 h, and material degradation was analyzed following the evolution of carbonyl and hydroperoxide groups by FTIR and crystallinity by DSC. All nanocomposites display intercalated-exfoliated structure being the largest particle disaggregation presented by the polymer with the largest molecular weight. Rheological results support these observations. Neither the chemical composition of the polymers nor the presence of nanoclay/compatibilizer affects the photo-degradation mechanism of copolymers although the composite structure promotes the matrix photo-degradation. A parabolic relation was found between carbonyl and hydroxyl indexes of all stabilized and extracted materials, with or without clay. An increase in crystallinity with UV radiation dose was observed in all systems with a maximum determined in the case of the extracted systems.

Blends of polypropylene (PP) and poly(ethylene-co-vinyl acetate) (EVA) having a PP/EVA viscosity ratio of 240 were prepared by melt mixing. EVA concentration varies from 2 to 26 wt%. All blends display two-phase structure with quasi-spherical EVA domains evenly distributed in the PP matrix. The diameter of the domains increases with EVA concentration from about 0.4 to 6 mu m. Each component crystallizes separately. The melting temperature of PP phase is no noticeably affected by the presence of EVA while the crystallization one gradually increases by 4 degrees C. The dynamic moduli of the blends are well predicted by the emulsion model of Palierne, revealing that the system PP/EVA has a very small interfacial tension. The thermal degradation behavior of the blends, determined by thermogravimetry, shows that the deacylation process in EVA is not affected by the presence of PP while the beginning of the degradation process of PP is increased by up to 20 degrees C due to the presence of EVA. This effect goes along with an increment in the maximum degradation rate of PP.

Five commercial random propylene-α-olefin copolymers were functionalized with maleic anhydride by reactive mixing. Materials and blends of the original polymers with the grafted ones were characterized by IR, SEC, rheology, XRD, and DSC. The effects of ethylene content and average molecular weights on the effectiveness of scission and grafting reactions were investigated. Functionalization gives place to thermo-rheologically simple materials whose dynamic properties are in agreement with the measured molecular weights. The blends, which stand as miscible ones, display terminal dynamic moduli and crystallization and melting temperatures that show slight positive deviation with respect to linear mixing rules.

ABSTRACTBranched polypropylenes (PPb) with markedly improved melt strength were produced without significantly affecting the processability of the original PP. A two‐step process of functionalization with MA and crosslinking with m‐XDA was used, both by batch mixing and by extrusion. Branching degrees of ~0.06 LCB/1000 monomer units or smaller were obtained. All PPbs display clear and significant strain hardening, being the PPb obtained by extrusion the one that shows the largest melt strength. This polymer has a zero‐shear‐rate viscosity slightly smaller than that of PP while its strain‐hardening index is about 10 times higher. Moreover, the nonlinear behavior of PP at elongation begins at a time similar to its terminal relaxation time or larger, while the ratio of these times reduces significantly with branching. PP/PPb blends were prepared to extend the range of obtainable melt strength in PP. They display rheological behavior between those of the mixed polymers with slight positive deviation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48845.

A random ethylene–butene copolymer was irradiated with high ionizing energy in environments with different oxygen concentration. The non-isothermal crystallization process of the materials was studied by differential scanning calorimetry. When the polymer was exposed to radiation under free oxygen ambient, the temperature and the crystallinity degree decreased almost linearly with dose because chain-linking reaction prevails. On the contrary, those thermal parameters increased in the material obtained by irradiating the copolymer in environments with oxygen availability where chain scission reactions dominate. It was also found that, at equivalent irradiation dose, the crystallization rates decreased with the dose at a given cooling rate and with the reduction in oxygen content. The parameters obtained from different applied models also confirm the tendencies observed for the experimental variables.

Long-chain branched polypropylenes were synthesized from a maleic anhydride grafted polypropylene (PPg). Different levels of branching were generated by reactive processing using four chain-linking agents: glycerol, 1,4-butanediol, 1,4-phenylenediamine, and the epoxy resin bisphenol-A diglycidyl ether. The results from Fourier transform infrared and size-exclusion chromatography confirm the grafting of the chain-linking agents onto grafted polypropylene and the generation of long-chain branches. In addition, the rheological and morphological results show that 1,4-phenylenediamine produces the largest increment of branching at significantly lower concentrations than the other chain-linking agents. Moreover, 1,4-phenylenediamine gives place to branched polypropylenes with narrower distribution of molecular structures. [GRAPHICS] .

ABSTRACTRandom propylene‐terpolymer (PEBC)/organophilic montmorillonite nanocomposites were prepared by melt mixing, using PEBC modified with maleic anhydride (PEBCg) as compatibilizer. Clay concentrations up to 8 wt %, compatibilizer/clay ratios up to 3:1 and concentrations of anhydride groups (AG) in PEBCg of 0.4 and 0.6 wt % were considered. The degree of exfoliation of the clay increases with PEBCg content and its concentration of AGs. The dynamic moduli allow estimating the percolation threshold of the nanofiller at 5.4 wt %, which yields an average of 11 silicate layers per tactoid at percolation, in agreement with the minimum thickness estimated from XRD data. The presence of exfoliated clay gives place to strain hardening and softening, depending on clay concentration and magnitude of the Hencky strain. The amount of exfoliated clay, however, plays a minor role in front of the content of AGs of the compatibilizer in regard with the oxygen permeability of the polymer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45840.

A reaction between a linear polypropylene functionalized with maleic anhydride (PPg) and epoxy resin (bisphenol A diglycidyl ether) was carried out on the molten state to generate long-chain branches (LCB) in the molecular structure of the PPg. Concentrations of epoxy resin (ER) of up to 3.15 wt% were employed to obtain different levels of branching. FTIR spectroscopy analysis indicates that during the reaction, anhydride groups in PPg are consumed and new ester groups are formed. The presence of branches was verified using multiple-detection size-exclusion chromatography and rheology. The degree of long-chain branching induced in PPg augments with increasing concentration of ER. Furthermore, the materials modified with higher content of ER display gel-like behavior. The long-chain branched polymers also display thermo-rheological complexity. Thermal characterization studies show that LCBs have a nucleating effect during crystallization and cause the augment of the crystallization activation energy of PPg.

Polymeric nanocomposites based on poly(propylene-co-ethylene-co-1-butene) (PEBC) were elaborated by melt mixing using an organophilic montmorillonite (o-MMT) and maleated PEBC (PEBCg) as compatibilizer. The effect of clay concentration, PEBCg:o-MMT ratio, and grafting degree of the compatibilizer were studied. X-ray diffraction and scanning electron microscopy show formation of partially intercalated structures in all compatibilized composites with well-distributed small tactoids. According to the differential scanning calorimetry results, the anhydride groups of the compatibilizer have a marginal nucleating effect, while the o-MMT causes a slight decrease in the crystallization temperature of the polymer. PEBC presents the largest activation energy of crystallization (E), while the composites show lower E than their matrices. It is also observed that the rate of degradation of PEBC is not affected by the presence of PEBCg. The nanoclay, on the other hand, retards the decomposition process of the polymeric matrix in about 40 degrees C and augments its rate of degradation approximately four times.

Polymeric nanocomposites based on poly(propylene- co-ethylene- co-1-butene) (PEBC) were elaborated by melt mixing using an organophilic montmorillonite (o-MMT) and maleated PEBC (PEBCg) as compatibilizer. The effect of clay concentration, PEBCg:o-MMT ratio, and grafting degree of the compatibilizer were studied. X-ray diffraction and scanning electron microscopy show formation of partially intercalated structures in all compatibilized composites with well-distributed small tactoids. According to the differential scanning calorimetry results, the anhydride groups of the compatibilizer have a marginal nucleating effect, while the o-MMT causes a slight decrease in the crystallization temperature of the polymer. PEBC presents the largest activation energy of crystallization ( Eα), while the composites show lower Eα than their matrices. It is also observed that the rate of degradation of PEBC is not affected by the presence of PEBCg. The nanoclay, on the other hand, retards the decomposition process of the polymeric matrix in about 40°C and augments its rate of degradation approximately four times.

The purpose of this study was to determinate the influence of the molecular crosslinking in the wear resistance of a linear polyethylene (PE) sliding against a rough steel surface. A set of PEs with different degrees of crosslinks were obtained by chemical modification of a PE with varying concentrations of organic peroxide. The amount of gel, molecular weight between crosslinks (M-c), crystallinity and Vickers microhardness were determined in the crosslinked PE's. The tribological performance of the materials was evaluated under dry sliding conditions using a block-on-ring tester. The coefficient of friction and the wear rate were determined in experiments in which a sample of polymer was contacted with the peripheral surface of a steel ring rotating at constant velocity. The wear resistance of the crosslinked materials increases with the amount of gel and when Mc decreases. The crosslinked PE showed a wear rate lower than the original PE when the amount of gel was larger than 80 % of the total mass. The coefficient of friction of the PE and crosslinked material was about 0.2 regardless of the normal load applied. The analysis of the worn surfaces by optical and SEM microscopy reveals that the primary mechanism involved in wear is abrasive wear.

Fil: Guapacha Martinez, Jorge Ariel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Planta Piloto de Ingenieria Quimica. Universidad Nacional del Sur. Planta Piloto de Ingenieria Quimica; Argentina

ABSTRACTNanocomposites of polypropylene and organophilic clay are produced by in situ functionalization of PP with n‐butyl acrylate (BA) during melt mixing. Three strategies for incorporating materials into the mixer are analyzed and the effect of clay concentration is evaluated. The materials are examined by FTIR spectroscopy, X‐ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermogravimetry, and rotational rheometry. The results show that all composites prepared in the presence of BA have similar intercalated clay structure, and that the largest degree of exfoliation is obtained using the sequential mixing technique. This method, which consists in adding the initiator and functionalizing agent to the molten polypropylene followed by the addition of the clay, also produces the largest reduction in molecular weight of the polymer and the largest increase of the elastic modulus. All polymers show similar crystallization and degradation processes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42585.

Polyethylene (PE)/clay nanocomposites were prepared by melt mixing using PE grafted with maleic anhydride (PEg) as compatibilizer. Concentrations between 2 and 15 wt% of an organophilic montmorillonite (MMT) and concentration ratios of 1:1, 2:1 and 3:1 of PEg/MMT were employed. The materials were characterized using X-ray diffraction, scanning electron microscopy (SEM) and thermogravimetry. The SEM images show that the presence of PEg results in a large degree of exfoliation at all clay concentrations. For 5 wt% MMT, the best degree of exfoliation is obtained for a 2:1 ratio of PEg/MMT. This ratio results in higher increase in the elastic modulus, mainly at low frequencies, with respect to that of the corresponding matrix. As the clay concentration increases, for a 2:1 ratio of PEg/MMT, the dynamic moduli increase showing pseudo solid-like behavior at clay concentrations higher than 8 wt%. Moreover, the nanocomposites show rheological properties that are affected by annealing at 200°C signaling further exfoliation or improved platelet and tactoid distributions. The oxygen permeability of PE decreases gradually with the clay concentration, reaching a maximum reduction of ∼30% for 15 wt% MMT.

The aim of this study was to evaluate the tribological behavior of polyethylene crosslinked by gamma radiation sliding against a steel surface. Two high-density polyethylenes were irradiated to a total dose in the range of 2−20 Mrad under vacuum and at room temperature. After irradiation, the materials were annealed at 423 K and then cooled slowly to room temperature. The same thermal treatment was applied to the non-irradiated polymer. The wear behavior of the polymers was determined under controlled ambient temperature of 298 and 333 K using a homemade tribometer. Sheet-shaped specimens were loaded against the surface of a steel disc with different normal loads to generate nominal contact pressures in the range of 0.25–1.5 MPa. The tests were performed under dry conditions using a disc rotation to produce an average sliding speed of 0.6 m/s and during a period of time to provide an average sliding distance of 1,080 m. The wear rate was obtained as the mass loss by the sample divided by the sliding distance, and the friction coefficient was determined by measuring the friction force. The results indicate that the wear rate increases with load in the case of non-irradiated polyethylene and low-dose irradiated polymers, while the wear rate reaches a maximum value with the load in the case of the irradiated samples with high doses. The samples irradiated with a dose of 10 Mrad showed the lowest wear. The coefficient of friction (COF) increases slightly with the load in all the cases. Most irradiated polymers show higher COF than the non-irradiated material when compared at a given load. The results show that the irradiation dose applied to the polyethylenes produced no noticeable effect on the COF values when a comparison was made at a given applied load.