nelson larocca - Academia.edu (original) (raw)

Papers by nelson larocca

Polymer, Mar 1, 2009

Rubber toughened polypropylene nanocomposites using two types of modified montmorillonite (organo... more Rubber toughened polypropylene nanocomposites using two types of modified montmorillonite (organoclay) were explored with the objective of achieving an improved balance between stiffness and toughness. The effect of three blending sequences on microstructure and properties of the ternary nanocomposites was also investigated. A commercial grade of ethylene/vinyl acetate copolymer (EVA) containing 18 wt% of vinyl acetate was used as the impact modifier for polypropylene and an acrylic acid grafted polypropylene was used to compatibilize the systems studied. The toughened nanocomposites samples were prepared by melt compounding in a twin-screw extruder; the morphology and mechanical properties of the resulting materials were characterized by X-ray scattering, electron microscopy and tensile and impact testing. The results show that incorporation of EVA increases the toughness of the polypropylene but its stiffness decreased markedly due to the incorporation of the low modulus component. The addition of organoclay increased the modulus slightly for all the ternary nanocomposites with respect to the blend, but it remains lower than that of neat PP. Surprisingly, addition of organoclay to the blends promoted a drastic increase in the notched Izod impact strength and a considerable alteration of the shape of the dispersed EVA phase when the organoclay is located in this phase. Moreover, it was found that the blending sequence effects on the morphology and properties of the mixtures are dependent on the organoclay used.

Langmuir, Dec 22, 2020

A detailed correlation between topographical features and wettability of chemically modified coat... more A detailed correlation between topographical features and wettability of chemically modified coatings based on silica nanoparticles (SiO 2) was performed. In this study, hierarchical structures were prepared by the layer-by-layer (LbL) technique using two different approaches: random roughened surfaces were obtained by exploring stacking defects spontaneously arisen after 15, 30, and 45 assembly cycles of 22 nm SiO 2 , and a particular structure, commonly known as raspberry-like, was obtained by depositing 22 nm SiO 2 over the first deposited 400 nm SiO 2. As an intrinsic attribute of the assembly process, the average slope of random roughened surfaces seems to be constant and virtually independent of the number of deposited layers. Additionally, the local slopes are always lower than a critical value (Φ crit) required to stabilize the solid−liquid−air interface; thus, a fully wetted Wenzel state is invariably observed with water contact angles (WCAs) ∼130°. On the other hand, since the local slopes of the raspberry-like structure follow a nearly spherical curvature, small SiO 2 can stabilize the solid−liquid−air interface by increasing the local contact angle and avoid the deep penetration of water into the surface asperities, resulting in a WCA ∼167°. The results also suggest that nanoroughness might also play an important role in the pinning effect of the solid−liquid−air contact line, favoring the maintenance of superhydrophobicity of raspberry-like surfaces.

Polimeros-ciencia E Tecnologia, Nov 19, 2010

Resumo: Foram desenvolvidos dispositivos para obtenção de fitas extrudadas de blendas poli(tereft... more Resumo: Foram desenvolvidos dispositivos para obtenção de fitas extrudadas de blendas poli(tereftalato de butileno)/terpolímero acrilonitrila-butadieno-estireno (PBT/ABS), que serviram para correlacionar diretamente as condições de preparação destas blendas em extrusoras com rosca dupla corotacional e interpenetrante (ERDCI) com as suas propriedades. Quando compatibilizada com terpolímero reativo metacrilato de metila-co-metacrilato de glicidila-co-acrilato de etila (MGE), a blenda ternária PBT/ABS/MGE apresentou maior viscosidade, menor entalpia de fusão e menor temperatura de transição frágil dúctil (TTFD) que a blenda binária PBT/ABS, devido possivelmente à reação do grupo epóxi do MGE com os terminais de cadeias do PBT. A blenda compatibilizada e processada com velocidade de rotação das roscas de 120 rpm apresentou maior viscosidade, menor entalpia de fusão e melhores propriedades de resistência ao impacto que aquela processada a 240 rpm. A maior velocidade de rotação das roscas pode ter degradado os componentes da blenda. A taxa de alimentação foi a variável de processo que mais influenciou nas propriedades da blenda, pois a taxa de 3,5 kg/h deteriorou completamente as propriedades de impacto, reduziu a viscosidade e aumentou a entalpia de fusão, quando comparada com a taxa de 7,0 kg/h. A deterioração das propriedades de impacto foi atribuída ao maior tempo de residência da blenda na ERDCI, que submeteu a blenda ao cisalhamento e à temperatura por mais tempo, causando degradação dos componentes da blenda. Palavras-chave: Blenda PBT/ABS, extrusora com rosca dupla, processamento de polímeros.

Polymer Engineering and Science, Aug 30, 2010

In this research, it was studied the effects of the processing parameters applied to a twin screw... more In this research, it was studied the effects of the processing parameters applied to a twin screw extruder on the morphology and impact strength of poly(butylene terephthalate)/acrylonitrile-butadiene-styrene blends with and without a reactive compatibilizer. It was found that the increase of the feed rate highly decreased the ductile brittle transition temperature (DBTT) and slightly increased the room temperature impact strength (RTIS) of the compatibilized blends. Besides the influence of the feed rate, it was also found that the compatibilized blends could reach high RTIS and low DBTT values by an appropriate combination of the compatibilizer feeding position in the extruder, the screw rotation speed and the width of the kneading discs of the screw. The DBTT was found to be at least partially controlled by the spatial distribution of the rubbery particles, which was quantified by finite body tessellation, a method applied for the first time in polymer blends.

Thin Solid Films, Apr 1, 2018

Superhydrophilic nanoporous coatings were prepared from layer-by-layer assembled silica nanoparti... more Superhydrophilic nanoporous coatings were prepared from layer-by-layer assembled silica nanoparticles (SiO 2) and a polycation. As expected, concentration of silica dipping suspension and particle size are closely related to thickness of the obtained multilayer films. However, wettability might not to be mainly governed by coating thickness as usually reported on literature; instead, superficial homogeneity should be carefully considered. It was found that if a uniform nanoporous structure is obtained, superhydrophilic behavior is observed and, at least for the studied system, increases in coating thickness are not followed by improvements on wetting performance. In turn, for obtaining uniform structures, the usage of dipping suspension with a hypothetical minimum silica nanoparticles concentration is mandatory. Below such critical value, stacking defects along the coating surface are observed and the manifestation of superhydrophilicity is inhibited. As an additional feature, low

Surface & Coatings Technology, Sep 1, 2018

Influence of layer-by-layer deposition techniques and incorporation of Layered Double Hydroxides ... more Influence of layer-by-layer deposition techniques and incorporation of Layered Double Hydroxides (LDH) on the morphology and gas barrier properties of polyelectrolytes multilayer thin films

Polimeros-ciencia E Tecnologia, Feb 11, 2011

Resumo: Blendas de poliamida 6 (PA6) com acrilonitrila-butadieno-estireno (ABS) foram preparadas ... more Resumo: Blendas de poliamida 6 (PA6) com acrilonitrila-butadieno-estireno (ABS) foram preparadas em uma extrusora de rosca dupla, utilizando-se o copolímero estireno-anidrido maleico (SMA), com 7% de anidrido maleico, como compatibilizante. O efeito de três sequências de mistura na microestrutura e propriedades das blendas foi estudado. A morfologia e as propriedades mecânicas dos materiais foram caracterizadas por microscopia eletrônica de transmissão (MET) e testes de resistência ao impacto e módulo de elasticidade, respectivamente. Os resultados mostraram que a morfologia e propriedades mecânicas das blendas ternárias foram bastante diferentes e dependem da sequência de mistura. A blenda preparada pela mistura simultânea de todos os componentes, em uma única extrusão, apresentou melhor tenacidade. Por outro lado, quando o ABS e o SMA foram misturados juntos em uma primeira extrusão, antes da incorporação da PA6 em uma segunda extrusão, o valor da resistência ao impacto encontrado foi menor que o da matriz PA6 e da blenda sem compatibilizante PA6/ABS. Evidências de reações químicas entre o compatibilizante SMA e a matriz PA6 também foram investigadas através de reometria de torque.

Polymer Engineering and Science, Dec 4, 2020

This study investigated the correlation between the electrical conductivity and the micro and nan... more This study investigated the correlation between the electrical conductivity and the micro and nanomorphology of multiwalled carbon nanotubes (MWCNTs)/ epoxy nanocomposites with and without the inorganic fillers montmorillonite (MMT), sepiolite and calcium carbonate (CaCO 3). The nanocomposites were prepared by dispersing the MWCNT and fillers through ultrasonication directly in the resin or solvent. For nanocomposites without fillers, the compositions prepared with solvent demonstrated higher electrical conductivities, which correlate with a microscale morphology formed by networks of highly interconnected MWCNT agglomerates. The addition of MMT induced a deleterious effect on the electrical conductivity of the nanocomposites since this filler hinders the formation of MWCNT agglomerate networks. The effect of sepiolite on electrical conductivity is also negative, but in this case, nonmorphological effects are likely of greater importance. The addition of CaCO 3 improved the electrical conductivity of the binary nanocomposites under specific conditions. For this filler, a synergic effect was achieved for the composition prepared with solvent, which resulted in an approximately sixfold increase in electrical conductivity relative to the nanocomposite without filler.

Applied Surface Science, Jun 1, 2013

Polysulfone/MMT nanocomposite membranes were prepared by a congruence of the wet-phase inversion ... more Polysulfone/MMT nanocomposite membranes were prepared by a congruence of the wet-phase inversion and the solution dispersion techniques. Different clay contents and two kinds of polysulfone were used in order to investigate the changes in the nanocomposite structure as well as in the thermal and mechanical properties. The increase in the basal spacing with the clay content increase was revealed by SAXRD. TEM images depicted the presence of hybrid morphology and SEM images showed that the clay particles were trapped inside the cross-section pores. By increasing the clay content and polysulfone molar mass, the onset temperature of decomposition was increased and the mass loss was decreased. From DTA studies, it was observed that PSf P-1700 low clay content membranes had higher values of enthalpies and the enthalpy values of PSf P-3500 membranes did not present a regular behavior. Also in the tensile tests, the increase of the clay content up to 4.0 mass% promoted the increase of elongation at break and tensile strength.

Journal of Thermal Analysis and Calorimetry, May 9, 2016

Since many polymer-organoclays nanocomposites are prepared in melt state, the thermal stability o... more Since many polymer-organoclays nanocomposites are prepared in melt state, the thermal stability of the surfactants present in these organoclays is extremely important. Alkyl ammonium salts are surfactants which have been used in organoclays, but the low thermal degradation temperature of these salts is a drawback for polymer nanocomposites preparation in the melt state at temperatures higher than 200°C. In order to obtain organoclays more suitable to be used in these polymer nanocomposites, in this work clay minerals were modified with more thermally stable organic modifiers than conventional salts. Two types of commercial clay minerals were organically modified with alkyl ammonium salt, alkyl and aryl phosphonium salts and an organosilane compound. X-ray diffraction, thermogravimetric analysis (TG) and infrared analysis results indicate that for both commercial clay minerals the preparation of the organoclays was efficient. TG analysis confirmed that phosphonium and silane organoclays are more thermally stable as compared with conventional alkyl ammonium organoclays. It was also observed that the thermal resistance of the organoclay depends on the type of the aluminosilicate used for the organic modification.

Polymer Engineering and Science, Mar 21, 2012

Toughening of polyamide 6 (PA6) can be achieved by appropriate addition of an elastomeric matrix ... more Toughening of polyamide 6 (PA6) can be achieved by appropriate addition of an elastomeric matrix phase; however, this leads to a loss of rigidity and mechanical strength. As a result, much research has been directed at obtaining an optimal balance between toughness and rigidity for these thermoplastics. The approach explored here is the formation of nanocomposites from PA6/acrylonitrile-butadiene-styrene (ABS) blends prepared by melt mixing with a modified montmorillonite (Cloisite 1 30B) and styrene/maleic anhydride copolymer as a compatibilizer. The effect of the mixing sequence of the components on the morphology and properties is a primary focus. The morphology and mechanical properties of the materials were characterized by X-ray diffraction, electron microscopy, and tensile and impact testing. Incorporation of the compatibilizer in the PA6/ABS blend increased toughness but decreased rigidity. A significant increase of modulus was observed for the nanocomposite blend compared with the blend or the matrix. This increase was attributed to the exfoliation of organoclay layers in the PA6 matrix phase. It was also observed that the morphology of the ABS dispersed phase was considerably influenced by the mixture sequence. POLYM. ENG. SCI.,

Journal of Membrane Science, Jul 1, 2003

The incorporation of low molecular mass additives to polyetherimide (Ultem ® 1000) led to the pol... more The incorporation of low molecular mass additives to polyetherimide (Ultem ® 1000) led to the polymer's antiplasticisation, an effect indicated by a reduction of its free volume, an increase of its ␥ sub-T g (T ␥) transition temperature and storage modulus, and a reduction of the sorbed carbonic gas level and the gas permeability coefficient. The extent of these changes, however, was found to be strongly dependent on a combination of additive properties, i.e. size, free volume, degree of interaction with the polymer, and the glass transition temperature. Based on a theoretical correlation between the diffusion coefficient and the segmental motion frequency, we argue that the increase in T ␥ , which indicates intensified segmental restriction, is related to a reduction of the permeability coefficient. However, the real influence of this transition on the permeability could not be analysed because the additives also change other parameters that influence gas permeability. We assume that several of these parameters are considered in the mixtures' fractional free volume (FFV), since a relatively good correlation was found between this parameter and the permeability. The scatterings found in this correlation were attributed to alterations in segmental motions and free volume distributions of PEI, which are not considered by the FFV parameter but that affect the gas permeability coefficients.

Materials Science Forum, Feb 18, 2008

Nanocomposites of PA6 / organoclay at different concentration were prepared via melt intercalatio... more Nanocomposites of PA6 / organoclay at different concentration were prepared via melt intercalation method using a corotating twin screw extruder. The composites were prepared with Brazilian clay that was treated with different modifiers based on quaternary ammonium salts to obtain three types of organoclays. After extrusion the mixtures were injection molded into specimens that were tested to obtain the properties of tensile strength, notched izod impact and heat deflection temperature. The structure and morphology of the nanocomposites were characterized by x-rays diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the modifier “dodigen” which promoted the intermediate expansion of the bentonite clay within the three salts used for the modification of the clay affects more significantly the mechanical properties, HDT and morphology of the polyamide 6 due to the higher level of exfoliation observed in these systems compared to the others modifiers. The improvement of the properties was correlated to the level of exfoliation/intercalation obtained which depends on the process technique used, surface treatment of the Brazilian clays with organic salts and interaction between polymer and clay.

WILEY-VCH Verlag & Co. KGaA eBooks, Sep 17, 2016

Blending polymers has become an essential and efficient procedure to develop new higher performan... more Blending polymers has become an essential and efficient procedure to develop new higher performance polymeric materials having a valuable combination of properties, under relatively short times and with low development and production costs. In fact, polymer blending can create materials with targeted properties and competitive prices, allows for fine tuning of the properties via adjustments of composition, and provides an interesting route for plastics waste recycling. In the field of polymer blends, functionalized polymers are currently employed to improve the compatibility and adhesion between immiscible polymers by a process called reactive blending. Compatibilization is based on a specific chemical reaction between two functional polymeric components during blending, and is known as reactive blending. Compatibilization, or compatibilization by the addition of a pre-synthesized copolymer, provides an opportunity to easily control the molecular architecture of the additive to be used

Journal of Polymer Science Part B, 2005

Blends of poly(butylene terephthalate) (PBT) with 30 wt % acrylonitrile–ethylene–propylene–diene–... more Blends of poly(butylene terephthalate) (PBT) with 30 wt % acrylonitrile–ethylene–propylene–diene–styrene (AES) were prepared with methyl methacrylate (MMA)/glycidyl methacrylate (GMA)/ethyl acrylate (EA) terpolymers (MGEs) as compatibilizing agents. These acrylic terpolymers were miscible with the styrene–acrylonitrile (SAN) phase of AES, whereas the epoxide groups of GMA could react with the PBT end groups; this could lead to the formation of grafted copolymers (PBT-g-MGE) at the PBT/AES interface during the melt processing of the blends if at least a fraction of this interface was formed between the PBT and SAN phases. This study found evidence of the aforementioned interfacial structure through the effectiveness of the MGE terpolymers in promoting the compatibilization, as evaluated by dynamical mechanical analysis, through the increase in the viscosity of the blends, and through the reduction of the AES particle size dispersed in the PBT matrix. These effects became more intense with an increase in the overall concentration of GMA in the blends and with a reduction of the molecular weight of MGE. Another effect promoted by the compatibilization was a remarkable reduction of the brittle–ductile transition temperatures of the blends, which was correlated with the reduction of the AES particle size. However, this correlation between the brittle–ductile transition temperatures and particle size did not hold for the blend with the lowest AES particle size, which showed a high ductile–brittle transition temperature. These mechanical behaviors were examined on the basis of the current theory of the toughening of thermoplastics, which takes into account the importance of the rubber interparticle distance and the cavitation process of these particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1244–1259, 2005

ACS omega, Dec 22, 2021

We report on the preparation of SiO2-based nanoparticles readily available for superhydrophobic a... more We report on the preparation of SiO2-based nanoparticles readily available for superhydrophobic applications. In contrast to usual approaches, our process is substrate-free and based on electrostatic adsorption of small SiO2 particles onto large SiO2 cores with the aid of poly(diallyldimethylammonium chloride) followed by calcination and chemical modification with trichlorododecylsilane. The as-prepared nanoparticles are in powder form and exhibit stable superhydrophobic behavior at room temperature because of the unique combination between the hierarchical raspberry-like structure and low surface energy. If properly stored, the nanoparticles retain their functional properties for several months.

DOAJ (DOAJ: Directory of Open Access Journals), 2010

In order to correlate processing conditions in intermeshing co-rotational twin-screw extrusion (I... more In order to correlate processing conditions in intermeshing co-rotational twin-screw extrusion (ICTSE) and properties of PBT/ABS blends, devices have been developed to obtain extruded strips from PBT/ABS blends. The PBT/ABS blend compatibilized with reactive copolymer methyl methacrylate- glycidyl methacrylate (MGE) has shown higher viscosity, lower heat of fusion and lower ductile-brittle transition temperature (DBTT) when compared to the non compatibilized PBT/ABS blend, possibly due to chemical reactions between MGE epoxy groups and the molecule end groups from PBT. Concerning the screw rotation, the compatibilized blend processed with 120 rpm has shown higher viscosity, lower heat of fusion and better impact strength properties than the one processed with 240 rpm. This could be a consequence of degradation of the blend components, caused by higher screw rotation. The feeding rate has presented itself as the processing parameter with the greater influence on blend properties. A feeding rate of 3.5 kg/h has severely compromised impact strength properties, reduced the viscosity and increased the heat of fusion, in contrast to a feeding rate of 7.0 kg/h. These observations can be attributed to a higher residence time, with the blend being submitted to higher temperature and shear for a long time, leading to the degradation of blend constituents.

Journal of Applied Polymer Science

Polímeros, 2011

Blendas de poliamida 6 (PA6) com acrilonitrila-butadieno-estireno (ABS) foram preparadas em uma e... more Blendas de poliamida 6 (PA6) com acrilonitrila-butadieno-estireno (ABS) foram preparadas em uma extrusora de rosca dupla, utilizando-se o copolímero estireno-anidrido maleico (SMA), com 7% de anidrido maleico, como compatibilizante. O efeito de três sequências de mistura na microestrutura e propriedades das blendas foi estudado. A morfologia e as propriedades mecânicas dos materiais foram caracterizadas por microscopia eletrônica de transmissão (MET) e testes de resistência ao impacto e módulo de elasticidade, respectivamente. Os resultados mostraram que a morfologia e propriedades mecânicas das blendas ternárias foram bastante diferentes e dependem da sequência de mistura. A blenda preparada pela mistura simultânea de todos os componentes, em uma única extrusão, apresentou melhor tenacidade. Por outro lado, quando o ABS e o SMA foram misturados juntos em uma primeira extrusão, antes da incorporação da PA6 em uma segunda extrusão, o valor da resistência ao impacto encontrado foi men...

Polymer Engineering & Science, 2020