Multi‐objective optimization of reactive extrusion by genetic algorithms

In reactive extrusion processes for polymerization, a multi‐objective optimization model maximizing the monomer conversion whilst ensuring the low energy consumption was constructed. The selections of reactive processing conditions could be set automatically using an optimization methodology based on genetic algorithms coupled with the numerical simulation routines. Various case studies were discussed. Comparison with experimental data indicates that the design of processing conditions can be performed according to the prespecified objectives. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41862.     

Morphology,thermal, and electrical properties of polypropylene hybrid composites co‐filled with multi‐walled carbon nanotubes and graphene nanoplatelets

In this study, nanocomposites of polypropylene (PP) with various loadings of multi‐wall carbon nanotubes (MWCNT) and graphene nanoplatelets (GnP) were formed by masterbatch dilution/mixing approach from individual masterbatches PP‐MWCNT and PP‐GnP. Melt mixing on a twin‐screw extruder at two different processing temperatures was followed by characterization of morphology by transmitted‐light microscopy including the statistical analysis of agglomeration behavior. The influence of processing temperature and weight fractions of both nanofillers on the dispersion quality is reported. Thermal properties of the nanocomposites investigated by DSC and TGA show sensitivity to the nanofillers weight fraction ratio and to processing conditions. Electrical conductivity is observed to increase up to an order of magnitude with the concentration of each nanofiller increasing from 0.5 wt % to 1.0 wt %. This is related with a decrease of electrical conductivity observed for unequal concentration of both nanofillers. This particular behavior shows the increase of electrical properties for higher MWCNT loadings and the increase of thermo‐mechanical properties for higher GnP loadings. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42793.     

Transcrystallinity and relevant interfacial strength induced by carbon nanotube fibers in a polypropylene matrix

For polymer composites, interfacial crystalline structures retain an important role in the macroscopic properties and are significantly affected by the processing conditions, such as the temperature, time, and external field. In this study, the transcrystallization behavior of the carbon nanotube fiber and isotactic polypropylene composite was investigated by polarizing light microscopy. The influence of the formation of the transcrystalline layer on the interfacial adhesion was evaluated by a single‐fiber fragmentation test. The results show that the growth rate of the transcrystalline layer was strongly influenced by the isothermal crystallization temperature, and the interfacial shear strength was markedly enhanced by the formation of the layer. The interfacial adhesion was further increased with the gradual perfection and growth of transcrystallinity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42119.     

Investigation on jet stability,fiber diameter,and tensile properties of electrospun polyacrylonitrile nanofibrous yarns

Electrospinning is a flexible and efficient method for producing nanofibers by using relatively dilute polymer solution. However, there are many parameters related to material and processing that influence the morphology and property of the nanofibers. This study investigates the influence of electric field and flow rate on diameter and tensile properties of nanofibers produced using polyacrylonitrile (PAN)‐dimethylformamide (DMF) solution. Stability of the spinning jet is investigated via fiber current measurement and an image system at different electric fields and solution flow rates. It is observed that a set of electric field and flow rate conditions favor producing thinnest, strongest, and toughest nanofibers during electrospinning process. Other conditions may lead to instability of the Taylor cone, discontinuous jet, larger diameter fiber, and lower mechanical properties. Finally, a simple dynamic whipping model is adopted to correlate the nanofiber diameter with volumetric charge density and is found to be excellent validating our experimental results. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41918.     

A multiobjective optimization framework for design of integrated biorefineries under uncertainty

A systematic approach for development of a reliable optimization framework to address the optimal design of integrated biorefineries in the face of uncertainty is presented. In the current formulation, a distributed strategy which is composed of different layers including strategic optimization, risk management, detailed mechanistic modeling, and operational level optimization is applied. In the strategic model, a multiobjective stochastic optimization approach is utilized to incorporate the tradeoffs between the cost and the financial risk. Then, Aspen Plus models are built to provide detailed simulation of biorefineries. In the final layer, an evolutionary algorithm is employed to optimize the operating condition. To demonstrate the effectiveness of the framework, a hypothetical case study referring to a multiproduct lignocellulosic biorefinery is utilized. The numerical results reveal the efficacy of the proposed approach; it provides decision makers with a quantitative analysis to determine the optimum capacity plan and operating conditions of the biorefinery. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3208–3222, 2015     

Coloration properties and chemo‐rheological characterization of a dioxazine pigment‐based monodispersed masterbatch

A dioxazine‐based color pigment was added to a commercial polyamide 6 (PA6) through an extrusion process, in order to prepare monoconcentrated violet masterbatches through different production set‐up. A detailed characterization of the resulting materials was carried out in order to find the best processing parameters combination to optimize pigment dispersion and to reduce the clogging power. The preparation of masterbatches with repeated extrusions markedly reduced the filter pressure value and increased the Relative Color Strength, while filtration did not significantly influence pigment dispersion. Rheological measurements and end‐groups analysis were conducted on the same materials with the aim to evaluate their thermal degradation resistance, and the thermal stability of the compounds was retained even upon three extrusions. Therefore, it can be concluded that a proper optimization of the process parameters could lead to an important reduction of the production waste, increasing the quality of the final product. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41452.     

Methods of long chain branching detection in PE by triple‐detector gel permeation chromatography

Long chain branching (LCB) in polyethylene is one of the key microstructures that controls processing and final properties. Gel permeation chromatography (GPC) with viscometer (IV) and/or light scattering (LS) has been intensely used to quantify LCB. The widespread method to quantify LCB from GPC with IV or LS is the method of LCB frequency (LCBf) based on the Zimm–Stockmayer (ZS) random branching model. In this work, the conventional approach was compared with the recently developed method, called gpcBR. The comparison of the sensitivity of both methods is made on highly branched polymer, that is, various grades of commercial LDPE and also on polymer with very low level of LCB, that is, a commercial HDPE with no LCB, converted into several branched test samples of gradually increasing LCB by multiple extrusion. Finally, the linkages of LCB quantities from both methods to the rheological data and processing properties are illustrated. The new gpcBR index can access lower LCB level and shows obviously better relationship with both rheological data and processing properties than LCBf from the conventional ZS model. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42222.     

Tailoring block‐copolyesters by reactive blending of polyethylene terephthalate and polyethylene naphthalate using statistical design of experiments

Block‐copolyesters of polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) were synthesized via reactive extrusion. The influence of processing parameters on the material properties on a molecular scale like degree of trans‐esterification, block length, and degree of randomness were investigated. The varied process factors were extrusion temperature and rotational speed. The effects of process parameter variation were investigated by ¹H‐NMR‐spectroscopy. The experimental results show a clear dependence of the molecular properties on the processing conditions. By using statistical experimental design (DoE), it was possible to prepare defined copolyesters from PET and PEN without addition of further chemicals. With a degree of randomness between 0.05 and 0.5, the presence of an actual copolyester was confirmed when appropriate extrusion conditions were applied. The reactive extrusion process was confirmed to be suitable to produce defined block‐copolyesters in a predictable and reproducible way. It was possible to produce designed sequence lengths, which could be adjusted within a range of 11–136 repeating units in the case of PET and, in the case of PEN, of 2.5–26. The produced materials can be used as barrier materials or barrier coatings to protect substrates against molecular oxygen and water vapour, e.g., in organic photovoltaic applications or food packaging. The described method is a one‐pot alternative method to the previously described chemical recycling pathway. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41997.     

Modification of polystyrene properties by CO2: Experimental study and correlation

The sorption of CO₂ in polymers entails their swelling and plasticization whose study is crucial for the design of processes and further applications. The operating conditions during foaming, purification, or impregnation of polymers in CO₂ are mainly determined by the mentioned binary system. In this work, the modification of polystyrene's physical properties (glass transition temperature and viscosity) has been experimentally studied. Since plasticization phenomena are very valuable for the processing of polymers, the amount of CO₂ absorbed into the polymer is related with the changes in the described properties. Furthermore, interfacial tension is also correlated with the sorption of CO₂ from literature data. The proposed correlation fits pretty well the properties shifts in the studied working conditions. Finally, the influence of pressure and temperature on the diffusivity of the CO₂ in the polystyrene is calculated through the measurement of viscosity along time. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41696.     

Microcellular foaming of poly(phenylene sulfide)/poly(ether sulfones) blends using supercritical carbon dioxide

Microcellular foaming of poly(phenylene sulfide)/poly(ether sulfones) (PPS/PES) blends presents a promising approach to produce high‐performance cellular materials with tailored microstructures and enhanced properties. This study investigated the effects of multiphase blend composition and process conditions on the foaming behaviors and final cellular morphology, as well as the dynamic mechanical properties of the solid and microcellular foamed PPS/PES blends. The microcellular materials were prepared via a batch‐foam processing, using the environment‐friendly supercritical CO₂ (scCO₂) as a blowing agent. The saturation and desorption behaviors of CO₂ in PPS/PES blends for various blend ratios (10 : 0, 8 : 2, 6 : 4, 5 : 5, 4 : 6, 2 : 8, and 0 : 10) were also elaborately discussed. The experimental results indicated that the foaming behaviors of PPS/PES blends are closely related to the blend morphology, crystallinity, and the mass‐transfer rate of the CO₂ in each polymer phase. The mechanisms for the foaming behaviors of PPS/PES blends have been illustrated by establishing theoretical models. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42634.     

Potato protein isolate‐based biopolymers

Thermal processing of two potato protein isolates (PPIs) with glycerol as a plasticizer was explored in this study. The PPIs were pretreated by alkali or alkali under reducing conditions. The PPIs before and after pretreatment were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The effects of plasticizer content and pretreatment on mechanical and thermo‐mechanical properties of the compression‐molded biopolymers were studied. The highest tensile strengths obtained were 20–25 MPa and the biopolymer can be brittle or ductile depending on the plasticizer contents. The molecular weight and protein structure of the PPIs markedly affected the resultant biopolymers’ static and dynamic mechanical properties. The pretreatment of PPIs caused distinctly different changes in the mechanical properties of the two PPIs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42723.     

Effects of EPDM‐g‐MAH compatibilizer and internal mixer processing parameters on the properties of NR/EPDM blends: An analysis using response surface methodology

This study evaluates the effects of ethylene‐propylene‐diene‐monomer grafted maleic anhydride (EPDM‐g‐MAH) and internal mixer melt compounding processing parameters on the properties of natural rubber/ethylene‐propylene‐diene rubber (NR/EPDM) blends. Using Response Surface Methodology (RSM) of 2⁵ two‐level fractional factorial, we studied the effects of NR/EPDM ratio, mixing temperature, Banbury rotor speed, mixing period, and EPDM‐g‐MAH contents in NR/EPDM blends. The study found that the presence of EPDM‐g‐MAH in NR/EPDM blends had a predominant role as a compatibilizing agent, which affected the processability and properties of the final material. We also determined the model fitting with constant determination, R² of 99.60% for tensile strength (TS) response with a suggested combination of mixing process input parameters. The reproducibility of the proposed mixing strategy was then confirmed through model validation with a minor deviation at +2.303% and higher desirability of 0.960. This study is essential in providing a process design reference for NR/EPDM blends preparation by melt‐blending and the role of a compatibilizer from the systematic Design of Experiment (DOE) approach. The experimental findings were further supported with swelling and cross‐link density measurements, differential scanning calorimetry analysis, and observation of fracture morphology using a scanning electron microscope. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42199.     

Development of a predictive model for choosing cure agents for elastomer blends

In elastomer blends with either polarity differences or unbalanced double bond concentration, cure agents have a preferential partition to one of the phases, with a tendency of having overcure in one phase and undercure in the other. To achieve proper vulcanization and improved performance in the final product, it is essential to have a correct balance between solubility and miscibility of each of the various cure agents in the elastomer blend composite. Cure agents with varying polarities and various reactivities have different crosslinking densities in the rubber compound. A homogeneous crosslinking density leads to superior mechanical properties. The method presented in this work includes a new tool based on a genetic optimization algorithm for assessing the partitioning of cure agents in different elastomers and their blends. The quantitative data allowed for a series of analyses of the solubility of the cure agents in the elastomer mixtures of different phases and was validated by correlation with their physico–chemical and mechanical properties of the resulting blend. This is an important tool for planning a cure system in rubber blends and to avoid incorrect partitioning of cure agents and consequent uneven curing of the final compound. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41929.     

Experimental study of the influences of the pellet shape on the bulk density and the frictional behavior of polypropylene

Bulk solids are the raw material for almost every polymeric thermoplastic product. Their properties determine the quality of solids conveying and also influence the melting behavior of the material in processing units. This study investigates the influence of pressure and temperature on the bulk density of two thermoplastic polypropylene pellets of different shapes. Furthermore, the external friction dependent on temperature and pressure of those materials is examined at conditions usually occurring in the solids conveying zone of smooth barrel plasticating units. The experiments are carried out using a tribometer for polymer pellets which was adapted for these tests by making the sample chamber, the piston, and the cylindrical roll heatable. The tests show that long cylindrical pellets exhibit low bulk densities at low pressure and temperature, which can be increased dramatically—even above the values of spheroidal pellets—as those parameters increase. Moreover, the external coefficient of friction is always higher for the long cylinders and strongly dependent on the temperature. Those facts add up and can cause a higher output of single‐screw extruders. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42197.     

Design of an antibacterial gelatin based on a covalent protein–protein coupling

An antibacterial peptide (AMP), i.e., nisin, was covalently bound to gelatin through a protein–protein coupling. Various reaction conditions were tested to study and optimize parameters of grafting e.g., orientation and density of AMP, which could impact the final antibacterial activity of the modified biopolymer. Modification was investigated by Fourier transform infrared (FT‐IR) spectroscopy and zeta potential. The antibacterial activity of the nisin‐enriched gelatin was evaluated against two staphylococci bacterial strains, i.e., Staphylococus epidermidis and Staphylococcus aureus. A higher activity was found for gelatin modified at pH = 7.4 revealing an influence of the nisin orientation on the protein antibacterial property. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41825.     

Cynara cardunculus as Raw Material for the Production of Binderless Fiberboards: Optimization of Pretreatment and Pressing Conditions

Abstract

Cynara cardunculus was pretreated and used to produce fiberboards without synthetic adhesives. The lignocellulosic material was steam exploded through a thermo-mechanical vapor process in a batch reactor. After pretreatment the material was dried, ground, and pressed to produce the boards. The effects of pretreatment factors and pressing conditions on the chemical and physico-mechanical properties of the fiberboards were evaluated and the conditions that optimize these properties were found. Response surface methodology based on a central composite design and multiple response optimization were used. The variables studied and their respective variation ranges were: pretreatment temperature, 160–240°C; pretreatment time 2.5–12.5 min; pressing temperature, 190–230°C; initial and final pressing pressures, 4–20 MPa, and initial and final pressing times, 1–9 min. Good properties were obtained at optimum conditions found (modulus of elasticity up to 5970 MPa, modulus of rupture up to 59 MPa, internal bond up to 0.8 MPa, thickness swelling as low as13.5%, and water absorption as low as 18.5%). Some of the boards fully satisfy the standard specifications although they were not produced at the optimum combination of process factors. Optimum operational conditions for producing binderless fiberboards from Cynara cardunculus that fully satisfy the European standards were found based on multiple response optimization methodology.     

The effect of mechanical recycling on the microstructure and properties of PA66 composites reinforced with carbon fibers

This article aims to prepare by injection molding recycled polymeric composites based on PA66 reinforced with short carbon fibers after artificial aging for applications in the automotive field. The aging cycles involves the combined action of UV radiation, moisture, and temperature in order to simulate the common outdoor conditions. The 100% recycled composites are obtained by the regranulation of the aged specimens followed by the remelting and re‐injection molding. The study is focused on the comparison between the mechanical behavior and the microstructure of the composites before and after mechanical recycling. The results of mechanical, thermal, and morphological investigations reveal that the recycling process had no significant effect on the final properties and microstructure of the recycled composites. Therefore the recycled PA66CF30 composites could be successfully used for structural or semi‐structural automotive applications guaranteeing good final performances and advantages from the environmental point of view. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42275.     

Effect of electrospun fibers of polyhydroxybutyrate filled with different organoclays on morphology,biodegradation, and thermal stability of poly(ε‐caprolattone)

The properties of nanocomposites of poly(ε‐caprolattone) (PCL) were studied, the pristine PCL was implemented with the introduction of electrospun fibers of polyhydroxybutyrate (PHB), containing a cationic (Cloisite) or an anionic (Perkalite) clay. These multicomponent composites containing a very low amount of clay confined in fibers are different from usual nanocomposite materials containing clay dispersed in the polymer matrix, which are produced by solvent casting or melt extrusion. To analyze the influence of the different fillers on the final composite, a preliminary study on PHB cast films and fibers prepared from the same solution was carried out, and then a thorough analysis was accomplished of the behavior of these particular nanocomposites PCL/PHB fibers/clay to elucidate the effects of the filled electrospun fibers on the PCL matrix. The structure and morphology of the samples were characterized by wide‐angle X‐ray diffraction and small angle X‐ray scattering; differential scanning calorimetry and thermogravimetric analysis were used to understand the influence of the fillers on the thermal behavior and stability; mechanical properties were evaluated and biodegradation studies were carried out. The PHB electrospun fibers and the fractured surface of the final composites were examined by scanning electron microscopy. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42342.     

Manufacturing and mechanical response optimization of epoxy resin/Luffa Cylindrica composite

The present investigation pertains to the existent possibilities of the fibrous natural material Luffa Cylindrica (LC) as reinforcement to thermoset resins. The main purpose was the manufacturing of an engineering material that would, simultaneously, lead to a more sustainable world. In an effort to optimize the final mechanical properties, semi‐ green Epoxy Resin/Luffa Cylindrica (ER/LC) composites were manufactured, applying a number of different manufacturing parameters combinations. The manufacturing parameters taken into account were: (a) fiber chemical treatments; (b) the external applied pressure during curing; (c) number of plies; (d) stacking sequence effect; (e) LC's structural characteristics; and (f) the influence of fiber weight fraction on composite's behavior. The elastic flexural response of the composite polymer was found improved with respect to neat polymer's response due to fibers' nature and the applied manufacturing optimization process. This improvement was reflected to material's stiffness which optimally increased by 48% for a mechanically applied pressure of 4.6 kPa during curing. Additionally, LC fibers chemically treated with Acetone/ CH₃COOH 1 wt % led to stiffness' improvement up to 30%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41992.     

Optimization of the spark plasma sintering processing parameters affecting the properties of polyimide

The present study deals with the optimization of polyimide (PI) mechanical properties, obtained by Spark Plasma Sintering (SPS), by using a method combining Design of Experiments (DOE) with physical, structural, and mechanical characterizations. The effects of SPS parameters such as temperature, pressure, dwell time, and cooling rate on the density, mechanical properties, and structure of PI were investigated. The experimental results revealed that the mechanical properties of the material were optimized by raising the sintering temperature up to 350°C. The optimized SPS processing parameters were a temperature of 350°C, a pressure of 40 MPa, and a dwell time of 5 min. Under these conditions, a relative density of 99.6% was reached within only a few minutes. The corresponding mechanical properties consisted of Young's modulus of 3.43 GPa, a Shore D hardness of 87.3, and a compressive strength of 738 MPa for a maximum compressive strain of 61.8%. Moreover, when working at 320°C and at 100 MPa, an increase in the dwell time was necessary to enhance the properties. Contrary to the other parameters, the cooling rate appeared to be a non‐significant parameter. Finally, correlations between the PI structure and the mechanical properties were made to demonstrate the densification mechanisms. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41542.