Solid-state Polymerization Process Research Articles

Conductive nano-Al/polyaniline composites prepared via mechanical milling

The conductive nano-Al/polyaniline composites were prepared by the milling method in the solid state. Here, aluminum nanostructures were prepared in two different mechanical methods, wire drawing and wire milling in the presence of lubricant oil. The effects of the preparation methods on the structures and morphologies of aluminum nanostructures were investigated by XRD and FESEM. The results show that the shape and size of aluminum nanoparticles in the preparation by the wire drawing method are significantly different than the wire milling method. The aluminum nanostructures were prepared by milling method have flake-like nanosheets while the wire drawing method leads to the formation of spherical ultrafine nanoparticles, which particles size are in the range of 30–60 nm. Then, polyaniline was produced using a solid-state polymerization process by the chemical reaction between aniline hydrochloride and potassium peroxydisulfate. Finally, nano-Al/polyaniline composites were prepared by mechanical milling at room temperature. The quantitative analysis was carried out with the materials analysis using diffraction (MAUD) method and weight fraction for aluminum and PANI were calculated 6.66% and 93.34%, respectively. Electrical conductivity measurements show the conductivity (1.2 × 10−2 S cm−1 at 25 °C) for polyaniline emeraldine salt and (1.02 × 10−3 S cm−1 at 25 °C) in nanocomposite respectively. The results show that by adding aluminum nanoparticles to the polymer the conductivity of nanocomposite (Al/PANI-ES) is lower than that for pure (PANI-ES). Thermogravimetry and differential thermal analysis curves show pure (PANI-ES) and nanocomposite (Al/PANI-ES) have a similar thermal degradation process. The total weight loss in TG curve of pure PANI-ES, in the temperature range 45–800 °C is 46.28% but, total weight loss observed in nanocomposite is 38.67%. Therefore, nanocomposite has higher thermal stability than that of the pure PANI-ES.

Eumelanin decorated poly(lactic acid) electrospun substrates as a new strategy for spinal cord injury treatment

Spinal cord injury (SCI) is characterized by neuroinflammatory processes that are marked by an uncontrolled activation of microglia, which directly damages neurons. Natural and synthetic melanins represent an effective tool to treat neuroinflammation because they possess immunomodulatory properties. Here, the main objective was to evaluate the effect of eumelanin-coated poly(lactic acid) (EU@PLA) aligned microfibers on in vitro model of neuroinflammation related to spinal cord injury in terms of inflammatory mediators' modulation. Aligned fibers were chosen to provide physical cues to guide axonal growth in a specific direction thus restoring the synaptic connection. Eumelanin decorated PLA electrospun substrates were produced combining electrospinning, spin coating and solid-state polymerization processes (oxidative coupling under oxygen atmosphere). Biological response in terms of antioxidant and anti-inflammatory activity was analyzed on an in vitro model of neuroinflammation [microglial cells stimulated with lipopolysaccharide (LPS)]. Cell morphology and EU@PLA mechanism of action, in terms of toll-like receptor-4 (TLR-4) involvement were assessed. The results show that EU@PLA fibers were able to decrease reactive oxygen species, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-кB) expression >50 % compared to PLA + LPS and interleukin 6 (IL-6) secretion about 20 %. Finally, the mechanism of action of EU@PLA in microglia was found to be dependent on the TLR-4 signaling. Protein expression analysis revealed a decreased in TLR-4 production induced by LPS stimulation in presence of EU@PLA. Overall, our results show that EU@PLA represents an innovative and effective strategy for the control of inflammatory response in central nervous system.

Evaluation of the Technical Viability of Distributed Mechanical Recycling of PLA 3D Printing Wastes.

3D printing PLA wastes were recovered from a well-known reference grade and from different sources. The recovered wastes were subjected to an energic washing step and then reprocessed into films by melt-extrusion, followed by compression molding to simulate the industrial processing conditions. The obtained materials were characterized and the optical, structural, thermal and crystallization behavior are reported. The mechanical recycling process leads to an increase of the crystallinity and a decrease of the intrinsic viscosity of the formulations, particularly in the sample based on blends of different 3D-PLA wastes. Moreover, the obtained films were disintegrated under composting conditions in less than one month and it was observed that recycled materials degrade somewhat faster than the starting 3D-PLA filament, as a consequence of the presence of shorter polymer chains. Finally, to increase the molecular weight of the recycled materials, the 3D-PLA wastes were submitted to a solid-state polymerization process at 110, 120, and 130 °C, observing that the recycled 3D-wastes materials based on a well-known reference grade experiences an improvement of the intrinsic viscosity, while that coming from different sources showed no significant changes. Thus, the results show that 3D printing PLA products provides an ideal environment for the implementation of distributed recycling program, in which wastes coming from well-known PLA grades can successfully be processed in films with good overall performance.

Poly(lactic acid) microcapsules: Tailoring properties via solid state polymerization

Active compounds encapsulation in polymeric carriers is a widely used technology as it protects and improves the physical characteristics of the active compound and controls its delivery. Polymeric microcapsules (MCs) effectiveness is strongly related to the barrier properties of the polymeric shell, which in turn are dependent on the shell molecular weight and crystallinity. Therefore, the aim of this study was to tailor these two MCs attributes via solid state polymerization (SSP) and to examine SSP efficiency as a post-encapsulation modification step. More specifically, double emulsion-solvent evaporation technique was efficiently applied to prepare unloaded PLA MCs of four different molecular weights which were then subjected to SSP in a fixed bed reactor under nitrogen flow. Post-polymerization reactions occurred in the shell of the microcapsules as evidenced by the increase of the molecular weight. In parallel, SSP on the MCs served as a post-crystallization step resulting in higher melting properties, i.e. melting temperature and crystallinity. Adapting the SSP process from the conventional bulk polymer scale to the microcapsule geometry scale was herein proved feasible to overcome any drawbacks of the conventional encapsulation stage and to produce customized application products.

Effects of Temperature and Concentration on the Determination of PET Viscosity

This work describes the use of experiment planning to investigate the effects of the variables temperature and concentration of the polymer solution on the viscosity test of polyethylene terephthalate (PET). For this, the response surface methodology was based on a central composite rotatable design (CCRD) to optimize the combinations of the analytical conditions. With the analysis of the standard sample of PET with intrinsic viscosity of 0.630 ± 0.008 dL g-1 and 2-chlorophenol solvent, it was observed that the solution flow temperature and PET concentration caused significant effects on the results, while the storage temperature of the solvent was not statistically significant. With the results and the model developed, an industrial solid state polymerization process of PET was evaluated with simulations of the production of 30 tons of PET, demonstrating the importance of controlling the variables to guarantee the performance in quality control laboratories.

Reprocessing and Solid State Polymerization on Contaminated Post-consumer PET: Thermal and Crystallization Behavior

This investigation deals with the exposition of poly (ethylene terephthalate) to a series of surrogates following protocol recommended by United States Food and Drugs Administration. The samples presented different molecular characteristics associated to the type of process, such as reprocessing by extrusion and solid state polymerization (SSP). The nonisothermal, quiescent and shear flow crystallization for these samples were studied using differential scanning calorimetry, polarized light optical microscopy and rheometry technique. The quiescent results show that the higher the molar mass, the slower is the rate of the crystallization process. The samples that undergone the SSP process do not have influence with the presence of contaminants as this process results in higher level of decontamination. The shear-induced crystallization show that the presence of contaminants significantly reduces the number of entanglements, increasing mobility of the chains and thus the entropy of the system. Despite the significant change in the crystallization behavior, the results of the nonisothermal analysis corroborate the effects of the contamination, recycling and SSP processes on the crystalline nature of PET. The evaluation of the crystallization characteristics, especially in non-quiescent conditions, is extremely important for the prediction of the physicochemical properties and can modify the processing characteristics and the final applicability.

A journey across the solid state polymerization to assess the role of critical factors influencing the molecular weight of polylactic acid

Solid state polymerization (SSP) offers an effective route for synthesizing green polymers with variable molecular weights depending on polymerization condition. In this work, critical factors governing the molecular weight of polylactic acid (PLA) in the course of SSP are manipulated systematically and their contributions to the efficiency of SSP process are discussed. The initial molecular weight of the prepolymer formed, the degree of crystallinity of prepolymer, and the SSP time are changed and analyzed for their effects through different analyses including differential scanning calorimetry, gel permeation chromatography, and Fourier‐transform infrared spectroscopy techniques. It was observed that PLA having highest molecular weight would be the result of formation of a prepolymer having low‐molecular weight, as detected by the analysis of functional group concentration. For the optimized sample, the rate of mass loss in SSP was 12,263 g/mol.day and a crystallinity drop over the hydrolysis process was 3.14 per day. The crystallinity of prepolymers was optimized at ca. 26% in regard with the PLA showing the highest molecular weight. J. VINYL ADDIT. TECHNOL., 25:165–171, 2019. © 2018 Society of Plastics Engineers

Eumelanin Coated PLA Electrospun Micro Fibers as Bioinspired Cradle for SH-SY5Y Neuroblastoma Cells Growth and Maturation.

Within the framework of neurodegenerative disorder therapies, the fabrication of 3D eumelanin architectures represents a novel strategy to realize tissue-engineering scaffolds for neuronal cell growth and control by providing both mechanical support and biological signals. Here, an appropriate procedure combining electrospinning, spin coating and solid-state polymerization process is established to realize the scaffolds. For biological analysis, a human derived cell line SH-SY5Y from neuroblastoma is used. Cell maturation on eumelanin microfibers, random and aligned, is evaluated by using confocal analysis and specific markers of differentiating neurons (βIII tubulin and GAP-43 expression). Cell morphology is tested by SEM analysis and immunofluorescence techniques. As results, eumelanin coated microfibers prove capable to support biological response in terms of cell survival, adhesion and spreading and to promote cell differentiation toward a more mature neuronal phenotype as confirmed by GAP-43 expression over the culture.

Modeling Coloration of a Radiochromic Film with Molecular Dynamics-Coupled Finite Element Method

Radiochromic films change color upon exposures to radiation doses as a result of solid-state polymerization (SSP). Commercially available radiochromic films are primarily designed for, and have become widely used in, clinical X-ray dosimetry. However, many intriguing properties of radiochromic films are not yet fully understood. The present work aimed at developing a theoretical model at both atomic and macroscopic scales to provide a platform for future works to understand these intriguing properties. Despite the fact that radiochromic films were primarily designed for clinical X-ray dosimetry, dose-response curves for the Gafchromic EBT3 film obtained for ultraviolet (UV) radiation were employed to develop our model in order to avoid complications of ionization, non-uniform energy deposition, as well as dispersed doses caused by secondary electrons set in motion by the indirectly ionizing X-ray photons, which might introduce added uncertainties to the model and overshadow the basic SSP processes. The active layer in the EBT3 film consisted of diacetylene (DA) pentacosa-10,12-diynoate monomers, which were modelled using molecular dynamics (MD). The degrees of SSP in the atomic scale upon different UV exposures were obtained to determine the absorption coefficients of the active layer, which were then input into the finite element method (FEM). The classical steady-state Helmholtz equation was engaged to model the reflection from the active layer using the FEM technique. The multifrontal massively parallel sparse direct solver (MUMPS) was employed to solve the present numerical problem. Very good agreement between experimentally and theoretically obtained coloration in terms of net reflective optical density was achieved for different UV exposures. In particular, for UV exposures larger than ~40 J/cm2, the reflected light intensity decreased at a lower rate when compared to other UV exposure values, which was explained by the densely cross-linked structure under near-complete polymerization, and thus the lower efficiency for further bond formation between DA monomer strands.

The use of melt rheology and solution viscometry for degradation study of post-consumer poly(ethylene terephthalate): The effects of the contaminants, reprocessing and solid state polymerization

Rheological measurements and intrinsic viscosity were performed to determine how the presence of contaminants, reprocessing and solid state polymerization (SSP) affects the degradation of post-consumer poly(ethylene terephthalate) (PET). First, post-industrial PET resin was contaminated with a series of surrogates according to a US-FDA protocol to simulate the worst-case scenario of misuse of PET packaging. The samples were submitted to recycling and SSP process in the presence of surrogates. The rheological data demonstrated that contaminated samples present degradation, even without any additional process. However, when the contaminated samples are submitted to melt extrusion the level of degradation increases. For the SSP process it was found that the surrogates do not interfere in the degradation process. In addition, an empirical analysis was derived based on the existing relationship. This analysis allowed the use of complex viscosity in higher frequencies, that is, out of the Newtonian plateau, and it shows to be as efficient as the zero-shear rate viscosity, allowing to associate the molar mass index of different samples. The data were corroborated from those obtained by the viscometric molar mass index, highlighting the importance of this new method to quantify the degradation in the polymer system.

A physicochemical route for compensation of molecular weight loss during recycling of poly(ethylene terephthalate)

This work is aimed to undertake the simultaneous effect of chain extension (chemical modification) and solid‐state polymerization (SSP) on the structural properties of recycled poly(ethylene terephthalate) to compensate the molecular weight (MW) losses caused by thermal degradation. This hybrid technique was qualified by tracking changes in the MW, intrinsic viscosity (IV), and concentrations of hydroxyl and carboxylic groups of various samples containing different concentrations of chain extender that experienced different residence times (2, 4, 6, 8, and 10 h) and different SSP process temperatures (190, 200, and 210°C). It was found that at high concentrations of chain extender, thermal degradation is facilitated owing to the lack of functional groups, as witnessed by a sharp drop in the MW and IV. The re‐recycled poly(ethylene terephthalates) experienced chemical modification followed by SSP physical treatment and revealed a rise in MW and IV. Accordingly, the synergistic effect of hybrid modification in comparison with the individual chemical modification was highlighted. J. VINYL ADDIT. TECHNOL., 22:387–395, 2016. © 2015 Society of Plastics Engineers

Parallel design strategy and rational study of crystal engineering of novel 3,4-ethylenedioxythiophene derivatives for solid state polymerization

Several 3,4-ethylenedioxythiophene (EDOT) derivatives containing different heteroatom linkers were rationally designed along parallel directions. They were synthesized and studied as potential candidates for solid state polymerization (SSP). The detailed characterization of these corresponding polymers was carried out using UV-visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and several key crystal structures were analyzed. Our study reveals that heteroatoms like C, Si and P are good linkers between EDOT units, and most monomers can be spontaneously polymerized successfully by annealing at a moderate temperature. Due to the flexible short single heteroatom linkers, these monomers may rotate freely under heating, to meet the requirement for the success of SSP. By carefully analyzing typical crystal structures, direct evidence for the success of SSP was obtained for better understanding of the SSP process. In addition, effective Hal/Hal distance was defined and a new SSP model was proposed.

Comparison between solid phase microextraction (SPME) and hollow fiber liquid phase microextraction (HFLPME) for determination of extractables from post-consumer recycled PET into food simulants

Hollow fiber liquid phase microextraction (HFLPME) and solid phase microextraction (SPME) methods for pre-concentration of contaminants (toluene, benzophenone, tetracosane and chloroform) in food simulants were investigated. For HFLPME 1-heptanol, 2-octanone and dibutyl-ether were studied as extracting solvents. Analysis by gas chromatography coupled to mass spectrometry (GC–MS), flame ionization (GC–FID) and electron capture detectors (GC–ECD) were carried out. In addition, the methods were employed to evaluate the safety in use of a PET material after the recycling process (comprising washing, extrusion and solid state polymerization (SSP)) through extractability studies of the contaminants using 10% (v/v) ethanol in deionized water and 3% (w/v) acetic acid in deionized water as food simulants in different conditions: 10 days at 40°C and 2h at 70°C. The HFLPME preconcentration method provided increased sensitivity when compared to the SPME method and allowed to analyze concentration levels below 10µg surrogate per kg food simulant. The results of the extractability studies showed considerable reductions after the extrusion and SSP processes and indicated the compliance with regulations for using recycled PET in contact with food.

Effects of molecular weight and catalyst on stereoblock formation via solid state polycondensation of poly(lactic acid)

This work reports the synthesis of stereoblock poly(lactic acid) (sb-PLA) by solid state polymerization (SSP) using a combination of PLA enantiomers with low molecular weight, focusing on effects of catalyst and molecular weight of the enantiomers. It was revealed for the first time that the PLA enantiomers synthesized with a novel methanesulfonic acid (SO) catalyst form sb-PLA with higher molecular weight at a higher yield, whereas the PLA enantiomers synthesized with a widely used tin(II) (Sn) catalyst causes a significant side reaction resulting in a low yield. These phenomena would be characteristic of the sb-PLA synthesized via SSP, since the side reaction of the lactide formation is promoted by vigorous sublimation of the lactide under the conditions of high temperature and a low pressure used for the SSP process. Reaction mechanisms were proposed for the SSP using the two different catalysts, which successfully explained the present results. It was also demonstrated that the molecular weight of the starting PLA enantiomers significantly affects the final molecular weight and sc crystallinity of sb-PLA.

Solid state polymerization of poly(lactic acid): Some fundamental parameters

Poly(lactic acid) (PLA) was submitted to solid state polymerization (SSP) in a fixed bed reactor under nitrogen flow, so as to examine technique efficiency for increasing the molecular weight and hence permitting the reduction of the melt polymerization residence times. In order to use a suitable starting material, SSP prepolymers of low and medium molecular weight were first prepared through solid state hydrolysis of commercial PLA grade under acidic and alkaline conditions. During these degradation runs, hydrolysis involved the random scission of ester groups in the polymer backbone, while the relevant kinetics and the resulting thermal properties were also examined. In a subsequent step, the prepolymers obtained were subjected to SSP at three temperatures, approximately 2.5–25.0 °C below their melting point. The process achieved an increase of up to 1.7 times the initial molecular weight, however, with different trends depending on the prepolymer characteristics, reaction temperature and time, as well as the pH of the hydrolysis medium. In addition to molecular weight build up, the effect of the SSP process on end product thermal properties was also investigated.

Solid state polymerization of poly(L‐lactide): Multiple‐fold increase in molecular weight via an efficient catalyst system

AbstractWe report the synthesis of high molecular weight (MW), high crystallinity (Xc) poly(L‐lactic acid) (PLLA), with improved thermal stability, by solid state polymerization (SSP) of low MW PLLA prepolymer, pre‐PLLA. SSP enabled pre‐PLLA is synthesized by ring opening polymerization (ROP) of L‐lactide using a ternary catalyst complex of L‐lactide, stannous octoate, and L‐lactic acid oligomer (OLLA). We demonstrate that this ROP, although a chain‐growth reaction, yields pre‐PLLA with end‐groups, which enable step growth SSP. MW increases ∼9 fold, with Xc reaching beyond 90%, during the SSP process. Such high values of crystallinity could be due to the synchronization of the crystallization rate with that of the slower and longer lasting step‐growth SSP. Nuclear magnetic resonance spectroscopy confirms that SSP is indeed a step‐growth reaction. In comparison, Zn(OLLA)2 only couples two pre‐PLLA chains during SSP. In addition, the radial spherulite growth rate has been quantified with annealing time of SSP synthesized PLLA. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

High molecular weight poly (L‐lactic acid) clay nanocomposites via solid‐state polymerization

AbstractWe propose here, a novel technique to synthesize high molecular weight (MW) poly (L‐lactic acid)‐clay nanocomposite (PLACN), via solid state polymerization (SSP). We synthesize prepolymer of PLACN (pre‐PLACN) from both,L‐lactic acid andL‐lactide, as starting materials. Synthesis of pre‐PLACN fromL‐lactic acid is carried out viain situmelt polycondensation (MP) ofL‐lactic acid oligomer, followed by SSP, to achieve high MW PLACN (Mw∼ 138,000 Da). In case ofL‐lactide as the starting material, we prepareL‐lactide–clay intercalated mixture which yields moderate MW pre‐PLACN during subsequent ring opening polymerization (ROP). Interestingly, ROP is performed by using hydroxyl functionalized ternary catalyst system (L‐lactide–Sn(II) octoate–oligo (L‐lactic acid) complex), which provides the terminal hydroxyl end‐groups, required for step‐growth SSP. Pre‐PLACN MW is now increased toMw∼ 127,000 Da, by the subsequent SSP process.1H NMR analyses confirm that these end‐groups, are indeed consumed during SSP. During SSP, the PLACN also achieves up to 90% crystallinity, which may be due to the synchronization of the slow step‐growth SSP of poly(L‐lactic acid) (PLA) with the crystallization kinetics. Optical purity of PLACNs is similar to that of neat PLA, whereas the thermal stability of PLACNs is significantly superior. As evidenced by wide‐angle X‐ray scattering/small‐angle X‐ray scattering analyses and in line with the literature, both, intercalated and exfoliated PLACN morphologies, have been synthesized, by suitable selection of clays. We also verify the correlation between the PLA semicrystalline morphology and the PLACN morphology, which is consistent with those of PLACN synthesized by other techniques. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Investigation of the effect of SSP in stabilizing the structure of condensation polymer blends via rheological measurements

We investigated the influence of solid-state polymerization (SSP) process on the reactions that could be taken place at the interphase of polycondensation polymer blends to stabilize the structure obtained after melt mixing. Polyethylene terephthalate (PET) and polyamide 66 (PA66) were melt blended in a mixer, and subsequent SSP process was performed for each sample. FTIR spectra indicated reactions between two polymers. Viscosity behavior and interfacial slip were investigated by measuring shear viscosity of components and blends before and after SSP and then compared with the viscosity calculated from the log-additivity model. The results showed that after SSP, there was no sign of interfacial slip, the slope of viscosity reduction with increasing shear rate became smaller, and the viscosity of blends showed positive deviation at all examined shear rate from the log-additivity model while this deviation was negative at higher shear rate before SSP. SEM micrographs, which were taken after shear stress was imposed on the samples, also indicated the morphological stability after SSP. Furthermore, we studied the effect of functional groups concentration on the reactions at the interphase by using hydrolyzed PET as a precursor for blends. The results showed that slip at the interface would decrease with increasing functional groups of the precursors. These results are particularly valuable for using recycled polymers.

ChemInform Abstract: Catalysis in Solid State Polymerization Processes

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State estimation of a solid‐state polymerization reactor for PET based on improved SR‐UKF

AbstractA state estimator for the continuous solid‐state polymerization (SSP) reactor of polyethylene terephthalate (PET) is designed in this study. Because of its invalidity in the application to some of the practical examples such as SSP processes, the square‐root unscented Kalman filter (SR‐UKF) algorithm is improved for the state estimation of arbitrary nonlinear systems with linear measurements. Discussions are given on how to avoid the filter invalidation and accumulating additional error. Orthogonal collocation method has been used to spatially discretize the reactor model described by nonlinear partial differential equations. The reactant concentrations on chosen collocation points are reconstructed from the outlet measurements corrupted with a large noise. Furthermore, the error performance of the developed ISR‐UKF is investigated under the influence of various initial parameters, inaccurate measurement noise parameters and model mismatch. Simulation results show that this technique can produce fast convergence and good approximations for the state estimation of SSP reactor. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.