Chemorheological Study Research Articles

Real-time monitoring of the starch cross-linking with citric acid by chemorheological analysis

Cross-linking has been used as a strategy to improve the mechanical properties of starch films. However, the concentration of the cross-linking agent and the cure time and temperature determine the structure and properties of the modified starch. This article, for the first time, reports the chemorheological study of cross-linked starch films with citric acid (CA) through monitoring the storage modulus as a function of time G′(t). In this study, a CA concentration of 10 phr showed a pronounced increase of G′(t) during the cross-linking of starch, followed by a constant plateau. Analyses of infrared spectroscopy validated the result chemorheological. In addition, the mechanical properties showed a plasticizing effect of the CA at high concentrations. This research demonstrated that chemorheology is a valuable tool in the study of starch cross-linking, which becomes a promising technique to evaluate the cross-linking of other polysaccharides and cross-linking agents.

Chemo-rheological studies and monitoring of high-Tg reactive polyphtalamides towards a fast innovative RTM processing of fiber-reinforced thermoplastic composites

In this work, a High Temperature hybrid process coupling “reactive Extrusion” and “Resin Transfer Molding” (HT-ERTM) was designed for the manufacturing of continuous Glass Fiber-Reinforced Thermoplastic Composites (GFRTC) with an elevated glass transition temperature. Hereto, a high-performance polyphtalamide (PPA) obtained from the chain extension reaction of its prepolymer was studied with the optimal stoichiometry ratio and at several temperatures. Due to the extremely fast reaction, the present work highlights that both the reaction kinetics and the increase in viscosity are not easily monitored at short times and at high temperatures by usual techniques such as DSC and titration methods. The chemo-rheological evolutions were first studied ex-situ by coupling rheology with fast scan FTIR. In a second step, the HT-ERTM process was equipped with specific dielectric sensors in order to in-situ track the reaction evolution and the flow properties up to injection inside the cavity. Meanwhile, the viscosity increase was then determined depending on time, temperature and molar mass growth. Specifically, it was possible to model its evolution at less than one minute whereas the reaction conversion reaches 85% on two minutes of processing window. Interestingly, it was found that the in-situ results corroborated their ex-situ counterparts mentioned above. Finally, GFRTC parts with fiber contents up to 60 wt% were obtained with a better control of both mechanical and thermo mechanical properties intended especially for high service temperature applications such as in the automotive or aerospace industries.

The effect of alginate on the mechanical, thermal, and rheological properties of nano calcium carbonate‐filled polylactic acid composites

Traditional plasticizers to modify polylactic acid (PLA) usually leads to limited biodegradation, due to its inherent non‐biodegradability of additives. In this work, we report a melt blending method to modify PLA using the alginic acid and two different alginates combined with nano CaCO3, a fully sustainable and biodegradable component. And, the mechanical, thermal, and rheological properties of the composites are investigated. We demonstrated that the filled samples show a lower tensile strength and higher impact strength which means a toughening effect occurs. Dynamic mechanical analysis experiments showed that the calcium alginate‐filled samples show higher performances than other filled samples not only in static mechanical but also dynamic mechanical properties. The fracture morphology of the samples shows that a better interfacial reaction has been constituted for gel calcium alginate between CaCO3 and PLA. Nevertheless, the thermogravimetric analysis results indicate that a lower thermal stability has been achieved in alginate filled samples. Chemorheological study indicated the alginate‐filled samples also show a lower modulus and viscosity than neat PLA. It was found that the complex viscosity decrease with the addition of alginates, in comparison with PLA/CaCO3 composites, and the samples filled with calcium alginate show a higher viscosity than those of sodium alginate and alginic acid. The alginate derivatives showed interesting potential as new green plastic additives attributed to origin from the biodegradable natural resources with a polymeric matrix. POLYM. ENG. SCI., 59:1882–1888, 2019. © 2019 Society of Plastics Engineers

Chemorheological study and in-situ monitoring of PA6 anionic-ring polymerization for RTM processing control

The main objective of this work was an experimental investigation making it possible to monitor, as well as achieve a deeper understanding of, the structural evolution of polyamide-6 as a thermoplastic-based composite matrix. Polyamide-6 from anionic ring-opening polymerization (AROP) of ε-caprolactam was chosen as a model matrix. Throughout this work, various formulations of PA with anionic polymerization from caprolactam were studied depending on different activator/catalyst pairs, concentrations and combinations. Moreover, chemorheological properties were first determined ex-situ by rheology coupled with FTIR and microdielectrometry. The extent of the reaction conversion was thus obtained and subsequently modeled. The formed PA6 matrix materials were fully characterized in terms of their viscosimetric properties and molar masses. In a second step, a hybrid extrusion resin transfer molding machine (T-ERTM) with an instrumented mold was designed for the in-situ monitoring. Thereby, specific dielectric sensors were used to follow the different processing steps for the manufacturing of complex and continuous glass fiber-reinforced parts. Furthermore, the reaction kinetics in competition with the crystallization were probed and quantified as a function of the processing parameters (mold temperature, times given for impregnation, time for demolding etc.). Calibration curves were obtained in which the ionic conductivity was correlated to the change of viscosity determined previously from ex-situ measurements. Indeed, a processing window was proposed for each PA6 system to ensure a good preform impregnation. Interestingly, the apparent conversion calculated from the online dielectric measurements corroborated the ex-situ values obtained from chemorheological studies. The viscosity and conversion evolution were then tracked in the mold. Based on the present findings and for the optimal formulation, a Time-Temperature-Transformation (TTT)-equivalent diagram was established from online measurements and related to the reactive processing to get a better handle on the PA6-based composite.

All Plant Oil Derived Epoxy Thermosets with Excellent Comprehensive Properties

Epoxidized plant oil (EPO) thermosets usually exhibit poor performance due to the short, brittle, and amorphous cross-link structures. To fabricate fully biobased high performance EPO thermoset, we synthesized dicarboxyl-terminated polyamide1010 (NYL) oligomers from castor oil derived monomers, i.e., sebacic acid and decamethylene diamine, and used the NYL to cure epoxidized soybean oil (ESO) to fabricate all plant oil derived epoxy thermoset through a catalyst-free curing method. Chemorheological study indicated that the curing rate decreases with increasing NYL chain length. The cross-link density of the epoxy thermoset decreases while the crystallization enhances with increasing NYL chain length, which results in drastic enhancement in tensile strength, Young’s modulus, and elongation at break of the resultant thermosets, enabling those parameters to enhance by up to 59, 145, and 18 times, respectively, compared to sebacic acid cured ESO thermoset. The melting temperature and thus the heat resistance o...

Chemorheology of thermoplastic polyurethane and thermoplastic polyurethane/carbon nanotube composite systems

Abstract In-situ polymerization of thermoplastic polyurethane (TPU) and carbon nanotubes (CNTs) is one of the best methods to obtain nanocomposites with well dispersed nanofillers and superior properties. The effect of nanofillers on reaction is an important factor during in-situ nanocomposite preparation. TPU/CNT nanocomposites were prepared via a sustainable in-situ polymerization of Polycaprolactonediol and 1,4- Phenyldiisocyanate (PPDI) in the presence of multiwall carbon nanotubes. Chemorheological studies conducted at different temperatures indicated that by increasing the temperature, in addition to linear polymerization, branching and crosslinking reactions contribute to viscosity evolution. Empirical and semi-analytical chemoviscosity models were employed to clarify the difference between reaction kinetics of TPU formation in the presence of CNTs. A semi-analytical model developed here, gave more insight into the reaction as well as system structural evolution. Activation energy of viscosity evolution due to polymerization was found to decrease by addition of carbon nanotubes. This acceleration effect is correlated to higher heat conductivity of the nanocomposite as well as CNT effects on the structure evolution in the polymerizing system.

Effects of high nano‐SiO2 contents on properties of epoxy‐modified polybenzoxazine

High‐performance nanosilica composites based on epoxy‐modified polybenzoxazine matrices are developed. Chemorheological study of benzoxazine–epoxy resin mixtures reveals that processing window of the benzoxazine resin (BA‐a) is substantially broadened with an addition of the liquid epoxy. Glass transition temperature (Tg) of the BA‐a copolymerized with epoxy resin shows a synergistic behavior with a maximum Tg value (174°C) at the benzoxazine–epoxy mass ratio of 80:20. The copolymer at this composition is also used as a matrix for nano‐SiO2 composites. A very low melt viscosity of the benzoxazine–epoxy mixtures promotes good processability with the maximum attainable nano‐SiO2 loading up to 35 wt%. From scanning electron microscopy investigation, fracture surface of the 35 wt% nano‐SiO2‐filled benzoxazine–epoxy composite reveals relatively homogeneous distribution of the nano‐SiO2 in the copolymer with good particle wet‐out. In addition, very high reinforcing effect was also observed in such high content of the nano‐SiO2, i.e., about 2.5 times in modulus improvement. This improvement is attributed to the strong bonding between the copolymer matrix and the nano‐SiO2 through ether linkage as confirmed by Fourier‐transform infrared investigation. POLYM. COMPOS., 38:2261–2271, 2017. © 2015 Society of Plastics Engineers

Chemorheological study of a polyfurfuryl alcohol resin system—Pre-gel curing stage

The rheological and chemorheological behavior of a new biomass-based polyfurfuryl alcohol (FA) resin aimed to be used as a matrix in composite materials is studied in this work. The viscosity dependence on the shear rate and temperature of the resin is studied under steady and oscillatory conditions. The FA resin exhibits a Newtonian flow behavior within the shear rate range tested. The dependence of the viscosity of the uncured resin on temperature is measured and modeled. The flow activation energy, as calculated by the Arrhenius model, is 63.3kJmol−1. The chemorheological study of the curing process showed that the flow activation energy of the resin is increased when the amount of catalyst is increased. Furthermore, the curing parameters of the FA resin using three amounts of catalyst of 2, 4, and 6% (w/w), are obtained by the Arrhenius model. The curing activation energy is found to be about 96kJmol−1 and with no dependence on the amount of catalyst. However, a significant difference of the logarithm of the pre-exponential curing parameter is found. This parameter increases from 28.9 to 30.7 when the amount of catalyst is increased from 2 to 6% (w/w). Based on the established values of the Arrhenius model parameters, predictions are made for the evolution of viscosity of the resin during isothermal curing with different temperatures, and different amounts of catalyst. This is of great importance in the design of the curing processes of the FA resin during development and improvement of composite manufacturing processes.

Chemorheological study of phosphorylated flame retardant epoxies

The aim of this work is to study the chemorheology of the phosphorylated novolac epoxy used in flame retardants. The rheological properties are measured by a parallel plate viscometer and are combined with the kinetics of the curing reaction to explore the conversion dependent character of the viscosity. It was found that dynamic viscosity is a unique function of the effective shear rate over a wide range of frequencies and strains after being corrected for temperature. The effective shear rate dependence of the viscosity is described with a power law with an exponent that depends on the conversion. The effect of temperature is described with an Arrhenius type equation with conversion dependent parameters. Differential scanning calorimetry was applied to determine the kinetic equation that is used, in combination with the thermal history, to obtain the conversion during the rheological measurements. Time–cure–temperature modelling was applied to study a variety of factors that had an influence on the chemorheology. It was also found that the Cox–Merz relation can be utilised to correlate the dynamic viscosity data to the shear viscosity data. The Castro–Macosko model is proposed when considering the combination effects of shear thinning viscosity and reaction kinetics.

Chemorheological study of DGEBA/IPD system for reactive rotational molding (RRM)

AbstractThe identification of kinetic parameters controlling the crosslinking of Diglycidyl ether of bisphenol/isophorone diamine reactive system was achieved via optimization program (Inverse method) based on Fourier transform near infrared spectroscopy results. The reactivity ratio (k2/k1) was determined using a new method based on the variation of amine conversion ratio versus epoxy conversion ratio. Gelation and vitrification of the reactive system were also analyzed. Time, temperature, transformation diagram was established to assess the rotational molding of this reactive system. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Chemorheological study of the curing kinetics of a phenolic resol resin gelled

The changes in the resin viscosity, conductivity, mass, and enthalpy during curing reactions have been studied to obtain kinetic parameters that allow modeling of the resin behavior throughout its industrial application. In this work, isothermal rheological tests of a phenolic resol resin were performed in order to study its complex viscosity during crosslinking reactions. Samples were prepared by a precuring treatment in a heated plate press to reach gel point of the resin. Rheological analyses of resol resin curing were carried out at five different temperatures (80–100 °C), and the kinetic models of Arrhenius and Kiuna were applied. The resol resin curing presented an activation energy of 72.1 kJ/mol according to the Arrhenius model. The Kiuna model was proposed to fit the non-linear evolution of the resin’s complex viscosity at the highest temperatures. This kinetic model was suitable for predicting the changes in the complex viscosity of the resol resin after its gelation, and the process activation energy obtained for the second order polynomial applied in this model was 88.1 kJ/mol. In addition, the profile for the degree of curing of resol resin was determined from measurements of the material’s elastic modulus.

Chemorheological behaviour of double-walled carbon nanotube-epoxy nanocomposites

In this work, we propose a chemorheological study of an epoxy resin cured with carboxy-double-walled carbon nanotubes (C-DWNTs) reacted with N-methyldiethanolamine (MDEA). The results showed that 1 wt.% C-DWNTs speed up the cure process of more than 40 min. The NMR analysis suggests that a possible explanation of these findings is due to the interaction between the carboxylic functionalities of the DWNTs with the MDEA amine groups creating the –NHCO groups. Finally, an excellent agreement between the chemorheological model and the experimental data was found.

Analyzing the dynamic chemorheology of curing resins: Extraction of model parameters associated with cure advancement

AbstractThe assessment of transient changes in reactive fluids has been described as chemorheology. While several individual chemorheological studies are published, few have investigated unifying principles that may help in identifying protocols for predictive modeling. We have extracted datasets from other published manuscripts on reactive resin curing, and have observed a range of exponential growth in viscosity with these reactive systems. We have found that regardless of the initial viscosity, the dynamic viscosity rise in many of these resins advances with a similar exponential rise, with the exponent varying between 0.02 and 1.5 min−1 Isothermal photopolymerization yielded more accurate viscosity models than corresponding crosslinked resins with a widely varying heating schedule. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Chemorheological studies on a dicyanate resin modified with polyethersulfone

AbstractThe chemorheology of a dicyanate resin modified with a polyethersulfone (PES) was investigated. The rheological and dielectrical property changes during curing of the dicyanate resin system catalyzed by an organic metal salt were monitored by a rheometer and dielectric analyzer, respectively, and used to investigate the curing behavior and chemorheology of the resin system. The curing rate of the dicyanate resin system decreased as the PES content was increased. A function that can describe the viscosity change of the dicyanate resin system during curing was determined by a nonlinear regression method using the rheometer data. The gelation time of the dicyanate resin system decreased with increasing isothermal curing temperature and with decreasing PES content. The curing behavior of the dicyanate resin system monitored by the dielectric analyzer coincided fairly well with that measured by the rheometer Copyright © 2004 Society of Chemical Industry

Chemorheological study of compatibilized blends of low‐density polyethylene and polydimethyl siloxane rubber

AbstractCompatibilization of the blends of polydimethyl siloxane (PDMS) rubber and low‐density polyethylene (LDPE) was achieved through reactive processing during extrusion in a Monsanto Processability Tester (MPT). The chemorheological characteristics of 50 : 50 LDPE : PDMS blends with varying proportions (0–8 wt %) of ethylene comethyl acrylate (EMA) were investigated at three different temperatures (170, 190, and 210°C) and four different shear rates (61.3, 122.6, 306.6, and 613.1 s−1). It was found that EMA reacts with vinyl groups of PDMS rubber at a temperature of 190°C during extrusion through the capillary of MPT, forming EMA‐grafted‐PDMS rubber (EMA‐g‐PDMS), which acts as the compatibilizer for the blend systems. The results are based on IR spectroscopy, melt rheology, and phase morphology of the blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2810–2817, 2003

Rheological Behavior and Gel-Point Determination for a Model Lewis Acid-Initiated Chain Growth Epoxy Resin

The sol−gel transition, or gelation, in a polymer network-forming system is defined as the critical point in the polymerization at which an infinite macromolecule is formed. There are many studies in the literature concerning the exact and accurate determination of the gel point and its interpretation in terms of the critical conversions of reactant functional groups. However, these have mainly involved step-growth polymerizations with few studies of chain-growth polymerizations such as that described in this study. Chemorheological studies on a cationically polymerized epoxy network-forming system are used to determine accurate gel times and critical conversions, which are interpreted in terms of classical branching and chemical bond percolation models for nonlinear polymerizations. Rheological studies during the polymerization of a trifunctional epoxide monomer, using BF3 as the Lewis acid initiator, yielded a gel conversion of 0.17 ± 0.02 and a power law dependence for the development of shear modulus, with a critical exponent n = 0.64 ± 0.03, which is shown to be independent of temperature and BF3 concentration. The viscosity at conversions close to the gel point was shown to vary according to a power law with a critical exponent k = 1.33 ± 0.03 in the pregel region. The critical behavior of this complex network-forming system is shown to be closely predicted by percolation theory.

Chemorheological and dielectric study of epoxy‐amine for processing control

Chemorheological and dielectric study of epoxy‐amine for processing control

Chemorheological and dielectric study of epoxy-amine for processing control

The curing of an epoxy prepolymer based on diglycidyl ether of bisphenol A (DGEBA) with isophorone diamine (IPD) as a hardener was analysed using differential scanning calorimetry, rheological measurements, microdielectrometry, and insolubles in THF for gel point detection. The effects of the initial hydroxyl concentration of the DGEBA prepolymer, the molecular features of which are different, were determined on the cure kinetics of epoxy networks Chemical reaction kinetics of this DGEBA/IPD system during isothermal conditions was studied in the 60–120 °C temperature range and a kinetic model relation based on assumption of an autocatalytic mechanism has been proposed. Gelation and vitrification phenomena of this reactive mixture were studied and allowed us to establish the TTT diagram. Furthermore, dielectric data and viscosity measurements have been interpreted with respect to kinetics. Indeed, it was shown that the modified percolation law equation suggested by Macosko et al can be used to describe the chemoviscosity as a function of temperature and extent of reaction by using a temperature- and conversion-dependent critical exponent. In other respects, dielectric properties such as ionic conductivity were related on one hand to viscosity through a Stokes-based equation in the 0 to 0.5 conversion range, and on the other hand to conversion through an experimental equation. © 1999 Society of Chemical Industry

An Approach to Chemorheology of a Filled SBR Compound

Abstract Three steps in complex chemorheological studies are necessary for complete rheological characterization of filled rubbers during cross-linking reaction. They include: (i) kinetic studies of cross-linking reaction, (ii) rheological studies of green rubber compounds, and (iii) correlation between the rheological parameters and the degree of cure. Basic experiments in the steps (i)–(iii) and their modeling are presented in this paper on the example of a filled SBR compound with sulfur accelerated vulcanization. The approach provides a unique possibility to trace therheological properties of rubber compounds from the green to completely cured states.

Chemo-rheological study of a dicyanate ester for the simulation of the resin-transfer molding process

The kinetic and rheological behavior of a liquid dicyanate ester catalysed by a copper salt has been studied with a view to establishing behavioral laws and investigating the resin-transfer molding (RTM) process. The time/temperature transformation diagram of the system has been studied in order to predict gelation and vitrification, and the rheological study has enabled us to determine filling times during injection. An empirical model relating viscosity and conversion has been established in order to carry out a simulation of the RTM process.