Determination of moisture content in nylon 6,6 by near‐infrared spectroscopy and chemometrics

The effects of moisture on the morphology and mechanical properties of polyamides have been extensively studied by a number of researchers. However, the assessment of water content in the resins has been carried out by thermal or thermogravimetric methods, which are destructive. In the present work partial least‐squares (PLS) calibration models based on near‐infrared (NIR) spectroscopy were produced in order to predict the moisture content of nylon 6,6. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and the loss‐on‐drying (LOD) method were used as reference methods. TGA, LOD, DSC, and NIR analysis were performed in parallel, and the obtained data were used for multivariate calibration purposes. Data pretreatment techniques such as derivation and multiplicative scattering correction (MSC) successfully eliminated the baseline offset present in the raw spectra and compensated for differences in thickness and light scattering of the analyzed samples. Calibration models were validated by full cross validation with the help of a test set. A comparison of the prediction ability of PLS models based on pretreated data was also done. NIR spectroscopy is a rapid and nondestructive method for the determination of moisture in recycled nylon. The moisture content can be predicted with a RMSEP = 0.05 wt %. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2165–2170, 2003     

In‐line monitoring of polyethylene density using near infrared (NIR) spectroscopy

Density and melt index are two key properties in grading commercial polyolefin polymers. For quality assurance, these properties must be controlled as accurately as possible in the production plant. However, the lack of suitable in‐line sensors for these properties makes feedback quality control difficult. In this study, an in‐line density sensor using near infrared (NIR) spectroscopy is developed. The NIR spectra of molten polyethylene in flow are collected by a fiber‐optic device attached to a single screw extruder. By the ratio of the absorption intensity at 1170 nm to that at 1213 nm, the densities of 14 grades of polyethylene were successfully measured. The results were very promising for quality control in the polyethylene production process.     

Mid‐infrared spectroscopy as a tool for real‐time monitoring of ethanol absorption in glycols

Fast, simple, accurate, and inexpensive methods for obtaining analyte concentration data are desirable in the industrial sector. In the present study, the use of Fourier transform mid‐infrared (FT‐MIR) spectroscopy, combined with partial least squares (PLS) regression, was investigated as a tool for real‐time monitoring of processes of ethanol absorption in glycols. Calibration was performed using simple synthetic samples containing ethanol, water, and monoethylene glycol (MEG) or diethylene glycol (DEG). The PLS models presented excellent performance, with correlation coefficients (R²) close to unity and root‐mean‐square errors of cross‐validation (RMSECV) and prediction (RMSEP) lower than 2% of the calibration data ranges for both analytes (ethanol and water) in both absorbents (MEG and DEG). The monitoring technique developed has potential to be applied in absorption processes and could also be used in other large‐scale unit operations, providing information in real time and enhancing process control.     

Lifetime prediction of the epoxy system DGEBA (n = 0)/1,2‐DCH modified with an epoxy reactive diluent by thermogravimetric analysis

Thermogravimetric analysis was used to predict the lifetime of two three‐component systems of diglycidyl ether of bisphenol A (n = 0)/1,2‐diamine cyclohexane [DGEBA (n = 0)/1,2‐DCH] modified with different concentrations of an epoxy reactive diluent, vinylcyclohexene dioxide (VCHD). Experimental results were treated using two methods. The first method was independent of the degradation mechanism, and the second was based on the thermodegradation kinetic mechanism. The activation energies of the reaction were determined using the Flynn–Wall–Ozawa method. These values were compared with those obtained using Kissinger's method. From experimental results it was found that the optimum temperature of service for these materials were different, so one or the other must be selected, depending on the application temperature considered. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3835–3839, 2003     

On‐line prediction of crystallinity spatial distribution across polymer films using NIR spectral imaging and chemometrics methods

A rapid and non‐intrusive on‐line NIR imaging sensor is developed for monitoring spatio‐temporal crystallinity variations across the surface of polymer films. A multivariate image analysis and regression (MIA/MIR) approach is proposed and compared with standard NIR calibration techniques using averaged spectra or second order derivatives combined with PLS regression. Predictions of both the local and global crystallinity variations of HDPE, LDPE, and PP polymer samples were obtained with each approach. Our results show that small variations in crystallinity introduced by changes in cooling rates can be predicted within experimental errors. Crystallinity spatial distributions were also validated and found consistent with processing conditions.     

Structure and properties of bio‐based polyamide 109 treated with superheated water

The structure and properties of bio‐based polyamide 109 (PA109) after treatment with superheated water (140 °C ≤ T ≤ 280 °C) were investigated and characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction, scanning electron microscopy and small‐angle X‐ray scattering. Below 170 °C, the hydrothermal treatment was considered to be a physical process, which exerted an annealing effect on PA109. It led to an increase in melting temperature, lamellar thickness and crystallinity, while the macromolecular structure, crystal structure and the order of crystalline regions were not affected. Above 170 °C, complete melting/dissolution of PA109 occurred with partial hydrolysis. Due to the high temperature and long reaction time, the hydrolysis reaction became more and more prominent, and the resin was completely hydrolyzed into oligomers at 280 °C. Also, above 170 °C, the hydrothermal treatment was accompanied by a chemical process and the melting temperature and molecular weight decreased progressively. Notably, the crystal structure was not altered, but the degree of perfection of crystals and the order of crystalline regions were broken, especially above 200 °C. The hydrolytic degradation reaction was significantly affected by temperature, while both time and the water to polyamide ratio were secondary factors which influenced it to a minor extent. The process could be considered as a typical nucleophilic substitution reaction which takes place step by step inducing the molecular weight to decrease gradually. Overall, this study provides a ‘green’ route for the processing, recycling and treatment of environmentally friendly polyamides based on hydrothermal treatment technology. © 2019 Society of Chemical Industry     

Distribution and diffusion coefficients of NaCl in polyamide (nylon‐6,6 and polyxylyleneadipamide) membranes

Thin membranes of an aliphatic polyamide (nylon‐6,6) and an aromatic polyamide (polyxylyleneadipamide) (PXAP) were prepared, and their distribution (K) and overall diffusion (D) coefficients of sodium chloride were measured with the unsteady‐state and steady‐state dialysis method. The overall diffusion coefficients at a zero concentration [D⁽⁰⁾] of sodium chloride for nylon‐6,6 and PXAP were 1.3–0.8 μm²/s (from 2 min of interfacial polymerization to 4 min) and 0.078, respectively. D⁽⁰⁾ for PXAP was about 3 times greater than that of a cellulose acetate (CA) membrane (0.024 μm²/s). The K values for nylon‐6,6 and PXAP were 0.7–0.5 from 2 to 4 min and 0.05, respectively. K for PXAP was almost the same as K for CA (0.06). A two‐part (dense and porous) model of the membrane structure was applied to obtain D_d (the diffusion coefficient in the dense part of the membrane) and D_p (the diffusion coefficient in the porous part of the membrane) for CA, PXAP, and nylon‐6,6 thin membranes. The values of D_d were almost the same for both nylon‐6,6 and PXAP (0.05–0.061 μm²/s) and about 10 times greater than the value for the CA membrane (5.6 × 10^?3 μm²/s). D_p for PXAP was almost the same as D_p for CA. However, D_p for the nylon‐6,6 membrane was 10–16 times greater than D_p for the PXAP membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2605–2612, 2002     

Synthesis and characterization of poly(methyl methacrylate‐co‐maleic anhydride) copolymers and its potential as a compatibilizer for amorphous polyamide blends

Poly(methyl methacrylate‐co‐maleic anhydride) copolymers (MMA‐MA) have been synthesized by solution method, using toluene as solvent and benzoyl peroxide as initiator. The MMA‐MA copolymers were characterized by size exclusion chromatography, Fourier transforms infrared spectroscopy (FTIR), and titration. It was found that the modified polymerization procedure used in this work was more effective in controlling the molecular weight when adding different amounts of maleic anhydride (MA) than procedures previously used. In spite of the significant difference in reactivity ratios between MMA and MA, up to 50% of the MA added to the reactor was incorporated into the copolymer. The evidences for reactions of the MA groups of the MMA‐MA copolymer with the amine end groups of the amorphous polyamide (aPA) during melt blending was obtained by rheological measurements. In this work, the molecular weight and the content of MA reactive functional groups in the MMA‐MA copolymer were varied independently and its effects on the interaction with aPA were studied. It was observed that a compromise between molecular weight and the level of reactive functional group of the compatibilizer should be sought to improve the compatibilization of the polymer systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of the structure on sorption and diffusion processes in polyamide 6, part 1: Activation energy and thermodynamic parameters of water desorption in oriented and unoriented polyamide 6

Effect of the structure on desorption of water in polyamide 6 is studied by differential scanning calorimetry and thermogravimetry. Oriented and unoriented polyamide 6 fibers annealed in water at 100°C for different times (2 s up to 1 h) are characterized by their structure and transport properties. It is found that water treatment leads to substantial change in the polymer structure (including phase transition even at room temperature). Activation energy and enthalpy of water desorption are determined, and their high values (E_a = 60–130 kJ/mol; ΔH_d = 950–1360 J/g) are attributed to the formation of strong sorbent–sorbat bonds. Both parameters are influensed substantially by the polymer structure (degree of crystallinity and orientation). Besides, it is found that the temperature of water desorption (T_d) is also very sensitive to the structure. The T_d‐values increase sharply with rise of degree of crystallinity, being always considerably lower for oriented fibers. This quite unexpected result is also confirmed and further interpreted in the next parts of the article. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Near‐infrared spectroscopy for the determination of lipid oxidation in cereal food products

The present study was aimed at determining the ability of near‐infrared (NIR) spectroscopy to in situ describe fat oxidation kinetics in three different cereal‐based products: salted crackers (20% saturated palm oil and lauric oil, sprayed on surface); healthy crackers (10% unsaturated rapeseed oil, homogeneously distributed inside the product matrix); and moist pasteurised Asian noodles (1.5% unsaturated rapeseed oil, sprayed on surface). Products were stored under accelerated oxidation conditions at 40 °C. Lipid oxidation rates were determined from peroxide value (PV) measurements. We observed no significant changes in PV for the dry crackers (3 meq/kg after 60 days), a slight linear increase in PV for the healthy crackers (40 meq/kg after 60 days), and a rapid increase for the Asian noodles (80 meq/kg after 20 days). The NIR spectra were recorded between 1000 and 2500 nm by using a Fourier Transform NIR spectrometer, using an external probe. Measurements were done directly in situ on the product, on the ground samples, and on the extracted fat phase. The analysis of NIR spectral data by PLS statistical methods demonstrated some correlation trends (R² = 0.575–0.897; RMSEC = 17–55%) for the products having a significant increase in PV. It was not possible to propose predictive models to calculate the oxidation rate.     

Investigating alternative routes for semi‐aromatic polyamide salt preparation: The case of tetramethylenediammonium terephthalate (4T salt)

In the current article, the effect of different techniques was investigated on the preparation of tetramethylenediammonium terephthalate (4T salt), which consists of an industrially important precursor of high‐performance polyamides. In particular, 4T salt was synthesized through solution, slurry, and solvent‐free techniques. In each case the salt was isolated as a solid, correlating for the first time the salt preparation/isolation method with attained properties and morphology. This correlation led to a generalized comparison between all synthesized 4T salt grades, aiming at understanding the preparation mechanism of 4T salt. Accordingly, highly pure 4T salt, free of any unreacted diacid traces, can be only obtained from a clear salt solution either by cooling or by nonsolvent addition. Furthermore, by altering the crystallization conditions of the salt, thermal and morphological properties can be significantly affected, which further result in a qualitative correlation with the rate of subsequent direct solid‐state polymerization (DSSP). The DSSP reactions were carried out in the microscale of a thermogravimetric chamber, where the different 4T salt grades were heated isothermally until full conversion. Polyamide grades of different thermal and analytical properties were received, underlining that the quality of the salt is a corner stone for subsequent DSSP. These findings can be further exploited also to the DSSP of other semi‐aromatic polyamides. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42987.     

Study of the composition effect of glass ceramic and silver on poly(vinyl butyral) thermal degradation with thermogravimetric analysis

The thermal degradation of poly(vinyl butyral) (PVB)/glass ceramic, PVB/Ag, and PVB/glass ceramic/Ag composites was investigated with thermogravimetric analysis in nitrogen and air. Thermogravimetric data revealed that the compositions of both inorganic materials in air could greatly influence the thermal degradation of PVB. The degradation reactions of PVB/ceramic and PVB/Ag composites began earlier and accelerated rapidly at lower temperatures. The overall degradation period was obviously shortened for the thermal degradation of PVB/Ag in air, whereas a longer time was required for the PVB/ceramic composite than for PVB. Moreover, dual effects of ceramic and Ag on the thermal degradation of PVB were observed for PVB/ceramic/Ag composites. In addition, the catalytic effects of ceramic and Ag on the degradation reaction of PVB in air were verified with a kinetic analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2142–2149, 2004     

In‐line near infrared spectroscopy monitoring of pharmaceutical powder moisture in a fluidised bed dryer: An efficient methodology for chemometric model development

This work proposes a novel chemometric methodology for in‐line near infrared spectroscopy (NIRS) monitoring of pharmaceutical powder moisture in a fluidised‐bed dryer. The collected spectra are analysed by multivariate chemometrics involving the preparation of numerous laboratory samples. A different methodology, using only plant samples, was tested in real‐time. A specially designed probe tip, allowing for robust in‐situ spectral acquisition, was designed. The results prove that NIRS can be as efficient as traditional quality analyses, e.g. loss‐on‐drying, in measuring powder moisture content in a fluidised bed dryer with a calibration model based only on plant samples. © 2011 Canadian Society for Chemical Engineering     

Microstructure and fracture behavior of (co)injection‐molded polyamide 6 composites with short glass/carbon fiber hybrid reinforcement

The mechanical and fracture properties of injection molded short glass fiber)/short carbon fiber reinforced polyamide 6 (PA 6) hybrid composites were studied. The short fiber composites of PA 6 glass fiber, carbon fiber, and the hybrid blend were injection molded using a conventional machine whereas the two types of sandwich skin–core hybrids were coinjection molded. The fiber volume fraction for all formulations was fixed at 0.07. The overall composite density, volume, and weight fraction for each formulation was calculated after composite pyrolysis in a furnace at 600°C under nitrogen atmosphere. The tensile, flexural, and single‐edge notch‐bending tests were performed on all formulations. Microstructural characterizations involved the determination of thermal properties, skin–core thickness, and fiber length distributions. The carbon fiber/PA 6 (CF/PA 6) formulation exhibits the highest values for most tests. The sandwich skin‐core hybrid composites exhibit values lower than the CF/PA 6 and hybrid composite blends for the mechanical and fracture tests. The behaviors of all composite formulations are explained in terms of mechanical and fracture properties and its proportion to the composite strength, fiber orientation, interfacial bonding between fibers and matrix, nucleating ability of carbon fibers, and the effects of the skin and core structures. Failure mechanisms of both the matrix and the composites, assessed by fractographic studies in a scanning electron microscope, are discussed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 957–967, 2005     

NIR Fluorogenic Dye as a Modular Platform for Prodrug Assembly: Real‐Time in vivo Monitoring of Drug Release

The ability to monitor drug release in vivo provides essential pharmacological information. We developed a new modular approach for the preparation of theranostic prodrugs with a turn‐ON near‐infrared (NIR) fluorescence mode of action. The prodrugs release their chemotherapeutic cargo and an active cyanine fluorophore upon reaction with a specific analyte. The prodrug platform is based on the fluorogenic dye QCy7; upon removal of a triggering substrate, the dye fluoresces, and the free drug is released. The evaluated camptothecin prodrug was activated by endogenous hydrogen peroxide produced in tumor cells in vitro and in vivo. Drug release and in vitro cytotoxicity were correlated with the emitted fluorescence. The prodrug activation was effectively imaged in real time in mice bearing tumors. The modular design of the QCy7 fluorogenic platform should allow the preparation of numerous other prodrugs with various triggering substrates and chemotherapeutic agents. We anticipate that the development of real‐time in vivo monitoring tools such as that described herein will pave the way for personalized therapy.     

In‐line near‐infrared spectroscopy: A tool to monitor the preparation of polymer‐clay nanocomposites in extruders

In‐line diffuse reflectance and on‐line transmission near‐infrared spectroscopy (NIR) measurements are performed at the same location of the barrel of a twin screw extruder during the preparation of a polypropylene/clay nanocomposite. Their performance is evaluated by means of a 7‐parameter chemometric model using off‐line rheological and structural (FTIR) data obtained from samples prepared under different screw speed, compatibilizer content and clay loading, as well as a process‐related thermomechanical index. Despite the higher variability of the diffuse reflectance signal, the two models present analogous high quality indices. The aptness of the reflectance measurements is thus validated, which has direct practical advantages, as this probe can be fixed in any typical melt pressure transducer port. The probe is then used for the real‐time in‐line monitoring of the production of the same nanocomposite but now using different throughputs, and the chemometric‐based predictions are compared with experimental off‐line characterization data. The nonlinear effect of throughput is correctly anticipated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Use of mid‐ and near‐infrared techniques as tools for characterizing blends of copolymers of styrene–butadiene and acrylonitrile–butadiene

There is increased technological interest in using blends of various dissimilar elastomers in applications for which service, material availability, or cost of a single elastomer do not provide the necessary processing, vulcanizate, or economic properties. The properties of these polyblends are sensitive to small variations in the amounts of the individual polymers used. Accurately estimating the elastomer composition of blends is of vital importance to the elastomer industry. This study illustrates the feasibility of using mid-infrared (MIR) and near-infrared (NIR) spectroscopy to estimate the amount of styrene–butadiene and acrylonitrile–butadiene copolymers in blends composed of varying ratios of the two elastomers. Sometimes it is difficult to obtain a film of an elastomer amenable to IR analysis; to address this problem, several techniques were developed in this study [MIR transmission of a film, attenuated total internal reflection (ATR)-FTIR of a chunk, and NIR using a fiber-optic probe]. A plot of the absorbance ratio (absorbance of the characteristic peak for styrene–butadiene rubber or acrylonitrile–butadiene rubber/absorbance of the CC stretching vibration of polybutadiene) versus the amount of each elastomer in the blend was used to predict the blend composition. In addition, the blends were also characterized by ATR-FTIR using a plot of the characteristic peak absorbance versus the polymeric content for a series of standards. A partial least-squares algorithm was used to develop a calibration curve for the NIR region. Finally, the accuracy of the test methods developed in this work is compared to results obtained by pyrolysis-GC/MS and thermogravimetric analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88:1653–1658, 2003     

Microwave‐assisted and classical heating polycondensation reaction of bis(p‐amido benzoic acid)‐N‐trimellitylimido‐L‐leucine with diisocyanates as a new method for preparation of optically active poly(amide imide)s

A new class of optically active poly(amide imide)s were synthesized via direct polycondensation reaction of diisocyanates with a chiral diacid monomer. The step‐growth polymerization reactions of monomer bis(p‐amido benzoic acid)‐N‐trimellitylimido‐L‐leucine (BPABTL) (5) as a diacid monomer with 4,4′‐methylene bis(4‐phenylisocyanate) (MDI) (6) was performed under microwave irradiation, solution polymerization under gradual heating and reflux condition in the presence of pyridine (Py), dibuthyltin dilurate (DBTDL), and triethylamine (TEA) as a catalyst and without a catalyst, respectively. The optimized polymerization conditions according to solvent and catalyst for each method were performed with tolylene‐2,4‐diisocyanate (TDI) (7), hexamethylene diisocyanate (HDI) (8), and isophorone diisocyanate (IPDI) (9) to produce optically active poly(amide imide)s by the diisocyanate route. The resulting polymers have inherent viscosities in the range of 0.09–1.10 dL/g. These polymers are optically active, thermally stable, and soluble in amide type solvents. All of the above polymers were fully characterized by IR spectroscopy, ¹H NMR spectroscopy, elemental analyses, specific rotation, and thermal analyses methods. Some structural characterization and physical properties of this new optically active poly(amide imide)s are reported. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1647–1659, 2004