Fluorescence temperature measurements: Methodology for applications to process monitoring

In previous publications, we described a technique based on fluorescence spectroscopy to monitor resin temperature during processing. The method consists of using optical fiber sensors to monitor fluorescence from a fluorescent dye that has been doped into the processed resin. Temperature is derived from temperature‐induced changes in the fluorescence spectrum. In practice, a temperature calibration function is obtained from the temperature dependence of the ratio of fluorescence intensities at two wavelengths. In this paper, we address several experimental design issues: (a) the supportive role of fluorescence anisotropy measurements to the measuring concept, (b) the experimental setup used for noncontact measurements during capillary rheometry testing, and (c) molecular‐level environmental issues that arise during reactive processing and temperature profiling. We find that fluorescence anisotropy of the dye bis(2,5‐tert‐butylphenyl)‐3,4,9,10‐perylenedicarboximide (BTBP) is independent of shear rate up to 250 s^?1, implying that isotropic orientation of the dye is maintained as the matrix resin undergoes dynamic shear flow, i.e. the calibration function made under quiescent conditions applies to dynamic shear flow conditions. Using this technique in a noncontact application to monitor temperature of the extrudate from a capillary rheometer required an optical design that neutralized the focusing attributes of the cylindrical extrudate. Application to reactive processing is complicated by changes in polarization that accompany the reaction, and, in some cases, produce wavelength shifts in the fluorescence spectrum. We overcome these effects by using a dye that yields a calibration independent of the polarization effects and by averaging over a large dataset to reduce measurement uncertainty. Polym. Eng. Sci. 44:898–908, 2004. © 2004 Society of Plastics Engineers.     

Fluorescence based temperature measurements and applications to real‐time polymer processing

We have used temperature sensitive fluorescent dyes, doped into polymer resins, to monitor the true resin temperature during extrusion processing. Two types of temperature sensitive fluorescent dyes were used: mobility dyes and fluorescence band definition dyes. When mixed with the resin at dopant concentrations, the fluorescent dye resides in a molecular neighborhood composed of resin molecules. Under these circumstances, its fluorescence spectrum reflects the resin temperature in its neighborhood. We apply this measurement concept to extrusion processing by using an optical sensor that accesses the machine at standard instrumentation ports. We show that, under processing conditions, the true resin temperature is significantly different from The machine temperature. Two examples of real‐time process monitoring arc presented: first, the effects of shear heating during extrusion were measured, and second, the effects of poor temperature control during extrusion were observed. The effects due to pressure on the fluorescence temperature measurements are examined. The fluorescence temperature measurements are compared to melt temperature thermocouple measurements.     

Real‐time monitoring of fluorescence anisotropy and temperature during processing of biaxially stretched polypropylene film

An optical sensor based on fiber optics has been developed to measure fluorescence anisotropy and temperature during processing of biaxially stretched polypropylene films. The sensor, containing optical fibers, polarizing elements and lenses, was mounted above the polypropylene film as it was processed in a tenter frame oven stretching machine. Fluorescence observations were made using the fluorescent dye, bis (di‐tert butylphenyl) perylenedicarboximide (BTBP), which was doped into the resin at very low concentrations. To monitor biaxial stretching, fluorescence anisotropy measurements were carried out with light polarized in the machine and the transverse directions corresponding to the directions of biaxial stretching. Fluorescence based temperature measurements were obtained from the ratio of fluorescence intensities at 544 nm and 577 nm. A matrix of experiments involving three levels of stretch ratio in both the machine and transverse directions was undertaken. We observed significant differences between anisotropy in the machine and transverse directions that we attributed to the sequential stretching operation, i.e., the film was stretched in the machine direction first, followed by stretching in the transverse direction, and to film temperature and strain rate for each stretching operation. The result was uniformly higher anisotropies in the machine direction. Film temperature obtained from fluorescence corresponded to oven thermocouple measurements within 2°C. Polym. Eng. Sci. 44:805–813, 2004. © 2004 Society of Plastics Engineers.     

A simple dilatometer for thermoset cure shrinkage and thermal expansion measurements

A simple capillary and bulb mercury dilatometer designed for specific volume measurements on thermoset resin systems during the curing reaction and as a function of temperature is described. The design, calibration, operation, data treatment, and error analysis are presented in detail, with data on the bisphenol A dicyanate resin system used as an example. Particular attention is directed at experimental difficulties such as monomer/prepolymer degassing, filling the dilatometer under vacuum, adhesive distortion of the curing resin on the dilatometer bulb, and the dilatometer bulb to capillary connection problem. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Fluorescence monitoring of twin screw extrusion

An optical fiber probe has been constructed in order to obtain real-time measurements of fluorescence radiation during twin screw mixing and extrusion of plasticized polybutadiene and calcium carbonate particulate. The probe consists of an optical fiber bundle which was inserted along the axis of a half-inch sensor bolt, and it was used to transmit optical excitation energy to the processed material and to detect the subsequent fluorescence. The source of fluorescence radiation was a fluorescent dye which was doped into the processed ingredients at very low concentrations. Although most of our measurements were taken with the probe positioned close to the exit die, the sensor bolt can be placed in any instrumentation port along the extruder line. Experiments were carried out to measure residence time distribution, quality-of-mix, and mix concentrations as a function of processing conditions. Product mix changes in response to variations in material feed rates and screw RPM were also observed. Values of residence time were obtained by measuring the transit times for the dye to travel from an upstream injection port to the measurement probe, a distance of 63 cm. Flow instabilities, such as mat formation of the solids, were observed by noting the abrupt changes and discontinuities in the fluorescence signal.     

Effect of gas diffusion on creep behavior of polycarbonate

Biaxial tension-tension creep experiments were performed to study the effect of gas diffusion on creep behavior of polycarbonate. Experiments were conducted on a thin-walled tubular specimen by applying both gas pressure and axial tension at room temperature, and measuring axial strain and gas absorption. Experiments were performed with helium, nitrogen, air, carbon dioxide and Freon-22

1 Registered trademark, E. I. duPont de Nemours Co., Inc.

. It was found that the creep deformation was highly affected by the solubility controlled gases, carbon dioxide and Freon. The absorption measurements showed that the gas absorption behavior was clearly affected by the creep deformation of the material. Also an anomalous diffusion-type behavior appeared even in permanent gas-polymer systems under creep conditions. The modified superposition principle satisfactorily predicted the recovery following creep. The axial creep for the biaxial tension-tension experiments was also computed from data previously reported for creep under combined tension and torsion of a different sample of polycarbonate.     

Fluorescence based measurement of temperature profiles during polymer processing

We describe a novel noninvasive method to measure temperature profiles during processing. A key feature is the use of a temperature-sensitive fluorescent dye that is incorporated into the polymer resin at dopant levels. By monitoring spectral features of this dye, we can effectively measure its temperature. A focusing technique that we call “confocal fluorescent optics” then allows us to measure the temperature as a function of position into the resin. We present results of critical tests of the device. Namely we test the spatial resolution and its ability to measure a linear temperature profile in a quiescent polymer. Finally, we present the first on-line temperature profile measurements, carried out in a circular die at the exit of a twin screw extruder. Temperature gradients on the order of 5°C/mm in a polyethylene resin are observed between the outer wall and the center of the die.     

Tensile Properties of Extruded Zein Sheets and Extrusion Blown Films

Zein‐based plastic sheets and films were formed by extrusion through a slit‐die or blowing head. Zein was plasticized with oleic acid and formed into a wet moldable mass (resin) to feed the extruders. Both single‐ and twin‐screw extruded sheets showed higher elongation at break, lower tensile strength, and lower Young's Modulus than non‐extruded samples. Stress‐strain plots for extruded samples showed evidence of plastic behavior. Observed necking of samples under tensile stress was also taken as evidence of plastic behavior. Small differences in tensile strength and elongation at break between single‐ and twin‐screw extruded samples were attributed to the effect of small voids observed by SEM in single‐screw extruded samples. Blown film extrusion was affected by feed moisture content and barrel temperatures. Optimal moisture content was determined at 14–15% while temperature at the three extruder zones was maintained at 20–25, 20–25, and 35 °C, respectively. Temperature at the blowing head was 45 °C. Film samples blown after either single‐ or twin‐screw extrusion showed similar tensile properties to those of slit die extruded samples.

Blown extrusion of zein film with single‐screw extruder.     

Viscoelastic melt behavior of poly(2,6-dimethyl-1,4-phenylene oxide), high-impact polystyrene,and a 35–65 blend

The viscoelastic melt behavior of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO

1 PPO is a registered trademark of the General Electric Company.

resin), high-impact polystyrene (HIPS), and a 35–65 blend of these polymers has been characterized by measuring the steady shear viscosity and primary normal stress difference and the dynamic storage and loss moduli as functions of shear rate or frequency and temperature. Time–temperature superpositioning was used to generate master curves of each type of data for a reference temperature of 260°C. This procedure required five different empirical shift factors for each material. These shift factors show large differences between PPO resin and HIPS and exhibited large deviations from the WLF equation with universal constants. This result suggests that the temperature dependence of the relaxation processes in PPO resin is significantly different from the temperature dependence of HIPS relaxations. Flow activation energies computed from the viscosity data for PPO resin are much higher and more shear sensitive than those calculated for HIPS. The computed relaxation spectra clearly display the effect of long-time relaxation mechanisms associated with PPO molecules when compared to HIPS. The 35–65 blend exhibits general rheological compatibility with material parameters and responses intermediate between PPO resin and HIPS. This result is indicative of a high degree of segmental mixing for the two components in the blend.     

The hierarchical structure and flexure behavior of woven carbon fiber epoxy composite

The hierarchical structure and flexure behavior of woven carbon fibers epoxy composite were investigated in this work. First, the hierarchical structure of the composite is characterized on three levels: composite, ply, and yarn. Structura imperfections,

1 In this paper, “structural imperfections” is used to describe the inherent structural characteristics of the actual composite, which deviate from the theoretically ideal and perfect composites, control, that are used in composite theories.

such as, ply‐ply misalignment, ply‐ply offset, and resin pockets, are identified and described. Second, a four‐point bending arrangement is used to study the flexure properties of the composite. Additionally, in‐situ traveling microscope and acoustic emission (AE) techniques are utilized to gain insight to the failure proceses during flexure test. AE showed early stages of matrix cracking before visual observation, which makes it a valuable tool for early failure detection.     

Infrared melt temperature measurement of single screw extrusion

An infrared temperature sensor has been used to provide real time quantification of the thermal homogeneity of polymer extrusion. The non‐intrusive sensor was located in the barrel of a single screw extruder, positioned such that it provided a measurement of melt temperature in the channel of the metering section of the extruder screw. The rapid response of the technique enabled melt temperature within the extruder screw channel to be monitored in real time, allowing quantification of the thermal stability of the extrusion process. Two polyethylenes were used in experiments with three extruder screw geometries at a range of screw speeds. Data generated by the infrared sensor was found to be highly sensitive to thermal fluctuations relating to the melting performance of the extruder screw. Comparisons made with an intrusive thermocouple grid sensor located in the extruder die suggested that the infrared technique was able to provide a similar level of information without disturbing the process flow. This application on infrared thermometry could prove highly useful for industrial extrusion process monitoring and optimization. POLYM. ENG. SCI., 55:1059–1066, 2015. © 2014 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers     

Photochemical and thermal stability of amaranth (FD&C red no. 2) in aqueous media

The decomposition of the formerly

1 This dye was delisted by the U. S. Food and Drug Administration in 1976, and has not been legally used in the U. S. in foods, drugs, or cosmetics since that date.

used food and pharmaceutical dye amaranth (FD&C Red No. 2) in water was studied under a variety of conditions. A matter of some concern is that one of the decomposition products is α-naphthylamine, a known carcinogen.     

Deformation‐Induced Color Changes in Melt‐Processed Polyamide 12 Blends

Blends of polyamide 12 and small amounts (0.15–1 wt%) of the excimer‐forming fluorescent dye 1,4‐bis(α‐cyano‐4‐octadecyloxystyryl)‐2,5‐dimethoxybenzene (C18‐RG) are produced by melt‐processing. While green monomer fluorescence from well‐individualized chromophores is observed at low dye concentration (0.15%), higher dye concentrations lead to aggregation of the dye so that the emission characteristics are dominated by red excimer fluorescence. Upon mechanical deformation of samples with appropriately selected dye content (0.25 wt%), a pronounced mechanochromic effect can be observed, which manifests itself through a mechanically induced transformation from excimer‐dominated to monomer‐rich emission. The monomer to excimer emission ratio I_M/I_E is increased by a factor of up to 2 in a step‐wise manner when samples are uniaxially deformed past the yield point.

     

Ground State Complexes between 5-(4-Carboxyphenyl)-10,15,20-Tritolyl Porphyrin and Benzoquinones

The interactions of 5-(4-carboxyphenyl)-10,15,20-tritolyl porphyrin (TTPa)

1 Abbreviations: TTPa: 5-(4-carboxyphenyl)-10,15,20-tritolyl porphyrin; BQ: 1,4-benzoquinone; DQ: 2,3,5,6-tetramethyl 1,4-benzoquinone; CHLQ: 2,3,5,6-tetrachloro 1,4-benzoquinone; DMSO: dimethyl sulfoxide

with benzoquinones have been studied by spectrophotometry and steady state and transient fluorescent methods. TTPa forms a 1:1 molecular complex with 1,4-benzoquinone, 2,3,5,6-tetramethyl 1,4-benzoquinone and 2,3,5,6-tetrachloro 1,4-benzoquinone in dimethyl sulfoxide at room temperature. The equilibrium constants for the interaction of TTPa with the different quinones were evaluated.     

Full range of continuous mixers

B&P Process Equipment Co. offers twin screw continuous compounding extruders in a 19–450mm screw diameter range. The CT Series of high torque/high speed twin screw extruders offer standard machine diameters from 25mm to 133mm and L/D ratios of up to 52:1. The screw and barrel components are segmented. In addition to the CT Series, the company offers the PC Series of high free volume ‘clam shell’ continuous compounding machines. Standard machine sizes are from 15mm to 160mm, with L/D ratios of up to 50:1. B&P adds that the modular barrel and segmented screw design with individual paddles and hexagonal shafts for simple screw design changes.This is a short news story only. Visit www.addcomp.com for the latest additives and compounding industry news     

Optical sensor for aliphatic amines based on the simultaneous colorimetric and fluorescence responses of smart textile

The pH indicator proposed is a water‐soluble dye based on benzo[de]antracen‐7‐one. Dissolving in buffered aqueous solution, it changes color from yellow to orange and in the mean time decreases its fluorescence emission as a function of the amine concentration. Viscose fabric, dyed with the same dye has been investigated as a new reversible colorimetric and fluorescent sensor material for ammonia and aliphatic amines in buffered solution. The high value of the dye pK_a and the influence of the textile matrix on the selective detection of dimethylamine compared to ammonia, trimethylamine, and metylamine have been studied. The different response of the solution and textile matrix as well as the optical analyses both as a color change and a fluorescence emission have been discussed. The advantage of this sensor is the fact that depending on the analytical problem to be solved and the available instrumentation it can be used either as a fluorogenic or as a chromogenic chemosensor. In addition, the textile sensor is characterized by facile fabrication, low cost, sensibility, and reproducibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Rigid‐rod polybenzoxazoles containing perylene bisimide: Synthesis,structures and photophysical properties

A novel perylene bisimide dye bearing carboxylphenylene substituents on the imide N atoms was synthesized and four conjugated copolymers containing different contents of perylene bisimide dye were synthesized via PPA/P₂O₅ copolymerization method. The structures of the four copolymers were characterized by FTIR, elementary analysis, ¹H‐NMR and XRD. The copolymers showed good thermal stabilities but poor solubilities due to the high rigidity of the backbone. The photophysical characteristics of the copolymers were investigated by UV‐Vis and PL spectra in solutions and films. Because of the conformational change of perylene bisimide chromophore, the absorptions of perylene bisimide core in copolymers showed a large blue‐shift (56 nm) compared to that of the perylene monomer. In PL experiments, when exciting the benzoxazole, an obvious fluorescent quenching was observed in all copolymers, which can be attributed to the energy transfer from benzoxazole units to perylene bisimide fragments and fluorescence quenching. With increasing perylene content, the copolymers turned to layered and friable. The XRD test showed that the interchain distances increased slightly with increasing perylene content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Design and synthesis of novel fluorescence sensing perylene diimides based on photoinduced electron transfer

Two novel tetraester- and PAMAM-branched perylene diimides were synthesized and configured as “fluorophore-spacer-receptor” systems based on photoinduced electron transfer. Due to their long alkylester and alkylamine terminal groups the examined compounds were well soluble in organic solvents. Photophysical characteristics of the dyes were investigated in DMF and water/DMF (1:1, v/v) solution. The ability of the synthesized perylene diimides to detect cations was evaluated by the changes in their fluorescence intensity in the presence of metal ions (Zn²⁺, Co²⁺, Cu²⁺, Fe³⁺, Pb²⁺, Hg²⁺, Ag⁺ and Ni²⁺) and protons. The dyes under study displayed “off-on” switching in its fluorescence as a function of pH, which is attributed to disallowing photoinduced electron transfer from the receptor moiety to the fluorophore. PAMAM-branched dye displayed a good pH sensor activity (FE = 6.4), however the pH sensing ability of tetraester was substantially higher (FE = 184). In the presence of Cu²⁺ and Pb²⁺ ions tetraester quenched its fluorescence intensity (FQ = 22 and 12 respectively), while PAMAM-branched dye enhanced its fluorescence intensity with pronounced selectivity to Cu²⁺ and Fe³⁺ (FE = 3.2 and 4.9, respectively). The results obtained indicate the potential of the novel compounds as fluorescent detectors for metal ions with pronounced selectivity towards Cu²⁺, Pb²⁺ and Fe³⁺ ions and highly efficient “off-on” pH switches, especially a tetraester-branched perylene diimide.     

In situ cure monitoring of epoxy resins using fiber-optic Raman spectroscopy

Fiber-optic Raman spectroscopy was used to monitor the curing of epoxy resins in situ for eventual application to polymer composite processing. A 200-μm diameter quartz fiberoptic sensor immersed in liquid resin was used to obtain Raman spectra for a concentration series of diglicidyl ether of bisphenol-A in its own reaction product with diethylamine using an 820 nm continuous-wave diode laser excitation. A Raman peak at 1240 cm^?1 was assigned to a vibrational mode of the oxirane (epoxide) ring and its normalized intensity was found to be linearly related to the concentration of epoxide groups in the resin mixtures. Raman peaks at 1112 and 1186 cm^?1 associated with phenyl and gem-dimethyl resin backbone vibrations, respectively, did not change in intensity due to the curing reaction and were used as internal references to correct the Raman spectra for intensity changes due to density fluctuations and instrumental variations during the experiments. Fiber-optic Raman spectroscopy was used to monitor the extent of reaction in situ for the room-temperature cure of phenyl glicidyl ether with diethylamine. The extent of reaction of the epoxide groups calculated from the Raman spectra were in excellent agreement with kinetic data from Fourier transform near-infrared absorbance measurements made under the same conditions. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Molecular weight variations in perylene‐doped poly(methyl methacrylate) for luminescent solar concentrators

Integrating highly efficient luminescent dyes into poly(methyl methacrylate) matrices with well‐defined parameters, such as degree of polymerization and dispersity, is a key step in the development of emerging technologies such as fiber‐based solar collectors, sensors, contactless coupling devices and integrated light sources. In this work, four perylene‐based fluorescent dyes, perylene from Sigma‐Aldrich, Lumogen F Yellow 083 from BASF, Perylene Orange from TCI and Lumogen F Red 300 from BASF, were polymerized in bulk with methyl methacrylate. The molecular weight distribution was controlled by the ratio between the chain transfer agent and initiator and was measured by size exclusion chromatography. A dopant‐dependent increase in the degree of polymerization, in which the dye causes a drop in the concentration of active growing polymer chains, was observed. Spectroscopic online monitoring of the process in transmission mode confirmed this observation and indicated the formation of stable perylene radicals during the polymerization. Comparative experiments with fluorescent (metal) organic dyes did not show a similar effect. Fitting models for the dye‐dependent molecular weights for Lumogen Yellow and Lumogen Red are proposed. © 2018 Society of Chemical Industry