Mixtures Of Isocyanates Research Articles

141 Total Reactive Isocyanate Group (Trig) Measurement – a Commentary

Abstract Exposure to airborne isocyanates has, for decades, been a leading cause of occupational. As respiratory sensitisers, isocyanates can induce allergic respiratory diseases with symptoms persisting even without further exposure. As this cause of occupational asthma is recognised it should be almost entirely preventable. In several countries isocyanates are assigned occupational exposure limits based on the total of reactive isocyanate groups (TRIG). The measurement of TRIG has some significant advantages over the measurement of individual isocyanate compounds. This exposure metric is explicit, simplifying calculations and comparisons across published data. It reduces the risk of underestimating exposure by ‘missing’ important isocyanate compounds that may be present but are not the target analytes. It allows for quantification of exposure to complex mixtures of isocyanates, di-isocyanates monomers, prepolymers, polyisocyanates, oligomers, and/or intermediate forms. This is becoming increasingly important as more complex isocyanate products are being used in the workplace. There are many methods and techniques for measuring air concentrations / potential exposure to isocyanates. Several established methods have been standardised and published as International Organization for Standardization (ISO) methods. While some may be applied directly for determination of TRIG, others (developed for determination of individual isocyanates), require modification. This presentation aims to highlight the relative merits and limitations of those methods capable of determining TRIG and also considers potential future developments.

Total Reactive Isocyanate Group (TRIG) Measurement: A Commentary.

Exposure to airborne isocyanates has, for decades, been a leading cause of occupational asthma. As respiratory sensitizers, isocyanates can induce allergic respiratory diseases with symptoms persisting even without further exposure. As this cause of occupational asthma is recognized it should be almost entirely preventable. In several countries isocyanates are assigned occupational exposure limits based on the total of reactive isocyanate groups (TRIG). The measurement of TRIG has some significant advantages over the measurement of individual isocyanate compounds. This exposure metric is explicit, simplifying calculations, and comparisons across published data. It reduces the risk of underestimating exposure by 'missing' important isocyanate compounds that may be present but are not the target analytes. It allows for quantification of exposure to complex mixtures of isocyanates, di-isocyanates monomers, prepolymers, polyisocyanates, oligomers, and/or intermediate forms. This is becoming increasingly important as more complex isocyanate products are being used in the workplace. There are many methods and techniques for measuring air concentrations/potential exposure to isocyanates. Several established methods have been standardized and published as International Organization for Standardization (ISO) methods. While some may be applied directly for determination of TRIG, others (developed for determination of individual isocyanates), require modification. This commentary aims to highlight the relative merits and limitations of those methods capable of determining TRIG and also considers potential future developments.

Thermal stability of isocyanate as particleboard’s adhesive investigated by TGA (Thermogravimetric Analysis)

The objective of this study was to evaluate the thermal stability of isocyanate as particleboard adhesives by means of TGA (thermogravimetric analysis). In this study, thermal properties particularly thermal stability of isocyanate-water/wood system was studied up to a temperature of 500 ºC using thermal analyzer (Mettler Toledo). When isocyanate was used as the binder in particleboard system; the reactive –NCO group reacted with water (because wood is a hygroscopic material and contains free and bound water) and also with the –OH group from wood. The isocyanate was H3M purchased from PT. Polichemie Asia Pacific and the wood particle was Eucalyptus sp. taken from PT. Toba Pulp Lestari. About 10 mg of the mixture either isocyanate with water or wood in various weight ratios were scanned at two different heating rates (slow and fast; 2.5 and 20 °C/min, respectively) with a temperature range from 25 to 500 °C. Results of this study indicate there were more resistant segments to heat in the mixture of isocyanate and water shown from the residual weights about 61-71% compared to in the mixture of isocyanate and wood particle (only 54-62%). Furthermore, there were fewer steps to degrade in the mixture of isocyanate and water shown from the number of peak temperatures about 1-2 peaks than that in the mixture of isocyanate and wood particle (2-4 peaks). New evidence also emerges that isocyanate reacted with water first shown from the weight loss from the low temperature in the mixture of isocyanate and wood particle.

Enhanced mechanical and thermal properties of polyurethane/functionalised graphene oxide composites by in situ polymerisation

ABSTRACTIsocyanate-functionalised graphene (iGO) was prepared and incorporated into a thermoplastic polyurethane via an in situ polymerisation. Firstly, graphene oxide was successfully modified using a mixture of isocyanate- and diisocyanate-containing compounds, leading to the formation of good dispersions of resulting functional graphene oxide in organic solvents, such as N,N-dimethylacetamide and N,N-dimethylformamide. The addition of iGO into polyurethane matrix improved both mechanical and thermal properties in the polyurethane/iGO composites relative to neat polyurethane. An addition of only 0.03 wt-% of functionalised graphene into the polyurethane increased Young’s modulus by 1.4 times and tensile strength by two times. Meanwhile, the elongation at break was similar to that of the neat polymer. In addition, dynamic mechanical analysis also confirmed the improvement in storage modulus of the polymer composites especially at high-temperature range. We believe that the developed modification approach for graphene oxide and polyurethane/graphene composites presented herein could be useful in polymer/graphene composite development.

ChemInform Abstract: Catalytic Enantioselective Addition of Isocyanoacetate to 3‐Methyl‐4‐nitro‐5‐styrylisoxazoles under Phase Transfer Catalysis Conditions.

AbstractThe reaction of styrylisoxazoles (I) with ethyl isocyanoacetate (II) in the presence of N‐benzylcinchonidinium bromides TFCB or DTBC leads to diastereomeric mixtures of isocyanates (III), which are readily cyclized with N‐ethyldiisopropylamine to afford chiral 2,3‐dihydropyrroles as a single diastereomer with good to high enantioselectivity.

Implementation of surface tension force in fluid flow during reactive rotational molding

During Reactive Rotational Molding (RRM), it is very important to predict the fluid flow in order to obtain the piece with homogeneous shape and high quality. This prediction may be possible by simulation the fluid flow during rotational molding. In this study we have used a mixture of isocyanate and polyol as reactive system. The kinetic rheological behaviors of thermoset polyurethane are investigated in anisothermal conditions. Thanks to these, rheokinetik model of polyurethane was identified. Then, to simulate the RRM, we have applied Smoothed Particles Hydrodynamics (SPH) method which is suited method to simulate the fluid flow with free surface such as occurs at RRM. Modelling and simulating reactive system flow depend on different parameters; one of them is the surface tension of reactive fluid. To implement force tension surface, the interface between polymer and air is dynamically tracked by finding the particles on this border. First, the boundary particles are detected by free-surface detection algorithm developed by Barecasco, Terissa and NAA [1, 2] in two and three dimension. Then, analytical and geometrical algorithms have been used for interface reconstructions. The aim of this work is the implementation of surface tension force in the SPH solver applied to RRM. To illustrate that, we used novel and simple geometric algorithm fitting circle and fitting sphere, in two and three dimensional configurations, respectively. The model has been validated using a well-known dam break test case which covered the experimental data.

Study on Hot-Pressing Process of Low-Cost Straw Particle Board

The mixture of isocyanate and urea-formaldehyde adhesive resin was used to manufacture low-cost straw particle board by hot-pressing process. Influence of the hot-pressing temperature, hot-pressing time, board density and the amount of isocyanate adhesive on straw particle board mechanical properties were studied. The resulted showed that, within a certain range, the straw particle board physics performance was improved with the increase of hot-pressing temperature, hot-pressing time, board density and the amount of isocyanate adhesive. The proper hot-pressing process of cost-straw particleboard is hot-pressing time for 40s/mm, MDI applied amount of 3%,a density of 0.7 g/cm3, hot-pressing temperature of 180 °C

Airborne Isocyanate Exposures in the Collision Repair Industry and a Comparison to Occupational Exposure Limits

Isocyanate exposure was evaluated in 33 spray painters from 25 Washington State autobody shops. Personal breathing zone samples (n = 228) were analyzed for isophorone diisocyanate (IPDI) monomer, 1,6-hexamethylene diisocyanate (HDI) monomer, IPDI polyisocyanate, and three polyisocyanate forms of HDI. The objective was to describe exposures to isocyanates while spray painting, compare them with short-term exposure limits (STELs), and describe the isocyanate composition in the samples. The composition of polyisocyanates (IPDI and HDI) in the samples varied greatly, with maximum amounts ranging from up to 58% for HDI biuret to 96% for HDI isocyanurate. There was a significant inverse relationship between the percentage composition of HDI isocyanurate to IPDI and to HDI uretdione. Two 15-min STELs were compared: (1) Oregon's Occupational Safety and Health Administration (OR-OSHA) STEL of 1000 μg/m3 for HDI polyisocyanate, and (2) the United Kingdom's Health and Safety Executive (UK-HSE) STEL of 70 μg NCO/m3 for all isocyanates. Eighty percent of samples containing HDI polyisocyanate exceeded the OR-OSHA STEL while 98% of samples exceeded the UK-HSE STEL. The majority of painters (67%) wore half-face air-purifying respirators while spray painting. Using the OR-OSHA and the UK-HSE STELs as benchmarks, 21% and 67% of painters, respectively, had at least one exposure that exceeded the respirator's OSHA-assigned protection factor. A critical review of the STELs revealed the following limitations: (1) the OR-OSHA STEL does not include all polyisocyanates, and (2) the UK-HSE STEL is derived from monomeric isocyanates, whereas the species present in typical spray coatings are polyisocyanates. In conclusion, the variable mixtures of isocyanates used by autobody painters suggest that an occupational exposure limit is required that includes all polyisocyanates. Despite the limitations of the STELs, we determined that a respirator with an assigned protection factor of 25 or greater is required to protect against isocyanate exposures during spray painting. Consequently, half-face air-purifying respirators, which are most commonly used and have an assigned protection factor of 10, do not afford adequate respiratory protection.

Morphological features and thermal and mechanical response in segmented polyurethane elastomers based on mixtures of isocyanates

A family of segmented polyurethane elastomers (SPUs) was synthesized. Hard segments were chosen to be generated from two isocyanates: the rigid 4,4-diphenylmethane diisocyanate (MDI) and the flexible 4,4-dibenzyl diisocyanate (DBDI), alone or as mixtures. A polyester soft segment polyethylene adipate of molar mass 2000 g mol−1 and a small molecule chain-extender diol, ethylene glycol, were used. Hard segment fraction was maintained at ∼40%. The structure–property relationship of SPUs was investigated using several characterization techniques. Morphological features such as interdomains of the soft and hard segments were identified by means of atomic force microscopy. The thermal and mechanical behavior was evaluated by using dynamic mechanical analysis, differential scanning calorimetry and uniaxial tensile tests. Structural changes induced by varying the type and the number of isocyanates and the order of their introduction were also followed by using wide-angle X-ray. Materials with hard segments based on the single diisocyanate DBDI were observed to crystallize. Crystallinity was strongly reduced when DBDI was mixed with MDI. Improvement in elastomeric properties was obtained when both diisocyanates were included and reacted together in a random manner.

Hard Segment Inelastic Effects on the Stress–Strain Response of Polyurethane Elastomers Based on Hard Segments of Variable Geometry

A study was made of a family of thermoplastic polyurethane copolymers, in which the nature and number of the hard segment components (crystallizing or not) were varied. Materials were synthesized with ethylene glycol (EG) as chain extender. Changes induced by varying the type and the number of isocyanates and the order of their introduction were followed and the mechanical responses were measured in cyclic tensile tests and stress relaxation in interrupted tests. Polymers based on DBDI hard segments showed lower strain recovery and strain energy recovery on cycling than did the conventional materials with MDI and the materials based on mixtures of isocyanates MDI/DBDI. Such features of the response were attributed to differences in hard phase plastic flow stress; hard domain hydrogen bonding exerted strong influences on the inelasticity of polyurethane elastomers. Stress-strain cycles reflected the resistance to plastic deformation occurring in the hard domains. This was enhanced by more pronounced hydrogen bonding achieved in the more mobile DBDI than in MDI.

Chemical transformations in the course of modification of crystalline polyolefins with mixtures based on 2,4-toluene diisocyanate and-caprolactone

Chemical modification of polyolefins (polypropylene, high-density polyethylene) with mixtures of isocyanates and e-caprolactone was studied. Chemical transformations occurring in the course of modification of polyolefins with a binary modifying system containing 2,4-toluene diisocyanate and e-caprolactone in the presence of sodium caprolactamate catalyst were studied using model systems based on α-olefins.

Synergistic phenomena in modification of polyolefins with mixtures of isocyanates and epoxides

Modification of commercial polyolefins with binary mixtures of isocyanates and epoxides was studied; the influence of the order of adding components on the performance of the modifying system was examined.

Isomerization of a perfluoro-α-lactam

Prolonged heating of the perfluoro-α-lactam (CF 3) 2C(CO)(NC(CF 3) 3) ( I) at 110–150 °C gives a mixture of isocyanate (CF 3) 3CC(CF 3) 2NCO ( V) (as the main product), acylimine (CF 3) 2CNC(O)C(CF 3) 3 ( III), (CF 3) 3CC(CF 3) 3 ( VI) and other products. A radical mechanism is proposed for the reaction.

Capillary gas chromatographic method for the determination of complex mixture of isocyanates and amines

A capillary gas chromatographic method using nitrogen-selective detection was developed for the analysis of complex mixtures of isocyanates and amines in air. The isocyanate group was converted directly in the air sampling step into urethane by reaction with ethanol using potassium hydroxide as a catalyst. The amine group was converted into an amide using pentafluoropropionic anhydride in an extractive derivatization procedure. The complex pattern of air pollutants after thermal degradation of a polyurethane polymer, based on toluene diisocyanate (TDI) and 3,3′-dichloro-4,4′-diaminodiphenylmethane (MOCA), was investigated. Substantial amounts of amines, isocyanates and aminoisocyanates, molecules containing both an amine and an isocyanate group, were found. Consideration must be given to these findings when using current methods for isocyanate and amine determination. The detection limits for isocyanates, amines and aminoisocyanates, essentially depending on the nitrogen content of the molecule, were about equal and in the order of 40–80 fmol.