Styrene Emission Research Articles

Emission modeling of styrene from vinyl ester resins

The use of vinyl ester (VE) resins in the composites industry has increased in the last decade, and the trend is projected to continue. Styrene is a commonly used co-monomer in VE resins, which acts as a reactive diluent and is required in many liquid molding methods to reduce viscosity and increase gel time. The emission rate of styrene from VE resins is affected by various parameters, including styrene content, temperature, and resin surface-to-volume ratio. This study experimentally measured the effect of these parameters on styrene emission rates from VE resins. It was observed that the emission rate and amount of styrene decreased with decreasing surface-to-volume ratio, temperature, and styrene content. It is also shown that diffusion coefficient and evaporation coefficient of styrene have an exponential relationship with temperature, while they remained constant with initial styrene concentration and aspect ratio. Emission rate and amount decreased with increasing resin initial depth to radius ratio. The emission profiles were self-similar for different aspect ratios and were scaled by the ratio of the instantaneous sample depth to radius. Overall, the effect of these various parameters on the emission profile can be accurately modeled using a modification of a simple one-dimensional diffusion model based on the Crank solution to diffusion through a planar sheet.

Real-time emission characterization of organic air toxic pollutants during steady state and transient operation of a medium duty diesel engine

An on-line monitoring method, jet resonance-enhanced multi-photon ionization (REMPI) with time-of-flight mass spectrometry (TOFMS), was used to measure emissions of organic air toxics from a medium-duty (60 kW) diesel generator during transient and steady state operations. Emissions of gas phase benzene, toluene, ethylbenzene, o-, m-, p-xylenes (BTEX), styrene and polycyclic aromatic hydrocarbons (PAHs) were measured at levels in the 10–500 ppb range with a measurement frequency of 10 s −1; this enabled rapid emission characterization as a function of operating conditions: cold starts, hot starts and load changes. The sensitivity, selectivity and real-time monitoring capabilities of the jet REMPI-TOFMS system discerned transient concentrations of organic air toxics (e.g., benzene and naphthalene) during cold starts exceeding 15 times their steady state levels. Time-integrated concentrations obtained by jet REMPI-TOFMS compared well with standard EPA methods. The jet REMPI-TOFMS system provides a means to rapidly characterize air toxic emission factors that enables users to alter operational procedures to minimize air toxic formation. The relative concentrations between startup and steady state emissions, as well as the transition period between these levels, were specific for each type of compound found in the diesel exhaust.

Printing Systems: Meeting Market Demands for Healthy Indoor Environments

Acceptable indoor environmental quality is a necessary requirement for today's office buildings, schools, public facilities, and personal residences. On a global basis, indoor air quality is one of the top three environmental issues facing all countries and all people. Toxic chemicals, inorganic gases, particles, and microbes that are released by products into the indoor environment can contribute to human irritation, discomfort, and long term health consequences to those exposed. These human effects can lead to excessive medical costs, significant loss of productivity, and undesirable litigation. Printing devices are known contributors of indoor pollution such as respirable particles, volatile organic compounds (VOCs) such as styrene and formaldehyde, and ozone. Sources of these include construction materials, electronic and heating processes, inks and toners, papers and transparencies, plastics, and cleaning solvents. Manufacturers of office equipment are proactively designing for the environment, including indoor air quality as an important part of their product stewardship. Eco-criteria have been established for acceptable levels of airborne contaminants released by operating equipment. This paper will review current international programs addressing allowable emissions from print devices (including Blue Angel, Greenguard, and the State of California), test procedures, and representative emissions data from printers, copier, and computers.Eco-criteria are based on the performance of operating office equipment and acceptable contributions of certain pollutants. Acceptable pollutant emissions of respirable particles, formaldehyde, styrene, benzene, and total volatile organic compounds are based on existing health and safety data with some consideration for protecting sensitive people from irritants and odorants. The primary measurement technique, environmental chamber technology, has been validated to test products under realistic use conditions and to determine emission rates of pollutant release. These data can be used in exposure models to predict and estimate potential human exposures, and to compare product data with prescribed eco-criteria. This measurement technology has been accepted on a global basis and ISO documentation is being prepared as a joint US/European effort.

Mechanical Properties of Composites Based on Low Styrene Emission Polyester Resins for Marine Applications

Glass fibre reinforced polyester composites are used extensively for hulls and decks of pleasure boats. Boat-builders must optimise manufacturing technology, not only with respect to mechanical properties but also limiting volatile organic compounds (VOC) emissions. One way to achieve this is through modified polyester resin formulations such as low styrene content, low styrene emission or combinations of these. The resin matrix selection procedure is based on design specification (mechanical behaviour) but also manufacturing requirements and cost considerations. For this application post-cure is rarely used so it is important to optimise curing conditions. In this study the influence of the curing cycle on mechanical properties was examined first for two polyester resins. Then for one cycle (16 h at 40°C) the properties of eight resins have been determined. Significant differences in failure strain are observed, from 0.9% to 3.3%. The resins with improved VOC performance are the most brittle. The transverse tensile behaviour of these resins in composites with unidirectional glass fibre reinforcement and the limit of linearity for composites with glass mat both depend on these failure strains. These results are discussed in terms of admissible composite strains for boat design.

Recycling collaborative combats legislation threat

Composites are today under siege from factors ranging from rising raw materials and energy costs, to caps on styrene emissions, from health and safety rules to waste legislation and limits on landfill. In the important automotive sector, arguably the biggest current threat is the European Union (EU)'s End-of-Life Vehicle (ELV) Directive, which effectively starts to bite this year. George Marsh reports.

Nienasycone zywice poliestrowe w swietle wymagan Unii Europejskiej

Recent achievements in the field of chemistry and technology of unsaturated polyester resins (UP) have been discussed and commented. The review bases on 141 literature references mainly_from the period 1998-2004. The following problems were presented: nanostructural polyester composites, UP of limited flammability, analysis of the process of thermal degradation of UP of increased flame resistance, curing comonomers, UP of decreased styrene emission, waterborne polyester resins. Especially ecological aspects of the theme were discussed from the point of view of European Union requirements.

Fatty acid-based monomers as styrene replacements for liquid molding resins

One method of reducing styrene emissions from vinyl ester (VE) and unsaturated polyester resins (UPE) is to replace some or all of the styrene with fatty acid-based monomers. Methacrylated fatty acid (MFA) monomers are ideal candidates because they are inexpensive, have low volatilities, and free-radically polymerize with vinyl ester. The viscosity of VE resins using these fatty acid monomers ranged from 700–2000cP, which is considerably higher than that of VE/styrene resins (∼100cP). In addition, the Tg of VE/MFA polymers were only on the order of 80°C, which is significantly lower than that of VE/styrene polymers. Decreasing the length of the base fatty acid chains from 18 to 12 carbon atoms improved the Tg by 20°C, while lowing the resin viscosity from ∼2500 to ∼1000cP. Residual unsaturation sites on the fatty acid backbone decreased the cure rate of the resins thereby decreasing polymer properties. Ternary blends of VE, styrene, and fatty acid monomers also effectively improved the flexural, fracture, and thermo-mechanical properties and reduced the resin viscosity to acceptable levels, while using less than 15wt% styrene, far less than commercial VE resins.

DETERMINATION OF BIOLOGICAL KINETIC CONSTANTS USING RESPIROMETRY FOR THE WATER9 AIR EMISSIONS MODEL

The U.S. E.P.A. Water9 air emissions model can be used to estimate air emissions, biological removal and adsorption of organic compounds in wastewater treatment and collection systems. Although the model contains an extensive database of physical property data and biological treatment kinetic constants for organic compounds, the Water9 documentation recommends that site-specific biotreatment kinetic data be used whenever available. The Water9 model uses a zero-order substrate removal constant (Kmax) and a first-order substrate removal constant (K1). While these appear similar to, and have the similar units as, the Monod maximum substrate removal constant qmax and the quotient of the Monod qmax divided by the half-saturation factor (Ks), the procedures given for determining the Water9 kinetic factors by batch testing (40CFR Part 63 Appendix C) indicate that there are important differences. The Water9 factors are based on the entire biomass population as measured by the mixed liquor suspended solids, while the intrinsic Monod kinetics are based on the active biological population only. In addition, an effective K1 is determined at the substrate concentration of interest, rather than being a more generally applicable intrinsic constant. Water9 modeling of styrene emissions from an industrial biological wastewater treatment system using the default physical property and kinetic data gave estimated effluent concentrations and air emissions considerably greater than indicated by effluent analytical data, and as indicated by the lack of any styrene odor at the treatment plant. Batch respirometry testing using biomass from the industrial plant and pure styrene as the substrate was used to generate a styrene removal profile based on Monod kinetics. The substrate removal profile was used in place of substrate analytical data in a modification of one of the recommended procedures for determining the Water9 kinetic constants. Using the site-specific biorate constants resulted in estimates of the styrene effluent concentrations in much better agreement with measured concentrations in the plant effluent. The styrene air emissions estimated by the model decreased by several orders of magnitude.

Potential for Reducing Indoor Styrene Exposure from Copied Paper through Use of Low-Emitting Toners

Tests were conducted using 53-L dynamic chambers to determine airborne styrene emission rates over time from freshly copied paper. Copies were produced on a single photocopier using two toners manufactured for this copier but having different styrene contents. The resulting emission models were used to predict whether indoor styrene concentrations resulting from copied paper in a typical office might be significantly reduced by use of a low-emitting toner for a given copier. The styrene emissions were best represented by either a 3rd-order decay model or by a power law model having an exponent between 0.3 and 0.5 (R2 = 0.94–0.99). The two toners resulted in copied paper having significantly different styrene emissions (p < 0.01), with unit mass emissions over 1000 hr being nine times greater with the higher-emitting toner. But copied paper is predicted to produce peak indoor styrene concentrations in a typical office no more than 1% of the World Health Organization health-based guideline. Thus, for the toners considered here, indoor styrene exposures from copied paper appear to be too limited to provide incentive for switching to the lower-emitting toner. The ability to generalize these conclusions is limited by the fact that only one copier and two toners could be tested.

Spray equipment adapts for success

Despite poor economic conditions and government restrictions on styrene emissions, spray-up is still holding its own as the most widely used composites processing method. Katherine Simpson reports.

The Effect of Spraying and Rolling Process Factors on Styrene Emission During the Application of Unsaturated Polyester Resins

In recent years the awareness of the problems caused by styrene emission during the processing of unsaturated polyester resins has enlarged. The spray-up application of gel coats is especially problematic, and it produces high styrene emission rates. The emission of styrene has been reduced through material changes, work practice controls, and add-on controls. However, the influence of the spray-up process factors on styrene emission has not been studied before. The aim of this study was to examine possibilities to reduce styrene emission by optimization of spray-up process factors. The following factors were studied under controlled laboratory conditions: orifice size and angle of the spray gun tip, spraying pressure, distance between spray gun and mold, and shape of the mold. The influence of the rolling pattern during lamination was also studied. Several significant factors were found. High pressure and long spraying distance increased both the unit styrene emission and the emission rate. The orifice size had two effects; a large orifice decreased the amount of styrene emitted per sprayed amount of resin but increased the emission rate of styrene. The shape of the mold did not affect the styrene emission. Styrene emission is greater if the entire mold area is rolled. To achieve lower emission is it necessary to roll an area as small as possible; this is especially important if a large mold is laminated. The results showed that emission of styrene can be reduced significantly by an optimal selection of the spray gun settings and the way of working. Optimal settings also increased the transfer efficiency resulting in decreased material loss.

Influence of mechanical stresses on the hydrolytic aging of standard and low styrene unsaturated polyester composites

AbstractStandard and low styrene emission glass fiber‐reinforced unsaturated polyester (FRP) composites were aged by immersion under flexural and tension loads, to evaluate modifications to the mechanical properties as a function of exposure time under stress. The application of a mechanical load does not modify either the quantity of the absorbed water or the diffusion coefficients significantly. For an applied stress of less than 10% of the fiber strength, the influence on aging is small, but for larger applied stresses, the rate of reduction in the mechanical properties is accelerated and, in some cases, premature rupture is observed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2185–2195, 2002

Styrene Emissions from the Spray-Up and Vacuum Injection Processes—A Quantitative Comparison

Styrene emissions were studied during manufacturing of two identical glass-fiber reinforced plastic boats by two different manufacturing methods. The manufacturing methods were spray-up, which is an open method, and vacuum injection, which is a closed method. Changing the manufacturing process from an open method to a closed method decreased the styrene evaporation dramatically in this particular case. By using vacuum injection, the styrene emission during the laminate application was reduced by 98% compared with the styrene emission during laminate application by spray-up. Gel coat application by spraying will remain a major source for styrene emissions. The greatest environmental benefit is achieved with closed manufacturing methods when products without gel coat are made. The whole manufacturing process can then be performed in a closed system virtually free from emissions.

Styrene Emissions from the Spray-Up and Vacuum Injection Processes—A Quantitative Comparison

Styrene Emissions from the Spray-Up and Vacuum Injection Processes—A Quantitative Comparison

Spray-up offers process improvements

Spray-up is often thought of as the ‘dirty’ end of the reinforced plastics industry. But as styrene emission standards continue to tighten up and composites fabricators demand more from their suppliers, spray-up equipment manufacturers are coming up with ‘greener’, cleaner and more versatile products. Amanda Jacob reports on some of the latest developments.

Pilot-scale evaluation of new resin application equipment for fiber-reinforced plastics

Styrene is the monomer used as a cross-linking agent in the majority of fiber-reinforced plastics manufacturing processes. Its evaporation is undesirable from environmental, health and safety, and economic perspectives. The effect of a proprietary Fluid Impingement Technology™ (FIT™) nozzle, developed by Magnum Industries, on styrene emissions was evaluated and compared to other conventional application equipment — conventional spray guns and flow coaters (operated at both low and high pressure). The FIT™ nozzle produced less styrene emissions during both gel coating and resin testing, with significant emissions reduction occurring during the application process.

Reduced styrene content offers answer for LSE

The tightening up of legislation on styrene emissions continues to be one of the major challenges facing the composites industry. George Marsh looks at some the current strategies and products designed to reduced emissions.

Removal of styrene vapor from waste gases by a trickle-bed air biofilter

The trickle-bed air biofilter (TBAB) performance for the removal of high-strength styrene was evaluated under different gas flow rates and influent concentrations. Under pseudo-steady-state conditions, the elimination capacity increased but the removal efficiency decreased with the increase of styrene loading. More than 90 and 80% removal efficiencies were achieved for influent styrene loadings below 32 and 55 g/m 3/h, respectively. The TBAB appears to be an effective treatment process for controlling high-strength styrene emission under low-to-medium loading conditions, and the effectiveness could be maintained over 140 days of laboratory operation.

Biofiltration of Air Contaminated by Styrene: Effect of Nitrogen Supply, Gas Flow Rate, and Inlet Concentration

The biofiltration process is a promising technology for the treatment of dilute styrene emissions in air (less than 1 g·m-3). The efficiency of this process is however strongly dependent upon various operational parameters such as the filter bed characteristics, nutrient supplies, input contaminant concentrations, and gas flow rates (gas residence times). The biofiltration of air containing styrene vapors was therefore investigated, employing a novel biomass filter material, in two identical but separate laboratory scale biofiltration units (units 1 and 2), both biofilters being initially inoculated with a microbial consortium. Each biofilter was irrigated with a nutrient solution supplying nitrogen in one of two forms; i.e., mainly as ammonia for unit 1 and exclusively as nitrate for unit 2. The experimental results have revealed that greater styrene elimination rates (up to 141 g·m-3·h-1) are achieved in the biofilter supplied with ammonia as the major nitrogen source in comparison to the lesser elimina...

Evaluation of a Local Exhaust System Used in the Manufacture of Small Parts Made of Reinforced Plastic

Fiber-reinforced plastics are used to manufacture a large variety of products, particularly for the transportation sector. Hand lay-up molding and projection molding are the main methods of manufacture. The users of these processes are exposed to appreciable emissions of styrene; in Quebec, more than 3000 workers work in this industry. A statistical analysis of styrene concentrations measured over a five-year period by the Institut de recherche en santé et en sécurité du travail (IRSST, Occupational Health and Safety Research Institute) reveals that for all of the main manufacturing sectors involved, between 40 percent and 78 percent of the results exceed the exposure standard of 50 ppm. This study evaluated the effectiveness of a ventilated table in controlling worker exposure to styrene and acetone in a shop that manufactures fiber-reinforced plastics parts. The evaluated local extraction system consists of a ventilated table with a surface area of 1.2 m x 1.2 m. During molding, the styrene emissions are exhausted through the ventilated table as well as through the slots in a lateral hood. Replacement air, introduced vertically through a supply air shower located above the worker, limits the diffusion of contaminants toward the worker's breathing zone. The reduction in worker exposure to styrene and acetone during hand lay-up molding was measured in the breathing zone for two sizes of molds. The results show that exhaust ventilation reduced the styrene concentrations by 91 percent and that the introduction of replacement air increased the efficiency of the ventilated table to 96 percent. The evaluation performed indicates that the ventilated table adequately controls worker exposure to styrene and acetone during the molding of small components.