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Nowadays, people spend most of their time indoors. Thus, a good indoor air quality is important. Emissions of volatile organic compounds (VOCs) from furniture and building materials can cause health complaints1. Quantitative VOC-emission testing is carried out under standardized conditions in emission test chambers. In the presented project an emission reference material (ERM) is developed that emits a defined mixture of VOCs which is required for quality assurance and -control (QA/QC) measures. Porous materials (e.g zeolites, activated carbons, MOFs or aerogels) are used as reservoir materials and impregnated with VOC. The porous materials are selected, among others, by their pore size, pore size distribution, polarity and availability. Due to their regular pore structure zeolites are tested at first. For a prediction of the emission profile, the ERM is supposed to exhibit a constant emission rate over time. The aim is a stability of ≤ 10 % change in the emission rate over a minimum of 14 days.
Method
For impregnation, the material is placed into an autoclave inside a rotatable basket. The VOC is added and the autoclave is closed. Afterwards, CO2 is inserted. The closed system is then heated to the supercritical point of CO2 (31 °C, 73.75 bar). In this state, the CO2 acts as solvent for the VOC. By rotating the basket, the distribution of the VOC is ensured. After a few minutes, the pressure is decreased slowly and the CO2 is released. For the determination of the emission profile, the impregnated sample is placed into an emission test chamber. These chambers can be operated either with dry or humid air (50 ± 5 % rel. humidity). Every second to third day, air samples are taken and analyzed by gas chromatography. For an ideal impregnation, several different pressures and temperatures as well as impregnation times are tested.
Results
Two zeolite materials tested in dry air conditions reach emission profiles with a decrease of less than 10 % over 14 days (heptane and toluene, respectively). Further it was discovered that smaller pellets of the same zeolite show better results than bigger particles. When the pore size of a zeolite is too small, e.g. 0.3 nm, the VOC cannot be absorbed sufficiently. The main disadvantage of zeolites is their hygroscopicity because it has a large impact on the release of VOC when they are used in emission test chambers under standardized test conditions (23 °C, 50 % rel. humidity). Activated carbons have emission profiles with a larger change over 14 days. However, the high hydrophobicity allows measurements in humid air conditions which was not possible with the before mentioned hygroscopic zeolites. It is possible to impregnate powdered materials as well, and thus powdered non-hygroscopic (n.h.) zeolites were impregnated. Their emission profiles are comparable to those of the activated carbons. The use of methylated hygroscopic zeolites with a decrease in hygroscopicity did not yield successful emission measurements. The change over 14 days is calculated only for the stable phase (~250–300 h).
The desired stability of ≤ 10 % change of the emission rate over 14 days could already be reached under dry testing conditions. Further investigations under humid conditions show that zeolites with high Si/Al-ratios are non-hygroscopic and comparable to activated carbons (20–30 % change). The next step is to reduce the change in the emission rate of these materials to the aimed ≤ 10 % over 14 days.
Since nowadays people spend most of their time indoors, a healthy environment is essential. Volatile organic compounds (VOCs) emitted from furniture and building materials are reported to cause health complaints. Therefore, the usage of low emitting materials will improve the indoor air quality. Quantitative VOC emission testing is usually conducted in emission test chambers under specified controlled conditions as described in DIN 16000-9 and DIN EN 16516.
For reasons of quality control/quality assurance (QC/QA) and for a better comparability of test results from different laboratories, suitable emission reference materials (ERM) are needed. Here, it is important to have a homogenous material with known emission rates over a specific time. Different approaches can be found in literature, inter alia polymer films loaded with the target compound to be released again, or a lacquer material to which a VOC mixture is added. After curing of the lacquer, the material can be loaded into a test chamber. Drawback of those approaches are their relatively fast decreasing emission profiles. For QC/QA purposes according to the test standards, VOC sources with constant emission profiles are desirable.
The EU-funded research project MetrIAQ “Metrology for the determination of emissions of dangerous substances from building materials into indoor air” is working on a multi-component ERM with an envisaged instability of ≤ 10 % in the emission rate over at least 14 days.
Within a doctoral thesis porous materials are impregnated with VOCs. Supercritical CO2 is used as solvent. Thus, the impregnated material does not contain any solvent that may show a measurable amount of emission in the emission test chamber. Furthermore, CO2 has the benefits to have a good availability and low costs. For the selection of porous materials several properties like the pore size, the surface, and the interaction with the components in the atmosphere need to be considered. The impregnation method is optimised while the different porous materials are tested. For the selection of porous materials the pores need to be large enough for the VOC molecules, further influence of the pore size is tested.
There is a need for an assessment of the emission properties of volatile organic compounds (VOCs) from consumer products. A method comparison was carried out to evaluate adapted and cost-effective procedures for such items. Smaller and automated emission chambers depicted similar kinetics compared to a 203 L standard chamber. Toy samples made of PVC (Polyvinyl chloride) emitted more VOCs compared to other tested polymeric products. The emissions from 2 selected samples were studied to allow an evaluation of the resulting room concentration and external exposure of a child. Obtained concentrations were not of concern.
3D-printing or additive manufacturing has many promising and unique advantages. Especially low cost molten polymer Deposition Printers are increasingly populär in the private and educational sector.
Their environmental friendliness can be questioned due to recently reported ultrafine particle and suspected VOC emissions, To further investigate 3D-printing as a potential indoor air pollution source we characterized fine and ultrafine particle emissions from a molten polymer deposition printer producing a 3D object with ten marketable polymer filament materials under controlled conditions in a test chamber. VOC emissions from the filaments have also been compared. Using a straightforward emission model time dependent and averaged particle emission rates were determined. The results indicate that under comparable conditions some filament materials produce mainly ultrafine particles up to an average rate of 1013 per minute. This value is in the upper ränge of typical indoor ultrafine particle sources (e.g. Smoking, frying, candle light, laser printer). The observed material-specific rates differ by five Orders of magnitude. Filament-specific gaseous emissions of organic compounds such as bisphenol A, styrene and others were also detected.
Our results suggest a detailed evaluation of related risks and considering protective measures such as housing and filtering.
Summary: A screening test for potential emissions of volatile organic compounds (VOC) was run on different thermoplastic filaments used for 3D printing. The method of direct thermal desorption was used to simulate the high temperatures during the 3D printing process and to identify the main compounds emitted from the filaments. A large number of unexpected compounds were detected that might affect the user’s health and have an impact on indoor air chemistry.
Introduction: The use of desktop 3D printers is increasing. Compared to other devices with known emissions, e.g. laser printers, there is still a lack of information on possible emissions of VOC and ultrafine particles during operation and the effect on indoor air quality. Most of the commercially available desktop 3D printers operate with a molten polymer deposition. For this process a solid thermoplastic filament is heated in an extrusion nozzle. Most filaments for desktop 3D printers use either acrylonitrile butadiene styrene (ABS) or polylactic acid (PLA) as filament. Alternatives are polyvinyl alcohol (PVA) or polycarbonate (PC).
Method: Eight different thermoplastic filaments for 3D printers were analysed by direct thermal desorption followed by GC-MS identification of the emitted substances. Direct thermal desorption was done by desorbing 5 mg of the feedstock for 1 minute at a temperature of 210°C. This is an average temperature for 3D printing with thermoplastic filaments.
Results and conclusions: The comparison of the 4 different filament groups showed the highest overall emissions from ABS, followed by PLA, PC and PVA. Filament ABS 2 emitted mainly SVOCs and triphenyl phosphate, the latter has the highest emission for a single compound from all evaluated filaments.
Thermoplastic filaments are a new source of VOC emissions due to the high temperatures associated with 3D printing, which can reach up to 270°C. Some of the detected compounds like lactic acid, lactide and bisphenol A have never been described before in the indoor environment. Additionally some of the main substances could not be identified and some others might have the potential to affect the indoor air chemistry.
The appearance of some newly detected compounds raises concerns about potential health effects for the users of 3D printers at home.