Chemical emissions tests are mandatory for construction product manufacturers to show regulatory compliance. This often requires the implementation of routine in-house tests for quality control as well as ‘reference’ tests for product certification. However, the ‘small’ chambers used for the reference methods are costly and impractical for routine screening because it can take up to a month to complete analytical studies. The Micro-Chamber/Thermal Extractor (µ-CTE) can be used as a complementary technique; it is less expensive than the ‘small’ chamber and allows sample collection from six samples at a time, significantly increasing the throughput. This enables manufacturers to screen material prior to these expensive third-party certification tests and carry out routine factory control/quality control.
Regulations affecting construction product manufacturers
Building materials release volatile organic compounds (VOCs) into the indoor air environment such as in our homes and workplaces. Prolonged exposure to VOCs has been associated with an increase in the incidence of eye, nose and throat irritation, allergic skin reactions, headaches, dizziness and fatigue. Conditions such as asthma can often be triggered by VOCs, and some are known to cause cancer, while others are suspected causes.
As a result, the demand for improved assessment and labelling of products with respect to their intentional or unintentional release of VOCs has led to high-profile international regulatory developments.
VOCs of concern are solvents, residual monomers, plasticisers, formaldehyde and allergens. As they are widely used in the manufacture of construction products, the regulations affect a large proportion of the industry, such as producers of flooring, paints, coatings, adhesives, sealants, plasterboard (drywall), insulation (such as spray polyurethane foam) and wall coverings, together with all their suppliers. It is the responsibility of manufacturers and suppliers to demonstrate products are safe for use leading to compliance with regulations.
Regulations include Germany’s AgBB scheme (evaluation of VOC emissions from construction products), France’s construction and decorative products regulation set up by ANSES, and EU REACH (Registration, Evaluation, Authorisation and restriction of CHemicals). Similar regulations have been set up in the US, such as Standard 189.1 and the LEED ‘green buildings’ program. ‘Chinese REACH’ makes similar requirements to the European equivalent.
However, it is the European Construction Products Regulation (CPR) that has arguably the biggest worldwide impact on construction product manufacturers. Put in place to prevent trade barriers across the EU and to harmonise European product standards, it stipulates that all construction materials made or sold within the European Union must be certified with the CE mark. To achieve this, ‘reference’ emissions tests must be carried out by an accredited third-party laboratory.
VOC emissions ‘reference’ tests
The ‘reference’ tests typically involve placing a representative material or product sample inside a ‘small’ chamber (Figure 1) (typically 50–1000 L) so that only the emitting surface is exposed. At ambient, or slightly elevated temperature, a flow of clean air is applied to sweep VOCs from the sample into a tube containing a sorbent, which retains the VOCs. These sorbent tubes are then analysed using thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS), which gives the concentration of each compound released from the sample. TD is a pre-concentration technique, which introduces the VOCs from the sorbent tube to the GC in a very small volume of carrier gas, maximising the sensitivity to enable detection of trace-level target compounds.
Figure 1: A typical 1m ‘small’ chamber used for final product certification. Image credit: SP Technical Research Institute of Sweden.
The material is kept in the chamber for up to 28 days and samples are taken after three days (to simulate the material’s first application in a real room) and at 28 days (to simulate occupancy of the room). The analysis is conducted in accordance with one or more standard methods. Key methods include ISO 16000-6, ISO 16000-9, EN 13999 (for adhesives), EN 16516, ASTM D5116, ASTM D6196 and California Specification 01350.
In-house tests
It is often cost effective to implement in-house emissions screening tests for quality control. The tests ensure batch-to-batch product quality and can be useful for research and development. For example, screening can be used to compare product types, compare a product with a competitor’s, assess the effect of manufacturing processes and for troubleshooting, such as determining the cause of failure of a product.
The ‘reference’ tests described earlier are the best available approach for simulating real-world use of products. However, the length of time needed for these tests (3 to 28 days in Europe and 10–14 days in the USA) and the stringent conditions that need to be maintained (23°C and 50% relative humidity) make these tests expensive, time-consuming and impractical for routine quality control. Consequently, there is a demand for quicker and simpler sampling methods.
Direct desorption is one option. Small pieces of a material are placed into an empty TD sample tube (Figure 2). The tube is placed directly into a TD unit for desorption and analysis. The method is simple and readily automated. However, it is only applicable to small, relatively homogeneous samples, and results may not correlate well with data from ‘reference’ emission tests because VOCs are typically extracted from the whole sample, often at increased temperatures and the results cannot be correlated with the real use of the product or material.
Figure 2: Direct desorption of a solid sample carried out using a thermal desorption tube.
A microchamber, such as the Micro-Chamber/Thermal Extractor (µ-CTE) from Markes International (Figure 3), overcomes the drawbacks of both ‘small’ chambers and direct desorption. Microchambers are based on the same fundamental principles as ‘small’ chambers, but in scaled-down form, meaning that equilibration and sampling can be carried out much more quickly. The samples can be substantially larger than for direct desorption, which results in improved reproducibility for composite samples.
Figure 3: Examples of microchamber/thermal extractor units. Left: A six-chamber model. Right: A four-chamber model.
The operation of these microchambers is simple. When the unit has reached the set temperature, the microchambers containing the samples are placed within it, and the lids sealed. A controlled flow of air or gas (optionally humidified) is passed through all chambers simultaneously. After equilibration (typically for 20–30 minutes), conditioned sorbent tubes are attached to each microchamber, and the air/gas flow sweeps vapours from the material and onto the sorbent tube. No pumps or additional mass flow control equipment is required, making the system easy to use and ideal for routine operation. Microchamber tests can be carried out at ambient or elevated temperature.
For testing emissions from construction materials or products, moderate temperatures (30–60°C) are used to boost sensitivity and compensate for the relatively small sample size without affecting correlation with ambient-temperature data from ‘small’ chambers. Typical equilibration times for sampling VOCs range from 20–30 min, with subsequent vapour sampling for 15–20 min at 50 mL/min. These conditions allow four or six samples (depending on the model) to be processed every hour. Optional toggle valves allow the gas flow to unused chambers to be turned off, reducing gas consumption, and a humidifier accessory can supply the unit with 50% humidified air. This allows closer simulation of conditions used in ‘reference’ tests and can enhance the recovery of some less volatile polar compounds. The µ-CTE can also be operated at higher temperatures and flow rates for extended periods.
After vapour sampling, the sorbent tubes are analysed by TD–GC–MS. The analytical process is carried out off-line, allowing a fresh set of samples to be introduced to the µ-CTE while analysis of the previous set continues.
The µ-CTE is available in two models, both of which allow multiple samples to be tested simultaneously. The four-chamber model (Figure 4) has a maximum temperature of 250°C and a chamber volume of 114 cm and the six-chamber model has a maximum temperature of 120°C and a chamber volume of 44 cm.
Figure 4: The microchambers inside a four-chamber µ-CTE.
Both offer three modes of operation:
- Bulk emissions testing is valuable for emissions profiling, and for testing of raw materials (Figure 5A).
- Surface emissions testing is suitable for determining area-specific emission rates from planar samples (Figure 5B).
- Permeation testing uses a dedicated accessory to allow volatiles permeating through a thin layer of material to be measured (Figure 5C).
Figure 5: Operation of the µ-CTE for sampling emissions of volatile chemicals (A) from bulk samples, (B) from the surfaces of flat samples and (C) permeating through a thin layer of material.
The µ-CTE is required for compliance with several standard methods, including ISO 16000-25 (building products), ASTM D7706 (products), ASTM WK40293 (spray polyurethane foam), the GUT Emission Test (carpets), and VDI 2083-17 (cleanrooms). It is also cited as a secondary screening method in EN 16402 (paints and varnishes) and EN 16516 (construction products).
Emissions data obtained using the µ-CTE has been proven to show indicative correlation to the results from ‘reference’ methods. In addition, the fast emissions-screening data obtained using the µ-CTE has been found to allow reliable estimation of longer-term results from ‘small’ chamber tests, enabling demonstration of continued compliance with certification requirements.
Conclusions
As well as third-party certification of products, market demand for new low-emission (higher-value) products and the need for raw material checks and factory production control of product emissions means that many companies will benefit from in-house emission-testing capability. Microchamber technology and robust TD–GC–MS systems have a key role to play in making chemical emissions testing a practical and useful in-house test facility for construction product manufacturers.
Markes’ µ-CTE is a valuable tool for assessing VOC emissions from a wide range of construction materials and consumer products. Key benefits are reproducibility and speed of sampling – up to six samples can be processed in parallel in less than 60 minutes, enabling reliable comparison between samples and offering significant benefits for sample throughput. Another major advantage of the µ-CTE is that the results obtained can be used to predict emissions from the expensive long-term certification tests required by national and global regulations, reducing costs and saving time in the process of optimising formulations.
This article was written by Elinor Hughes, technical copywriter at Markes International, Gwaun Elai Medi-Science Campus, Llantrisant, UK. For more information, visit www.marks.com.