Creating Furniture Fit for the Outdoors: Overview of Laboratory Accelerated Aging for the US
Consumers are increasingly incorporating outdoor space into their living environment, bringing with it the need for durable, safe and attractive outdoor furniture.
Sales in outdoor furniture are predicted to grow steadily in the next few years, reaching USD 1,600 million by the end of 2022.1 This will provide many opportunities for manufacturers who can demonstrate to consumers that their products can resist the negative effects of weathering.
The increasing use of outdoor space for dining and relaxation comes at the same time as a generational shift in those that are buying outdoor furniture. It is predicted that during 2019 Millennials, defined as those aged between 20 and 35 in 2016, will overtake the Baby Boomers, aged between 52 and 70, as the dominant population group in the US.2 This will have a profound effect upon the sector, as customer’s expectations and requirements alter.
In a recent Casual Living study, Millennials were shown to favor muted colors (57% preference) and modern styles (six out of ten Millennial consumers). Millennials, who are more inclined than other generations to live in urban environments, are looking to capitalize on tighter outdoor spaces with multipurpose and convertible furniture. The survey also showed they expected to use the furniture for an average of two to four years and over half would only buy a product if they had tried it.
Quality and durability are therefore two key considerations in the decision-making process when a millennial decides to buy a piece of outdoor furniture. It must retain its strength, stability and aesthetics despite being exposed to a variety of environmental factors, primarily temperature, sunlight and moisture.
Finally, while market research predicts that dining sets are set to lead the global outdoor furniture market until at least 2022, it is chairs, tables and seating seats that will continue to remain the most lucrative products in the sector – expected to account for 80%of the market.3
Laboratory Accelerated Aging
To test the performance of outdoor furniture, manufacturers can undertake a variety of test methods to accelerate the aging process seen in the outdoor environment. The procedures use aggravated environmental factors to speed up the normal aging process, helping manufacturers understand the long-term effects of exposure to environmental factors in shorter timeframes and under standardized laboratory conditions.
The effects of exposure to the elements can broadly be split into two types:
- Changes in visual properties or aesthetic appeal – fading, yellowing, color change, gloss reduction
- Changes in physical properties – cracking, peeling, embrittlement, loss of tensile strength
While alterations to the visual properties of a product will result in it being less appealing to the eye, they can also be symptomatic of changes to the physical properties of the product and this may signal a safety issue.
Resistance to Sunlight
The primary driver in altering the visual appearance of outdoor furniture is the sun, with heat and moisture acting as catalysts. The outdoor natural exposure method is the most straightforward exposure assuming that time permits. However, with the variability of climate from site-to-site, test data are only applicable for that specific site. In a controlled environment, laboratory weatherometers accelerate sunlight degradation so that more consistent results can be generated, in comparison to outdoor exposure methods.
Heat and light oxidation, (also known as photooxidation), in pigments, binding agents and other coating additives – cause molecular chains in the product to break down, resulting in embrittlement and visual changes.
The two primary laboratory practices used to replicate harmful effects of sunlight are:
- Fluorescent Ultraviolet, using ASTM G154 – Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials
- Xenon Arc, using ASTM G155 – Standard Practice for Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials
Each practice simulates sunlight alongside heat and moisture, but the primary difference is the sun’s wavelength they replicate. Xenon Arc reproduces the radiation of full spectrum sunlight, thereby replicating a close simulation of outdoor sun exposure. A UV chamber focuses on sunlight’s UV band. The fluorescent UVA and UVB lamps replicate the 300 – 400 nm wavelengths, the spectrum band responsible for much of sunlight’s physical damage.
Manufacturers can use the methods to test for different facets of the aging process. Xenon Arc is best utilized for evaluating color change of outdoor pigments and dye over time, while QUV is used to test for embrittlement and physical change, especially in polymers and durable outdoor coatings.
Resistance to Temperature Extremes
Some weathering applications require extreme temperature swing to be the primary variable. For evaluation of extreme temperature affects, again one can turn to industry methods. It is important to note that for elevated temperature methods their application can be made redundant by the incorporation of elevated temperature tests in other aging methods.
Methods for testing include:
- ASTM D1211 – Heat and Cold Resistance
- ASTM D2247 – Head and Humidity Resistance
- ASTM C666 – Rapid Freeze and Thaw of Concrete
Resistance to Corrosion
Corrosion is the gradual degradation of refined materials, usually metals, into a more stable form. This reaction occurs naturally through chemical and/or electrochemical reaction but can be accelerated using laboratory practices.
ASTM International’s ASTM B117 – Standard Practice for Operating Salt Spray (Fog) Apparatus services as the principal corrosion testing guidance document.
ASTM B117 creates a controlled corrosive environment using a 5% salt solution that is atomized into a “salt fog”. Samples are left in this environment for pre-determined amounts of time, or until a failure is identified.
Another practice, ASTM D5894 – Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal uses both UV and corrosion chambers to produce a closer simulation of outdoor exposure. There is evidence that exposure to one element will affect the way a product reacts to other weathering agents. Materials are therefore exposed to alternating periods of UV and salt fog exposure.
Limitations of Laboratory Accelerated Weathering
Accelerated weathering practices have their limitations.
- Space: Chambers have limited space and so often only material samples are tested; the full complexity of a product and how each material may affect the other constituent parts is not
- Correlation: There is no agreed upon correlation between testing time and length of environmental exposure – e.g. some authorities say 1,000 hours of ASTM G154 UV equates to a year in Florida, but others think it’s double
- Singular Replication: Practices only recreate one environment, but real-life climates can vary drastically – e.g. Arizona is hot and dry, Maine is wet, and Florida is both hot and wet
However, proper design of the weather evaluation study can address these limitations.
Designing an Accelerated Weathering Study
When designing an accelerated weathering study, it is critical to review the following factors:
- Objective: The objective of an accelerated weathering evaluation is to ascertain how a piece of outdoor furniture will perform in its intended use environment. However, as previously discussed a foolproof correlation of laboratory and real-life exposure does not exist, thus it is advised to corroborate test results with real-life observations in the field. Furthermore, these methods are ideal when comparing one material versus another, and can be very useful in material selection
- Product Construction: A product’s material composition and construction are critical as materials react differently when exposed to varying types of exposures – concrete and stone can withstand sunlight, but are susceptible to cracking due to water absorption and freezing temperatures
- Primary Intended Use Environment: To address wildly varying environments, it is suggested to replicate the most severe use environment. Focusing on the most harmful exposures will limit a study’s lead time, cost, and sample requirements
- Criteria: It is imperative that an accelerated weathering study have quantitative criteria with results that can be used as a basis for evaluation and subsequent decisions. Just as weathering affects a product visually and physically, criteria can be established for both areas
Evaluation of Results
It is preferred to evaluate the furniture item by re-performing the loading, stability, and leg durability tests post exposure. However, limitations of chamber size often make evaluating the entire product difficult, making component level testing the best option.
Weathering practices typically do not specify evaluation procedures. One must look to specific component and/or attribute methods for guidance.
Once criteria have been identified they will be used to evaluate the product in the “as received” state. It is critical to establish this “as received” benchmark as the tests will be repeated afterward to ascertain changes as a result of the exposure.
Common visual evaluation methods include:
- Color: ASTM D2244 – Standard Test Method for Calculation of Color Differences from Instrumentally Measured Color Coordinates – a spectrophotometer is used to measure the samples color before and after the test
- Gloss: ASTM D523 – Standard Test Method for Specular Gloss – identifies gloss change
- Surface Corrosion: Standard Test Method for Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments – includes procedures to evaluate subsurface corrosion, surface corrosion, edge corrosion, and corrosion of non-uniform areas
Numerous evaluation methods exist that focus on physical changes:
- Paint adhesion – ASTM D3359 Standard Test Methods for Measuring Adhesion by Tape Test
- Elongation and Tensile Strength – ASTM D2370 Standard Test Method for Tensile Properties of Organic Coatings
- Flexibility – ASTM D522 Standard Test Methods for Mandrel Bend Test of Attached Organic Coatings
- Abrasion Resistance – ASTM D4060 Taber Abrasion
- Moisture Content – Primarily used for wood, a moisture meter can quantify changes in product’s moisture content, which can lead to warping or cracking
For a plastic outdoor furniture, ASTM has created specific standards:
- ASTM F1561 Standard Performance Requirements for Plastic Chairs for Outdoor Use
- ASTM F1838 Standard Performance Requirements for Child's Plastic Chairs for Outdoor Use
- ASTM F1858 Standard Performance Requirements for Multipositional Plastic Chairs with Adjustable Backs or Reclining Mechanisms for Outdoor Use
- ASTM F1988 Standard Performance Requirements for Plastic Chaise Lounges, With or Without Moving Arms, With Adjustable Backs, for Outdoor Use
With sales of outdoor furniture predicted to increase significantly in the next few years, manufacturers need to produce furniture that conforms to the expectations and demands of consumers. SGS has considerable experience in offering efficient and cost-effective testing solutions for outdoor furniture to help manufacturers bring quality, durable products to the marketplace.
To learn more, contact:
Senior Technical Manager - Hardlines
SGS - North America, Inc.
t: +1 973 461 1505