Plant-based materials hold surprising versatility and one of their most surprising applications over the last decade has been in optical lenses and eyewear frames, where plastics currently dominate.
Eyewear globally reached $142 billion dollars in sales in 2022, presenting a huge consumer market for biobased material manufacturers. What’s more, the optometry industry and consumer market are increasingly supportive of more sustainable production.
Plastics became the norm in eyewear over the 20th century. For centuries before that, lenses were made from glass, stone, or crystal: the only materials that had the transparency, scratch-resistance, and durability for use in corrective eyewear.
The invention of oil-based plastic changed the optical eyewear industry, which leapt on the new polymerized methyl methacrylate (PMMA) in the 1930s. In the 1940s, an acrylic resin made of allyl diglycol carbonate (CR-39), which originated as a liner for B-17 bomber fuel tanks, became a common lens material.
Plastic became popular in eyewear for two reasons. The new chemical industries scaled in the 1900s. They were then helped along by the war economies of 1914 and 1939, when military demand made oil as fuel and feedstock much cheaper.
Cheap, abundant oil-based materials were a windfall for the eyewear industries. It just so happened that plastic lenses gave a higher index than glass. This is one of the most important properties for a lens material since a higher index means it can be thinner while offering the same sight-correcting, light-bending properties. Another cost-lowering advantage of plastics over glass was they did not require surface chemical treatment or heat tempering to improve impact strength.
Plastics hold a host of other technical advantages: polycarbonate lenses naturally absorb all UV radiation below 380 nanometers while glass must be treated with chemicals to achieve the same effect. Plastics are also less prone to scratching and are hypoallergenic.
Acetate is now the dominant plastic used by eyewear manufacturers. Colours can be incorporated into the material, rather than sprayed on and liable to chip. The material also has a shiny gloss finish that is hard to achieve with other plastics.
The evolution of bio-based lenses
With all the advantages of polymers, glass-based eyewear does not look likely to make a comeback. Yet the carbon footprint of petroleum feedstock and the huge amounts of plastic waste that come as part of eyewear manufacturing means there is now appetite for the industry’s material mix to change once again, this time using renewable sources.
One of the earliest biomaterials developed for eyewear lenses is MR-174, made by Mitsui Chemical. It has a high refractive index lens, meaning they bend light effectively even when the lenses are thin, and can be 80 to 90 percent biomass. It is estimated that producing MR-174 produces 326 kg less carbon emissions per 100 kg of resin compared to the oil-based version of the material.
However, the major drawback is that MR-174 is not biodegradable and not recyclable. Lenses from the material therefore have a limited lifespan and are likely to end up in landfills. This could also mean its full lifecycle emissions work out larger than oil-based lenses: polycarbonate is recyclable.
Bio-based lens production has made progress on recyclable alternatives. Hong Kong bioplastics producer Wingram developed the recyclable bio-acetate S70. From 2022, Hong Kong lens manufacturer Yuehong Optical began to offer glasses with this material.
S70 was only recently commercialised but already it has made its way into the consumer eyewear market. OJO Sunglasses, a Japanese-inspired eyewear brand founded in 2012, has used the material for the frames in their eco range of biodegradable sunglasses.
Many other brands are bringing bio-based acetate lenses to the wider market, making it relatively easy for the consumer to find more sustainable options.
Italian eyewear company De Rigo has managed to develop a biodegradable, partly bio-based lens. Around 40% of their nylon lens is made from castor plants. It has won a string of contracts with high-end brands for its bio-lenses. One is luxury fashion house Mulberry whose 2021 Penelope and Belgrave sunglasses are made from material. In the same year, De Rigo announced a collaboration with luxury jeweller and watchmaker Chopard.
Ray-Ban has also introduced bio-based nylon lenses into their collection, composed of at least 40% biological content.
Biobased lenses are moving into eyewear at lower price points too. Millmean, an optical company in the UK, is now aiming for B-corp status on the back of their efforts to use sustainable materials in their collections. They aim for all Continental Eyewear to use recycled or biodegradable lenses.
The growing popularity of bio-based frames
These days, consumers would be hard pressed to find glasses with non-plastic frames thanks to the materials’ shape-shifting moldability and ability to retain colour. However, market penetration of bioplastics is far more advanced in eyewear frames than in lenses, which have highly technical specification requirements.
Bio-based acetate has started to enter the eyewear frame industry at all price points. At the higher end, Mulberry made 100% of their autumn winter 2023 collection from the plant-based version of the plastic, with feedstock from seed fibres from cotton and wood fibres from conifers and deciduous trees.
At lower price points, British retailer SpecSavers has its ReWear collection offering glasses made from various sustainably sourced materials, from recycled bottle caps to bio-acetate. Mid-range US eyewear brand Arnette have gone further, using bioplastics in the frames of all their models since July 2019.
A large portion of the frame bioplastics on the market today comes from the producer Mazzucchelli, which launched its patented M49 bio-acetate in 2010. The material uses vegetable-based plasticisers to increase its biodegradability. Many eyewear manufacturers have adopted it in their designs, including British frame designer Eyespace Eyewear, ethically inspired British brand eco beach, fashion conscious Barner, and the mid-market boutique Raen.
The Italian brand that has managed to carve out a rare position for a bio-based plastics producer as a name associated with luxury and craftsmanship. Its reputation is helped along by the fact that the company started out in 1849 manufacturing combs and buttons from bone and shell for the fashion industry. Now, it specialises in replicating the fashion industry’s favourite plastic using renewable feedstock.
In an unstable economic climate, however, the higher costs of producing sustainable eyewear can make it harder for brands to make their ranges fully bio-based. Pala Eyewear was one of the few brands focused on making frames and lenses from sustainable materials and adopted Mazzzuchelli’s M49 in its products. In September 2023, the B-Corp is closing after seven years in operation, citing market pressure and high inflation pushing down consumer spending.
However, other names are filling Pala Eyewear’s shoes. Neubau announced its biobased line that is 3-D printed from its own materials like natural3D (100% biobased) and naturalPX (65% biobased). The company’s aim it says is to demonstrate that high end need not be incompatible with respect for people and planet.
Eastman fills recycling gap
There is a catch to the pollution-reducing potential of bioplastic eyewear. Right now, there are promising biodegradable materials on the market but a severe lack of specially equipped facilities capable of breaking them down into reformable components at the end of their product life.
Wingram’s S70 and Mazzuchelli’s M49 are biodegradable according to ISO standard 14855, which marks out a substance that breaks down under controlled composting conditions after 180 days. This means they need to be processed in specially equipped recycling plants. Yet because bio-acetate recycling capacity is so low, lenses and frames made from them are just as likely to hit landfills as their oil-based counterparts.
One company is filling this gap. From 2022, Eastman Chemical Company began collecting bio-acetate waste from the eyewear industry to process using their molecular recycling technology. Their method is targeted at hard-to-recycle materials.
In a 2022 supply partnership, Eastman agreed to collect waste from Mykita, an eyewear brand that is aiming to transition towards sustainable materials. Mykita will in turn buy Acetate Renew, a material produced by Eastman from 60% sustainably sourced wood pulp and 40% certified recycled acetate. The final acetate sheets used to make MYKITA frames consist of 70% Acetate Renew flakes and 30% additives. Another eyewear company it is working with is Warby Parker, from whom Eastman are collecting discarded demo lenses to turn into Eastman’s Acetate Renew material.
Brooklyn-based Lowercase are an innovative sustainable eyewear brand that are also using Eastman’s wood pulp-derived acetate for fashion-conscious frames all worked in small batches at their New York workshop. The company offers a good blueprint for a materially mindful, localised supply chain equally focused on giving consumers aesthetic choice.
Material innovation and more recyclers needed
The eyewear market can be a challenging one for new biobased entrants. In many regions, including the EU, UK, and the US, spectacle frames and lenses are considered medical devices and must demonstrate quality, durability, and safety through numerous lab tests.
With such restrictive criteria, there are only a few biobased options that do the job. This signals the need for more feedstocks and material mixes to come onto the market.
Although an increasing number of manufacturers are starting to buy from bioplastics suppliers, there are still only a handful of patented substances, limiting choices for eyewear producers There are also very few producers with the know-how across optical lens and frame manufacturing and material science so that they can develop renewable materials that match the performance oil plastics at a viable cost.
At the other end of the eyewear life cycle, biobased plastic recycling infrastructure needs to catch up with the spread of novel bioplastics. A lack of bioplastics recycling infrastructure encourages more material extraction, albeit of renewable origin, to make more products.
Low recycling capacity is not just a problem for the eyewear industry but is a more general issue across bioplastics, holding back the sustainability gains offered by plant-based polymers. Right now, it is incumbent upon individual eyewear manufacturers to maximise the sustainability of their products. One way to do this would be to offer customers a drop-off service for used glasses and forge partnerships with specialist bio-plastic recyclers capable of repurposing the material.