Bio-based and renewable raw materials

Three different claims, often given the same name

“Bio-based” is used in the market to mean at least three things that behave differently on a press and in a specification. The first is measured bio-based carbon, where the carbon atoms in the material came from recently grown biomass and can be detected as such by radiocarbon analysis. The second is mass balance attribution, where a plant runs fossil and renewable feedstock through the same crackers and reactors and allocates a share of the renewable input to a nominated output, so the molecule in the drum is chemically the same as the fossil one and the renewable content sits in the chain of custody records rather than in the material. The third is a drop-in identical molecule, where a renewable route produces a substance with the same structure as its petrochemical equivalent, so performance is unchanged and only the origin differs. All three can be legitimate. They are not interchangeable, and a supplier statement that does not say which one applies has not said very much.

• Measured bio-based carbon. Physically present biogenic carbon, determined by radiocarbon methods such as ASTM D6866, with ISO 16620-2 for plastics and EN 16785-1 for products generally covering similar ground.
• Mass balance attribution. A chain of custody allocation, of the kind described in ISO 22095. Nothing in the product itself can be measured to confirm it, and the figure depends entirely on the allocation rules of the scheme used, so the scheme has to be named for the number to mean anything.
• Drop-in identical molecules. Same structure, same behaviour, renewable origin. These do carry biogenic carbon and will show up under ASTM D6866, so this claim overlaps the first one, but they change nothing about the formulation.

Vegetable oil in offset inks is a real history, and a different claim

Paste inks for sheetfed offset have used linseed, soya and other vegetable oils as vehicle components for decades, long before renewable content was a marketing subject. That history is genuine, but it does not transfer to the claims now being made. A sheetfed offset vehicle sets oxidatively in a high viscosity paste. Heatset web offset is not the same system: it sets mainly by evaporation of petroleum distillate from the vehicle, and the vegetable oil fraction there is smaller and does a different job. In both cases the renewable fraction sits in one component of one part of the formulation, and the pigments, driers, resins and mineral oil around it are unchanged. Liquid inks for wide-web gravure and flexo, narrow-web UV and LED-UV inks, and the coating families built around them are different chemistries: solvent borne resin solutions, water borne dispersions and emulsions, and acrylate systems, where those oils cannot simply be substituted in. When a vegetable oil heritage is quoted next to a percentage on a modern liquid ink or overprint varnish, the two are usually unrelated.

Bio-based polyols and acrylates

The renewable building blocks that matter for coatings are the ones that enter the polymer backbone rather than sitting alongside it. Castor oil derived polyols, sebacic acid from castor oil and azelaic acid from oleic acid, fermentation products such as 1,3-propanediol and succinic acid, and bio-derived alcohols esterified with acrylic acid all give resins and monomers that can be characterised by the ordinary methods: hydroxyl and acid value, molecular weight distribution by gel permeation chromatography, glass transition temperature by differential scanning calorimetry to ISO 11357-2, and solution viscosity. Epoxidised vegetable oil acrylates are established in energy curing systems as oligomers and flexibilisers; they are not reactive diluents, since their viscosity is high rather than low. What changes with these materials is usually reactivity, initial colour and odour, and the balance between flexibility and hardness. The long aliphatic chains that come with plant oils lower glass transition temperature, and the fatty acid double bonds that survive epoxidation and acrylation leave a film that goes on oxidising after cure. The answers are known ones: a harder or more functional co-resin to recover the hardness, a revised photoinitiator package and lamp setting to recover the cure speed, antioxidant and synergist adjustment for the yellowing. Each of them costs something in the recipe.

Rosin and shellac: the renewables already in the building

Rosin derivatives are among the largest volume renewable raw materials in printing ink and have been in use for well over a century. Rosin esters and rosin modified maleic and phenolic resins are standard binders in publication gravure and in many solvent flexo systems, and shellac remains in use in paper and board overprints where its gloss and hold-out are hard to match. Both are harvested products, so their properties move with source, season and grade in a way that synthetic resins do not, and both bring their own limits: rosin systems oxidise and yellow, and shellac is sensitive to heat and to alkali, in which it saponifies, and can block on reheat. A formulator working with these materials spends effort on incoming specification and on batch-to-batch consistency rather than on the renewable claim itself. Neither was adopted for its renewable origin, which is why they rarely appear in bio-based percentages unless someone has gone looking for a number.

Where renewable content costs performance, and where it does not

The cost is not uniform. Where the film has to survive heat, chemicals or mechanical work, renewable substitution is hardest. A softer binder lowers the temperature at which the surface starts to stick, which narrows the gap between a clean run and blocking or transfer. Chemical and stain resistance drop as aliphatic content rises. Oxidation of the double bonds left in plant oil derived chains drives yellowing, read as yellowness index calculated to ASTM E313 from instrumental colour measurement, and it shows most under a white or a light pastel. Rub and scuff performance, usually assessed on a Sutherland type rub tester (the ASTM D5264 practice has been withdrawn, although the test itself remains the common shop reference), and tape adhesion by the cross-hatch method of ASTM D3359 where film build and substrate suit it, are where the difference tends to appear first. Where the film’s job is optical, or where the substrate is forgiving, the cost is often close to zero: paper, board and corrugated work, matt and satin overprints, and primer layers on absorbent stock tend to tolerate renewable binders well. Process conditions need not change. Wide-web gravure inks are typically run in the region of 15 to 25 seconds on a 4 mm efflux cup of the DIN pattern, which is a comparative press-side reading rather than a standard measurement, since ISO 2431, which superseded DIN 53211, specifies its cups for flow times of roughly 30 to 100 seconds. Narrow-web UV flexo curing typically calls for something in the region of 60 to 120 mJ/cm² depending on colour and film weight, with peak irradiance and lamp spectrum mattering as much as dose, particularly under LED-UV, where a figure borrowed from a mercury lamp does not carry across. Both ranges are industry-typical, not an Arctic measurement and not a guarantee, and a well built renewable system should sit inside the same envelope rather than demand a new one.

A percentage without a basis is not a number

This is where most bio-based claims fall apart. A renewable percentage can be quoted on the total wet formulation, on the dried solids, or on the binder alone, and the same material gives very different answers. Take a resin whose bio-based content is 40 per cent by mass, used at 30 per cent of the solids in an ink that is 35 per cent solids: it contributes about 12 per cent of the dried film and about 4 per cent of the wet ink. None of those three figures is dishonest, and none is informative on its own. A bio-based carbon figure cannot be put through that arithmetic at all. ASTM D6866 returns the biogenic fraction of the carbon in the sample tested, not a fraction of its mass, so a carbon-basis percentage has to be converted before it can be combined with mass fractions. The method matters as much as the basis. Because radiocarbon measures carbon, inorganic pigments and extenders carry little or no organic carbon and largely fall outside the result, while carbon black and organic pigments are fossil carbon sitting in the denominator, pulling the measured biogenic fraction down; carbonate fillers need separate handling, because their carbon is not biogenic either. A heavily pigmented ink and a clear varnish are therefore not comparable on that basis. It also matters whether the wet ink or the dried film was submitted, since the solvent leaves the film and takes its carbon with it. Mass balance figures are not measurements at all and cannot be verified on the product. Any percentage a converter is asked to rely on should carry three things with it: the basis, the method, and whether it is measured or attributed.

Arctic’s position

Arctic makes no bio-based content claim for any product in the Arcova, Arcoflex, Arcray, Arclear or Arcfibre families, or for any other family, and nothing on this page should be read as one, or as a certification, approval or compliance statement of any kind. Renewable raw materials are treated as any other candidate raw material is: evaluated in the technical centre and laboratory in Greater Noida against the same methods as the incumbent material, on the same substrates and at the same film weights, with a candidate expected to hold adhesion, rub, block and heat performance before its origin becomes relevant. Across a portfolio of over 550 products, the practical constraint is often consistency rather than chemistry, since harvested and fermentation derived inputs vary more than petrochemical ones, and a production line built for batch-to-batch consistency has to absorb that variation rather than pass it to the press. If and when Arctic has a measured renewable content figure to state, it will be stated with its basis and its method attached.