The biggest change in the coffee culture in recent years has been the way people prepare their coffee at home. An increasing number of households use single serve brewing (pods, capsules) for producing a fresh cup of coffee, resulting in an increased amount of waste. Replacing the current coffee packing materials is not straightforward, and obviously there are several challenges related to it. In this blog post I will play with the idea how microfibrillated cellulose (MFC) could support the development of new, more environmentally friendly, compostable or biodegradable coffee capsules.
The single-served coffee is often brewed from capsules made of plastic or aluminum, with or without a paper filter. There is a definite challenge when it comes to the recyclability of the empty coffee capsules, regardless the material(s) from which they are produced.
Importance of well performing coffee capsules
The packing of ground coffee requires accurate methods. Moisture, oxygen, and light will all affect the quality, but oxygen is the enemy number one. Oxidation of the acids, aromatics, and oils in coffee, meaning the essential components for the taste, will lead to a bad tasting cup of coffee. Ground coffee is often packed in plastic bags, containing a layer of aluminum or other high oxygen barrier products. In the single used capsules, the challenge is even bigger, as the surface of the packing is relatively large, related to the amount of coffee. Therefore, the packing material should have extremely low oxygen as well as moisture permeability.
Compostable and biodegradable coffee capsules
The most common commercially available compostable plastics nowadays are polylactic acid (PLA), polyhydroxyalkanoates (PHA) and thermoplastic starch. Unfortunately, many of them have only decent to low barrier properties. Also, there are challenges related to the strength and processability of the plastics. Despite these difficulties, several companies have already introduced their versions of either compostable or biodegradable coffee capsules, such as Ahlstrom, Lavazza and Ethical Coffee Company.
MFC as a barrier material in multilayer products
Unlike the compostable plastics, MFC shows excellent oxygen barrier properties. The following values, taken from a review article by Aulin et al., demonstrate that MFC is a much better oxygen barrier than, for example, PLA. Moreover, MFC also acts as an efficient oil barrier.
(cm3 μm/m2 day kPa)
|Unmodified MFC||3.52-5.03||50% RH|
|Carboxymethylated MFC||0.85||50% RH|
|Carboxymethylated MFC||0.0006||0% RH|
Clearly, there are also challenges; The barrier properties of MFC depend on humidity. One option to overcome this is to combine MFC with a more hydrophobic material. The traditional way to modify the properties of polymers is to mix different polymers to enhance the properties. As for MFC, one should also consider multilayer approach, since MFC, as a high shear thinning polymer, can be easily applied to surfaces, for example by spraying. MFC also has excellent adhesion to several materials. In particular on the ones containing functionalities capable of forming hydrogen bonding. Also, MFC has also successfully been deposited on more hydrophobic surfaces, such as PLA.
As we may have learned, MFC can act as an effective oxygen barrier when used together with moisture barrier polymers. I am quite optimistic that we will shortly see a coffee capsule containing MFC or other packages utilizing the notable oxygen and oil barrier properties of MFC.
Otto Soidinsalo works as a technical application manager at Borregaard. He has a Ph.D. in organic synthesis from the University of Helsinki and his working experience ranges from organic synthesis, cellulose ethers and its applications to nanocrystalline cellulose and microfibrillated cellulose.
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