“Lightproof bottle” for the dairy Industry

newoldmilk

On the left is the new lightproof bottle, on the right is the standard bottle. The Auckland skytower is in the middle 🙂

(I am not employed by Fonterra and these are not the views of my employer, I’m just curious about the science)

Anchor, Fonterra’s flagship brand, announced that they have “engineered New Zealand’s first recyclable triple layer, light-proof milk bottle.”1

They were kind enough to send me their media release which had some basic information about the advantages of the new bottle.

I was also able to get my hands on one of these new bottles thanks to an anonymous donation.

According to Fonterra Brands Managing Director Peter McClure “Our triple-layer light proof bottle is the most significant innovation project we have undertaken at Fonterra.”1

milkvssaw

There is only one way to find out what’s inside this new bottle – let the dissection begin!

Apparently the new bottle is the “same shape and weight as the current design. It will also be recyclable.”2 (note a spokesperson from Fonterra has not stated that the new bottle weight 1g more than the old bottle)

Olaf van Daalen from Fonterra says that “light damaged vitamin B2, which went on to react with proteins and fats and change the taste”.3

I’m always fascinated by the introduction of new materials to the products I buy, so I thought I’d go through the basics of milk bottles and how I think Fonterra have designed these new bottles (I should state that I do not work for Fonterra, and everything written here is based on my knowledge as a materials scientist, and the media release I have seen).

The first question we need to ask is what are milk bottles made from?

If you turn your milk bottle over you should see a symbol with a number inside a triangle like this:

Left picture is the standard anchor milk bottle, right picture is the new Lightproof bottle, both are labelled as HDPE. The number within the triangle indicates what type of plastic the bottle is made from. You can look up which plastics we recycle in New Zealand here

This is the recycling number and tells us what the bottle is made out of.  For milk bottles it is usually number 2 which stands for HDPE or High Density Polyethylene.   Polyethylene is a very common polymer (polymer is the scientific term for plastic) and comes in two forms, High Density and Low Density (LDPE).  The high density form is much stronger than the low density form which is used for common items such as shopping bags.

Fonterra state that their new bottles are recyclable implying that all three layers are made from HDPE rather than incorporating Titanium dioxide into the HDPE which would would be another way to make it more light resistant (think sunscreen for milk bottles).  We can see when we turn over the new bottle that it is indeed made from HDPE as it was before.

The next question is how do they make this new bottle?

blowextrusion

Extrusion blow molding is the most common way for plastic bottles to be made for commercial products.

Milk Bottles are made by extrusion blow molding, where we take HDPE powder, extrude it through a screw while adding some heat to soften it to make a soft little rod (called a parison) around a tube.

This rod is placed inside a mold with the shape of the bottle and pressurized air is blown through the tube into the rod causing the soft polymer to coat the sides of the mold.  The polymer is cooled which causes it to solidify, and the two halves of the mold separate to reveal the hollow milk bottle structure.

To make a triple layered bottle, 3 separate extruders will be needed to create each layer (called co-extrusion) which all inject to create a triple layered rod.

This probably won’t add too much cost or extra total material to the manufacturing process if the bottles are made in a factory with triple screw extrusion facilities.

The third question is what will the layers be?triple layer2

Going back to the fact that it is recyclable and the recycle number indicated that it is all made from HDPE, my guess is that they will use different dyes to absorb and reflect light.  A recent article5 states they use carbon black in the middle as a black dye and Titanium dioxide (most likely used as a pigment called titanium white) for the outer layers.

Most people expect their milk bottle to look white which represents the white colour of the milk inside, however black HDPE has much better UV (ultraviolet) light resistance which is what Fonterra are trying to improve.

micromilk3

Optical microscope image of the cross-section of the new lightproof bottle showing three distinct layers.

If UV resistance is what is desired, then a metal film coating would have been an option (think about potato chip packets), however this would make the bottles too difficult to recycle, so I’m glad that Fonterra didn’t decide do that.

So I dissected the new bottle to take a look at the layers inside, and I found what I expected, three layers, two white ones (the outer one was significantly thicker to make your bottle look more white on the outside) and a black middle layer.

The only problem with having a black light resistant layer in your bottle is that now you won’t be able to see how much milk you have left!

Finally, is it really Lightproof?

The word “lightproof” was what caught my interest in this article. Polymers are naturally amorphous in their structure (so they have lots of gaps for light to pass through, as opposed to being crystalline like most metals) which means that light usually can pass through quite easily.  To have a totally lightproof polymer that could block all wavelengths of light would be a true advancement in materials engineering – however upon closer inspection I find that the term is actually trademarked on the official press release (although the TM has been omitted in any news article I’ve seen), so it’s not really light-proof, but they are calling the bottle technology LIGHT PROOFTM  to emphasise that it is more UV light resistant than standard milk bottles.

Phew – that was hard work, I’m off to find a cookie to go with that super fresh, minimal vitamin damaged milk!

UPDATE!

I’ve seen a lot of common questions in the social media space that I’d like to comment on:

1 – Why don’t we just go back to using the rectangular Tetra Pak milk cartons, they were lightproof.

Tetra Pak use a product they call Tetra Brik for packing milk, which consists of different layers of the plastic low density polyethylene (LDPE) and cardboard (the different materials make it hard to seperate them on recycling).

milkcartonActually, they are not lightproof as they are just made from paper and transparent plastic, both of which let light in.  This means that they are classed as light resistant and they are also not recyclable New Zealand wide (currently only Auckland and Christchurch recycle stations will accept Tetra-Pak cartons) due to the mix of materials making them hard to separate into their original components.  I cut one open to take a look, and in New Zealand it is just the paper and LDPE version, however Tetra Pak also make cartons for long life milk which also have a layer of aluminium in the middle.

2 – Why don’t we just use glass milk bottles?

Glass can be recycled, however it takes a lot more heat and thus energy to recycle glass.  If we were to re-use the glass (wash the glass bottles and have them re-filled) then this would be a better option for the planet, but probably impractical in our disposable society – when was the last time that you re-filled your glass bottle rather than just put it in the recycling bin to be crushed and remade? Glass is also really heavy (40% of the weight of a bottle of milk is glass for 600ml bottle) which means that transport energy costs are high and its not a good thing for the environment to be shipping around lots of empty glass bottles.

Glass is also transparent so it doesn’t solve the vitamin degradation issue.

3 – How much BPA will leach from these new bottles?

BPA (bisphenol A) is a chemical used primarily in polycarbonate products.  These new bottles are still made from HDPE which is the same material that they were made from before, with the addition of a new colour (black) so BPA is not an issue in these bottles.

4 – Are these new bottles going to be worth the extra cost?

The extra cost in producing these new bottles will be minimal, as the materials are basically the same, the only difference is that the manufacturing process will be a 3 screw extrusion rather than a single screw extrusion process, and there is probably a slightly higher cost in adding black dye to HDPE.  As a consumer, if you have been happy drinking your milk in its current bottle, if you drink the whole bottle well within the shelf life, and if you are not concerned about obtaining your nutrients from milk, then the new bottle may not be an advantage to you.  We all still have choice in our supermarkets, there are plenty of options, so you don’t have to pay the extra if you don’t think you need it – it’s all about consumer choice.

5 – Why don’t we just keep the fridge door shut and keep the light off?   Then we won’t need this bottle.

The milk that you put in your fridge will have been exposed to a lot of different types of light before you take it home, including UV light when being transported from the bottling plant to the delivery truck, as well as from that delivery truck to your supermarket.  While it is sitting on the shelf in the supermarket waiting for you to take it home it will be exposed to the fluorescent lights in the shop (unless you shop in the dark), all of which would have degraded your milk before you even got it home.

Studies show that milk lost 90% of the added Vitamin A and 8% of the Vitamin B2 from 24 hours exposure to fluorescent lighting used in supermarket fridge displays.6

6 – Will the milk taste different?

I just carried out a very unscientific test with some of the people I work with.  It was a blind taste test where anchor blue milk kept in a standard bottle and the new bottle were tested and the comments on each were noted.  Out of the 42 people I carried out this taste test on, 100% of the respondents aged 30 years or under (28 people) said that they could taste a significant different, that the milk in the old container tasted sweeter and that the milk in the new container tasted much more creamy.  They were divided in which they preferred, some saying that like liked the old bottle milk as it tasted more “normal” some saying they preferred the new bottle milk as it tasted “creamier” and reminded them of the taste of hot milk.  All of the respondents aged over 30 years (14 people) couldn’t taste any difference between the two milk samples, or if they could they said it was subtle and not noticeable.

Results from my blind taste test showed that those under 30 could taste the difference

Results from my blind taste test showed that those under 30 could taste the difference

Fascinating – makes me wonder what the effects of age on our taste buds are, however I don’t have time to get into that!

7 – Can you really recycle black HDPE?

Yes, HDPE packaging is capable of being recycled into new products and the majority of HDPE that is recycled in New Zealand comes from bottles.

The bottles leave your recycling bin and are taken to a central depot where they are sorted into different grades, the uncoloured bottle grade and the coloured bottle grade like cleaning product bottles.

There is no difference in the amout of energy it takes to recycle coloured or non-coloured HDPE, both are transported to a Materials Recovery Facility (MRF) and sorted into two streams:

• Opaque or “natural” – milk and juice bottles (HDPE)
• Coloured bottles – laundry, cleaning, juice and flavoured milk bottles (HDPE)

Coloured HDPE containers are sorted at the recycling centres and processed into non food grade items, such as milk crates, garden stakes and pipes.8

However a recent article in the New Zealand Herald4 quotes the spokesperson from Reclaim a recycling company as saying “In terms of the value of the resource as a recyclable resource, they’re less valuable. But they’re more expensive and more resource-dependent to make, because they’re using three different types of HDPE plastic to make those layers, so [the bottles are] heavy on resources and quite inherently wasteful”.

However with this new bottle, Fonterra have also reduced by 10% the amount of waste to landfill from their Takanini site by changing to a recyclable label backing.7

What we have to remember is that New Zealand law prevents recycled plastic from coming into contact with food, so your milk bottle won’t be recycled into another milk bottle whether it is a lightproof bottle or a normal bottle, it will just be recycled into a non-food containing product.  There is however a higher price paid for natural coloured bottles compared to the opaque and coloured bottles as they can be recycled into a greater number of things.

And finally:

I have to drink a lot of milk to write this blog….just saying 🙂

milkset

Media references:

1 – http://tvnz.co.nz/business-news/anchor-launches-game-changing-new-milk-bottle-5376482

2 – http://www.3news.co.nz/Fonterra-launches-light-proof-bottle/tabid/423/articleID/291229/Default.aspx

3 – http://www.stuff.co.nz/business/farming/8454933/New-milk-bottles-on-the-way

4 – http://www.nzherald.co.nz/business/news/article.cfm?c_id=3&objectid=10880559

5 – NZ Tcchnology article “Let there be no light” Volume 48, No 3, April 2013

6 – Shipe W.F., Senyk G.F. 1981 “Effects of processing conditions on lipolysis in milk”, J. Dairy Sci, 64 2416-2149

7 – http://www.wasteminz.org.nz/news/2994/

8 – “Recycling Guide for Fillers Marketing in HDPE” www.aoteaplas.co.nz

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18 Comments

  1. http://www.tetrapak.com/Document%20Bank/Products_and_services/packaging/8690_pack.pdf tetra pak lets it from 3-0.5% of light which does not have any effect on quality of milk as per this document.
    It is recyclable in Auckland and only reason that it is not recycled anywhere else is because there is not enough used for packaging

    I believe even placing this into landfill is much better than plastic bottles.

    I want to see test with strong light bulb inside of the bottle/tetra pak side by side. (I will do one myself if you dont just need to get hold of one of these bottles)

    Fontera is only trying to lengthen store shelf life as once milk is in the fridge at home it does not get much light at all!

    Tetra pak – you dont transport air when empty as you do with plastic bottles

    Tetra pak mainly made out of cardboard/pines RENEWABLE! rather than plastic !

    Reply

  2. Thanks Michelle,

    The bottle is not composed of HDPE only (by Fonterra’s own admission in this months (April) NZ Food Technology article, p3), the additives which render the bottle lightproof are carbon black (not HDPE) which form the black middle layer and white Titanium dioxide (a white colourant which is also not high density polyethylene) which renders the inner and outer layer white opaque.

    This makes the bottle harder to manufacture (addition ingredients and co-extrusion) and harder to recycle (v HDPE only) due to the increased complexity introduced by the triple layer (reduced options as to what the material can be recycled into (as you point out with reference to detergent bottles).

    Regards

    Reply

  3. As a small town resident who spent years making everyone recycle I am gutted about these new bottles. It is only just viable for a truck to collect the clear bottles. These will become landfill. Nice work anchor

    Reply

  4. Have changed from Anchor because of the new “improved” light proof bottles. My grandkids do not get the shake the bottle test & shake till the bottle is filled with froth then no one can see how much is in it. 2 little kids now no longer get paid to check the milk before we go shopping. Will have to find some other chore for them to earn money for an ice block when I take the grocery shopping or change brand which is the way I have gone

    Reply

  5. Both carbon black and titanium dioxide are pigments not dyes, i.e. they are fine insoluble particles which do not combine chemically with the bulk material.

    I suspect the titanium dioxide whitener will prevent these bottles from being able to be recycled into black plastic, so the bottles can only be turned into very low value gunge-coloured plastic.

    I imagine the real motivation for the three layer bottle is to allow the later use of very low cost gunge coloured recyled plastic for the middle layer of the bottle.
    Whenever using recycled plastic in food containers has been discussed in the past I have seen the requirement for the “three-layer solution” mentioned as the economic barrier. The ongoing rise in oil price and improved manufacturing technology may have made it economic, along with the marketing solution of the “lightproof” angle. Supermarket HID and fluoro lights do give off UV so the UV degradation story is not implausible.

    The opaque-ish titanium dioxide-loaded outer layer blocks most of the light on its own, making the dark layer less relevant than it might be.

    The innermost layer may be white not just for visual appeal (flavoured milk has been sold in pure black bottles) but to allow quality assurance of the continuity and thickness of the inner layer, since the real purpose of the virgin inner layer is to protect the food from the risk of contaminants which might get into the recycled plastic stream from e.g. pesticide containers.

    If all the above is correct it would make PR sense to use all virgin plastic for a start, and not switch to a recycled inner layer until after the initial public discussions has died away.

    Reply

  6. I heard a Fontera Spokesman reported as saying that the new bottles contain “only” an additional gram of plastic, which is contray to this article. I wonder what percentage increase this represents and how many tonnes it adds up to when multiplied by annual sales – It could be many many hundreds of tonnes!!! (Example: 4.5 million people, if 35% buy Anchor, and 40% of them Buy 2 Litre bottles and they use one bottle per week = 30,000 tonnes a year of extra plastic used)

    Reply

  7. What about the fact that HDPE breathes like crazy and that air passing into and out of the milk is a greater cause of taint than UV? This also makes a mockery of their freshness seal as the bottle is breathing the entire time.

    Reply

  8. I think you’ll find that fonterras own website is claiming the product to be “100%” light proof, surely that would be false advertising according to your article ?

    Reply

    1. They are making that claim based on a reference to a set of data as follows:
      “The samples were tested for diffuse spectral transmittance by the Measurement Standards Laboratory of New Zealand a division of Callaghan Innovation Research Limited, March 2013”

      As they do not state the wavelength of light that they tested, I have to assume that the bottle was lightproof when tested with diffuse spectral transmittance for the wavelengths that they tested for which you would hope to be the same wavelengths that we know causes damage to milk.

      Reply

  9. This has been very helpful! Thank you very much. You make your statements clear to understand but at the same time your statements are factual and worth reading! Thanks again!

    Reply

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