Last June, I took part in the InnoCentive Challenge # 9933575 - Polypropylene Packaging Film Replacement. I submitted a written proposal for novel packaging materials to replace polypropylene films, providing a better biodegradability and the same or greater moisture barrier. Since the Seeker Scientists have chosen not to employ the solution that I submitted, I am now placing it in the public domain for all to see and use freely if it suits them.

Summary
1. Best Replacement for polypropylene packaging film is a polypropylene film with some properties that are different such that the problems that polypropylene films cause in land fills are solved.

2. There are many standards and definitions of bio-degradability. These standards do not meet real life needs of having matter in landfill bio-degrade.

3. For land fill to fulfill their desired purpose, it is necessary that society pays the cost of aerating them and cultivating microbes inside them. Till that time the improved polypropylene film will only aid to limited extent in improving the bi o-degradation of waste. It aids by disintegrating into smaller pieces and allowing air, moisture and microbes to reach to other boo-degradable materials that are in the landfill.

4. The improved polypropylene film can be obtained by three broad methods described as Plan A, Plan B and Plan C respectively.

5. Under each plan a large number of families of material are described, some of which will result in the improved polypropylene film.

6. Family of materials in order of being further away from bio-degradable.
Sugars
Starches
Carbohydrates
Oils and fats
Chlorophyll, cellulose and lignins
Viscose
Proteins
Bone marrow

7. Each plan is designed to be very easy and in-expensive to implement at a lab level.

No consideration has been given to how to scale up to full factory production level.
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Best Replacement for polypropylene packaging film
is a polypropylene film with some properties that are different such that the problems that polypropylene films cause in land fills are solved.

If such a film can be found, indeed it would be the best replacement to the existing polypropylene film.

This solution outlines three alternate plans for finding such a polypropylene film.
It lists families of materials that can be utilized to generate the replacement polypropylene film.

The families do not have any metals in them and are naturally occurring organic compounds or products closely derived from them.

Finally the three solutions are so designed that they can be tried out in a lab in an inexpensive manner.
Issues of scaling up are ignored in the present solution.

Properties of present polypropylene film
The present polypropylene films have the following desirable properties:
Transparent
Sparkling
Water tight
Air tight
Light weight i.e. covers a large area for unit weight

The undesirable properties are:
Very slow to bio-degrade
Photo degradable under long UV exposure.

Biodegradability – different definitions.
Bio-degradability is big business.
This has lead to different definitions/ standards as well as a different standard bio-compostable.
Also the differences between aerobic bio-degradation and anaerobic bio-degradation are exaggerated /praised as if methane is not an natural compound.
ASTM D6400 - Test for Compostability prescribes those properties that are required to determine if plastics and products made from plastics will compost satisfactorily, including biodegrading at a rate comparable to known compostable materials.
D6868 - Biodegradable Plastics is very similar to ASTM D6400
European Standard EN 13432: has two different requirements
1.Proof must be made that at least 90% of the organic material is converted into CO2 within 6 months.

2. Disintegration in compost: After 3 months’ composting and subsequent sifting through a 2 mm sieve, no more than 10% residue may remain, as compared to the original mass.

Under all these tests/standards existing polypropylene film will not be regarded as compostable /bio-degradable.

Photo degradation of polypropylene films
When exposed continuously to sunlight for a period of about six months polypropylene films start cracking up and break into powdery bits that have very low strength.
When polypropylene films have various oxidants incorporated in them, this process is much faster.[See http://www.ncbi.nlm.nih.gov/pubmed/18975797]

Typical life cycle of a polypropylene film
Obviously there will be variations from the time frame given in this description which is not based on any scientific study but is based on personal observations of a tiny portion of the United States.

The description helps to establish the framework used to seek the solution.
A typical package with a polypropylene film is displayed on the shelves of a supermarket within a fortnight of its being so packaged.
It sits on the shelf for about a week.
The package gets opened in a house with two to three weeks of its purchase. The opening of the package results into a few strips that are long but about one inch thin. The rest of polypropylene film is torn into two or three parts which are bigger than six inches by six inches.
Within a week of being torn apart, the pieces of the polypropylene film are dumped into a land fill.

Everyday a fresh layer of dump gets added on its top.

Much before photo degradation can effectively break it down, it is so deep down that no further degradation takes place.

It is also a barrier to bio-degradation of other materials that it surrounds.

Definitions are not valid in real life.
In the paragraphs above I have not reproduced any definitions of bio-degradability and photo-degradability. That was deliberate for the definitions are of no value to real life and in fact mis-direct the efforts toward a better life.

They mis-direct because, normal citizens believe that if they use bio-degradable materials, the material will degrade.
But in fact , in the land fill the bulk of the material mummifies as the layers above it seal off the bio-degradation and preserve the material intact after a small decay.

University of Arizona who dug a landfill has the following to say :
“Many products that are biodegradable in soil – such as tree trimmings, food wastes and paper – will not bio-degrade when we place them in landfills, because the artificial landfill environment lacks the light, water and bacterial activity required for the decay process to begin.

Image: Biodegradable waste

The Garbage Project is a study of waste conducted by a group at the University of Arizona, USA. The project has unearthed from landfill hot dogs, corn cobs and grapes that were 25 years old and still recognisable, as well as newspapers dating back to 1952 that were still easily readable!

The solution attempts:

The solution does not attempt to find a replacement for polypropylene film that will be bio-degradable in the conventional sense.

It looks at a more limited (but perhaps a more effective solution) that will attract microbes to the film and will induce the microbes to punch holes in the film so that the the polypropylene film no longer protects other more readily bio-degradable materials from undergoing bio-degradation in the land fill. The polypropylene film with holes and perhaps broken into smaller areas will allow air, moisture and microbes to penetrate deeper into the landfill and breakdown more of it.

The three Plans:
The improved polypropylene film can be obtained by three broad methods described as Plan A, Plan B and Plan C respectively.

Under each plan a large number of families of material are described, some of which will result in the improved polypropylene film.

Each plan is designed to be very easy and in-expensive to implement at a lab level.
No consideration has been given to how to scale up to full factory production level.

Before the three plans are discussed , I discuss the families of materials that each plan will use.

Bio-degradability and the families of materials.
Though science knows of many types of diverse microbes that have very many digestive systems and can thrive in near impossible environments such as high sulfur environment near the ocean floor, for real bio-degradability on earth, we are essentially counting upon microbes that mimic the digestive system of human beings.

It is well known that sugars can be directly used by cells to obtain energy and the waste products are carbon dioxide and water.

Family of materials that are being listed below are roughly in the order of being further away from being digestible or being bio-degradable.

Sugars
Starches
Carbohydrates
Oils and fats
Chlorophyll, cellulose and lignins
Viscose
Proteins
Bone marrow

The properties of all these materials are well known to science and I will not waste time in re- describing them except occasionally pointing out a few properties.

Sugars
Ordinary white table sugar is an excellent material to start with. It need not be refined or even bleached. It has a melting point of 140C to 160 C which is very close to that of polypropylene.
Thus the two can be co-melted and blown together. On cooling it forms a thin film. When it is spun in a small centrifuge it results into long extended fiber like candy very popular with kids.

Brown sugar, dextrose, fructose, glucose are all candidates for the replacement as all attract the microbes to themselves.

Starches
Ordinary household cooking prepares food for human digestion by converting carbohydrates to starches. Human body has the enzymes that convert starch to sugars.
Ordinary starches are white soluble powders and when dissolved, heated and cooled they form transparent stiff films.
There are many cheap sources of starch including corn starch.
Though not a starch, the kernel of a corn cob has many properties that make it bio-digestable. It is about 60% cellulose rest being lignins.

Carbohydrates
Carbohydrates come in huge varieties with differing physical properties and readiness to convert to starches.
They all are bio-digestable by microbes.

Oils and fats
Oils and fats have many properties that do not make them an attractive candidate. They are likely to smear the underlying package under the improved polypropylene film.
But there are many very cheap sources of oils and fats such as residue from expeller oil or discarded engine oil that make a case for considering them under the three plans.

Chlorophyll, cellulose and lignins
Most sources of cellulose and lignins are likely to have associated chlorophyll with them. Chlorophyll is essentially not bio-digestable. However, if the improved polypropylene film gets a green tinge from natural chlorophyll, it will be an excellent marketing point with the general public.

Cellulose and lignins are difficult to mangle physically and are not readily bio-digestable. However Ruminants are mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through bacterial actions.

Since these cellulose and lignins digesting bacteria are in a isolated place in animals, it may be possible to cultivate them in landfills also.
See http://link.springer.com/article/10.1007%2FBF02825659#page-1 for an attempt to make an improved polypropylene film using lignins.

Viscose
This industrial product made from cellulose and lignins is an excellent candidate to consider for the improved polypropylene film. It is transparent and can be made into a film. It can be co-melted with polypropylene. Left intact, it provides licking effect for tiny bits of moisture to pass through. It bio-degrades creating holes.

Proteins
Proteins are large chains of amino acid residues and are essentially not bio-degradable in an aerobic manner. In anaerobic conditions they release methane gas.

However they contain essential chemicals that some microbes use to further bio-degestation of other materials listed above.
In tiny quantities, they be useful to make an improved polypropylene film.

Bone marrow
There is not much to recommend this material for making an improved polypropylene film.

The essential points in its favor are that (1) it is cheap and (2) it is also a constituent for animal glue which forms a thin transparent film that can bio-degrade over time creating holes in the polypropylene film.
This might make an candidate for Plan C.

Making polypropylene granules
In making the improved polypropylene film, no change is envisaged in stages upto making of the polypropylene granules.

Making improved polypropylene film from the granules.

Plan A calls for making minor alteration in the hot melt process.

Plan B calls for making changes in the post bubble formation stage by adding an extra process.
Neither of the two above processes result in any immediate loss of strength of the polypropylene film.

Plan C calls for making changes in the post bubble formation stage by adding an extra process that results in an immediate loss of strength.

Plan A:

Plan A is for injecting 500 to 10,000 parts per million of the desired material into the hot melt portion of polypropylene film extruder. The injected material will ideally melt at the same temperature as the polypropylene granules.

If the desired material does not co-melt with polypropylene, it may be melted outside the extruder and injected into the hot melted polypropylene granules,allowed to mix with the polypropylene and then extruded into a film.

The aim is that the improved polypropylene film would contain half hidden (covered with polypropylene) and half exposed (sticking out of the polypropylene film) materials that attract bio-degrading microbes to the film that would eat out the material and induce holes in the film that would allow moisture and microbes to pass through it to attack the bio-degradable material in the land fills. The improved polypropylene film will break into smaller pieces over time.
The illustration below has been taken from http://www.atlapac.com/polypropylene-cellophane-bags/materials-applicati...
and has been modified to illustrate the intervention point in Plan A.

The copyright in the image continues to belong to the previous right holders.

There will be some loss of transparency.
At times the film will let some moisture through it even while it is still protecting the package.

In the lab, the first step would be to test if the material can be co-melted or needs to be melted separately.

Second step would be to try different amounts of the material in the polypropylene film and see the reduction in strength and transparency.

Third step would be to make small quantities of films and se how they attract microbes.

Once an interesting film has been found full tests need to be conducted to assess the market potential.

Plan B:

Plan B does not tamper with the polypropylene film extrusion process.

It calls for an equivalent of a rotary printing press to be placed between the balloon gather and film roll up stage.
The illustration below has been taken from http://www.atlapac.com/polypropylene-cellophane-bags/materials-applicati...
and has been modified to illustrate the intervention point in Plan B.

The copyright in the image continues to belong to the previous right holders.

As the film has not been slit at this stage, it can be thought of as having two sides, both of which need to be printed. The sides inside the film will not get printed.

The material to be applied is dissolved in water ,or, if need be, in an solvent that will not lower the strength of the polypropylene film by interacting with it. This would rule out most of alcohols as a solvent.

The printing roll can have dots placed on it in a random manner so that the coated film has microbe attracting materials placed all over it.

The amount of the matter to be placed on the improved polypropylene film is about 1.5 to 2 times the magnitude as in the hot melt process.

The film will attract the bio-degrading microbes and the hope is that some of them will eat into the film and puncture tiny holes into it facilitating aeration and degradation of other bio-degradable material in the land fill.

No loss in strength of the improved polypropylene film is expected.

Transparency will be lower than conventional polypropylene film.

As normally the packing film itself is not printed, the inability to print sharp images on the improved polypropylene film will not affect its marketability.

Steps to test the improved film will be similar to Plan A.

Plan C:

Plan C also does not tamper with the polypropylene film extrusion process.

It calls for directly inserting solid / semi-liquid /gel material directly into freshly made holes in the improved polypropylene film.

It calls for two machines to be placed between the balloon gather and film roll up stage of a conventionally extruded polypropylene film.

The first machine makes tiny random punctures in the film.

The second machine forces material in powder form or semi liquid form into the holes and subsequently cleans the surface of the film of any excess material.

The two machines are placed similar to the position of printing pres in Plan B and hence no fresh illustration is given here.

The advantages of Plan C over Plan A and Plan B are that
(I) It can consider many more materials for attracting the microbes.
(ii) It guarantees that the film will aerate and allow moisture and microbe pass through in the land fill.

Its disadvantages are :
(i) The film may stretch/ break if handled in the conventional manner while packing the product in the downstream factory. Fresh settings will have to be taught to the downstream industries.
(ii) Transparency will be lost more than the other plans.
(ii) Strength loss will be greater than in other plans.

Besides the steps outlined in Plan A for testing the improved film, here additional steps are required to find an optimal piercing scheme (optimise areas of holes, distance between holes and shapes of holes).

Pushing mechanism will have to be fabricated.

Cleaning mechanism will have to be fabricated.

Conclusion
The three plans and the huge family of materials that are available under each plan, give rise to an optimistic thought that the replacement film for a polypropylene film need not be based on a fresh chemical substrate with all its issues of new technologies and production mechanisms.
The replacement film can be produced with the innovations outlined above.