By Mervyn Dias
Plastic is used in many applications within the household and commercially. Polythene bags have become the most widely used commodity in plastics when compared with other plastic items. It is used worldwide in supermarkets and shops and is one item that is creating huge problems. Therefore, we will be considering aspects relating only to plastic bags.

Before and after (right) being partly recycled

There are two types of bags in the market. The bag manufactured out of HOPE- High Density Polythene- is given by the supermarkets and shops to their customers, while bags manufactured from LOPE -Low Density Polythene is generally high in price and given by departmental stores.

The advantages of these 'sili sili' bags (HOPE) are that they are very light in weight, can carry heavy weights, frozen food such as ice cream, can be used on rainy days and are low in price.

The bag can be recycled and re-used again in the process to manufacture more bags. The major problem in polythene is that these bags are not environmentally friendly as they do not decay, as against all the many advantages they have.

The resins that have been used are all imported to manufacture plastic bags. In 1998, 44 million kgs were been imported and in 2003 this increased to 64 million and 10 million kgs and 16 million kgs of plastic bags have been exported during the above two years.

Therefore, 34 million kgs in 1998 and 48 million kgs in 2003 have been used to manufacture plastic bags to the domestic market. (Data 1 Customs statistics) These quantities would be buried somewhere for many decades in Sri Lanka.

The environmentalists suggest a ban of plastic bags saying that paper bags are an alternative to plastic bags. But is a paper bag a substitute? No. Paper bags cannot replace plastic bags.

Because they
. Cannot be used to carry heavy weights.

. Cannot use to carry frozen foods or carried on rainy days.
. Will need many bags instead of one plastic bag to carry the same weight in a plastic bag.

If paper bags are to be used, trees will have to be cut down to manufacture paper bags. It is generally believed that 17 trees will be required to manufacture one MT of paper bags. Franklin report -1980 of USA says that paper bags:

* Use 500% more raw material to produce than plastic bags.
* Takes three times more energy to make paper bags compared to plastic bags.

* Paper bags are found to be six times heavier and take up 10 times the storage volume of plastic bags.

* It would take seven times the number of trucks to deliver the same amount of bags. This will create seven times more transport pollution. Therefore as you can see there would be more environmental pollution if paper bags are used.

Then the other item that is used very heavily is the food wrapping sheets. Is there an alternative for food wrapping sheets? No, other than 'kehel kole' .

Therefore, is there any alternative for polythene bags? No. Can this be banned? No, mainly due to the fact that there are no substitutes. If a ban is to be implemented an environmentally friendly replacement should be found.

Solution
In order to solve this problem the only answer is to introduce an environmentally friendly polythene bag. The criteria of such a bag should be:

* They must disintegrate and leave no visible trace.
* The disintegration should happen in a reasonable time frame.

* The bag should not leave behind any toxic substances.

Are there are any polythene bags that satisfy these criteria? Yes. There are different types of degradable bags.

Starch based bags
These are manufactured using starch based material and need to be in a microbial environment such as in a landfill or compost heap for the bags to degrade.

Photo degradable bags

These will degrade under sunlight.

Oxo-degradable bag

This can also be called oxo-biodegradable bags. The most commonly used degradable bag is the oxo-degradable bag where the lifetime can be controlled when compared with other types of degradable bags. To manufacture these bags a very small amount of prodegradant additives ( an additive that will trigger and accelerate the degradation process) is mixed with the resin and this will change the behaviour of the plastics. These will accelerate the degradation when exposed to light, heat, stress and does not depend only on microbes.

Our field results show that the degradable bag will degrade even inside cupboards when bags are buried and in beaches. This will continue until the material is reduced to carbon dioxide and water.

Oxo-degradable bags can be programmed to give a certain length of time at the time of manufacture. Different percentages of additives will have to be added and the lifetime of the bag can be controlled accordingly.

We have tried several additives and the best found so far in terms of cost effectiveness is PDQ-H from Willow Ridge Plastics, USA and has been tested for several years and acts well.

The lab testing including field testing done by us has shown that there is a definite useful lifetime for these bags depending on the dosages during which period these bags maintain the same quality as that of a non degradable bag.

The degradation period can be controlled according to the customer requirements. This can vary from thee months to two years. There are many advantages in using these oxo degradable bags.

1. The bag can be recycled and material reused again in the process.

We have recycled the degradable polythene scrap and reused in the process and tested for degradability. The bags do not show any degradability. The additive has to be added again to make the bags degradable. The degradable polythene scrap can be recycled as any other non degradable bags. When degradable plastics are recycled degradation is arrested and acts like normal plastics.

2. These bags dumped on garbage dumps will not make those areas infertile after degradation.

3. Will not use good land for land filling. Land would be available for other purposes.

4. Will not block drains, create floods.

5. Safe to come in direct contact with food. Complies with EC directives.

(This will apply only if PDQ-H is used to manufacture degradable bags. These films are tested and certified in UK for conformity with respect to EC directives But this may not be the case if another additive is used. )

6. The degradable bags can be manufactured with the same machinery.

7. The price difference between the degradable and the non degradable is negligible. For example, if a 50cts. degradable 'sili sili' bag is manufactured the price difference would be four to five cents only.

The main problem with polythene is that it is not environmentally friendly. Degradable or non degradable bags can be recycled and reused in the process. If these bags are either recycled, made thicker or have a plastic tax will this solve the environment problem? No. Simply because whatever options are considered the bags will be there on earth somewhere for many decades and will pollute the environment. Is this what we require?

We are not talking of polythene but safe guarding the environment. It is up to the public to decide which one is better - a non degradable bag that is there for decades or a bag that degrades within a certain timeframe. The decision is yours.
(The writer is Chairman, Plastic Packaging Pte. Ltd.)