Woven polypropylene cement sack recycling can bring in cost savings and sustainability

Abstract:

A global trend towards sustainability and its resultant cost savings have forced decision makers across to revisit strategies within their operations. The objective of this study is to understand whether a similar approach can be implemented in recycling woven polypropylene cement sacks. We would be analyzing the current scenario, the scope for other regions to follow and the corresponding impact in terms of viability and cost savings. Our analysis will also include the use of recycled polymers for making cement sacks or any other products.

Woven polypropylene cement sack – waste management supply chain:

Cement sacks are primarily made up of three components namely: Virgin material, Masterbatch and UV Coating. There are two product outcomes while recycling woven polypropylene cement sacks: 1) Recycled polymer (polypropylene) and 2) Calcium Carbonate (CaCo3).

The most common method of cleaning the sacks is by water; this allows agglomeration of cement (lumps) that is left in the bag. Hence, 80-85 percent of recycled polypropylene is churned out in grey (not white) and the remaining 15-20 percent is calcium carbonate formed from the cement already available in the sack. While washing with air is another option, it is not widely used given its high cost. The output is the same colored polymer and less calcium carbonate. The reason behind these polymers being colored is due to the use of masterbatch or UV coating while making them.

How are the recycled polymers used?

The most predominant situation is that these recycled polymers are used for making cheaper plastic products such as mugs, buckets and slippers manufactured by blow-molders. Recycled polymers are used based on regulatory standards for making cement sacks; it is known that the tensile strength of a cement sack made with more recycled polymer is reduced compared to a cement sack made with virgin material.

Although, this can be analyzed comparing two scenarios globally

• Developed Regions – USA, Europe
• Developing Region – Asia (India, China)

Developed Regions

The recent past has seen a subdued demand for cement; although, this is expected to recover and grow. It is common practice in most construction projects to use silos rather than cement sacks; this provides less scope for recycling. Stringent regulations on tensile strength of cement sacks limit the use of recycled material to less than 3-4 percent.

Almost all used cement sacks from this region are sent to the Asian market for recycling. The recycled polymers are sent to nearby regions where blow-molding industry is predominant for conversion. In Europe there has been a technical advance where an Austrian machine manufacturer has integrated air cleaning with recycling for cement sacks to reduce overall time and cost. This innovation comes at a time when countries such as India and China have imposed trade restrictions (anti-dumping) on import of hazardous goods such as cement sacks.

Developing Regions

Growth in infrastructural development in these regions has increased manifold recently paving way for the consumption of cement. Unlike developed regions, sacks are preferred over silos since construction happens in remote/developing areas where silos cannot be operable.

• is the largest recycler of plastic waste in the Asian region; this is also the only region where there is high amount of recycled polypropylene used in making woven cement sacks. Using masterbatch they are made as yellow or grey cement sacks. The regulatory standard here allows for ~35 percent usage of recycled polymer and 10 percent calcium carbonate in making new woven polypropylene cement sacks. However, certain sack manufacturers here use up to 100 percent recycled polymer, because the regulatory body in this country is not as stringent when compared to developed regions. Also, handling of these cement sacks play a vital role to preserve tensile strength. In China, much of the handling system is semi-automated reducing manual interface. The reason is to reduce throwing or stacking more than required that may cause breakage of such sacks. An ideal semi-automated handling system uses less than 6 people. Handling includes right from filling cement into the sack till the point of delivery (i.e. construction site).

We will study in detail the Indian market for recycling cement sacks to understand the salient features of adaptability, regulatory compliance and handling systems.

Indian Scenario

Dhoraji, Ahmedabad in Gujarat is the recycling ‘hub’ for all plastic scrap in India; other regions include Aurangabad in Maharashtra and Hyderabad in Telangana. Nearly 30 percent of the cement sacks are cleaned and re-used by farmers and small scale industry manufacturers to collect/pack manure, waste, by-product, scrap etc.

The BIS (Bureau of Indian Standards) allows 15 percent calcium carbonate and only 10 percent recycled polymers while making cement sacks. There has been recent debate to include more recycled polymers and reduce the calcium carbonate content. There is scope for adding 35 percent or more recycled polymer while making cement sacks.

The reason for lesser use of recycled polymer is because the handling system in India is mostly manual involving 8-10 people across the supply chain. This increases the scope for breakage and tearing. There is a bursting system that indicates the number of cement sacks that can be stacked atop of one cement sack; its breakage is tested depending on the number of sacks that are stacked before the bottom sack could burst. In China the bursting standards are 7:1 i.e. 7 cement sacks stacked upon 1 whereas in India it is 5:1. Baling of cement sacks would spread the risk of breakage.

Cost

• Waste collectors in India buy re-used cement sacks based on ‘tearing’. Thread open used cement sacks are brought at INR 4 or 5/kilo whereas torn open bags cost INR 2 or 3/kilo
• After cleaning, these bags are sold at INR 3 or 4/bag to farmers and small-scale industries
• Recyclers buy unwashed cement sacks at INR 2 or 3/kilo from scrap collectors. Average woven polypropylene cement sacks cost INR 40-50/kilo (11-13bags) whereas the recycled polymer costs INR 65-70/kilo
• Recycled sacks are used by plantation and agro-chemical industries which buy sacks at about INR5 or 6/bag

Conclusion

Globally woven polypropylene cement sacks are recycled and are used for making cost-effective plastic products such as mugs, buckets and slippers. India has not adopted the use of recycled woven polypropylene cement sacks. However, compared to other regions, India has better prospects if it were to improve its handling system and increase the use of recycled polymers. This would help cement manufacturers to establish themselves as sustainable players with their intent to reduce carbon foot-print or improve sustainability. However, given the costs, companies may not have substantial savings.