Among bag types, the garbage bag is perhaps the one that attracts the least attention, yet it is the one put under the most strain. The weight, shape and moisture of what goes into it cannot be known in advance; a sharp edge, wet waste or pulling a full bag out of the bin strains the film from every direction.
So the expectation from a garbage bag differs from that of a carrier bag. What matters is the film’s resistance to puncture and to tear propagation, and the leak-tightness of the bottom seam.
Types of garbage bag
Garbage bags can be grouped by where they are used. Thin, light bags are used for small household bins, medium-sized bags for kitchens and offices, and larger, thicker bags for building and business waste.
- Flat-bottom bags: A single straight seal seam at the bottom; the most common form.
- Star-seal bags: The film is folded at the bottom and then sealed; the full bag fits the shape of the bin better.
- Drawstring bags: A tape or strip running through the mouth lets the bag be closed easily.
- Tie-top and handled bags: The mouth has tie flaps or a handle cut suitable for tying.
What raw material is it made from?
LDPE and LLDPE blends are often used in garbage bags. The high elongation of LLDPE helps the bag resist by stretching when it meets a sharp object, rather than puncturing at once. LDPE makes the film easier to process and to seal.
The garbage bag is regarded as one of the most suitable applications for recycled polyethylene. Because expectations of appearance are low, colour variations or small surface defects do not cause as much of a problem as they would in a shop bag. Even so, since the quality of recycled raw material can vary from batch to batch, the strength of the film should be checked regularly.
This is also one reason why black, grey or dark-coloured garbage bags are common: dark masterbatch hides the colour differences that come from recycled raw material. For household bags, coloured or scented options may stand out as a marketing choice.
A good garbage bag goes unnoticed; only a bad one reminds you of itself, at the worst possible moment.
Production steps
Garbage bag production starts on the blown film line. The tubular film is set to the width of the bag and wound onto rolls. Most garbage bags are unprinted, so the printing stage is usually skipped.
At the converting stage, the film is sealed at bag length and a perforation, that is a tear line, is made between two bags. This way the bags stay joined to each other instead of being cut one by one, and can be wound into a roll. For star-seal bags, the film is folded by a special device before sealing.
Quality control checks the leak-tightness of the bottom seam, whether the perforation tears easily but does not break on its own, and whether the number of bags on the roll is correct. Consistent film thickness along the length of the bag is important to avoid weak spots.
Balancing thickness and strength
In a garbage bag, thickness alone is not a measure of strength. A thick but brittle film can tear more easily than a thin but flexible one. What matters is how well the film resists the spread of a hole once one has formed. Films with a high LLDPE content are more tolerant in this respect.
The film’s strength in both directions should also be balanced. On a blown film line, how far the bubble is inflated and how fast it is drawn affect the direction in which the molecular chains align. An unbalanced film may look strong in one direction while splitting easily in the other. So garbage bag film is assessed not only by thickness measurement but also by tear and impact strength.
Roll and pack presentation is also part of the user experience. Household bags are sold in small rolls wrapped with a band or label. Large bags used by businesses can also be supplied in folded stacks instead of rolls. Which presentation is chosen depends on where and how often the bag will be changed.
Choosing the right garbage bag
When choosing a garbage bag, the first thing to look at is the size of the bin. The width of the bag is set according to the bin’s circumference, and the length according to the bin’s depth and the allowance that will hang over the rim. A bag that is too narrow is stretched over the bin and strained as it fills; a bag that is too large means unnecessary material.
The second question is the type of waste. Wet kitchen waste strains the bottom seam, glass or metal pieces strain the film’s puncture resistance, and bulky but light waste strains the bag’s volume. In businesses, using different bags for different types of waste can be more efficient in terms of both material and use.
Waste separation and the use of bags in specific colours may be governed by rules in some institutions and municipalities. Bags for special waste types such as medical waste are subject to separate requirements; such uses should be assessed according to the relevant legislation.