Insights / Packaging Resources / Packaging Fundamentals

Answers to Questions about Glass Recyclability & Cleaning

By: Berlin Packaging Specialist
Date: January 26, 2020

Glass Recyclability

Who collects glass for recycling and who uses it? Glass is collected by companies appointed by the individual municipalities. The collectors treat the glass cullet in special industrial plants that wash it, break it into very small pieces, and separate off the impurities. The recycled glass is then sold to glass factories that mix it in with the batch formula.

Is glass “biodegradable?” What impact does glass have on the environment? No. Glass is a mineral and the labels on glass containers generally state “please dispose of responsibly”. Over time, the glass will tend to “return to sand”, especially if it is thrown away on beaches, in the sea, or wherever it may be repeatedly moved by natural elements.

How much recycled glass should be used in production? There is no technically fixed quantity. Cullet can be used as a support to the melting of the raw materials since it melts at a lower temperature and thus offers significant economic and environmental advantages (less energy consumption). For extra-flint glass, in particular, the quantity of glass cullet is kept as low as possible (10%) in order to avoid impurities appearing in the recycled material.

Another solution is for the producer to use cullet exclusively from their own recycled product. Some glass factories that produce colored glass can use 60% or more of cullet since any color impurities in the cullet will not have a significant impact on the final result. It is also possible to manufacture new containers using only cullet, but in this case, it is important to adopt special strategies to keep complete control of the material in order to ensure the homogeneity of the molten materials.

Is it possible to recycle glass that is already a product of recycling? Glass recycling can be repeated indefinitely; a 600 gram container will produce another container of the same weight without any loss. The original “mineral” does not change: the process of melting to the semi-liquid form is repeated (some people would define glass as a highly viscous liquid), the shape is changed, it solidifies as it cools, and is then used again.

Is it possible to detect glass packaging with recycled content? No. When “cullet” is melted, it returns to its original purity as if it was “new glass”.

Since glass objects are thrown indiscriminately into glass banks regardless of their color, what color is the final recycled glass product? A recycled glass of mixed colors is generally used to produce dark glass (green, antique green, or yellow). Cullet (crushed and mixed) is used in the normal mixture of raw materials, with the addition of colorants that guarantee a uniform final result. Melting takes place at over 1500°C and at this stage there is a viscous, perfectly homogeneous and purified mixture.

Why are glass water bottles returned and how are they reused? This is a question of relative cost, balancing the cost of water with the cost of the glass bottle, as these are both “low cost” items. It is necessary to take into account the cost of returning the bottle to the filling plant, as well as the cost of the necessary processing before it can be reused: such processing is quite complex in terms of equipment and water consumption for washing in order to ensure the completely hygienic condition of the bottle independently from its previous use.

Why shouldn’t lids be reused? Because the mastic used for the lid, the material which allows the “air-tight” seal, doesn’t have the same elasticity after the first use. The “threads/lugs” that ensure the coupling of the lid to the jar finish become deformed after the first use.

If glass containers should be “cleaned” before they are used by the food industry, what is the most efficient cleaning method? Glass containers arrive at the end of the uninterrupted production chain clean and packaged. Before using the container, the filling company must ensure that no internal contamination has occurred during storage and unpacking. A washing or blowing procedure is generally adopted on the production line. The blowing procedure — which is the most commonly used — is carried out by a machine placed in between the depalletizer and the product filler, which blows air forcefully into the inverted container. In this way, the combination of air pressure and gravity together eliminate any impurities which may have been introduced during the storage or unpacking phases.

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