The recycling of hollow glass
Hollow glass is enjoying steadily growing popularity as a packaging material. And for good reason: it is versatile, transparent, hygienic, absolutely airtight, and ecologically advantageous. Hardly any other packaging material is so excellently and environmentally friendly for multiple uses. Glass can be formed into new bottles or glass containers almost infinitely without any loss of quality – thus operating in an almost closed material cycle.
What is meant by hollow glass?
The term hollow glass encompasses various types: construction hollow glass (such as glass blocks), utility glass (glassware and drinking glasses for household, table, and kitchen), and – for packaging – container glass and glass bottles. The latter are well-suited for filling due to their three-dimensional shape with an opening. At the same time, this opening can be securely sealed for packaging purposes. This optimally protects liquids and bulk or filling goods from external influences. The glass does not interact with the packaged goods, remains always taste-neutral, and is dimensionally stable even at high temperatures.
Hollow glass as a packaging solution has various advantages. There is not only a wide range of shapes and applications, pure glass can also be remelted any number of times without any loss of quality and is therefore almost 100% recyclable. Even single-use glass is environmentally friendly and an important part of the value chain as waste glass. Reusable glass, such as yogurt jars or beverage bottles, significantly improves the ecological balance. Since glass does not absorb any foreign odors or substances, refilling with different liquids is also possible without any problems.
The recyclability of hollow glass
Hardly any other packaging material is as well-suited for multiple use as recycled glass. It can be returned to the melting process and processed into new products as often as desired, all while maintaining consistent quality. As a reusable bottle, glass containers can also undergo up to 50 cleaning and refilling cycles thanks to their smooth and chemically resistant surface before being fed into the recycling cycle. This means that glass reusable bottles can go through more than twice as many filling cycles compared to PET reusable bottles before the bottle needs to be recycled again.
In the container glass industry, recycled glass has now become the most important raw material component. However, its use depends on the production-specific requirements for the purity level of the shards. For example, colored glass cannot be used to produce white glass. To produce white container glass with appropriate shard usage rates, a color purity of 99.5% or higher is generally required. The tolerated proportion of off-colors in brown glass is usually about 10%. Only green glass allows for a significantly higher proportion of off-colors.
The recycling of hollow glass
As early as the beginning of the 1970s, the first material cycles for waste glass were initiated in Germany. Enormous efforts by glassworks and waste glass processors to advance glass recycling led to ever higher recycling rates. Nowadays, around 2 million tons of waste glass are collected annually in Germany and processed into new glass containers. Although the processing of the collected container glass is largely fully automated and automated color sorting is already standard in many recycling plants, for economic and ecological reasons, it is still recommended that consumers collect glass containers separately by color. The purity of the collected glass quantities is a prerequisite for their return to the melting process for the production of new glass containers. Over 250,000 waste glass containers for the separate collection of white, brown, and green glass are in use nationwide for this purpose. And with success: According to waste statistics, the recycling rate for container glass placed on the market in 2019 was 84.1%.
Although waste glass has excellent recyclability, its processing is laborious and cost-intensive. The collected material must be cleaned of all non-glass components and incorrect colors must be sorted out. First, coarse waste (coarse garbage, plastic bags, ceramic parts, stones, etc.) is manually sorted out. Lightweight materials such as labels, plastic rings, closures, etc. are removed by suction and metals by magnetic separation, eddy current separators, and special Fe/Ne metal separators. For further separation of impurities such as CSP (ceramics, stones, porcelain), heat-resistant glasses, or lead glass, state-of-the-art high-tech sorting devices are available. It is important for the melt that almost one hundred percent of the highly problematic contaminants such as metal, CSP, or heat-resistant glasses are separated, otherwise, inclusions in the product or disruptions in production may occur.
At the end of the laborious sorting and cleaning process, ideally, furnace-ready glass shards are produced, which are qualitatively in no way inferior to the original raw materials for container glass production and also have the decisive advantage of requiring significantly less melting energy.
The advantages of hollow glass recycling
In addition to a significant reduction in waste generation, the recycling of hollow glass offers a whole range of advantages:
Reduced need for primary raw materialsThe use of used glass packaging reduces the need for primary raw materials. Whereas a glass bottle used to consist mostly of quartz sand, the proportion is now sometimes only 10% in production due to the recycling of shards. In 2011, more than 12 million tons of raw materials (quartz sand, soda, lime) were saved in Europe alone through glass recycling.
Reduction of energy consumption and improvement of the ecological balanceUsed glass packaging requires lower temperatures for melting and consequently less energy than the mixture of primary raw materials (quartz sand, lime, and soda). According to a rule of thumb, about 2 to 3% of energy is saved for every 10% of used glass added to the melting furnace. This automatically results in a reduction of CO2 emissions. Overall, about 74 percent of all glass bottles end up in used glass containers in Europe each year – and are processed into high-quality glass packaging again.
Increasing demand for glass packagingThe question of environmental compatibility and recyclability now plays a major role in purchasing decisions. Glass is already an extremely popular packaging material thanks to its high-quality and aesthetic properties. Through its recycling and reuse, it becomes even more attractive many times over.
Recycling-friendly glass design
Like plastic packaging, hollow glass containers must also meet certain criteria to be considered recyclable. The Central Agency Packaging Register Foundation summarizes these criteria as follows: Recyclable glass is transparent and the label is easy to remove. Glass as a packaging material is primarily characterized by its transparency. The contents are visible. This property must be preserved in recycling.
Opaque glass pieces are often automatically recognized as contaminants by optical sorting systems and are removed. Painted glass containers can also be lost to the glass cycle, as they are often not transparent due to their coating or convey a "wrong" color and are therefore removed in many facilities. All "non-glass components" of the glass packaging, such as labels, must also be as easy to remove as possible. For glass design, it is therefore advisable to use as few fully glued labels as possible. If adhering labels cannot be sufficiently removed during the process, the glass becomes opaque at the corresponding spot and is also sorted out.
Conclusion
Hollow glass is an excellent example of a closed material cycle. It can be recycled indefinitely without loss of quality when properly collected and processed, saving raw materials and energy in the process. For this reason, it is becoming increasingly popular as a packaging material among both manufacturers and consumers. However, there are some basic prerequisites for successful glass recycling: First, the glass containers must be designed for recycling. Second, consumers must dispose of the used glass properly—separated by color and type of glass. And third, highly modern sorting facilities are needed to achieve remeltable glass shards of the highest quality from the collected used glass, from which new glass bottles are then produced.