Recycled LDPE Bags: How to Avoid Quality Problems

The world of recycled LDPE bags is widely represented by the type we use every day for separate waste collection which, through their different colours, help us to separate waste correctly.

The trend in bag production was represented by the maximum reduction in thickness and the use of increasingly lower quality raw materials. All this was part of a market logic in which the bag had to cost less and less, thus creating products that were increasingly less performing from a qualitative point of view.

The major problems encountered were the following:

• Fragility of the bag under the effect of the weight of the waste introduced with breakage of the walls due to breakthrough

• Detachment of the welding points of the lips of the bag with vertical opening of the same

• Cutting the bag if there are impurities on the wall

• Irregularity of the surface with phenomena called “partridge's eye”

• Difficulty in creating colours

• Pungent odor from the bags even after a long time

• Dryness of the bag due to the use of collected films degraded by the sun, especially the waste coming from agricultural greenhouses

All these problems should be analyzed individually as each point has a long story to tell and a clear path to its resolution.

In today's article we take a leap, arriving directly at the recipes that can solve all these problems, allowing the production of qualitatively correct bags with an eye on general production costs.

Most of the problems listed derive from the 100% use of post-consumer input , from separate collection or agricultural sheets, whose mechanical recycling, although excellent with the new production lines, involves many of the problems mentioned.

Certainly, a higher quality of the recycling lines , understood as selection, washing, densification, filtration and extrusion of the granules, corresponds to a lower quantity and importance of problems, but the mechanical recycling of waste coming from separate waste collection or from the agricultural sector, however, has of the qualitative limits that have not yet been resolved to date.

For this reason, the attention to the preparation of recipes for compounds, created with attention to the resolution of these problems, gives the possibility of creating LDPE granules, coming from recycling, with superior qualities, remaining in the perspective of the circular economy which requires the consumption of waste that we create every day.

The compound should contain a significant part of an LDPE film input that does not come from separate waste collection , not necessarily of post-industrial origin, but from waste that has not been mixed and polluted by other mixed plastic materials.

Based on the characteristic of the final product to be made, it will be decided how to compose the input recipe, so as to be able to guarantee the quality expected by the customer.

The qualitative indices must solve the problems we have talked about by taking into account some indications:

• Allow bag production starting from 20 microns

• The elasticity must be greater than a recipe with 100% post-consumer

• The sealing strength, even when cold and under the weight of the contents of the bag, must be high.

• The absence of small foreign bodies, which are formed due to the degradation of materials other than LDPE during extrusion, which affect the accidental longitudinal cut of the product.

• Being able to create a smooth surface, without small corrugations or irregularities.

• The recipe must include the possibility of making films with light and dark colours, semi-transparent in smaller thicknesses.

• Absence or marked reduction of the pungent odor typical of post-consumption must be possible.

On the basis of correct modulation of the material input and attention to the recycling and granulation phases, it is possible to significantly improve the quality of the LDPE bags produced , with a greater contribution margin on production and greater satisfaction of the end customer, always having costs under control.

Category: news - technical - plastic - recycling - LDPE - post-consumer - bags - film - quality

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