Advantages and disadvantages in blowing bottles with recycled HDPE granules loaded with Talc or Calcium Carbonate

The production of single-layer HDPE bottles has always been competence of virgin polymer until a few years ago, with which colors, thicknesses, finishes, fragrances and shapes were made without worrying too much about the polymer-blow molding ratio.

The advent of recycled HDPE in the blow molding world has been gradual and quite complicated, as there was a certain mistrust on the use of rHDPE, motivated by hypothetical doubts on mechanical strength, on the quality of the surfaces, on the seal of the handle, on the smell of the blown packaging, on the realization of the colors and the transparency to see the liquids inside, on the sealing of the welds, on the micro perforations of the surfaces, on the availability of the material and on the small difference in price compared to virgin raw material.

All legitimate objections for those used to using virgin polymer, but many of them were general preconceptions about recycled material, which was still seen as synonymous with lower quality general.

There is no doubt that the first years in which HDPE recycled in blow molding granules arrived on the market, the quality of the recycling and sorting plants attributed to the raw material some objective limits.

The main critical issues were related to some technical factors:

• Impurities contained in the granule

• Excessive presence of PP

• Presence of residual moisture

• Persistent odor

• Hardly manageable color

We do not go into how the recycling sector has technically, over the years, solved the problems exposed, managing to create a recycled HDPE granule that is comparable, from point of overall performance, many times to the virgin one.

Perhaps, in some cases and with some machines, the question of the thickness of the bottle is still an open topic, as, at times, it may be necessary to increase in thickness using rHDPE compared to the first choice.

The reason why it may sometimes be necessary depends on many factors, such as the shape and size of the bottle, the blow molding machine you use, the quality of the recycled granule, all elements necessary to achieve a correct ratio, between the compressive strength of the bottle and the weight that weighs on it once inserted into a vertical pallet.

It is possible to overcome this inconvenience, after verifying and solving the previous problems, through the use of mineral fillers such as talc or calcium carbonate.

The function of mineral fillers is to increase the vertical compressive strength of the bottle, without having to increase its thickness, through the use of percentages that do not exceed usually 10-15%, depending on the size of the product to be made.

It should be noted, by engaging loaded granules, that the bottle enjoys advantages relating to load resistance and torsion, thus improving portability and economy in the production phase .

There are, however, some information to keep in mind when deciding to operate by blowing with an rHDPE granule loaded with talc or caco3:

• The screws of the blow molding machine must be cleaned often, as the first stages of using an abrasive mixture, such as loaded HDPE, facilitates the transport of contamination present in the blowing machine with the possibility of creating holes in the bottle.

• The presence of mineral fillers can affect the transparency, or semi transparency, of the product.

• The creation of colors must take into account a possible different color result compared to a rHDPE without fillers.

• The presence of PP, even in low percentages, in a loaded granule, further reduces the sealing and sealing capacity of the bottle, especially in the handles or in points with particular angles.

Automatic translation. We apologize for any inaccuracies. Original article in Italian.