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Blister packs polypropylene is best: Peter Forsmark, Technical Director, Recipharm (Stockholm, Sweden) explains why polypropylene blister packs are better than aluminium and PVC blisters now that the technical barriers to manufacturing them have been overcome.

Blister packs made entirely of PP (polypropylene) have many advantages compared with aluminium and PVC blisters, the most common type on the market. Among these advantages are lower weight and production costs, higher performance and less environmental impact throughout the production process. Polypropylene monoblisters typically consist of two plastic films with different properties, such as Etimex Purelay Pharm and Purelay Lid films (Figure 1). The 'Pharm' film is a PP thermoforming film that is similar to the PVC or PvdC (polyvinylidene chloride)-coated PVC films used in an aluminium/PVC blister, whereas the PP push-through lidding film seals the blister and serves the same purpose as the aluminium. Examples of when PP monoblisters have replaced PVC/ aluminium blisters are Reliv and Alvedon, two paracetamol products widely used in Sweden.

One advantage that PP monoblisters have compared with aluminium/PVC types is that they do not curve during late-stage production, making it easier to slot them into cartons or other packets. This is because they are made of a single material, and do not suffer from differential expansion between the aluminium and PVC. The thermoforming and sealing films each have advantages compared with aluminium and PVC. PP thermoforming films are more cost-effective than PVC films coated with PVdC sealant wrap and much cheaper than mono-PVC. This is because fewer raw materials are required to produce the same amount of extruded film--owing to better water vapour transmission rates. For example, 1 kg of PVC/PVdC produces 2.5 [m.sup.2] of film while the Purelay Pharm yield is 3.5 [m.sup.2], giving 40% more film for the same price per square metre (Figure 2). However, PVC films coated with PVdC have the same or better barrier properties than PP and can be produced in ordinary thermoforming stations, such as those for PVC.


PP thermoforming films are also better than PVC in other respects. They are less dense, lighter and more transparent, and the stiffness of PP is better suited to pushing tablets from the packaging. In addition, PP thermoforming films produced by heating and quenching the polypropylene have excellent thermoforming behaviour and barrier properties. The PP sealing film is also comparable with, or better than, aluminium. It is compatible with all standard blister pack printing processes and is as easy to push tablets through as ordinary aluminium foil. In addition, its sealing properties are comparable with aluminium. Figure 3 represents the required push-through force in 'childproof' packaging for medicines for the various blister packs.

Another advantage of PP-blisters is that they have lower environmental impact than aluminium/PVC blisters. Since its founding in 1995, Recipharm (then Recip) has been strongly committed to being an environmental trendsetter in the pharmaceutical industry. Recip was one of the first pharmaceutical companies to be certified according to ISO 14001 in 1997 and, in 2001, Recipharm undertook a product lifecycle analysis to assess its green credentials. At that time, a complete lifecycle analysis on a pharmaceutical product had never been done before. The purpose of the analysis was to study the environmental effects that arose from the production of a single package of painkillers. The lifecycle--then and now--includes the extraction of raw material and packaging material, the production of pharmaceutical granulate and, finally, the production of the product. Transportation between these steps is also included. The study resulted in factors that were compared with different environmental threats, such as the greenhouse effect, acidification and so on. The study showed that the global warming potential of PP blisters is 86% less than conventional aluminium/PVC blisters (see Figure 2). This is mainly because the production process of the packaging materials is less energy intensive than for aluminium and PVC. At the end of their useful life, polypropylene blisters also have environmental advantages compared with aluminium/PVC blisters. They are easy to recycle as the blister pack is made of a single material, and this gives them a higher recycling value. Aluminium and PVC are not as easy to recycle because they need to be separated before the blister pack can be recycled.


Despite these many advantages, there are still fewer PP monoblisters on the market than PVC/aluminium blister packs. This is because PP monoblisters were traditionally more difficult to produce than PVC/aluminium blister packs. One reason for this was older packaging machines, which required manual intervention to compensate for PP shrinkage during processing. Newer machines automatically compensate for PP shrinkage, speeding up production. Another reason is that the PP films are temperature sensitive and must be evenly preheated before sealing. This means that the speed at which the film passes through the heating roll, and the temperature range used, must be carefully adjusted and maintained. Finally, the PP forming process requires two steps--mechanical and hot air--whereas PVC is formed in a single step using compressed air.

To overcome the above-mentioned barriers, Recipharm had to invest in new format parts and learn new techniques. In older machines, heating elements are used for the preheating step during the sealing process. In some new machines, these elements have been replaced by NIR techniques. For the forming step, new forming plugs that are adjusted for PP film were used. The plugs must be preheated to achieve good forming. With the new techniques, combined with months of test runs and hard work, Recipharm managed to introduce the new PP blisters successfully. PP monoblisters have numerous advantages compared with aluminium and PVC blister packs, including lower environmental impacts and cost. Until recently, the extra steps and added complexity of production prevented them replacing aluminium/PVC packs. But, even with today's more advanced machinery, the introduction of a new material, like PP, is challenging and requires a lot of knowledge and experience.
Figure 2: Purelay Pharm yields 3.5 [m.sup.2] of film, 40% more film
for the same price per square metre.

                                         [m.sup.2] yield      Density

PVC/PVdC 250 [micro]m/ 40 [m.sup.2]           2,5               1,4
pp 300 [micro]m                               3,5               0,91

Note: Table made from bar graph.

Figure 3: Required push-through forces for various blister packs.

Purelay[R] Lid (90 [micro]m)               25N
Aluminium foil (16 [micro]m)               27N
Aluminium (9 [micro] m laminated to paper
(40g/[m.sup.2])                            25N

Note: Table made from bar graph.

For more information

Recipharm AB

Lagervagen 7

SE-136 50 Haninge, Sweden.

Tel. +46 8 602 5200
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Title Annotation:solid dosage; polyvinylidene chloride
Author:Forsmark, Peter
Geographic Code:4EUSW
Date:May 1, 2009
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