TECHNOLOGY | ODOURS AND EMISSIONS
Figure 1: Potential sources of odour and emissions in the plastic processing sequence from compounding to moulding
Source: Byk
Odours and VOCs in the plastic part can be caused by a variety of factors, which Byk says can be broadly assigned to the polymerisation process, processing aids and additives. The company adds that emissions from plastic components are often further determined by environmental influences, with heat and sunlight being major factors. Process- ing steps that a plastic part undergoes are also relevant (Figure 1). “These include pre-drying procedures and process parameters, such as temperature and dwell times. In addition, the influence of machine specifications, such as screw design, the degassing zones and the available vacuum, cannot be underestimated,” says Garlinsky.
State-of-the-art “Current state-of-the-art processes use microporous materials to adsorb VOCs and odours. The disad- vantage of many adsorber products, such as activated carbon or zeolites (aluminosilicate), is that VOCs or odours are bound to the surface by physical forces – Van der Waals forces. Adsorbers can absorb water and other low-molecular substanc- es and release them when heated without the crystal structure of the adsorber being destroyed,” he says. In certain circumstances, Garlinsky says volatile components can be released from the adsober — in summer in vehicle interiors where temperatures exceed 70°C, for example. In such cases, adsorbers can delay, but not rule out, the release of bound substances. They can also result in some impair- ment of mechanical characteristics. “Another method for reducing odours and emissions is directly feeding an entrainer in the form of water, nitrogen or carbon dioxide straight into the melt during the extrusion process,” he says. “By means of suitable degassing during the extrusion process, which should be carried out primarily via a vacuum, it is possible to remove unwanted odours and VOCs from the process. The
50 COMPOUNDING WORLD | March 2021
disadvantage of this process is that it requires more elaborate technical solutions and, as a result, additional investment in machine technology.” With Byk-P 4200, the company says that it has developed an additive that uses the concept of an entrainer but simplifies the process. The granulated additive is based on a polypropylene carrier and can be added to the extrusion process with relative ease, like a masterbatch, via the main feed or a side feeder. It affects two steps of the extrusion process. In the first step, the active substance is released during processing by shear and heat in the melt and finely distributed. This results in an intensive exchange between the entrainer additive and the polymer matrix, with the pressure build-up in the process preventing the additive from expanding prematurely. In the second step, the entrainer additive evaporates in the vacuum degassing zone resulting in foaming of the polymer melt. Gas bubbles are formed, which in turn create a large inner surface (phase boundary). Byk says the entrainer significantly reduces the solubility of the volatile components, which can then be extracted during degassing.
Proven results
Byk says it has carried out experimental trials that have determined a significant reduction in odour and VOC in unfilled and talc-filled PP compounds using the additive. In the first, a polypropylene homopolymer with an MVR of 25 cm³/10 min (2.16 kg) was processed on a twin screw extruder (KraussMaffei ZE 25 UT). Vacuum was applied, zeolites were added as an adsorber and BYK-P 4200 was also added to reduce odour and VOCs. At the end of the extrusion process, degassing was carried out via vacuum degassing at approximately 50 mbar. The process was consistently kept at a speed of 600rpm and a throughput of 25kg. In a second example, 40% of Luzenac 1445 type
www.compoundingworld.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62
