Bronisław Samujło, Robert Sikora

Department of Polymer Processing

Technical University of Lublin,

36, Nadbystrzycka St., 20-618 Lublin

The course of PE extrusion process modified by Mg(OH)₂

More and more common requirements of reduced flammability as well as decreased or eliminated toxicity and corrosivity of decomposition and combustion products of plastics induce to undertake research on receiving and processing new polymer materials. These requirements can be fulfilled by plastics modified by halogen-free reducing flammability agents, such as aluminium hydroxide, magnesium hydroxide, basic magnesium carbonate, agents based on ammonium phosphate find wider and wider application [1, 2]. For the sake of the operation mechanism of these agents they are introduced into the polymer in relatively big quantities, most often from 50 to 70% which causes, apart from reducing polymer flammability, disadvantageous influence on the extrusion process and worsening of the mechanical properties [3, 4].

As a part of a wider research program, which selected fragments were presented on PPS North American Meeting, Canada 1998 end PPS 15^th Annual Meeting s'Hertogenbosch, Netherlands 1999, the studies were conducted of the extrusion process of medium density polyethylene (PE-MD) with melt flow index equalling 0,712 g/10 min [5, 6]. The polyethylene was modified by magnesium hydroxide Mg(OH)₂ indicated as FR 20, of the average grain size equalling 2,5 µm. Antiblocking and lubricant agents were also introduced into the polymer in the form of polyethylene concentrates indicated as 020-04, 020-15 characterised respectively by the concentration of the antiblocking agent equalling 4 and 10% and the lubricant agent 1,2 and 5% and Lifoslip 220 PE with the concentration of the lubricant agent equalling 20%.

The studies of the extrusion process were conducted on the Brabender laboratory extruder, Plasti-corder PLV 151 type. The stand enabled the measurement of the turning moment on the screw, pressure in the extruder head, control of the rotational speed of the screw and temperature in the respective zones of the plasticating system and extruder head. The plasticating system was fitted out of three heating zones and the screw used was characterised by the ratio L/D = 25, diameter D = 19 mm. The line consisted of the head for extruding panels of the die length 102 mm and maximum die width 2,1 mm and the receiving device. The extrusion process was conducted at the following parameters: rotational speed of the screw 0,75 s^-1, temperature of heating zones of the plasticating system respectively - 160, 170, 170°C, temperature of the extruder head - 170°C, extrusion velocity - 1,72 mm/s, temperature of the surrounding - 20°C.

During the extrusion process the pressure in the extruder head, the turning moment measured on the extruder screw and dependence of the flow rate among other things were studied. The dependence of the pressure in the extruder head in the fig. 1, the dependence of the turning moment on the screw in fig.2 and the dependence of the flow rate in fig.3 on the contents of magnesium hydroxide in the PE were presented.

From the above presented dependencies it turns out that the value of the pressure in the extruder head, the value of the turning moment on the extruder screw end the value of the flow rate increases with the increase of Mg(OH)₂ contents in the PE, with the clear influence of antiblocking and lubricant agents on the character and numerical values of the measured quantities. The lowest values of the pressure and the turning moment were received using Lifoslip 220 PE agent which proves a clear influence of this agent on the polymer which modifies its properties. As it turns out from the above presented dependencies, the above mentioned influence is most clearly visible at the relatively low magnesium hydroxide contents in the PE, while at the higher contents (57,5%; 60%) the values of the pressure and of the moment come close to the values received for other auxiliary agents of lower concentration of active substances.

References

1. Troitzsch J.: Kunststoffe 1995, 12, 2191.

2. Horn W.E., Smith D.R., Stinson J.M.: 50th Annual Technical Conference ANTEC, Detroit 1992, 2020.

3. Beluch W., Jaworski J., Stabik J.: Polimery 1994, 11-12, 698.

4. Szabłowska B., Pełka J.: Polimery 1991, 7-9, 294.

5. Sikora R., Samujło B.: The Polymer Processing Society North American Meeting, Toronto, Canada 1998, 183.

6. Samujło B., Sikora R.: The polymer Processing Society, 15^th Annual Meeting s'Hertogenbosch, Netherlands 1999, 133.

Spis podpisów pod rysunkami

Fig.1. Dependence of the pressure in the extruder head on the contents of Mg(OH)₂ in PE: 1- 020-04 agent, 2 - 020-15 agent, 3 - 220 PE Lifoslip agent

Fig.2. Dependence of the turning moment on the screw on the contents of Mg(OH)₂ in PE: 1- 020-04 agent, 2 - 020-15 agent, 3 - 220 PE Lifoslip agent

Fig.3. Dependence of the flow rate on the contents of Mg(OH)₂ in PE: 1- 020-04 agent, 2 - 020-15 agent, 3 - 220 PE Lifoslip agent

Summary

As a part of a wider research program the studies of the extrusion process of medium density polyethylene PE-MD modified by magnesium hydroxide Mg(OH)₂ were conducted. During the extrusion process dependences of the pressure in the extruder head, of the turning moment measured on the extruder screw and of the flow rate on the contents of Mg(OH)₂ in PE were studied and presented in fig. 1÷3.

Key words: polymer extrusion, halogen-free reducing flammability agent, magnesium hydroxide

Streszczenie

Jako część szerszego programu badawczego przeprowadzono badania procesu wytłaczania polietylenu średniej gęstości PE-MD modyfikowanego wodorotlenkiem magnezu Mg(OH)₂. Podczas procesu wytłaczania wyznaczano ciśnienie w głowicy wytłaczarskiej, moment obrotowy mierzony na ślimaku wytłaczarki oraz wydajność procesu wytłaczania w zależności od zawartości Mg(OH)₂ w PE, co przedstawiono na rysunkach 1 ÷ 3.

Słowa kluczowe: wytłaczanie tworzyw, bezhalogenowe środki zmniejszające palność, wodorotlenek magnezu

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