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Experimental Investigation of the Single Screw Extruder With Grooved Melting Zone.

NTRODUCTION

Single screw extruder (SSE) possesses many advantages such as high efficiency, continuous processing, simple structure, and low cost, which makes it as the most widely used polymer processing equipment. However, there are still some shortcomings in traditional SSE with smooth barrel, such as high specific energy consumption, low conveying efficiency, low specific throughout, etc.

An effective solution to improve the conveying efficiency is to groove the inner surface of the barrel along the axial direction, which was introduced by Schneider [1] at Institute of Plastics Processing (IKV) in 1960s. The grooves can greatly increase the apparent friction coefficient at the interface of the barrel and the solid plug. The effects of structural parameters on the apparent friction coefficient of the barrel were studied by Rautenbach and Peiffer [2], Grunschloss [3], and Potente [4], Later, the helical grooves were made in feeding zone by Grunschloss [5] to improve the solid conveying efficiency and enhance the ability of building pressure, ensuring the stable delivery of the material. Meithlinger [6] compared the performance of the SSE with axially grooved feeding zone and helically grooved feeding zone. The influence of grooves on equivalent friction coefficient of the barrel surface was investigated and the calculation of the solid conveying angle was corrected at the same time. Besides, Sasimowski et al. [7], and Dungen et al. [8] studied throughput, melt temperature, and energy consumption of SSE with grooved feeding zone, respectively. A solid conveying theory called double-flight driving theory was proposed for helically grooved SSE by Pan et al. [9], The results showed that the positive conveying could be achieved after optimizing the extruder design; the extruder designed by double-flight driving theory had a higher yield, while the screw torque and energy consumption were also greatly reduced, compared with traditional SSE.

In the extrusion of SSE with grooved feeding zone, it was generally found that the melting quality was poor and the extrusion was not stable because the melting efficiency of the melting zone did not match the delivery efficiency of the feeding zone. In order to overcome this problem, researchers did a lot of works on screw structure, such as using barrier screw, which was widely used due to its excellent plasticizing effect. Wortberg and Michels [10] studied the extrusion process of axially grooved SSE with barrier screw. The results showed that it had a high specific throughout and excellent melting quality. Later, Schlafli and Zweifel [11] discovered the relationship between the throughput of extruder, structural parameters of barrel groove, screw speed and polymer density. Womer et al. [12] studied the performance of three different structures of barrier screw and the result showed that the influence of screw structure on throughput, pressure, and melt temperature was very significant.

It is also an innovative solution to study on barrel structure of SSE to improve the melting efficiency. Grunschloss [13, 14] firstly extended the grooves in the feeding zone to the melting zone and a SSE named HELIBAR with excellent plasticizing property was developed. The relative positions of barrel grooves and screw channels in melting zone were analyzed and a physical model of plasticizing process was established by AvilaAlfaro et al. [15, 16]. The results showed that the melting rate of SSE with grooved barrel was significantly higher than that of conventional SSE and the melting rate reached the maximum with a specific combination of the groove number and groove width. However, the effects of different combinations of barrels and screws on the melting performance were not studied yet and the melting process was not observed by visualization.

One of the most difficulties in studying SSE with grooved melting zone is that it is hard to observe the melting state during extrusion. In this study, a new hydraulic quick-opening SSE platform was constructed and the melting state of polymer could be monitored in real time. A novel melting mechanism for SSE with grooved melting zone and anticompression screw was proposed. Two kinds of polymers, high-density polyethylene (HDPE) and polypropylene (PP) were investigated. Melt pressure and melt temperature were measured. Besides, effects of different combinations of barrels and screws on the melt starting point, melt length, and throughput were also studied in the article.

MELTING MODEL

Based on the assumption that the solid plug existed in the grooved melting zone and then was ruptured into upper solid plug and lower solid plug, some researchers [17] suggested that main source of the melting heat was the internal friction heat generated by two solid plugs, which were in the barrel groove and the screw channel, respectively, rubbing against each other. However, in this study, it was found that the upper solid plug only existed for a short period of time in the barrel groove of melting zone and then melted quickly.

The melting process of SSE with grooved melting zone is described in Fig. 1. The model of this study is based on the fact that the polymer in the grooved feeding zone is gradually compacted into a solid plug, which does not subject any shear [9], At the beginning of the melting zone, the internal bonding of the whole solid plug is weakened by being heated. Under the shear between the barrel groove and the screw channel, the whole solid plug is subjected to shear fracture and a large amount of internal friction heat is generated (Fig. la). Coupled with the heat conduction from the barrel, the upper solid plug in the barrel groove quickly reaches the melting point and the groove is filled with molten polymer (Fig. lb). This process takes very little time because the depth of the barrel groove is shallow, basically within one screw pitch, which can be neglected. As the screw rotates, tremendous liquid-solid shear heat is generated by the molten polymer in barrel groove and the lower solid plug in screw channel rubbing against each other. In addition, viscous dissipation is also produced by the friction drag between the melt in barrel groove and the solid plug in screw channel. The solid polymer at the interface melts and a melting film is developed due to the liquid-solid shear heat and the viscous dissipation. The melting efficiency is improved because the liquid-solid shear heat is much larger than the heat from the external friction in traditional extruder. The liquid-solid shear heat and the viscous dissipation are the main melting heat source during the plasticizing process. It is necessary to mention that an anticompression screw is chosen to use in this model and the reason why the normal screw is not adopted is explained in Comparative Experiments With a Normal Screw section. Thus, along the transport direction, volume of the barrel groove gradually reduces due to the reducing depth of the barrel groove, while volume of the screw channel gradually increases due to the increasing depth of the screw channel. As the volume of the barrel channel is decreasing and the volume of the screw groove is increasing, the melt in the barrel groove and newly melted polymer are forced into the screw channel by the couple driving of screw channel and barrel groove, as shown in Fig. lc and d. The volume-increased screw channel provides just enough room and a melting pool is developed in the front of the screw channel because the density of the melt is lower than that of the solid. The solid plug is stacked in front of the screw flight and is gradually melted, as shown in Fig. le. After the melting is over (Fig. If), the melted polymer is then pumped through the metering zone and the die to mold the desired product.

EXPERIMENTAL

Apparatus

It is necessary to utilize an appropriate experimental method to realize the accurate observation of the melting process. The traditional visualization of melting performance in conventional extrusion is not suitable for this study. Such as "screw pulling-out" technique by Wilczyriski et al. [18], the ejection of the screw would destroy the molten state of the polymer in the screw channel and it is hard to observe the melting state of the polymer in the barrel groove. In order to investigate the melting behavior of the polymer during the extrusion, a novel hydraulic quick-opening SSE platform was constructed, which is shown in Fig. 2. Sealed copper bars were used at the interface between the upper barrels and the lower barrels to prevent the leakage of polymer. In the case that hydraulic rod was fixed outside the upper barrels, there was little free surface for the heating components. Thus, a number of heating rods were adopted to heat the barrels of the three zones, while the extrusion die was heated by cast aluminum heaters.

The barrels (BI, B2, and B3) and screws (SI and S2) used in this study are shown in Fig. 3. B1 was a smooth barrel. B2 was a barrel with grooved feeding zone. B3 was a barrel with grooved feeding zone and grooved melting zone at the same time. B2 and B3 were manufactured with helical grooves and both the screw thread number and the barrel groove thread number were 8. SI was a normal screw with positive compression, while S2 was an anticompression screw. The screw diameter (D) of the two screws was 45 mm and the length/diameter (L/D) ratio was 20.

Temperature/pressure sensors were used to on-line measure the temperature and pressure of the polymer in the melting zone and the die. The positions of sensors in B3 and die are shown in the Fig. 4, which are the same positions of the sensors as B1 and B2.

Materials

The polymers used in the study were a high-density polyethylene (HDPE, 6100M) and a polypropylene (PP, B8101), kindly provided by Sinopec Beijing Yanshan Branch. The physical properties of the polymers are shown in Table 1.

Procedure

For better understanding the melting performance of the SSE with grooved melting zone, comparative experiments were conducted. Combinations of barrels and screws are shown in Table 2. The setting temperatures of barrels and the die are present in Table 3. The melt temperature and melt pressure of the polymer were able to be directly obtained through temperature/pressure sensors.

A hydraulic quick-opening SSE platform was used to investigate a polymer behavior along the screw axis. After the extruder reached a steady state, screw rotation was stopped. Then the upper half barrels of the feeding zone, melting zone, and metering zone were able be quickly pulled up by the hydraulic device. The melting process could be monitored by opening the barrels. In particular, the melt starting point and the melting length were also accurately observed. To better investigate the melting mechanism, photographs of polymers in the screw channel and in the barrel groove were taken, respectively.

RESULTS AND DISCUSSION

Verification of the Melting Model

In this study, a hydraulic quick-opening SSE platform was constructed to investigate the polymer behavior. Both PP and HDPE were used to validate the model. The screw speed was set at 10 r/min. After the machine reached a steady state, screw rotation was stopped and the barrel was quickly opened to observe the state of PP in the barrel groove and screw channel. A graduated ruler was disposed on the edge of the screw to mark out every screw pitch. The results are shown in Fig. 5.

According to Fig. 5a, the solid plug in screw channel was gradually compacted into a whole solid plug in 5D-6D of the feeding zone. The melt was gradually generated and gathered in the front of the screw channel to form a melting pool at 6D-8D. With the plasticizing process continuously going on, the solid plug in the screw channel gradually reduced while the melt gradually increased. Until the screw channel was filled with the melt, the plasticization was over. Figure 5b shows the melting state of PP in the barrel groove corresponding to the position of Fig. 5a. It can also be seen that the groove was filled with transparent molten polymer at the beginning of melting zone because the solid plug in barrel groove was rapidly melted under the interface shear heat and the heat conducted from the barrel.

Figure 5c shows the cooling state of PP, observed when opening the barrel. It can be clearly seen that the whole solid plug was present in the screw channel of 6D-7D and gradually melted to form a melting pool in the front of the screw channel of 8D-10D, while the barrel groove was filled with molten polymer for the entire melting zone.

The same method was used to open the barrel to observe the cooling state of HDPE, as shown in Fig. 6. It can be also seen that as the melting process going on, the width of the melting pool in the front of the screw channel was increasing (Fig. 6a). Figure 6b shows the melting state of HDPE in the barrel groove corresponding to the position of Fig. 6a. The groove was filled with transparent molten HDPE in the whole melting zone and the white particles were the unmelted material bonded from the screw channel.

From the above experiments, it can be known that the experimental studies are consistent with the melting model in Fig. 1 and the hydraulic quick-opening SSE platform is reliable for the research of melting and plasticizing performance of SSE with grooved barrel.

Comparative Experiments With a Normal Screw

The positive compression screw (normal screw) is widely used in the plastic processing field due to establishment of stable pressure for extrusion. First, the barrels with different structures (Bl, B2, B3) and a normal screw (SI) were utilized to study the plasticizing performance of SSE with grooved barrels. Two kinds of polymers (HDPE and PP) were used to avoid the occasional results. The screw speed was 10 r/min and the barrel temperatures are shown in Table 3.

The effect of barrel structures on the melt pressure of the melting zone with SI is shown in Fig. 7. It can be seen that, when the inner wall of the barrel was equipped with helical grooves, the melt pressure in B2 and B3 was much higher than that in Bl. The melt pressure in B3 was even higher than that in B2 at every detecting point. In addition, at the position of 13D, the melt pressure in barrel of B3 reached the peak, at 54.8 MPa for HDPE and 60.4 MPa for PP, respectively, which had exceeded the safe pressure of the SSE (49 MPa). The hydraulic system and sealed copper bars were even unable to keep the polymer from leaking in barrel of B3. It is very dangerous to run the machine under that pressure.

For the SSE with grooved barrels (B2, B3), the transport capacity of solid-phase polymer increased significantly due to the driving of screw flight and barrel flight in the grooved feeding zone. On the one hand, the depth of the melting zone in normal screw decreased along the transport direction, that is, the transport capacity of the melting zone was weakened. The transport capacity of the melting zone was not compatible with that of the feeding zone. On the other hand, the liquid density of the polymer was lower than that of the solid. A larger volume of the screw channel, which a normal screw did not have, was required to accommodate all the liquid polymer. This two reasons resulted in a blockage of polymer at the end of the feeding zone, as shown in Fig. 8. Therefore, the melt pressure reached too high along the melting zone. For the combination of SI and B3, the depth of the barrel groove and the screw channel decreased at the same time in the melting zone, while the combination of SI and B2 had a smooth barrel in the melting zone and no change on the depth of the barrel groove. Combination of SI and B3 had a larger compression ratio, so that the melt pressures in B3 was higher than that in B2 along the melting zone.

Thus, a conclusion can be obtained that a normal screw is not suitable for SSE with grooved melting zone. It can also explain why a normal screw is not adopted in Experimental section.

Comparative Experiments With an Anticompression Screw

An anticompression screw has the screw channel which is gradually enlarged in depth. A larger volume of the screw channel can meet the transport requirement of SSE with grooved feeding zone. Thus, an anticompression screw would be the better choose for SSE with grooved barrels in the melting zone.

In this part, three types of barrels (Bl, B2, B3) were also used, in order to study the effects of the barrel structures of SSE on the yield and plasticizing properties like melt pressure, melt temperature, melt starting point, and melting length. Two kinds of polymers (HDPE and PP) were also used. The screw speed was 10 r/min and the barrel temperatures are shown in Table 3.

Melt Pressure. The effect of barrel structures on melt pressure in the melting zone with S2 is described in Fig. 9. It can be seen that the melt pressure in B3 was reasonable for both HDPE and PP, which also proved the availability of the anticompression screw for SSE with grooved feeding zone and grooved melting zone.

It is also observed that the melt pressure in B2 for both polymers was slightly higher than melt pressure in B1 and B3 in the melting zone. For combination of S2 and B2, the solid-phase polymer throughput increased significantly due to the driving of screw flight and barrel flight in the feeding zone. But there were no barrel grooves in the melting zone. It was because of the anticompression screw (S2) that the melt pressure did not soar that high, compared with melt pressure in SI. For combination of S2 and Bl, smooth barrel of the feeding zone meant that the transport capacity was not that strong and less melt polymer was delivered to the die. Therefore, the melt pressure at the die was the lowest for both HDPE and PP. For combination of S2 and B3, due to the presence of grooves in the barrel, the transport capacity of grooved melting zone was perfectly compatible with that of grooved feeding zone. Tremendous liquid-solid shear heat, which was generated between the barrel groove and the screw channel in grooved melting zone, guaranteed that the material was melted in time. So it still had a good plasticizing quality and a reasonable pressure distribution along the whole melting zone.

Melt Temperature. Figure 10 shows the effect of barrel structures on melt temperature in the melting zone with S2. The melt temperature of combination of B3 and S2 was the highest among the three combinations. The reason was that a large amount of liquid-solid shear heat was generated under the coupling shear of barrel groove and screw channel. The melting rate was promoted and the melt temperature rose. Both HDPE and PP had the same trend. The actual melt temperature in the grooved barrel (B3) was about 10[degrees]C higher than the temperature in the smooth barrel (B1 and B2) averagely. That meant lower set temperature was able to achieve the same heating effect and the energy consumption could be reduced.

Melt Starting Point. After the machine had reached a steady state, screw rotation was stopped and the barrel was quickly opened. By observing the melting state of the polymer with different combinations, the melt start point and melting length were determined.

Figure 11 is the melt starting points in the melting zone with S2. For both HDPE and PP, the melt starting points were at position of 6D in Bl, while the melt starting points were at position of 7D in B2 and B3. The melting zone of Bl was a smooth barrel and the polymer in the screw channel directly contacted external heat source conducted from the barrel, so that the polymer melted rapidly at the beginning. As soon as it entered the melting zone, it began to melt at position of 6D. Although the melting zone of the barrel of B2 was also a smooth barrel, the melting efficiency could not match the increased delivery efficiency of the grooved feeding zone. The melt starting point was delayed to the position of 7D. For combination of B3 and S2, on the one hand, the solids transport capacity of the feeding zone was enlarged and more melting heat was needed; on the other hand, the interface shear heat was utilized by not only polymer in the barrel groove, but also polymer in the screw channel, so that the polymer in the barrel groove was melted firstly and the actual melting starting point of the polymer in the screw channel was also delayed.

Melting Length. The melting length is determined by the melt starting point and melt ending point. The melt ending points in the melting zone with the screw of S2 are presented by Fig. 12. The melt ending points of HDPE in barrel of BI, B2, and B3 were at 14D, 17D, and 11D, respectively and the melt ending points of PP in BI, B2, and B3 were at 12, 15D, and 10D, respectively. The melting lengths are shown in Table 4. It can be seen that melting length in B2 was longest among the three barrels for both HDPE and PP. Because the solid-phase polymer throughput increased significantly in the grooved feeding zone and there was too much polymer to melt for the melting zone with smooth barrel. The heat provided by external heat source was less than the required melting heat, resulting in a decrease of melting rate. It can also be seen that melting length in B3 was shortest among the three barrels for both HDPE and PP because the presence of the barrel groove greatly improved the plasticizing efficiency in the melting zone. The large amount of liquid-solid shear heat generated greatly promoted the melting rate in melting process. Besides, the melting length was shortened in B3, even shorter than that in Bl. It meant that SSE with barrel grooves can be designed with shorter screw and barrel. The structure of SSE can be further optimized.

In order to further investigate the main melting heat source in the plasticization process, the barrel's setting temperature of the melting zone was changed to observe the melting behavior of HDPE under different conditions. It was found that the melt starting point of the polymer would be delayed when the barrel's setting temperature of the melting zone was too low (below 150[degrees]C). The length/diameter (L/D) ratio of the screw used in this study was only 20. The melt starting point of polymer was too late, resulting in poor plasticization. Therefore, the barrel's setting temperatures of the melting zone were set to (1) 150[degrees]C, (2) 160[degrees]C, (3) 170[degrees]C, (4) 180[degrees]C, respectively. It is worth mentioning that the setting temperature of the melting zone in the experiments was lower than that of normal smooth single screw extruder.

As can be clearly seen from the Fig. 13a, for HDPE, when the barrel's setting temperatures of melting zone rose from 150[degrees]C to 180[degrees]C, the melt starting points remained stable at position of 6D-7D. The barrel's temperatures of the melting zone have little effect on the position of the melt starting points. The heat conduction from the barrel was not the main resource for melting. The melt ending points of HDPE of 150[degrees]C, 160[degrees]C, 170[degrees]C, 180[degrees]C were at 14D, 13D,13D, and 12D, respectively, and the corresponding melting length were at 7D, 7D, 7D, 6D, respectively. The melting length remained essentially constant. That means the liquid-solid shear can still play a leading role in lower barrel temperatures and screw speed. Only in the high speed of traditional single screw extruder, the friction heat between the inner wall of the barrel and the solid plug in the screw serves as the main heat source. Therefore, it can be seen that the liquid-solid shear heat is the main heat source of the plasticizing process.

Throughput. The throughput is an important parameter for SSE. The throughput of SSE was defined by the melt mass flows through the die in a certain time, after the machine had reached a steady state.

Table 5 shows the throughput with different barrels and the screw of S2. It was obvious to see that the throughput with Bl was much smaller than that with other barrels and the throughput with B3 was the highest among the barrels. Both HDPE and PP had the same trend. The throughput in B3 was 4.6 times as much as that of the B1 for HDPE and throughput in B3 was 4.4 times as much as that of the Bl for PP.

Due to the driving of screw flight and barrel flight in the feeding zone for B2 and B3, transport capacity increased significantly. The anticompression screw gradually built up pressure along the transport direction. The polymer was continuously conveyed, increasing the extrusion throughput. It can also be seen from the table that the gap between the throughput in B2 and B3 was very small, which indicates that the barrel groove of the feeding zone was the main factor affecting the throughput of SSE. The presence of the barrel groove significantly increased the throughput of the extruder, which was of great significance in industry.

CONCLUSIONS

A novel melting mechanism for SSE with grooved melting zone and anticompression screw was proposed, and a new hydraulic quick-opening SSE platform was constructed to verify the model using materials of PP and HDPE. Tremendous liquid-solid shear heat and viscous dissipation were found to be the main melting heat source for the SSE with grooved melting zone and anticompression screw. Comparative experiments were carried out to investigate melting behavior of different combinations of barrels and screws. It is the anticompression screw that fits SSE with grooved melting zone, but not the normal screw. Compared with conventional SSE, it was found that actual melting temperature was about 10[degrees]C higher in the case of SSE with grooved melting zone and anticompression screw. Although melting of polymer in the screw channel started at a later time, the melting length of SSE with grooved melting zone was greatly shortened by 50%, compared with that of traditional extruder. The melting efficiency was significantly improved. In addition, the throughput of SSE with grooved melting zone increased to 4.5 times that of traditional extruder averagely.

REFERENCES

[1.] K. Schneider, Chem. Eng. Technol., 41, 364 (1969).

[2.] R. Rautenbach and H. Peiffer, Kunstst. Ger. Plast., 69, 377 (1979).

[3.] E. Grunschloss, Kunstst. Ger. Plast., 74, 24 (1984).

[4.] H. Potente, Kunstst. Ger. Plast., 75, 439 (1985).

[5.] E. Grunschloss, Kunstst. Ger. Plast., 75, 850 (1985).

[6.] J. Meithlinger, Kunstst. Plast. Eur., 93, 17 (2003).

[7.] E. Sasimowski, J.W. Sikora, and B. Krolikowski, Polimery, 59, 505 (2014).

[8.] M. Dungen, S. Hartung, and M. Koch, AIP Conf. Proc., 1779, 030011 (2016).

[9.] L. Pan, P. Xue, M.Y. Jia, K.J. Wang, and Z.M. Jin, eXPRESS Polym. Lett., 6, 543 (2012).

[10.] J. Wortberg and R. Michels, SPE ANTEC Tech. Pap., 1, 48 (1997).

[11.] D. Schlafli and Y. Zweifel, ANTEC Conf. Proc., 5, 195 (2001).

[12.] T.W. Womer, W.S. Simith, and R.P. Wheeler, ANTEC Conf. Proc., 1, 267 (2005).

[13.] E. Grunschloss, Plast. Technol., 49, 15 (2003).

[14.] E. Grunschloss, Int. Polym. Proc., 17, 291 (2002).

[15.] J.A. Avila-Alfaro, E. Grunschloss, S. Epple, and C. Bonten, Int. Polym. Proc., 30, 284 (2015).

[16.] J. A. Avila-Alfaro and C. Bonten, AIP Conf. Proc., 1779, 050005 (2016).

[17.] X.M. Jin, M.Y. Jia, P. Xue, J.C. Cai, L. Pan, and D.Q. Yu, J. Mater. Process. Technol., 214, 2834 (2014).

[18.] K. Wilczynski, A. Lewandowski, and K.J. Wilczynski, Polym. Eng. Sci., 52, 1258 (2012).

Ke Chen [iD], Xudong Lin, Ping Xue, Mingyin Jia, Chenxin Li

Institute of Plastic Machinery and Engineering, Beijing University of Chemical Technology Beijing 100029, China

Correspondence to: M. Jia; e-mail: jiamy@mail.buct.edu.cn

Contract grant sponsor: National Natural Science Foundation of China; contract grant number: 21404007.

DOI 10.1002/pen.24743

Published online in Wiley Online Library (wileyonlinelibrary.com).

Caption: FIG. 1. The melting model of single screw extruder with grooved melting zone: (a)whole solid plug; (b) generation of the melting film; (c) forming of the melting pool; (d) melting continuing; (e) melting pool expansion; (f) melting over.

Caption: FIG. 2. The hydraulic quick-opening single screw extruder platform. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 3. Schematic diagrams of barrels and screws.

Caption: FIG. 4. The positions of temperature/pressure sensors in B3 and the die.

Caption: FIG. 5. The melting behavior of PP in the grooved melting zone: (a) melting state of PP in the screw channel; (b) melting state of PP in the barrel groove; (c) cooling state of PP in the screw channel. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 6. The melting behavior of HDPE in the grooved melting zone: (a) cooling state of HDPE in the screw channel; (b) melting state of HDPE in the barrel groove. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 7. The effect of barrel structures on the melt pressure in the melting zone and the die with SI: (a) HDPE; (b) PP.

Caption: FIG. 8. Blockage at the end of the feeding zone with the combination of S1 and B2 for PP. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 9. The effect of barrel structures on melt pressures in the melting zone and the die with S2: (a) HDPE(b) PP.

Caption: FIG. 10. The effect of barrel structures on melt temperatures in the melting zone and the die with S2: (a) HDPE (b) PP.

Caption: FIG. 11. The melt starting points in the melting zone with S2: (a) HDPE; (b) PP. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 12. The melt ending points in the melting zone with S2: (a) HDPE; (b) PP. [Color figure can be viewed at wileyonlinelibrary.com]

Caption: FIG. 13. The effect of barrel's setting temperature of the melting zone on the melting behavior of HDPE: (a) melt starting point; (b) melt ending point. [Color figure can be viewed at wileyonlinelibrary.com]
TABLE 1. Physical properties of HDPE and PP used in the experiments.

Polymer        Melt flow       Bulk density       Melting
                 index        (kg/[m.sup.3])       point
               (g/10 min)                       ([degress]C)

HDPE              0.13             952              130
PP                0.45             900              165

Polymer         Tensile       Elongation at
             strength (MPa)     break (%)

HDPE             21.57             500
PP                23.5             200

TABLE 2. Combinations of barrels and screws.

Screw                  Barrel

S1                     B1
                       B2
                       B3
S2                     B1
                       B2
                       B3

TABLE 3. The setting temperatures of barrels and the die.

                         Temperature ([degrees]C)

Polymer    Feeding zone     Melting zone     Metering zone    Die

HDPE       80               180              185              175
PP         100              230              235              225

TABLE 4. The effect of barrel structures on the melting length with S2.

                       Melting length (D)

Polymer        B1             B2             B3

HDPE           8              10             4
PP             6              8              3

TABLE 5. The throughput of different barrels with S2.

                         Throughput (kg/h)

Polymer        B1             B2             B3

HDPE           2.96           11.8           13.6
PP             2.58           10.66          11.28
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Author:Chen, Ke; Lin, Xudong; Xue, Ping; Jia, Mingyin; Li, Chenxin
Publication:Polymer Engineering and Science
Article Type:Report
Date:Sep 1, 2018
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