the influence of extrusion parameters on the mechanical properties of polypropylene sheet.

1.
Brief introduction the latest progress in materials and process machinery has increased the popularity of thermoforming processes used to convert extruded thermoplastic sheets into sheets
Gauge barrels and containers in the food and beverage packaging industry (1-6).
Thermoforming simply describes a process in which the plastic sheet is formed or formed when heated to a temperature above the softening point (1-5).
When soft and soft, with the help of a combination of vacuum or mechanical plugs and pressures, the plate is stretched or entered into the cooling mold of the desired geometry.
Once the material is configured with a mold, it cools down to maintain its new shape (1-5).
The unique physical, chemical and thermal properties of polypropylene make it a quality material for food packaging applications.
These properties include low density, high melting point (
Therefore, the service temperature is very high)
With good impact properties, hardness, clarity, chemical inertia, good barrier properties and sensory neutrality (7-11).
As a result, polypropylene has experienced significant growth in the rapidly expanding food packaging sector, at the expense of other amorphous materials such as polyethylene-based chlorine and high impact polystyrene (7).
However, several materials hinder the successful thermoforming of polypropylene
Related issues (12-15).
Polypropylene exhibits a low melting strength during the thermoforming process, resulting in inconspicuous dents and thinning of inconsistent plates.
This is combined with a very narrow temperature range (
Processing window)
The plate can be successfully formed within the scope of the part (8, 9, 11, 13, 16-23).
In order to obtain any degree of consistency in thermoforming products and to minimize the need for changes in the setting of thermoforming processes, extruded sheet materials must have consistent high quality.
The purpose of this work is to determine how changes in sheet extrusion parameters, such as Cold Roller temperature or wire speed, affect the performance of the final polypropylene sheet.
This information is critical for the subsequent thermoforming of polypropylene sheet manufacturers as it demonstrates how robust the fluctuations in sheet quality in process variables are.
With this knowledge, the processor can determine the degree of control of the extrusion parameters required to produce high quality thermoforming extruded sheet materials.
This paper attempts to establish a connection between the morphology of polypropylene sheet made under various Extrusion conditions and the measured mechanical properties.
While some generalization can be made at this point, it is recognized that the preliminary studies presented in this publication are in no way allowed to make conclusive suggestions on the hot plains.
In order to do this, further experimental work must be carried out. 2.
Materials and methods the thermoforming grade of polypropylene used in this study is BASF 1184 L.
This is a kind of nuclear average polymer with a melting index of 6g/10 min (230 [degrees]C/2. 16kg)
And an average molecular weight of weight ([M. sub. w])of 265 000.
Extrusion conditions the polypropylene sheet is manufactured on the diammonium 100/45 extruder.
Figure 1 shows the name of the plate surface at the exit from the mold.
Initially, a set of standard extrusion parameters were selected, as shown below.
By systematically changing one processing parameter at a time, 15 0.
A polypropylene roll of 46 m wide x 50 m long was produced.
Table 1 records the Extrusion conditions used in these trials.
In order to produce the sheet at different wire speeds, it is necessary to adjust the machine output accordingly to keep the sheet thickness at 1. 4 mm.
Similarly, when making plates with reduced thickness, in order to keep the wire speed at 5, the extruder output is reduced together with diegap. 0 m/min.
Experimental method sdsc measurements were obtained using Perkin Elmer dsc7 power-
Compensation meter.
In the aluminum pan, the known sample weight is about 10 mg.
The controlled heating rate used to analyze all samples is 10 degC/min.
The value of 209 J/g for100 % crystalline polypropylene homopolymers was used in the calculation of the Crystal percentage (24). Standard dumb-
The Bell sample for the tensile test is from 1.
2782 specification sheet of mold made using BS 4mm specification.
The room temperature tensile properties of polypropylene sheets were determined using JJ Lloyd DS M30K tensile tester.
Experimental procedures outlined in UK standard plastics test methods BS 2782: Part 3: method 320A (1976)was followed.
At least 10 samples were tested in the machine and lateral direction of each polypropylene roller.
High temperature stress/strain data are obtained by Instron universal testing machine equipped with air circulation oven.
At the tensile temperature of 200% [all samples are elongated to a total elongation of 155]degrees]
The speed of C and adraw is 1000/min.
According to the procedure outlined by Malpassand White, before applying the tensile load, all the samples are subject to a test temperature of 12 minutes (25).
The room temperature impact performance of polypropylene sheet samples was obtained using the Rosand IFWIT7U instrument drop hammer impact tester.
Standard methods for testing plastics in the uk bs 2782 experimental procedures outlined: Part 3 (1991)was followed.
At least 10 samples were tested in each case, and the average total energy per mm thickness was obtained by calculating the area integral under the main peak of the force/deflection curve. Wide angle X-
X-ray diffraction has determined the use of the sample aSiemens D5000 X-
Ray diffraction.
Radial scan of the angle of intensity verusdiffraction, 2 [Theta]
Record in range 4-50 [degrees]for 2[Theta]
Under the same settings that use nickel to filter CuK [Alpha]
Radiation of wavelength 1. 506 [Angstrom]
Scan speed is 0. 05[degrees]/sec.
Calculate the percentage of crystals per sample using Hinrichsen\'s method (26)
, Where trueintenity is considered to be above the curve drawn along the bottom of the Crystal peak above the amorphous halo.
The Crystal percentage is the ratio of the area under the Crystal Peak to the total area of the diffraction pattern recorded on the trajectory.
The values obtained using this method are compared to the values calculated by DSCanalysis.
These two programs consistently produce a5-
Band 7%.
To measure shrinkage, a sample of 50x50mm in size is cut from the extruded paper and marked with indelible ink in order to identify the machine and the lateral direction.
Priorto test, the size of the sample is measured [+ or -]0.
01mm use the cursor calipers.
Soak the sample in the silicone oil bath for 5 minutes.
The temperature of the bathtub is kept at 155 [degrees]C [+ or -]1 [degrees]C.
After taking out from the oil bath, each sample is cooled at room temperature and its size is determined in the machine and in the transverse direction.
The contraction of the plate is expressed as: % shrinkage = [L. sub. 0]-L/[L. sub. 0]x 1where: [L. sub. 0]
= The initial length of the sample.
L = the length of the sample after heating and subsequent cooling in the air.
Five samples were tested for each volume.
Only accept results within each other\'s a5 % range. 3.
The influence of chill-
The effect of the roll temperature on the mechanical properties of extruded polypropylene SHEETOn from the outlet of the mold, the molten polymer sheet is rapidly quenched and solidified through a series of highly polished, Heat controlled cooling processesrollers. The chill-
Roller temperature (
Cost rate, therefore)
It plays an important role in determining the shape and mechanical properties of extruded polypropylene sheets (18).
The degree of crystal, the perfection of crystal and the thickness of the sheet are all reduced with the cold
Reduce the roller temperature and then increase the Roller Speed (27, 28).
On the contrary, when highkill-
Roller temperature (
So the cooling rate is slower)
The perfection of crystal and Crystal has increased.
The lower cooling rate allows the growth of thicker, stronger crystal layers in the polymer, due to the enhanced chain fluidity at higher Crystal temperatures.
In this case, the Crystal time is enough to adapt to the large-scale and good development.
Defined spherical crystal, the elastic modulus and yield strength of the extruded sheet are increased at the same time (27, 28).
The cooling rate also determines the degree and degree of separation or segregation within the crystalline melt.
This process involves the separation of materials with poor or uncrystalline crystals in the intersphere (29, 30).
As the spherical crystal grows into the melt, the uncrystalline material is pushed to the front of the crystal.
This material is then collected in areas where two or more ball boundaries meet and impact.
In rapid cooling, rapid crystals hinder the diffusion of molecules in polymer melt, resulting in a large amount of insufficient separation time for non-crystalline impurities in the boundary region between crystals.
This material is then prioritized into the spherical crystal itself.
In contrast, slow cooling provides more time for separation.
Therefore, a larger proportion of the amorphous material is ejected from the spherical crystal boundary, followed by a weakening of the spherical crystal boundary.
So the potential power
Developed crystals with high crystal degrees may be weakened by the boundary (29, 30).
Another important factor associated with the height of the adopted cooling rate is the chain density.
The iron chain is used to connect the crystal block to determine the mechanical continuity of the system (29, 31).
They act as local stress sensors in flakes and globules, thus controlling any deformation or fracture process.
As the molecular chain is effectively frozen and there is almost no diffusion in the melt, rapid cooling results in slow crystals.
Therefore, the system is interconnected by many binding molecules that promote the toughness mechanical behavior of materials during deformation (29, 31)
Under the condition of slow cooling, the molecular chain has a large fluidity.
In this case, the density of the bound chain is reduced because the moving chain can be partially separated from each other and then combined into the crystal sheet.
Therefore, the system becomes physically less physically connected to each other, so any applied load is concentrated in a position with less surface of the crystal.
This creates a large concentration of stress, reducing the applied stress required for the deformed sample (28, 29, 32).
From the data shown in the figure
2. it can be seen that the gradual increase of chill will slow down the cooling speed
The rolling temperature produces an increase in crystal from 50 °c. 1% to 56.
7% for segmented samples.
Therefore, the results show that by applying a slower cooling rate to moltensheet when it exits the mold, the degree of crystal of the sheet may increase to more than the level produced separately by the nuclear agent.
The crystalline degree of the samples collected from two sheets of paper also showed an upward trend.
Naturally, a higher level of crystal is developed in the plate sections, where the cooling rate is lower compared to the cooling rate applied on the surface of the two plates.
Due to direct contact with the Smooth Roller, the surface of the plate is subjected to a faster cooling rate.
It was found that the elastic modulus was significantly correlated with the percentage of crystals present in the sample.
For example, the discovery and cultivation of 12% crystals thechill-
Roll temperature from 30 to 80 [degrees]
C with the increase of elastic modulus from 163 to 179 N /[mm. sup. 2]
Samples tested in the direction of the machine (
Sample display in transverse direction increased by 20 N /[mm. sup. 2]).
Similarly, the yield strength will increase as the degree of cold increases
Roller temperature.
A yield strength increase of 42% was obtained in the direction of the machine, and an increase of 39% was observed horizontally.
The yield strength of the sample depends on factors such as the degree of crystal, the degree of crystal perfection, the thickness of the plate layer and the strength of the amorphous region between crystals (29, 33).
The first three parameters will increase with the gradual increase of chill-
Roller temperature. High chill-
Rolling temperatures and slower cooling rates produce a greater degree of crystals, with enough time to grow larger, stronger, and more perfect globes made up of thick flakes.
Enhancing the combined action of these three factors increases the stress required to cut the crystal block and start yielding in the tensile test.
However, a decrease in connection chain density due to slower cooling rates may reduce the stress required to produce samples by reducing the strength of the intercrystal amorphous phase.
It is clear from the results obtained that the increase in yield strength caused by the former dominates any potential decrease in yield strength caused by the latter.
It can be clearly seen from the figure
3 as the application gradually increases the chill, the decrease of the density of the connecting chain and the increase of the crystal and segregation effects
In the tensile strength at room temperature, the roller temperature decreases.
The percentage of broken elongation also showed a similar reaction.
In cold weather, the breaking elongation in the direction of the machine dropped significantly from 676%
30 \"roll temperature]degrees]
C % in achill-20
80 \"roll temperature]degrees]C.
For lateral samples, comparable declines from 716% to 37% were observed.
In the cold
Roller temperature (30 [degrees]C)
With the possible formation of the molecular chain, the molten flakes undergo a faster cooling rate.
In the case of applying an external load, many tie chains are able to destroy the thin sheet crystals that exist, thus giving riseto a toughness mechanical behavior.
The presence of smaller spherical crystals, lower crystals and less segregation effects in these samples also helped to produce this behavior in room temperature tensile tests.
Brittle mechanical behavior of samples produced at the highest cold
80 \"roll temperature]degrees]
C reflects the higher degree of crystal, the larger the crystal, the less iron chain and the greater the grading effect.
Therefore, in these samples, the British break occurs at the Inter-sphere boundary, with very few symbols drawn in advance.
Increase in Crystal observed in changing the cold-
Temperature from 30 to 60 [degrees]
C in increments of 10 [degrees]
C produces an expected increase in the high temperature value of the elastic modulus and yield strength.
Figure 4 illustrates the impact of chill-
Roller temperature on elastic modulus (Measurement at 155 [degrees]C)
For example.
The increase in elastic modulus means greater potential
Support properties for tables (i. e.
, Anti-sagging)
In the heating steps before thermoforming.
This, in turn, may help to promote uniform stretching of the final molded part and improve the distribution of wall thickness.
Although from 50, the degree of Crystal has increased significantly. 1 to 56.
Measure 7% when increasing cold
Roll temperature from 60 to 80]degrees]
C, the elastic modulus and yield stress decreased significantly for this coldRolling temperature.
This is a surprising result, as it is expected that an increase in the degree of crystalline will have a positive impact on these parameters.
Impact tests were performed on each of the five rollers.
These results are shown in the figure. 5.
It can be seen that the impact energy is slightly reduced when increasing the cold
Roller temperature of 30-60 [degrees]
C. a rapid decline was subsequently observed and further increased to 80 [degrees]C.
It can be predicted that the decline in impact performance may be due to the increase in the degree of crystal, resulting in the gradual brittle of plate samples.
In addition, the higher chill-
The roll temperature, so the cooling rate is slow, will enhance the segregation of the uncrystalline material in the area of the larger spherical crystal boundary, resulting in more potential weaknesses while the impact performance decreases.
Interpretation of the rapid decline in impact performance and thermal tensile parameters observed in cold-
80 \"roll temperature]degrees]
C is by checking X-
Ray diffraction chart
The chill of the sample making of Thesheet,
Roller temperature of 30, 40, 50 and 60 [degrees]
C reveals the maximum value of characteristic diffraction in the clinic [Alpha]-
Crystalline form of polypropylene (34-36).
However, thin sheet samples made in cold
80 \"roll temperature]degrees]
C. a small part of the evidence is shownBeta]-spherulites (
8% of all crystal materials).
This can be clearly seen from a small diffraction peak of 2 [Theta]value of 16. 4[degrees](34-36).
Seems to be the slowest cooling rate from the cold
80 \"roll temperature]degrees]
C. a small proportion in favor of development [Beta]-
Modification of polypropylene.
The existence [Beta]-
Closere also confirmed the crystal.
Examination of the internal heat of melting of relevant DSC samples.
On the low temperature side of the temperature peak of about 147 [a small shoulder is obvious]degrees]C.
Unfortunately, computer software is unable to break the melting peak and the main melting peak into two discrete peaks.
Therefore, the existence [Beta]-
Spherical crystals may be the reason for the sharp drop in impact performance observed in increasing cold
Temperature from 60 to 80 [degrees]C.
Development]Beta]-
Species can also provide a reasonable explanation for the significant decline in thermal tensile parameters.
It is reported that these Globes began to melt at a temperature of about 147 [degrees]C (34).
Therefore, at the temperature of the thermal tensile test adopted, 155 [degrees]C, the [Beta]-
The spherical crystals present in the thin sheet sample have melted, resulting in a greater rate of decrease in elastic modulus and yield strength. 4.
Effect of wire speed on mechanical properties of extruded polypropylene sheet this part of the work quantifies the effect of extrusion wire speed on mechanical properties and subsequent thermoforming properties of extruded polypropylene sheet.
In addition to increasing extrusion yield, the increase in linespeed will determine the orientation level given to the plate and the conditions under which the crystals occur.
Higher line speeds gradually increase the orientation of the non-crystalline and crystal regions in the direction of applied stress.
This results in a simultaneous increase in the number of parallel chains, as the chain unfolding from the crystal sheet block occurs during orientation (37).
The density of the molecular binding chain in the undeformed area and its subsequent degree of orientation will play a great role in determining the modulus of the sheet, the mechanical continuity of the system and the shrinkage properties of the sheet at high temperature (29, 37). Yamada et al. (37)
The report said that the number of tightening has increased
In the deformation process of semi-crystalline polymer, the binding molecules produced due to the larger orientation of the amorphous chain are accompanied by the generation of modulus.
It can be predicted that the increase in the modulus of the sheet will increase its anti-sagging and self-
Support performance during pre-forming heating steps.
It is possible to more evenly heat the sheet showing the tendency of the depression, resulting in an improved material distribution in the final part.
Higher paper strength will eventually lead to enhanced product aspects
The strength of the wall and increase the resistance to extrusion.
However, with the increase of thickness, the degree of stress relaxation shrinkage of the solid is inevitable when the plate is heated.
Stress relaxation shrinkage is a dimensional change that occurs when a sheet or thermoforming item is heated to a temperature below its melting point.
This releases the entropy part of the freeze.
In stress, it mainly comes from the orientation of the molecular chain during the tensile process of the material.
Elastic elements can be relaxed at room temperature;
However, entropy deformation can only be recovered if the product is heated to the temperature at which the molecule can freely recover its most stable spiral configuration with maximum entropy. Yamada et al. (37)
Annealing studies were carried out and they reported loosening of the band molecules that were tightened at high temperatures.
The interaction of tie molecules leads to heat shrinkage and for those samples containing the highest targeted tie chain population, the reported shrinkage is the greatest.
The change in tensile speed will change the properties of the crystalline process.
An increase in the tensile speed may result in a decrease in the time-sharing cooling rate of the sheet because the extruded sheet is in contact with the refrigerant
With the increase of line speed, the time of the volume will be shorter and shorter.
The reduction of cooling rate will extend the time of crystal.
This may allow for the development of higher levels of crystals inside the sheet as awell-forms at the same time
The developed crystal structure composed of thick flakes has higher cohesive energy.
The lower cooling rate will also increase the degree of isolation that occurs at the Inter-sphere boundary and reduce the number of connection chains that connect crystal flakes (29).
From a thermodynamic point of view, a larger arrangement of the molecular chain in the molten material will facilitate the crystalline process (27).
Increasing the line speed will naturally lead to more molecular orientation in the direction of the machine, because when the paper leaves the mold, it will withstand greater tension.
Therefore, the potential increase in the nuclear rate caused by strain-induced crystals may also help to increase the degree of crystal of the plate at a higher tensile speed.
Figure 6 shows the effect of line speed on the crystal of the sheet.
The value of the report again represents the sample obtained from the paper section and the two surfaces.
Increase line speed from 3.
5 to 5 m/min only produces a slight increase in the crystal degree of the sample of the section of 48. 8 to 49. 7%.
Therefore, it seems that at these special wire speeds, very little orientation occurs inside the plate, which subsequently promotes the strain-induced crystalline process.
By contrast, the picture
6 reveals a further increase in straight line speed from 7. 0 to 9.
At 0 m/min, the crystalline degree was greatly improved from 49 ℃ to 49 ℃. 7 to 54. 3%.
This suggests that the larger orientation of the molecular chain occurs at a higher speed with the onset of strain-induced crystals.
At a higher wire speed, a decrease in cooling rate may also affect the increase in the crystal of the sheet.
It can be predicted that with the increase of line speed, the degree of crystal and the degree of molecular orientation will increase, and the mechanical direction elastic modulus at room temperature will also increase.
This is confirmed in the results shown in the figure.
7, display increased from 27 to 163N /[mm. sup. 2]
About the speed of the line from 3. 5 to 5. 0 m/min.
Since then, the growth rate is faster, up to 194 N /[mm. sup. 2]
At maximum wire speed.
When the line speed is greater than 5, the elastic modulus increases rapidly.
0 m/min indicates the increase of crystalline degree and the greater orientation of the binding chain in the amorphous phase.
The elastic mold measured horizontally also shows a larger crease rate at a higher velocity of 7. 0 and 9. 0 m/min in Fig.
Although the growth rate is not as obvious as the direction of the machine.
This may be due to an increase in molecular orientation in the direction of the machine, resulting in a decrease in the concentration of lateral binding molecules.
It was found that there was a similar relationship between the room temperature value of yield strength and the applied line speed.
No significant change either on the machine or in the lateral direction of the line speed up to 5 m/min, in which case no substantial molecules occur in the direction of the machine
Then, when increasing the line speed from 5 m/min to 7 m/min, it was observed that the elastic modulus increased more significantly (
Machine directions 14%.
Then a large increase was made between the line speeds of 7. 0 and 9. 0m/min (
Machine directions 3%.
Although at the line speed of 9 m/min, the binding chain concentration and molecular orientation reached the maximum, the yield strength of the machine direction increased slowly, this can be considered to be the degree of orientation of the molecular connection chain at the highest line speed.
It can be suggested that in the room temperature tensile test, tiechains that have been tightened will reduce the carrying capacity.
This may lead to a broken connection chain, thus reducing the stress required to produce the sample.
The lateral yield strength increased only slightly from 34 to 36 n /[mm. sup. 2]
When the line speed from 5. 0 to 9. 0 m/min.
This result may have two opposite effects.
A reduction in the concentration of the transverse connecting chain is expected to reduce the stress required to yield in that direction.
On the contrary, it is expected that an increase in the degree of crystals will have a positive impact on yield strength.
The results show that the latter is dominant in increasing lateral yield strength.
Figure 1 shows the effect of line speed on lateral elongation during machine and fracture8.
Almost no change was observed at the line speed of 3. 5 to 5.
The direct result of the direction orientation of the minimum machine is 0 m/min.
After that, the breaking elongation of the sample in the direction of the machine dropped rapidly from 700 to 100%.
Fracture elongation is considered to indicate the residual potential of amorphous iron chain molecular stretching at high altitude.
Thus, the machine direction samples manufactured at the highest speed already contain highly oriented coordination molecules with littlescope for further stretching.
Therefore, with the increase of line speed, their breaking elongation gradually decreases.
In contrast, the smaller the degree of orientation of the transverse connecting chain, the smaller the drop in the breaking elongation from 708% at the straight line speed of 3.
From 9: 5 m/min to 500%. 0 m/min.
This value is expected to increase at higher line speeds.
This reduction can be considered as an indication of the population of the connected chain at a lower lateral level (
Thus reducing the stress and strain requirements when the fracture occurs)
At a higher line speed, the increase in the degree of crystalline (
Crispy sample).
The thermal tensile test showed that the elastic modulus of the extruded sheet samples increased at high wire speeds.
The results show that due to the presence of greater molecular orientation in the sheet, greater melting strength is achieved at a higher wire speed, thus increasing the resistance to dents.
This feature will obviously help to heat the paper more evenly before stretching.
Impact tests were performed on samples produced at all line speeds.
Breaking value of impact energy (
Expressed as a function of thespecimen thickness)
I was shown to be directly related to the trend observed by the Crystals. e.
The impact performance decreased with the increase of the crystalline degree.
Figure 1 illustrates this relationship. 9.
When increasing the line speed from 7, it is observed that the impact energy drops rapidly. 0 to 9. 0 m/min (
1 side 37%, 2 side 63%).
Samples produced at a wire speed of 9.
On a clean line parallel to the direction of the machine, 0 m/min was observed to break in atotally brittle mode.
This indicates that an unsatisfactory high level orientation has been induced in these samples, followed by a decrease in impact performance.
A high level of plate orientation like this may eventually lead to side wall splitting in subsequent thermoforming containers.
The shrinkage test shows that the machine direction shrinkage is expected to increase as the line speed increases.
This is illustrated in Figure 1. 10.
Sheet shrinkage is considered to be an indication of the degree of molecular orientation in the sample.
This can be clearly seen from the picture.
9, where the sample is extruded at a wire speed of 9.
0 m/min is affected to the maximum extent by the orientation of the machine direction, so it is subjected to the maximum shrinkage force in this direction.
It was found that the transverse contraction was basically not related to the line speed.
Although the orientation of the machine gives greater power and self
Supports the performance of the extruded sheet, and during the pre-forming heating process, the start of a larger shrinkage causes the sheet to warp. Post-
Articles with higher orientation will also have production shrinkage.
This will damage the dimensional stability of the container, especially in high temperature applications such as microwave food trays.
In this case, it is clear that shrinkage should be minimized. 5.
Effect of sheet thickness on mechanical properties of extruded polypropylene sheet the purpose of this test is to study the effect of sheet thickness on subsequent mechanical properties of sheet.
When the molten extrusion plate is urgent from the mold, its cooling speed is partially affected by its thickness.
The cooling rate in turn affects the shape and mechanical properties of the resulting sheet.
For example, thin gauge sheets are exposed to high-speed cooling at the exit from the mold.
This leads to a structure characterized by a small sphere of low degree of crystal, consisting of thin and weak flakes that are connected by molecular chain molecules to each other.
At the same mold temperature, the plate with a larger thickness will experience a lower cooling speed and a more perfect crystal in its core, with a fewinterconnecting tie chain, and develop a higher level of crystal and strength in the film.
The morphology resulting from the change in cooling rate is reflected in the tensile properties of the material.
Thin sheets containing small incomplete balls, which are divided into weak sheets, will show the mechanical behavior of pipes with low yield strength and high elongation.
Plates of larger thickness, characterized by large spherical crystals, high crystals and larger spherical crystal boundary segregation, will be more inclined to have high yield stress and smaller break elongation values30, 38).
However, the degree of plate orientation imposed by the extrusion process must also be properly considered.
At the exit of the mold, the athin molten sheet cooled quickly, resulting in a sudden stop in molecular movement.
Therefore, when the plate is squeezed, there is little chance of releasing any molecular orientation caused by the tension of the plate.
In contrast, thicker plates are able to retain more heat when leaving the mold, allowing for greater relaxation in the direction of the machine.
Figure 11 shows the percentage of crystal of the plate part and surface as a function of the plate thickness.
These values are related to X-
X-ray diffraction analysis
About the thickness of the plate from 0. 4 to 1.
4mm, the Crystal rate of the thin sheet sample increased from 43. 2% to 50. 0%.
The larger crystals formed in the thickest sheet reflect a lower cooling rate on its core during extrusion.
The presence of a larger molecular orientation in the sheet may promote a small range of strain-induced crystals;
However, the increase in crystal resulting from this process is clearly dominated by the opposite effect of higher cooling rates on crystal.
Both room temperature and high temperature tensile tests reveal the dominance of the plate orientation on the crystal when determining the mechanical properties of the plate.
As expected, the yield increases as the thickness of the sheet increases.
However, the calculation required for the elastic modulus, yield strength and tensile strength each contain the thickness of the tension.
Therefore, the values obtained for these values isolate the effect of the change of crystal and orientation.
Although the crystalline degree increased by 14% as the thickness of the sheet increased, the elastic modulus reported in figure 1
12 with the increase of the thickness of the plate, the direction of the machine has dropped by 10% and the horizontal has dropped by 6%.
These results may be considered as signs of an increasing number of directional iron plates in thin-gauge plates that do not have the opportunity to relax during extrusion. Fig.
12 It is shown that for samples tested horizontally, the rate at which the elastic modulus decreases with the increase of plate thickness is uneven.
This shows that the horizontal connection chain concentration decreases as the orientation level of the machine direction increases.
The study shows that the yield strength of the machine direction increases as the thickness of the plate decreases.
It seems that the crystal direction strength of the intercrystal region is enhanced in the thinner flakes due to the presence of a larger concentration of directional Ferrin.
This factor dominates any possible drop in yield strength due to the presence of lower Crystal levels and thinner flakes in these samples.
The smaller group of tie-in chains, plus the lower degree of crystal of the plates, increased the lateral strength by 5% with the decrease of the thickness of the plates.
More tie chain molecules also seem to affect the increase in the tensile strength in the direction of the machine from 47 to 55 N /[mm. sup. 2]
As the thickness of the plate decreases.
As the thickness of the sheet decreases, the applied load is distributed over a gradually large number of tie molecules, followed by a higher stress required to destroy the sample.
A much smaller increase of 5% was observed in the transverse value of the tensile strength.
This again reflects a larger level of molecular orientation in the direction of the machine in the thin gauge film.
The rapid cooling rate applied to at least the thickness of the molten sheet will hopefully promote fine spherical structure, with little time for significant segregation effects.
In contrast, it can be envisaged that a slower cooling rate applied to a thicker plate will cause the core to form a larger sphere.
The existence of small ball crystals usually promotes the toughness behavior under load (30, 38); however,Fig.
13 shows that the percentage of fracture decreases with the decrease of plate thickness.
A significant decrease of 56% for machine direction samples.
Breaking elongation is considered as a way to measure the residual potential of the connection chain stretching.
Therefore, there is a large number of existing machine directions in the sheet, which excludes significant elongation before breaking in the room temperature tensile test.
The transverse samples showed that the percentage of fracture decreased by only 20% as the thickness of the plate decreased.
This shows that the lateral tie rod chain orientation generated during extrusion is very small.
Therefore, the lateral can withstand greater stretching before the fracture occurs.
Although there is a lower level of crystals in the thingauge sheet, it is clear that when determining the elastic modulus and yield strength at high temperatures, the molecular orientation has a greater effect than the crystals.
There is also evidence that the difference between the direction of the machine and the transverse samples is not as obvious as the difference encountered in the room temperature test.
This suggests that the high temperature used in the test may allow relaxation to a very small extent and may strengthen the film structure by annealing.
The shrinkage test showed that the mechanical direction shrinkage increased significantly by 76% as the thickness of the plate decreased.
In contrast, the change in the shrinkage value of the transverse measurement is small.
These results are shown in the figure. 14.
These tests further demonstrate the large number of machine orientation generated during thin gauge sheet extrusion.
In thermoforming, excessive shrinkage is undesirable because it causes the plate to cause warping during heating, resulting in poor distribution of product materials.
In addition, if most of the orientation is not removed before forming, then as the stress continues to relax, the dimensional stability of the final formed product will be affected.
Use highkill-
The roll temperature, thus reducing the cooling rate, may help to change the orientation of the machine direction and produce an excellent balance between the machine direction and the performance of the lateral plate.
Contrary to the orientation effect, the damage value of the impact energy seems to depend on the nature of the crystals that exist. These values (
Quote thickness per mm)
As shown in the figure, it is a function of the thickness of the plate. 15.
As the thickness of the plate increases, the impact performance may be reduced, due to the formation of spherical crystals in thicker sheet samples.
Larger pellets with higher crystalline values have inherent fragility and show a tendency to crack along the boundary line of pellets (27, 30).
This is because the slower cooling rate that allows them to grow also sets aside time for the greater separation of the non-crystalline in the sphere.
The process then weakens the pherulite boundary by providing a potential weakness plane during the testing process, followed by a drop in impact performance.
In contrast, a small amount of spherical crystals present in the thinnest sheet provides a greater barrier to crack growth under mechanical stress.
This is because the grading effect that occurs during the crystalline process does not weaken the crystal boundary to the same extent. 6.
It was found that the effect of extrusion melting temperature on the mechanical properties of extruded polypropylene sheets the change at extrusion melting temperature has little effect on the subsequent properties of extruded sheets.
Polypropylene is easily oxidized and degraded during extrusion because of the presence of tertiary carbon atoms on the length of its polymer skeleton (2, 39).
The increase in temperature accelerates this process, thus making the choice of extrusion temperature of polypropylene the key.
Degradation is usually accompanied by a reduction in the molecular weight and viscosity of the material, which is due to broken chains.
Power requirements are not reduced (i. e. , output)
It was recorded during the study.
This shows that the increase in the melting temperature adopted in this work does not significantly change the viscosity of the polymer melt.
To confirm this hypothesis, the average molecular weight of the four-roller weight extruded at different melting temperatures was analyzed ([M. sub. w])
High temperature gel penetration chromatography is used.
With the increase of melting temperature, the molecular weight did not change significantly.
It can be inferred that there will be no significant chain breakage at a higher temperature per barrel, and therefore no degradation will occur.
If a condition of constant plate thickness is applied, it may be foreshadowed that a molten sheet appearing from the mold at a higher temperature will retain a longer amount of heat than a sheet appearing at a lower temperature.
Greater potential thermal retention will reduce the cooling rate applied to the chip core, thus allowing the development of the crystal structure, which is characterized by a high degree of crystals and a larger spherical crystal.
If the amolten sheet that appears in the mold retains less heat at a lower temperature, the degree of crystal will decrease.
This will involve the growth of smaller ball crystals consisting of thin and weak flakes with many connecting chains (29).
Percentage of crystals (
Determined for sections and surfaces)
Shown in Figure 1 as a function of the melting temperature16.
The crystalline degree increased slightly from 50. 1% to 52.
For samples with melting temperature rising from 5% [220], was observeddegrees]C to 224 [degrees]C.
This result means that after extrusion at a higher melting temperature, a slower cooling rate is applied at the center of the plate.
There was no significant change in the crystal value obtained for surface samples.
This observation is worth looking forward to, because at all melting temperatures, torapid cooling is performed immediately on the surface of the sheet when exported from the mold.
The sheet samples were subjected to room temperature tensile tests both in the machine and horizontally.
The test shows that with the increase of the melting temperature, the observed increase in crystal accompanied by a slight upward trend in the room temperature value of the elastic modulus (
Measured at 5% strain)
And yield strength.
For mechanical and transverse elastic modulus, 4% and 2% were increased, respectively.
With the increase of the melting temperature, the yield strength showed a similar upward trend.
Therefore, it may be suggested that the stress required to yield is governed by a stronger sheet formed under a slower coolant produced at a melting temperature of 232 [degrees]C.
With the increase of the melting temperature, both the tensile strength at room temperature and the percentage of fracture showed a mild decrease.
These trends are considered to indicate that an increase in melting temperature has resulted in a slight increase in crystal degree and a decrease in chain density.
Thermal tensile test at 155 [degrees]
C. elastic modulus (
Measured at 5% strain)
Change from 220 [temperature]degrees]C to 232 [degrees]C.
This is represented by a graph. 17.
It can be inferred that a larger degree of crystal formed in the sheet extruded at a higher melting temperature may increase its melting strength to a small extent, thus minimizing the depression.
With the increase of the melting temperature, the gradual strengthening of the crystal structure is reflected in a similar slight increase in the yield strength value of 155 [degrees]C.
With the increase of melting temperature, the total impact energy decreased slightly.
As shown in the figure. 18.
This trend may indicate the crystalline properties produced in the sheet at different melting temperatures.
At the highest melting temperature of melt [degrees]
C, due to the weakening effect of the boundary, there may be greater crystals and large spherical crystals that will lead to a decrease in impact performance.
Conclusion the following conclusions can be drawn from the results of the study on the influence of extrusion parameters on the mechanical properties of polypropylene sheets. 1.
Increase in chill-
Rolling temperature up to 60 [degrees]
C increases the crystalline and modulus of the sheet.
Therefore, it can be predicted that the improvement of the performance of these materials will bring greater anti-concave resistance to the plate and improve the strength and clarity of the molded parts.
In addition, the paper produced in the cold was found
80 \"roll temperature]degrees]
Evidence showing [Beta]-
With the decrease of impact properties and melting strength, polypropylene is modified. 2.
Proof line speed is 7. 0 and 9.
0 m/min yields significantly greater molecular orientation of machine directions compared to lower line speeds in range 3. 0 to 5. 0 m/min.
As the orientation of the machine direction increases, the crystals, modulus and shrinkage increase, and the impact performance decreases.
Sheet extruded at 9.
0 m/min has particularly poor impact properties, such as sample splitting in a clean production line running parallel to the direction of the machine. 3.
Thin gauge film (0. 7 mm)
Develop a lower crystal content than a thick sheet (up to 1. 4 mm gauge)
Due to faster cooling from the mold outlet.
Nevertheless, 0.
The 7mm gaugematerial shows a mechanical strength superior to the thick sheet.
The analysis shows that this is due to the change in the direction of the machine. 4.
Minor changes in extrusion melting temperature (224 to 232[degrees]C)
There was no significant effect on the mechanical properties of the resulting sheet.
As the impact performance decreases at the same time, the Crystal degree increases slightly.
It is clear that an increase in the melting temperature does not seem to accelerate any potential degradation process that occurs in the melting of the polymer.
The work was funded by the Centre for Teaching companies in Northern Ireland.
The authors also thank Wilsanco Plastics Co. , Ltd. for using extrusion equipment and donating polypropylene resin in this study. REFERENCES1. J.
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