all-polymer composites from recycled woven polypropylene fabrics and polyethylene film.

by:Chengbai     2020-05-04
Brief introduction in recent years, the use of woven fabric of directional polypropylene tape has increased significantly for applications such as bulk transportation of agricultural and construction materials, packaging tape and ground stabilization net.
Therefore, more and more such materials are now entering waste logistics, which poses certain challenges to the treatment of economic and environmental benefits.
It is estimated that there are about 10,000 tons of woven polypropylene bags discarded from agricultural streams in the UK each year [1]
, This may be twice as much as the construction industry, as safety legislation prevents re-use through the deposit system [2].
In the UK, most of this material is currently processed through landfill sites.
Although it is possible to incorporate waste polypropylene from these resources into low
Application for grades such as wood replacement products [3-5]
In this regard, there are some problems, the melting point of the material is higher compared to polyethylene, polyethylene constitutes a large part of the recovery, and it is difficult to crush the woven material.
In addition, the traditional recovery including the melting of polypropylene will eliminate the orientation of the polymerization bands, thus losing the potential higher stiffness and strength of these bands.
A possible alternative to this study is to explore the full-
Aggregate the composite material, where the directional polypropylene tape acts as an reinforcing fiber in the composite material. The use of all-
In recent years, polymer composites have also developed greatly.
Many of the early work in this area was done by wards and colleagues, in the heat-
Compaction method]6-9].
This method involves heating woven aggregate fabrics to temperatures below their melting point under pressure.
The outer surface of each fiber or tape is melted and fused together, resulting in good
Compacted composites with considerable orientation and very good mechanical properties.
These materials are now commercialized and are used in more and more applications.
A potential disadvantage of this approach is the narrow processing window, so very good temperature control is required.
Another way to overcome this to some extent is to use the tape with the alower outer coating
Then, at any temperature, it can be compacted between the melting point of the polymer and the melting point of polypropylene. If all-
Polymer Composites will be made of waste polypropylene, and the second of these methods is impossible because it requires the application of polymer coatings during tape production.
Hot method-
In this case, the compaction is also not ideal for two reasons.
First of all, a very good request.
In the recycling operation, it can be difficult to control the process with a narrow temperature window, because it usually requires low cost and fast throughput.
Second, although there is a large amount of woven polypropylene entering the waste logistics, there are more low density polyethylene (LDPE)
This requires a viable recycling route.
These reasons lead to the method used here, that is, the use of low density polyethylene as a matrix material to combine polypropylene tape [11].
Therefore, the purpose of this work is to study the possibility of using a simple production method with a wide process window to produce simple flat composite materials from a combination of waste woven polypropylene fabric and low density polyethylene film.
Potential applications of this material are expected to be low
Cost board products, especially for outdoor applications where Wood
Basic materials are often limited.
The materials and processed raw materials for this study were provided by Llandeilo, a British Second Life plastics company, who collected discarded agricultural plastics from farms in western England.
The waste fertilizer bag is used as a raw material for woven polypropylene fabric with a plain weave of 3mm and a compression thickness of 0.
21mm Weight 115g /[m. sup. 2].
Two low density polyethylene films are also provided: one is a film with a thickness of 0.
15mm Weight 103g /[m. sup. 2]
And one of 0.
12mm, weight 73g /[m. sup. 2].
In addition to the different thickness, the two types of ldpe are the same, both of which are used to make the wider composition placed together with the AC sheet.
The DSC test of raw materials shows that PP has amelting points (midpoint)of 169[degrees]
C, indicating that it is polymer grade, while the melting point of low density polyethylene is 109 [degrees]C.
In most studies, the material is cut into 200mm squares for compression molding.
These materials are used in most cases
A small amount of surface dirt and water was received, and unlestherwise said that in this case all the results were for the material.
For some samples, the square is washed and/or air by water-dried.
The last set of samples used chopped polypropylene.
This is produced by a controlled manual cutting method that produces a single tape about 2 cm long (As shown in the figure. 1)
Or through a business method of producing more refined products (As shown in the figure. 2).
Then use the alternating layer of PP and hdpe to lay the sheet of PP and hdpe, and then compress and form between the heated sheet.
After a period of time, the compression die is water-
Cool and remove the composite.
The variables studied include: polyethylene quantity *.
This varies depending on the use of different combinations of polypropylene fabric and polyethylene film, with a polyethylene weight percentage between 30 and 100% (justLDPE). [
Figure 1 slightly]* Cleaning.
These materials are used in most cases
Received, there is a proper amount of dirt on the surface and very little surface water.
These are designated as dirty/dry.
Water cleaning and air drying for production cleaning/drying or cleaning/wet (with no drying).
By adding some water to theas-also produced dirty/wet samplesList received
* Compression conditions.
Compression temperature (
Template temperature)
Ranging from 150 to 200 [degrees]
C and the pressure applied changes from 0. 5 to 5 MPa.
The time when the material remains unchanged at the compression temperature for 10 minutes before it remains unchanged. * Lay-up.
In most cases, the 200mm square meters of PE and PP are arranged alternately, and the samples are cut from the 0/90 direction.
Cut some samples in one [+ or -]45 direction.
Create a plaque with a smaller random arrangement (~20 mm)pieces.
Patches were also generated by random arrangement of PP filaments and small pieces ofl.
The compressed patch is cut into parallel
Size 200X15mm (
About 6mm thickness).
These samples are used for bending tests.
For the ImPACT test, the sample was cut into two 100mm lengths, while for the tensile test, the dog
Cut the bone from the strap. [
Figure 2:[
Figure 3 slightly]
Mechanical testing and microscope bending, stretching and impact testing were performed on the produced samples.
Bending test is used with three-
Point bending geometry.
The length of 100mm is used, and the deflection rate is 5 mm/min.
The bending modulus and bending strength are calculated according to the force/deflection curve.
Tensile tests were performed using the Hounsfield mechanical and electrical testing machine at a tensile rate of 5 mm/min.
Impact test using Ray
Run the impact testing machine using a notch-free Izodconfiguration.
For bending and tensile tests, an average of 5 samples were used in each case;
An average of 10 times for impact testing.
Using Reichart-optical microscope observation by sample on polished slicesZheng Rong and microscope.
The fracture surface of some impact samples was observed by scanning electron microscopy.
Figure 3 shows the effect of the material composition on the bending strength and stiffness (
PP woven material, pressed at 160 [degrees]
C and 5MPa in the direction of 0/90).
It can be seen from this that with the increase of PP ratio, both strength and stiffness increase, reaching the maximum value at about 50% PP.
This shows that a certain amount of low density polyethylene is needed to make the PP layer well bonded, but the benefits of harder and stronger PP will decrease as the content is too high.
For further testing, a composition of 61% PP was used, as this is most conveniently achieved with alternating laying
Ups of the most common thickness materials found in agricultural waste logistics.
Figure 4 shows the effect of compression pressure (
PP woven material, pressed at 160 [degrees]
C. The composition is 61% PP and the orientation is 0/90).
It can be seen from this that the stiffness continues to increase slightly as the pressure increases, but the strength only changes slightly over 2 MPa. [
Figure 4 slightly]
Figure 5 shows the effect of compression temperature (
5 MPa compressed woven PP with a composition of 61% PP and A orientation of 0/90).
This shows the bending strength (
And reduce the stiffness to a certain extent)
Increase to a maximum of about 170 [degrees]
C subsequently decreased as the temperature further increased to 200 [degrees]C.
This effect may be due to the increase in temperature and the loss of PPorientation at high temperature, the adhesion between PP and hdpe layers has been improved.
These two effects will be further considered below.
It can be seen in the figure that the contact between materials has improved. 6-
8, showing the optical Microphotograph of these samples.
Figure 6 is compressed to 150 [degrees]
C and display PP tape (darkestregions), the LDPE (mid-grey regions)
, Install resin filled air-gaps (
Lightest area).
It can be seen that the contact between PP and low density polyethylene is relatively poor, which may lead to poor adhesion.
As the compression temperature increases to 170 [degrees]
C, as shown in the figure
7, the contact between pp tape and hdpe film seems to be much better.
The PP tape is still well defined.
Compression molding of 200 [degrees]
C, above the melting point of PP, as can be seen from Figure 1
Although all materials have been cured, PP has flowed into low density polyethylene and may have lost all orientation. [
Figure 5 Slightly][
Figure 6 slightly]
Figure 1 shows the effect of cleaning and drying9 (
Compression is 160 [for wovenPP [degrees]
C and 5 MPa, with 61% pp and 0/90 orientation).
This shows that although the strength and stiffness of clean samples are slightly improved, the difference between samples is small.
Surprisingly, in most cases, the presence of water seems to have slightly improved the performance, probably because of the additional internal pressure generated by water evaporation at a high temperature of compression molding.
Of course, the presence of a small amount of water will not result in a significant loss of property.
Change the effect of laying-
As shown in the figure, arrange up. 10and 11.
Figure 10 shows the bending strength, tensile strength and impact strength, whereas figure
11 shows the bending modulus.
For all of these samples, the ratio of PP is 61% and compression is 160 [degrees]Cand 5 MPa.
The woven 0/90 has an alternate laying
Along the test direction of PP tape, it consists of woven parts. The woven [+ or -]
45 wassimilar in addition to cutting samples at 45 [degrees]
To the suede
The comparison between the two shows that there is no significant difference in bending strength, while the tensile strength is significantly higher for the 0/90 orientation.
This shows that the bonding between the layers is the dominant factor for the bending test, so the orientation of the tape is not very important.
For tensile testing, the combination between layers is not important, so the orientation of 0/90 is much stronger.
For 0/90 samples, the bending stiffness is slightly higher, which indicates that the tape direction does have some importance in the initial part of the bending test.
Interestingly, the impact strength [+ or -]
The 45 samples are higher, probably because of the lower stiffness. [
Figure 7 Slightly][
Figure 8:
Careful substitute
Fabrics made of low density polyethylene and PP do have the best performance, but it must be recognized that the task of cutting and laying folds and folding fabrics may be prohibitive in potential commercial operations
In this case, a more automated process may be required, using the random direction of the widget.
The remaining data sets in the figure.
10 and 11 show this because of the random arrangement of small pieces (
About 20mm square meters)
And two kinds of chopped materials.
This shows that it is not surprising that all mechanical performance is declining as automation improves.
It seems that if you want to use random arrangement, it is better to have smaller parts, as can be seen from the better performance of the hand.
Crushed samples compared to small pieces.
This may be due to the fact that under random arrangements, PP has a smaller chance of contact with LDPEcontact, which is necessary for good integration.
If the number of these fragments is small, then the distribution of these fragments may be more uniform than that of larger fragments.
Attributes of hands-
In addition to the tensile strength, the crushing sample, although not as good as the woven sample, is still moderate, which may be a viable cycle route. [
Figure 9 omitted[
Figure 10 slightly]
Commercially chopped samples give the worst mechanical properties, in part because the scale of the shredding is very small and also because it contains lines for stitching cracks.
Figure 12 shows the fracture surface of the commercial crushing material impact sample, which clearly shows the presence of some of the stitching lines that are not bonded to PP or dlp.
The information from the sack manufacturer indicates that the sewing thread used is polyester, so it is not surprising that the adhesion to olefin is poor. [
Figure 11 omitted][
Figure 12:
From the above results, with the increase of temperature, PP tape loses some strength and stiffness due to the recovery of orientation. This is a well-
Cognitive phenomena of directional polymers [11-14].
To study this in more detail, a controlled recovery test was performed on a single PP tape.
These are dynamic mechanical thermal analyzers using flow measurement (DMTA)
, Operating in thermal mechanical analysis (TMA)
Mode, at high temperature, under controlled zero load, a single PP tape maintains the tensile direction (
140, 150 or 160 [degrees]C)
30 minutes.
The length of the tape is constantly monitored and then used to calculate the overall shrinkage (%)
Caused by heat treatment
The results of these tests are shown in the figure. 13.
It can be seen that the tape shrank by about 25% in [at14]degrees]
C. rise to nearly 60% at 160 [degrees]C.
Tried the test in 170 [degrees]
C, but at this temperature, the tape is notable to support its own weight.
With the recovery of the direction and the contraction of the tape, the modulus of the tape is expected to decrease.
Using the small strain tensile test mode, the tensile modulus of a single tape was measured on the DMTA before and after heat treatment.
Figure 1 shows the results of the heat treatment time of 10 minutes and 30 minutes14.
It can be seen from this that the modulus of the PP tape is about 4 before any heat treatment is carried out.
1 GPa, but at any heat treatment over 140 [this rate of decline is fastdegrees]C.
In the first 10 minutes of any heat treatment, the loss of modulus mainly occurs.
At160 with heat treatment]degrees]
C, the modulus dropped to about 700 MPa.
This value is the low end expected by PP, confirming the discovery of DSCfindings that it is a fairly low polymerstiffness. [
Figure 13:
The bonding strength test can also be clearly seen from the above results that the bonding between low density polyethylene and PP tape is important, which is measured for personal PP tape. Lap-
The shear samples were made using a separate PP tapesomeverlapping monolithic low density polyethylene film with an overlap length of 10mm.
These are heated in the compression mold (
Between slides)
At different temperatures, it is then compressed at a pressure of 5 to 10 MPa.
After cooling and careful removal, samples in DMTA can be tested in stretch test mode.
The shear strength results of these tests are shown in the figure. 15.
The temperature rises from 140 to 170 [degrees]
When C, the bond strength between hdpe and PP increased to 0. 45 MPa.
Interestingly, the same test was performed between the two PP tapes, with reasonable bonding strength at 160 and 170 [1]degrees]C.
It is shown again that the material is a polymer with a lower melting range.
The general conclusion is that it seems that the scrap ppin a all-
Polymer Composites and waste low density polyethylene are a potential viable option for the recovery of these materials.
The amount of each material is approximately equal and the best performance is obtained;
LDPErequired provides good bonding and directional PP to provide higher strength and stiffness. [
Figure 14 omitted][
Figure 15 omitted]
Through compression molding technology, the processing of this recycled composite material is relatively simple, and there are quite wide processing windows in terms of temperature and pressure.
This method is also relatively insensitive to the presence of dirt and water;
In fact, a small amount of water may be beneficial because there will be additional internal pressure when the water evaporates.
Using chopped PP does lead to poor performance, but automation can be much higher on a commercial scale.
If crushing is used, it seems important to remove the polyester stitching for PP bags.
The orientation of PP tape is over 140 [and a considerable recovery has indeed occurred]degrees]
C, accompanied by a significant decrease in PPmodulus.
In contrast, as the temperature increases, the adhesive strength between PP and hdpe and between PP tape increases.
Therefore, it seems that there is a balance between the two effects. if reasonable integration is to be achieved, the orientation will inevitably have considerable losses.
The original modulus of the PP band is assumed to be 4.
4 GPa, the best composite sample only reaches the elastic modulus of about 1, which is a bit disappointing. 5 GPa.
This is due to the fact that the dropin modulus of the heat treated PP belt is quite large, plus the importance of adding much lower modulus low density polyethylene to the interface bonding.
Nevertheless, the performance obtained is better than that obtained by complete melting
Mixture after treatment (As shown in the figure. 5).
The types of materials that can be achieved through this route will never compete with Virgin in terms of performance
Polymer composites, but it may have a place on a cheaper tablet
As property profile (
The stiffness is about 1.
5 GPa, strength up to 40 MPa, good performance)
Better than existing wood
Other recycled polymer products [15].
It will have good outdoor performance compared to wood
As a base material for complete recycling, it can be claimed to reduce the environmental impact (and recyclable)material. REFERENCES 1.
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