properties of uniaxially stretched polypropylene films.

Introduction to increase the strength of polymer film by stretching
Mature technology.
Filmmakers mainly rely on two-way stretching to strengthen machines and horizontal films (TD)
For the application of one-way stretching (
Direction)
More limited.
Some of these applications are in pet (PET)
Poly polyethylene chloride binding (PVC)
Food packaging with high fiber
Density Polyethylene (HDPE)
Woven bag with ribbon, double-layer lining breathable sanitary film, self
Adhesive labels, and polyethylene packaging and Lamination (Schut, 2005).
MDO is widely used in polyethylene and polypropylene (PP)
Film because of its large number of applications in packaging.
MDOunit typically includes casting extrusion lines, slit molds, large drum wheels for cooling, and multiple stretch units arranged in sequence.
Stretch in these units, which can be operated at different temperatures and stretch ratios.
MDO units provided by the polymer Application Research Center (CREPEC)
Contains two stretch areas as shown in Figure 1. [
Figure 1 slightly]
The MDO unit can be in-line or off-
By such as: DR, drawing speed, drawing time (
A film can be stretched many times)
, Stretching temperature and heat-
Set conditions.
The distance between the stretch rollers is 5 cm.
The use of MDO units is growing, mainly for specific polymers.
This process usually improves the strength and barrier properties of the film, but there are some shortcomings for the film produced.
For example, MDOprocess improves the barrier properties of nylon and vinyl ethanol (EVOH)
Polymer, but it also makes the film brittle in the direction of the machine, the tear resistance is very low (MD)(Schut, 2005).
For EVOH, MDO is selectively applied due to any two-way stretching that deteriorates barrier performance.
Stretching is usually carried out at high temperatures, resulting in highly oriented films that lead to the opposite sex. Nie et al. (2000)
The morphological development of PP films in the process of one-way and two-way stretching using atomic force microscopy (AFM).
They reported that the formation of the original fiber structure with thicker raw fiber in MD, while the thinner raw fiber is connected with thicker raw fiber, forming a whole powerful crystalDez et al. (2005)
The effect of stretching on the crystal and structure of two-way oriented PP film was studied.
Their results confirm the formation of directional crystalline fibers during stretching.
They also observed that the stretching ratio had no significant effect on the heating point of the stretched sample.
Small pool and Cakmak (2004)
Indicates the initial hybridization incubation of the flakes (
Sadeghi et al. demonstrated the typical morphology of PP films produced under low cooling conditions. (2005))
It is first broken down into small crystal fragments during stretching and then added to MD to form a directional microfilament.
Small pool and Cakmak (2004)
Observe a middle shish-kebab-
Crystal structure during stretching.
Using this method, Ashesh-kebab-
Just like the fiber structure that occurs in strain 1.
2 and the reported large raw fiber size is 3-5 [micro]m in diameter.
Rettenberger, etc. (2002)
The effect of temperature on stress was studied
Strain behavior during PP stretching.
They found typical toughness behavior of yield point, neck reproduction and strain hardening to 155 [temperature]degrees]C.
At a higher temperature, the deformation is not yield, but accurate. rubber-like.
This behavior is also reported when the film is stretched under a high filter (over 750 mm/s).
They also observed that
With the increase of strain rate, the uniformity of deformation is reduced. Srinivas et al. (2003)
Linear low stretch of metal elements is studied
Density Polyethylene (LLDPE)
And reported that the module and tensile strength increased almost linearly with the increase of DR (5) above DRs.
Gould also observed this DR dependence (1988)
In the cold drawing process of some polymers.
For nylon and polyester, the tensile strength obeys a strong linear relationship with the DR, while the forPP chart shows two regions: one at 5-
7 followed by the second area with a small slope, up to aDR 10.
Bheda and Spruiell (1986)
The optical transmission properties of oriented PP film are analyzed.
Samples with higher orientation show greater overall light transmission.
Bheda and Spruiell (1986)
The transmission of this light is first controlled by the roughness of the surface, and secondly by the internal morphology of the film. Taraiya et al. (1993)
The permeability of oriented PP film was investigated.
They propose that the main factors controlling the penetration of gas molecules, therefore, the blocking performance is the orientation of the amoeba.
The flow of gas through the amorphous phase of the polymer film can be expressed as P = DS, where P is the permeability coefficient, D is the diffusion coefficient, and S is the solubility of gas (
Adsorption of gas molecules on membrane surface).
The orientation of the amorphous phase affects these two parameters, especially the diffusion coefficient. Taraiya et al. (1993)
It is also shown that the oxygen permeability decreases with the decrease of the tensile temperature.
Although this is important, in the development of the microstructure of the film and the mechanical properties during the stretching process, there are few results reported on the MDO process.
The purpose of this work is to investigate the effects of different process conditions on the properties of two different PP films prepared using the industrial MDO line.
Two experimental materials of different PP grades were used in this study. PDC1272 (PP1272)
With melt flow index (MFI)of 0. 8 (230[degrees]C/2. 16 kg)
It is a high molecular weight grade of Basell and pp46 12e2 (PP4612)with MFI of 2.
8 is the ExxonMobil brand proposed for the production of oriented films.
The manufacturer reported the two resins as homogeneous resin, and the pp446 12 was introduced as a molecular weight distribution resin in Shuangfeng.
Infrared spectrum tests were carried out, and no trace of ethylene was found in the absorption spectra of both resins.
Determination of the flow properties of the resin by anARES rheometers (
New TA InstrumentsCastle, DE).
Frequency scanning test was performed at 230 [degrees]
C and time scan tests were performed on the sample at 230 [degrees]
C evaluate the decrease of elastic modulus over time.
The results showed that thermal degradation was less than 5% during the time required to run the frequency scan test.
Measure the Tensile viscosity through the new SER universal test platform of the Xpansion instrument (Tallmadge, OH).
The model we used in our experiment was SER-HV-
A01, is a double saturated stretch flowmeter designed specifically for the ARES Rhine platform.
Film preparation film preparation using two extrusion film production lines: The first is laboratory-
Scale device with slit mold (
20 cm widthand month. 19 cm gap)
Extrusion at 220 [degrees]C.
To cool the extruded film, a fan is installed to supply air to the surface of the film at the Mold outlet.
The cooling rate is very fast, so we can get a highly oriented film (
See Sadeghi and others. , 2007).
Since the extrusion speed at the exit of the mold is constant
The speed up determines the DR of film production.
The second isan industrial MDO production line of Davis standard company (Pawcatuck, CT)
Designed for directed film production.
Figure 1 shows a sketch of the theMDO line.
It includes single and double screwdriver (
We use a single screw extruder)
Equipped with a slit mold of 122 cm width, a cooling drum and a stretch unit consisting of two areas, each consisting of two rollers of 1370mm width.
Therefore, it is possible to operate at two different temperatures and different DRs.
Extrusion at 220 [degrees]
The distance from the mold outlet to the cold roller is 150mm.
We chose a constant rolling temperature of 140 [degrees]
C. for the first stretch zone, only the first stretch zone is used to operate under different DRs.
The mold outlet is not cooled, and the extrusion temperature drop between the mold outlet and the cooling roller is estimated to be negligible.
Film representation crystal orientation measurement using BrukerAXS X-ray (
Carlsruea, Germany)
Angle measuring instrument with Hi-STARtwo-
Size area detector.
The generator is set at 40kv and 40 mA, copper CuK [alpha]radiation ([lambda]=1. 542 [Angstrom])
Choose using graphite crystal monometer.
The sample of the detection distance is fixed at 8 cm.
Samples need to be carefully prepared for maximum diffraction intensity before measurement.
To get the best total thickness of about 2, this includes stacking several thin film layers. 5 mm.
Pole position number (1 1 0)and (0 4 0)
The Crystal reflective surface is measured and the orientation factor is determined according to the measurement results.
Field emission scanning electron microscope (FE-SEM-Hitachi S4700)
Used to observe movies.
The sample was etched in a solution of 60% [H. sub. 3]P[O. sub. 4]and 40% [H. sub. 2]S[O. sub. 4]
Mix with about 0. 5 wt.
% Potassium permanganate.
The etching time is 25 minutes and the sample is rinsed with dilute solution of sulfuric acid, hydrogen peroxide and distilled water.
For infrared spectrum measurement, the infrared spectrum was recorded on the NicoletMagna 860 infrared spectrum instrument of thermal electronics. (Waltham, MA)
UsingA DTGS detector with Resolution 4 [cm. sup. -1]
And it will accumulate 28 scans.
The beam is polarized through the spectrum-
Technology selenium zinc wire grid bias mirror from thermal electronics
The Crystal and amorphous orientation were measured based on the method explained in detail by Sadeghi et al. (2007).
Differential Scanning Heat Meter (DSC)
The test was carried out on the TA instrument (New-Castle, DE)
Q1000 using 20 [heating ratedegrees]C/min.
The oxygen transfer rate is determined using the modification of ASTM Standard method D 3985-81 with an Ox-
Tran model 2/21 equipment (Mocon Inc.
Minneapolis, MN)at 25[degrees]C.
The tensile test was carried out using Instron (
Instron structural testing systems, Novi, MI)5500R machine.
The program used is based on D638-
ASTM standard 02a.
Measure fog and clarity according to procedures specified in astm d 1003-97.
These measurements were made on aHaze Guard Plus [TM]instrument (Model 4725)
Made by BYK-Gardner Inc. (Columbia, MD).
Results and discussion the linear bullet-binding data of PP resin are reported in Figures 2 and 3.
It is observed from Figure 2 that PP1272 shows a huge complex viscosity in a very low frequency range, indicating that alarger zero-
Shear viscosity compared to pp46 12. [
Figure 2:[
Figure 3 slightly]
Taking into account the dependence of zero
As Sadeghi et al have done, the shear viscosity of the polymer to the molecular weight. (2007): [[eta]. sub. 0]= K[M. sup. 3. 4. sub. w](1)
The molecular weight of PP1272 was found to be 1.
3 larger than pp446.
Because we have calculated the molecular weight of pp46 12. (2007)
The molecular weight of PP1272 is 350 kg/mol, which is estimated to be 455 kg/mol.
Figure 3 shows the weighted relaxation spectrum of the two resins.
The relaxation light spectrum is particularly sensitive to molecular structure and may be used to study the existence of high molecular weight chains with long relaxation time.
The relaxation spectrum is calculated based on these data (G\', G\'\', [omega])
Using NLREG (non-linear-regularization)
Computer software package of Honerkamp andWeese (1993).
As shown in figure 3, the weighted spectral shape of pp46 12 is different, slightly wider than pp1272.
This can be attributed to the two-peak molecular distribution of pp46 12.
Transient Tensile viscosity of the resin at two different tensile rates measured at 200 [degrees]
C as shown in figure 4.
Due to experimental difficulties and limitations of equipment, reliable data cannot be obtained at 230 [degrees]C.
Low strain rate for 1 [s. sup. -1]
Although PP1272 is more sticky, both resins show a similar trend.
However, the pp46 12 in the henky strain rate curve for 5 [is slightly differents. sup. -1]
It was observed that a very slight strain hardening was again attributed to the molecular weight distribution of its Twin Peaks. [
Figure 4 slightly]
In order to solve the orientation and arrangement of the microstructure of the film produced, the width-angle X-
X-ray diffraction measurement (WAXD)
Infrared spectrum experiment was carried out.
Figure 5 shows the WAXD diffraction pattern of the PP1272 film obtained from both processes (
Laboratory equipment, low cooling conditions and MDO lines).
The analysis of the crystal direction can be obtained from the polar figure (1 1 0)and (0 4 0)
Reflective surface.
The position of the crystal plane relative to the direction of machine production (MD)
Described in the sketch of figure 5e.
The normal of 1 1 0 plane is the bisector of the axis and the B axis, and the normal of 0 4 0 along the B axis
Axis of unit crystal cells.
For PP1272 films obtained from laboratory devices under high cooling conditions, the strength (or orientation)
In 10 planes, TD and normal directions are concentrated almost equally (ND)
And the strength is small (
Smaller orientation)
Observed in MDdirection.
For PP1272 films obtained using MDO units, the orientation of the 1 1 0 plane is mainly the orientation of the TD and 0 4 0 planes (b-axis)
Mainly in the direction of ND.
The behavior of the polarization map of MDO samples of Pp46 12 is similar, and the orientation strength is slightly higher, so it is not described here.
Orientation of non-crystalline and crystal phases (c-
Axis relative to MD)
The samples were measured by Fourier transform infrared spectrum, and the results are shown in Table 1.
The orientation function is calculated according to the suggestions of Lamberti and Brucato (2003): [f. sub. i,MD]= (D -1/D + 2)(2)
Where D is the ratio of absorbance in the machine (parallel)
In TD.
For the orientation function of the crystal phase (c-
Axis relative to MD), [f. sub. c]Band 998 [cm. sup. -1]
So D will be considered ([A. sub. [parallel]]/[A. sub. [Vertical words]])
998, where A is absorbance.
Measurements include the total orientation of crystal and non-crystal phase orientation 972 [band]cm. sup. -1]
Selected and [f. sub. av](
Average orientation)
According 【([A. sub. [parallel]]/[A. sub. [
Perpendicular to]]). sub. 972].
Orientation of non-crystalline phase ,[f. sub. a]
, Can be determined by the following two values :[f. sub. av]= [X. sub. c][f. sub. c]+ (1 -[X. sub. c])[f. sub. a](3)where [X. sub. c]
The degree of Crystal calculated according to the dsc results.
As expected by the WAXD results, table 1 clearly shows that the orientation function of the crystal and amorphous phases increases with the increase of DR
However, as expected, MDO production lines are more efficient than laboratory units.
Similar results have been made by cream and others. (2001)for a HDPE.
The orientation value of the pioneer MDO film cooled under normal circumstances (cooling drum)
No stretching (DR=1)
Very low, indicating the structure of the ball.
The important point is about the pp46 12 film obtained from the MDO process, which shows a higher orientation compared to pp1272.
To speculate on the double-State Effect of molecular weight distribution (
The broader relaxation spectrum in figure 3 indicates this)
For MDOprocess, it is more effective than the molecular weight itself.
At this point, we also believe that the slight strain hardening observed in the Tensile viscosity compared to PP1272 (see Figure 4)
It is due to its double molecular weight distribution.
This results in a higher chain orientation in which the chain is stretched in a semi-molten state during MDO.
This is interesting because in our previous researchSadeghi et al. , 2008)
We found that for films obtained from high-cooling laboratory extrusion units, the most influential parameter of orientation is molecular weight.
Figure 6 reports the directional function of the PP1272 movie obtained using the MDO unit as a function of DR
The orientation of the crystal phase is always higher than that of the non-crystal phase, and both depend on DR (
Slope of curve)
Decreased as DR increased
It is worth mentioning that the difference between crystal and amorphous orientation factors increases with the increase of DR
Figure 7 compares the DSC results of PP1272 films produced by MDO process with laboratory results
The scale of the film and the initial PPgranules.
The results of pp46 12 were not reported due to similar trends.
Movies made using MDO lines show higher Fusion points (about 10[degrees]C)
Since there is a thicker crystal of a small shoulder at a lower temperature (
Thickness of double peak crystal sheet).
This is the opposite of what Dez and others reported. (2005)
Because MDO has a considerable effect on DSC results.
For film samples prepared using laboratory devices at high cooling rates, lower (
Compared to MDO)
, But a more sharp melting peak is observed in figure 7, which indicates that the uniformity of the crystal sheet is better.
Comparing the area under the film, the crystalline degree of the directional film sample was increased to 49. 7% and 49. 1% (
For laboratory units and MDO samples, respectively)
This is 46 compared to the initial polymer particles. 1%. [
Figure 5 Slightly]
To reveal the morphology of the film, SEM microphotos were taken from the surface of the film, as shown in figure 8 (
The machine direction is shown in Figure 8a (as shown in the arrow).
The sample was etched and stretched a little (3%)
Provide better quality for pictures.
Figure 8a shows the stacked sheet structure of the film prepared from the laboratory unit at a high cooling rate, whereas for MDO film samples of the same thickness, the fiber structure is observed (Figure 8b).
In our previous paper, the formation of the first sample stacked sheet structure has been studied (Sadeghi et al. , 2007).
However, for the second sample, the observation confirms the result of the text View (Nie et al. , 2000;
Koike and Cakmak, 2004).
Our understanding is to stretch at a temperature of 140. degrees]
C transforms the initial crystal structure and breaks down most of the flakes into tinypieces, so will be connected and reoriented to form a coarse long fiber.
This is consistent with the morphological development results proposed by Koike and Cakmak (2004).
DSC curves of Pp1272 film samples (Figure 7)
This may be a reflection of this mechanism, and the main peak may be due to the elongated crystal fiber and the shoulder corresponding to the tiny thin sheet connected. [
Figure 6 slightly][
Figure 7 Slightly]
As shown in Figure 9 and Figure 10, the most obvious difference appears in the tensile response of the sample.
The tensile test results performed in MD are shown in Figure 9.
PP1272 MDO film sample with DR = 1 (i. e.
, Original pioneer film with normal cooling and thickness of 150 [micro]m)
And a film with a thickness of 35 [micro]
M under low cooling conditions shows the typical behavior of spherical structure PP with obvious yield and strain hardening.
Thickness of PP1272 film and 35 [prepared by laboratory device under high cooling conditionsmicro]
M shows unique behaviors that have been extensively studied in our previous work (Sadeghi et al. , 2007).
This behavior is due to a highly oriented slab structure (Figure 8a).
Continuous strain hardening after the elastic region indicates this structure.
This is the result of the Crystal block stretching and reorient (Sadeghi et al. , 2007).
Almost completely elastic (solid-like)
Behavior was observed in MDO films prepared by Dr 3, 5 and 6.
The strength is very high and this behavior is attributed to the formation of strong, long, thick fibers. [
Figure 8:[
Figure 9 omitted[
Figure 10 slightly][
Figure 11 omitted]
The response to the film tensile test in TD is another sign of the difference in the crystal structure of the film sample.
As shown in Figure 10, the PP1272 MDO film exhibits obvious yield behavior, while the pp46 12 MDO film breaks immediately after applying stress, indicating that the strength in the td direction is very poor.
The same behavior was observed using pp46 12 obtained using laboratory devices under high cooling conditions.
These poor properties may be due to the Twin Peaks distribution and fiber orientation of the pp46 12 molecular weight, as mentioned earlier.
In the PP1272 film, The PP1272 MDO sample of DR = 1 (MDO = 1)
Strain hardening is shown.
This is expected because the orientation in both directions is low, resulting in similar stresses-
Two-way strain behavior.
One of the main interests of the MDO film is the reduction of gas permeability and the improvement of barrier properties.
This is most likely the result of amorphous phase orientation (Taraiya et al. ,1993).
Figure 11 reports the oxygen permeability of PP1272 films obtained using the MDO process as a function of DR (
Results have been standardized relative to film thickness).
We observed a significant decrease in the penetration rate of DR from approximately 150 x [10. sup. -6]
Than 60 x [10. sup. -6]Lm/[m. sup. 2]
The day DR increased from 1 to 6.
In lowerDRs, the decrease in oxygen permeability was more significant.
Optical Transmission (transparency)
Packaging Film has always been a concern of producers.
To this end, two parameters are introduced: Haze and clarity.
In film production, quantitative evaluation of clarity is as important as smog.
Clarity depends on the linearity of the light through the material.
The slight deflection of light caused by scattering in the material can cause the image to deteriorate.
Smoke is defined as the percentage of more than 2 beams scattered from film samples. 5[degrees].
In other words, the smoke measurement is measured by the width-
Angle, while clarity is made by small-
Angle Scattering.
Figure 12 shows these two parameters as a function of DR for pp1272 film samples prepared using MDO units.
Haze decreases with DR and reaches the plateau of DR> 5, while clarity increases with DR
One explanation: With the increase of DR, the deformation of the Crystal increases, and more crystals are converted into fibers.
These long fibers are more oriented and therefore have increased clarity.
Another effective factor in reducing smoke and improving clarity is the reduction in sample thickness using DR (
The corresponding thickness is reported in Figure 10).
We also tested it with pp46 12 film (MDO = 6)
And get a similar haze value (4. 2)
To be clear (96. 8).
This may mean that the effect of molecular weight and dual mode on the optical transmission performance of MDO films made with high DRs is not significant. [
Figure 12:
Conclusion in this work, we investigated the effect of process parameters on the properties of two different PP resins.
The processing unit is a single-layer film stretching MDO industry-
Scale machine and alab-
Dial line at high cooling rate.
Two grades of PP with different molecular weight and molecular weight distribution were studied.
Due to the deformation of the initial crystal structure, MDO produces a highly oriented fiber crystal structure.
With the increase of DR, the fiber structure becomes stronger, so the strength of the film increases, showing the solid-
Elastic Behavior in Tensiletest.
Compared to other linear PP with narrow distribution, the resin with a two-peak molecular weight distribution shows that the orientation function of the film produced by MDOline is slightly larger, although the molecular weight is lower.
A very poor tensile strength of td was measured for laboratory unit samples.
This test on the MDO sample reveals the strain hardening behavior before the failure of the Shuangfeng resin pp46 12 (DR = 6).
With the increase of MDO film DR, the permeability to oxygen is greatly reduced.
Finally, the hazeproperty of the MDO sample decreases with the plateau period of DR reaching 5, while the clarity continues to rise with the increase of DR
Financial support for NSERC (
Natural Science and Engineering Research Council of Canada
And from (
Foundation for Nature and Technology)
Acknowledge gratefully.
We also recognize the large amount of infrastructure grants received from the Canadian Innovation Foundation (
Government of Canada and Quebec)
This allows us to build a unique POLYNOV facility.
Thank you, sir. P. Cigana, L. Parent and P. M.
Thanks for their technical help.
Received the manuscript on April 6, 2008;
The revised manuscript was received on June 4, 2008;
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Farhad Sadeghi ([dagger])and Pierre J.
Carreau * Department of Chemical Engineering, Center for Applied Research in polymer and composite materials, CREPEC, Ecole polytechnology, Montreal, QC, H3C 3A7 *, CanadaE-
Mailing Address: pcarreau @ polymtl. ca ([dagger])
Current Address: Department of Chemical Engineering, Isfahan University, Iran.