Effect of cold extrusion and heat treatment
`on the mechanical properties of polypropylene
`
`Y.W. Mai( 1 ), B. Cotterell and J. Fante
`
`Department of Mechanical Engineering, University of Sydney, Sydney, NSW 2006, Australia.
`
`Polypropylene rods are cold extruded through a die with three nominal area reductions of
`18, 40 and 64 o/o. These extrudates are subject to subsequent heat treatments at 100°, 120°
`and 140 °Cfor two hours after which this is followed by either air cooling or water quen-
`ching. The effect of cold extrusion increases the tensile strength, the elastic moduli in ten-
`sion and compression as we/las the specific impact energy absorption. The 0.2 o/o offset
`yield strength in tension decreases slightly for the 18 and 40 o/o extrudates but increases
`above the value of the as received polymer at 64% coltl work. Howeve1, cold extlusion
`decreases the compressive yield strength and the density which is a measure of crystallinity
`of the cold worked polymer. Cold extrusion followed by heat treatment reduces the elastic
`moduli but raises the yield strengths of the extrudates. The impact energy absorption
`shows a sharp increase with annealing temperature and the fracture surfaces display
`increasing orientation effect with increasing amounts of cold work. Air-cooled and quen-
`ched samples do not have any significant differences in these macroscopic mechanical pro-
`perties. It is apparent that heat treatment increases the density and hence the crystallinity
`of the cold worked polymer. The improvement is marginally larger for the air-cooled than
`for the quenched samples. The results of this investigation suggest that it is possible to
`obtain a combination of mechanical properties of polypropylene by a suitable extrusion-
`heat treatment process.
`
`1. INTRODUCTION
`There has been considerable interest in applying
`metalworking processes to solid phase polymers in
`order to study the influence on subsequent mechanical
`properties. Cold rolling [I-9] is the most widely studied
`process for a wide range of amorphous and crystalline
`polymers. Improvements of both yield and tensile
`strengths, suppression of stress whitening, and postpo-
`nement of necking and cold drawing have been repor-
`ted. Another advantage not available in cold-worked
`metals is that cold-rolled polymers have a large increase
`of ductility [I, 5] if the cold work imparted is not exces-
`sive. This desirable effect has enhanced the drawability
`of cold-rolled polymers [2, IO, II]. The effect on the
`modulus of elasticity is, however, less clear as in some
`polymers increases are obtained [2-5] but in others
`reductions are reported [IJ.
`
`(I) The 1981 Robert L'Hermite Prize and Medal was granted to
`Dr. Mai who wrote the above paper on this opportunity.
`
`0025-5432/1982/99 !$ 5.00!© BORDAS-DUNOD
`
`Fewer investigations have been conducted on solid
`phase extrusion of polymers [I2]. While there is general
`agreement that cold extrusion increases the tensile
`strength and true strain at maximum load there is again
`no definite effect on the elastic modulus. For example,
`cold extruded amorphous polymers such as polycarbo-
`nate [I3, I4] and a crystalline ·polymer, polypropylene
`[I5], have higher elastic moduli compared to the as-
`received material. But for· some other crystalline poly-
`mers such as polyethylene and nylon [13] cold extrusion
`decreases the elastic moduli. Hot extrusion of poly-
`propylene produces even higher tensile strengths but
`lower elastic moduli than the cold extrudates [I5].
`Other metalworking processes that have been applied
`to polymers have been summarised by Broutman and
`Kalpakjian [2]. The list given is however not exhaustive
`and it does not include the more recent work related to
`cold drawing [13, 16] and upsetting processes [I7, 18].
`Metalworking followed by appropriate heat treatment
`
`99
`
`KASHIV1041
`IPR of Patent No. 9,492,393
`
`

`

`Vol. 15 - N° 86 - Materiaux et Constructions
`
`are commonly adopted in the metals industry to pro-
`vide a combination of mechanical properties to metals
`and alloys. This is a relatively unexplored method for
`polymers although a few investigations have been car-
`ried out previously on the effect of heat treatment on
`mechanical properties [7, 14, 20] and microstructures
`(21, 22] of cold-worked polymers. For amorphous
`polymers it is important that the heat treatment tempe-
`rature does not exceed the glass transition temperature.
`Otherwise, all cold-work effects induced in the poly-
`mers are erased [3, 7, 14]. Lee et a!. [14] have shown
`that heat treatment of polycarbonate raises the yield
`strength of the cold extrudates without a noticeable
`decrease in tensile strength. However, heat treatment
`tends to lower the elastic modulus, the true fracture
`stress [14] and the impact energy absorption [7] of the
`cold-worked polycarbonate samples. For crystalline
`polymers the annealing temperature is usually above
`the glass transition temperature but below that for mel-
`ting. Annealing at sufficiently high temperature usually
`encompasses partial melting which
`is followed by
`recrystallisation. This gives an increase of density for
`the cold-worked polymer and results in lamellar thicke-
`ning [21, 22]. For cold-drawn polypropylene fibres
`which are subsequently annealed at 140 oc Nadella et
`a!. [20] have demonstrated that compared to the as-
`.ill!!Il_fihres both the elastic_ modulus .and tensile
`strength are increased but the percentage elongation to
`break is decreased. In another crystalline polymer,
`polyoxymethylene, Bahadur [19] has studied the effect
`of annealing over a range of temperatures on the aniso-
`tropic mechanical properties of the cold-rolled poly-
`mer. Cold rolling increases the tensile strength and the
`ductility in the rolling direction. These increases howe-
`ver become less as the angle from the rolling direction is
`increased and there is almost no effect in the transverse
`direction. Annealing at 70 oc increases the ductility of
`the cold-rolled polymer in the rolling direction but
`decreases the yield arid tensile strengths as well as the
`elastic modulus. At higher annealing temperatures of
`120° and 170 oc the cold-rolled material has approxi-
`mately the same yield and tensile strengths in the longi-
`tudinal direction and the percentage elongation to
`break is smaller at the higher temperature. In the trans-
`verse direction all the mechanical properties are either
`inferior or at most approximately equal to the cold-
`rolled polymer. These results indicate therefore that it
`is possible to alter the mechanical properties of the
`polymer, as in metals, by cold-working and subsequent
`heat' treatment. Much future research work should be
`carried out in this direction.
`The present paper reports the results of an explora-
`tory experimental investigation to_ study the effect of
`cold extrusion and subsequent heat treatment on the
`mechanical properties of a typical engineering polymer,
`polypropylene (PP). There does not seem to be any
`such work reported previously in the literature on this
`polymeric material. Th!s work is confined mainly to
`mechanical properties and not microstructures of the
`polymer as affected by extrusion and heat treatment.
`
`100
`
`2. EXPERIMENTAL WORK
`
`The polypropylene used for the experiments was
`obtained from Cadillac Plastics (Australia) Pty. Ltd as
`a regular commercial material in the form of 16-mm
`diameter extruded rods. To avoid any variation in the
`processing conditions of the extruded rods all subse-
`quent test specimens were machined from rods of the
`same batch. Solid cylindrical billets of 12.7 mm diame-
`ter and 110 m long were prepared for cold extrusion in
`the experimental setup shown in figure 1. By using
`three dies of varying outlet diameters three "nominal"
`area reductions -
`18, 40 and 64 Oi'o - were available.
`All extrusion experiments were performed in a single
`pass at room temperature using an Instron testing
`machine with a crosshead speed of 10 mm per minute.
`For lubrication between contacting surfaces petroleum
`jelly was used.
`
`DIRECT EXTRUSION PRESSURE
`H'H
`
`EXTRUDED POLYPROPYLENE
`
`Fig. I. - Experimental setup for extrusion operation.
`
`For subsequent tensile and compressive testing a
`total of 35 standard round specimens was prepared for
`each reduction. These specimens were tested in the fol-
`lowing conditions : (1) as extruded; (2) as extruded and
`subsequently heat treated for two hours at 100°, 120°
`and 140 °C respectively, followed by either air cooling
`or water quenching. True stress (a)-true strain (l) curves
`were obtained from the load-diameter records using the
`standard definitions : a = 4 Fl7rD2 and · T = 2/n
`(Do/D), where F is the applied load, D and Do are the
`instantaneous and original diameters of the test speci-
`mens. The tensile and compressive tests were not car-
`ried to fracture due to the very large deformations that
`could be sustained by the polymer.
`Charpy impact tests were also conducted on the
`various heat treated samples containing notches accor-
`ding to the ISO Recommendation Rl79 but these were
`not successful as many testpieces did not break during
`impact and slipped out of the supports. To increase the
`bending stiffness non-standard round specimens
`(12.20, 11.50 and 10 mrfl diameter for the 18, 40 and
`64 Oi'o reductions respectively) with segmental cuts to
`depths of approximately 2 mm were eventually used in
`the impact experiments.
`Diametrical measurements were made for the as-
`extruded and heat treated specimens to determine the
`
`KASHIV1041
`IPR of Patent No. 9,492,393
`
`

`

`dimensional recovery or "spring-back" over a 48-hour
`period. Finally, to determine crystallinity changes of
`the polymer after extrusion and heat treatment density
`measurements were made on small off-cuts using the
`ASTM D-792-64 T method.
`As a basis for comparison all the above experiments
`were repeated for the as-received polypropylene.
`
`3. RESULTS AND DISCUSSIONS
`
`3.1. Dimensional Changes
`The significant elastic recovery or "spring-back"
`suffered by a cold-formed polymeric part has often
`been suggested as the major limitation of cold forming
`operations since this presents problems of dimensional
`control. However, if dimensions of cold-formed parts
`can be accurately predetermined given constant for-
`ming conditions, as have been shown from previous
`experiments [ 12, 18], "spring-back" should not be con-
`sidered as a serious obstacle to the use of cold-formed
`plastics. Figure 2 shows the magnitude of elastic reco-
`very for the polypropylene specimens after being sub-
`jected to various mechanical-thermal treatments. The
`percentage spring-back is calculated from the ratio of
`the diameter difference of the extrudate and die to the
`diameter of the die. For a given heat treatment tempe-
`rature, the larger the cold work the larger is the dimen-
`sional change. For the 40 and 64 OJo cold-worked poly-
`mer the heat treatment temperature has a considerable
`effect on the spring-back. There is no obvious diffe-
`rence between either air-cooling or water quenching on
`the spring-back. It may be noted that these elastic reco-
`veries are much larger than those obtained for polycar-
`bonate with similar mechanical-thermal treatments
`[14]. This may be partly due to the different glass tran-
`two polymers which
`temperature of these
`sition
`influences dissimilarly the relaxation behaviour.
`
`40,---------·--
`
`NO SIGNIFICANT DIFFERENCE
`BETWEEN AIR COOLED AND
`QUENCHED EXTRUDATES
`
`30
`
`-
`;;.
`
`w
`Cl
`$
`i5 u
`~ 10
`
`t.O% CW
`
`18% cw
`
`0
`
`20
`
`50
`80
`140
`120
`100
`HEAT TREATMENT TEMPERATURE. T. (CI
`
`150
`
`Fig. 2. - Variation of spring-back with heat treatment tempera-
`ture for the three nominal reductions : 18, 40 and 64 "lo.
`
`Y. W. Mai - B. Cotterell - J. Fante
`
`It has been suggested that the spring-back is directly
`related to the relative proportion of the crystalline
`region to the amorphous domain of the spherulite [18].
`The crystalline part takes up the plastic deformation
`and the amorphous part which is rubber-like influences
`the spring-back. This hypothesis provides an acceptable
`qualitative explanation for the results of the plain
`extrudates given in figure 2 (since as discussed in sec-
`tion 3.2 the crystallinity of the polymer decreases with
`cold work). It seems that there is no rigorous theoreti-
`cal analysis to date that can be used to predict the
`spring-back or elastic recovery of cold formed parts.
`The difficulties of modelling this phenomenon have
`been highlighted in [18]. For any successful analysis
`structural parameters must be built in the model to
`account for changes due to various mechanical-thermal
`treatments.
`
`3.2. Density Changes
`Density measurements give an indication of the gross
`molecular readjustments of the polypropylene samples.
`An increase in density for a crystalline material implies
`an increase in crystallinity and vice versa. Table I gives
`the density values of the as-received and various
`mechanical-thermal treated polypropylenes. It may be
`seen that increasing amounts of cold-work progressi-
`vely reduce the crystallinity and hence the density of the-
`polymer. Annealing tends to increase the density (and
`crystallinity) and the improvement is higher the higher
`the annealing temperature. These results are in agree-
`ment with those reported in [15, 21] for the same poly-
`mer. An additional information, not previously stu-
`is
`that quenched samples have consistently
`died,
`slightly lower density (and crystallinity) than air-cooled
`samples at the same heat treatment temperature.
`
`3.3 Mechanical Properties of Non-Heat Treated
`Extrudates
`A summary of the mechanical properties of the non-
`heat treated extrudates is given in Table I. Note that the
`yield strength is calculated based on the 0.2 OJo offset
`method and the tensile strength is determined from the
`maximum load sustained by the testpiece. Figure 3
`shows the true stress-true strain curves for the various
`cold worked extrudates and the as-received polymer.
`As noted in Table I small amounts of cold working (18
`and 40 OJo) reduce slightly the 0.2 OJo yield strength but
`at the maximum level of cold work (64 OJo) the yield
`strength is fully recovered to the value of the as-
`received polymer. It is however more remarkable that
`cold working improves both the tensile elastic modulus
`and the tensile strength. These results are in agreement
`with those reported by other investigators [15, 20].
`It is initially thought that the cold worked polymer
`can be regarded as the as-received material with an
`imparted equivalent prestrain (E;,) being determined by
`the degree of cold work. By matching the true stress-
`strain curves to that of the as-received· polymer as
`
`101
`
`KASHIV1041
`IPR of Patent No. 9,492,393
`
`

`

`Vol. 1 5 - N ° 86 - Materiaux et Constructions
`
`00,----------------------------------------·--------------,
`
`so
`
`IO
`Vl. 30
`Vl
`UJ
`
`~
`1:'! 20
`cr >-
`
`10
`
`03
`I €' I
`TRUE STRAIN
`Fig. 3. - Tensile true stress-true strain curves for the as-received and cold worked polypropylene.
`
`04
`
`05
`
`06
`
`01
`
`02
`
`TABLE I
`MECHANICAL PROPERTIES OF POLYPROPYLENE AFTER VARIOUS EXTRUSION-HEAT TREATMENT PROCESSES
`
`Nominal OJo
`reduction
`in area
`
`Heat
`treatment*
`
`0.2 OJo offset yield stress
`Elastic modulus
`Tension Compression Tension Compression
`(MPa)
`(MPa)
`(MPa)
`(MPa)
`
`Engineering
`tensile strength**
`(MPa)
`
`Specific impact
`energy absorption***
`(kJ/m')
`
`Density
`(gm/cm')
`
`~4Q- 0 GA
`
`As-received
`I8
`
`40
`
`64
`
`I I 50
`I2IO
`1160
`1150
`1128
`1120
`IQSO
`I050
`I329
`I270
`I250
`I200
`I205
`1130
`1120
`I400
`I223
`I220
`1148
`1144
`IOI9
`1025
`
`7IO
`1190
`952
`940
`788
`770
`+-:m
`725
`I2IO
`993
`985
`861
`845
`77I
`77I
`I480
`903
`885
`755
`775
`720
`7I5
`
`13.5
`I2.5
`I3.2
`I3.I5
`I3.20
`I3.25
`lJAO
`I3.40
`I2.90
`I3.20
`I3.20
`I3.40
`13.45
`13.70
`I3.80
`I4.0
`I4.20
`I4. I5
`I4.30
`I4.20
`I4.50
`I4.50
`
`I4.0
`IO.O
`I0.5
`I0.5
`Il.5
`Il.6
`n.2$
`I2.50
`Il.O
`I2.5
`13.0
`13.25
`I3.0
`I4.0
`I3.5
`I 1.5
`I0.75
`10.80
`I2.0
`I2.2
`I3.0
`I3.0
`
`None
`None
`100 oc A
`100 oc Q
`I20 oc A
`I20 oc Q
`140 oc Q
`None
`IOO oc A
`IOO oc Q
`I20 °C A
`I20 oc Q
`I40 oc A
`I40 oc Q
`None
`100 oc A
`IOO oc Q
`I20 oc A
`I20 oc Q
`I40 oc A
`I40 oc Q
`* Heat treatments were at indicated temperature for 2 hours. A implies air cooling and Q is for quenching in water.
`** Calculated from maximum load divided by original cross-sectional area.
`*** Calculated from energy absorbed divided by nominal ligament area of notched cylindrical specimens. For 40 OJo C. W. specimens fracture
`plane is not flat. None of the 64 OJo C.W. specimen breaks by the available impact energy.
`N.B. All values shown in the above table are average of at least three measurements.
`
`29
`33
`
`35
`
`43
`
`4.02
`5.65
`7.05
`6.60
`I5.88
`I2:20
`37.90
`24.73
`I4.05
`20.I5
`I8.0
`34.0
`33.0
`58.0
`56.0
`>60
`
`0.9I89
`0.9006
`0.9040
`0.90IO
`0.9058
`0.9029
`0.9090
`0.9032
`0.8868
`0.8988
`0.89IO
`0.9052
`0.9008
`0.9I38
`0.9I04
`0.8676
`0.9090
`0.9060
`0.9I30
`0.9IOI
`0.9I58
`0.9I07
`
`shown in figure 4 it is clear that Eo is not identical to the
`cold work induced prestrain. This implies that the
`structural changes (i.e. crystallinity transformation,
`molecular chain orientation, etc.) caused by cold extru-
`sion are not the same as by simple tensile pre-straining.
`The same finding has also been observed for an amor-
`phous polycarbonate polymer [3].
`To examine the effect of drawing on tensile strength
`specimens that were extruded with nominal 18 and
`40 Ofo cold work were. further drawn at room tempera-
`ture with an lnstron testing machine to a maximum
`draw ratio of 2. Standard tensile tests performed on
`these drawn samples showed that enormous improve-
`ments could be obtained for tensile strength as given m
`figure 5.
`102
`
`In figure 6 and Table I the compressive true stress-
`true strain curves are given. It is seen that cold working
`decreases the 0.2 % offset yield and the compressive ·
`strengths but it increases significantly the elastic modu-
`lus. The stress-strain curves for the extrudates are lower
`than the as-received polymer. Shayota and Babcock
`[ 17] have observed the same behaviour for polypropy-
`lene cold worked by upsetting and specimens cut along
`the billet axial direction. They explained the reduction
`of compressive strength in terms of the competing pro-
`cesses between molecular chain orientation which for
`the particular load/specimen configuration increases
`the strength and the breaking of backbone chains by
`upsetting which decreases the strength. Due to the lack
`of equipment we have not conducted any x-ray diffrac-
`
`KASHIV1041
`IPR of Patent No. 9,492,393
`
`

`

`Y.W. Mai - B. Cotterell - J. Fante
`
`60
`
`50
`
`~ 40
`.!
`
`vi
`Vl w
`~
`Vl
`w
`::::>
`0: >-
`
`10
`
`0
`
`01
`
`TRUE STRAIN. E
`Fig. 4. - Matching of the true stress-true strain curves of the extrudates to that of the as-received polymer.
`
`110
`
`100
`
`90
`
`00
`
`70
`
`60
`
`50
`
`40
`
`20
`
`10
`
`;f
`.!
`5 0
`iE.
`~ w
`~
`w .J
`Vi z
`~
`
`"' z a: w w z
`G z w
`
`Nomtnol l.O% CW
`
`Nomtnol 18% cw.
`
`CONDITION
`Ours
`IMPal
`29
`AS RECEIVED
`18% EXTRUDATE 33
`40% EXTRUDATE 35
`
`~~0--~12~~1L4--~15~--1L8---2~0--~2~2---2~4--~25
`
`100 /01
`DRAW RATIO
`Fig. 5. - Variation of tensile strength with draw ratio for the 18
`and 40 fl!o extrudates.
`
`tion and gel permeation chromatograph studies to
`investigate the molecular orientation and molecular
`weight change of the extrudates. There is ample evi-
`dence that extrusion tends to orientate the c-axis in the
`direction of extrusion and that the orientation increases
`with increasing cold work and temperature [15]. Little
`information is however known about molecular chain
`breakage (i.e. molecular weight reduction) due to extru-
`sion. We cannot therefore conclude whether the unfa-
`vourable chain orientation and/ or the chain breakage
`mechanisms are responsible for the reductions in com-
`p!"essive strength
`The impact resistances of the as-received and cold
`worked polymers are given in Table I. There is a consi-
`derable improvement in the Charpy value as the
`amount of cold work is increased. At 64 Olo cold work
`the potential energy available in the impact tester is
`unable to cause complete fracture of the notched sam-
`ples (i.e. C.V. > 60 kJ/m'). It is further noted that the
`orientation effect becomes increasingly dominant as the
`cold work increases. The fracture plane is at an angle to
`the longitudinal axis of the sample at above 40 % cold
`work and its surface roughness also increases with cold
`working (jig. 7). Impact resistances enhanced by cold
`working should widen the use of the polymer in engi-
`
`40.----------------------------------------------------,
`
`30
`
`18%CW
`40%CW
`
`64%0N
`
`0
`
`-""""o~o5;o------ -o1o- -- ---,.0~15----------,co 2"'o _______ -:o~.25
`
`TRUE STRAIN . E'
`
`Fig. 6. - Compressive true stress-true strain curves for the as-received and cold worked polypropylene.
`
`103
`
`KASHIV1041
`IPR of Patent No. 9,492,393
`
`

`

`Vol. 15 - N° 86 - Materiaux et Constructions
`
`Fig. 7. - Fracture surfaces of polypropylene. Left to right :(a) as-
`received, (b) 18 OJo C.W., (c) 40 OJo C.W. and (d) 64 OJo C.W.
`
`neering applications where toughness is needed to
`improve wear and crack propagation resistances.
`
`3.4 Mechanical Properties of Heat Treated Extrudates
`
`The mechanical properties of the heat treated extru-
`dates are given in Table I. Since in engineering design it
`is the 0.2 O'Jo offset yield strength that is required only
`this value is given in the Table. It is clear that heat treat-
`ment of the various cold worked extrudates tends to
`decrease the elastic moduli but increase the yield
`strengths both in tension and in compression. This ten-
`dency is more visible at higher annealing temperatures
`but it is not distinguishable between air cooling or
`water quenching. After the yield point, the true stress-
`true strain cotves, whether in tension 6r compression,
`are generally slightly raised for the air cooled specimens
`in comparison to the quenched specimens at a given
`heat treatment temperature. Some selected true stress-
`strain curves are given in figures 8 to 11 . A significant
`engineering implication from these results is that suita-
`ble thermal treatments can raise the tensile stress-strain
`curves (figure 9, 60 O'Jo cold work) and the compressive
`stress-strain curves (figures 10 and 11, 40 and 60 %
`cold work respectively) of the extrudates. For compari-
`son the true stress-strain curves are even raised close to
`that of the as-received polypropylene. These findings
`have not been previously reported elsewhere and an
`
`explanation to the results obtained must be sought in
`terms of microstructural changes of the polymer in the
`future.
`The Charpy energy absorption values for the heat
`treated extrudates are given in Table I. For a given
`amount of cold work the higher the heat treatment tem-
`perature the larger is the impact resistance. There is no
`significant difference between air-cooled and water
`quenched samples. It is also noted that these experi-
`mental results are in direct contrast to those of an
`amorphous polycarbonate polymer which has been
`subjected to cold rolling [7]. It is shown that for this
`latter polymeric material annealing reduces the residual
`stresses and relaxes the molecular orientation so that
`the impact resistance is decreased. These explanations
`however cannot be used for the heat treated polypropy-
`lene extrudates and it is thought that the annealing
`induced "lamellar" microstructure may be responsible
`for the improvement in impact strength [21].
`
`4. CONCLUSION
`
`Within the limitec range of mechanical-thermal
`treatments used in this exploratory investigation it is
`shown that the mechanical properties of polypropylene
`can be controlled and altered to suit specific enginee-
`ring applic;itioris. Improvements in elastic moduli, ten-
`sile strength, resilience to plastic deformation, and
`particularly impact resistance can be promoted in the
`polymer by a selective combination of cold working
`and heat treatment operations. Except the density mea-
`surements which show that cold work decreases the
`crystallinity of the polymer and that heat treatment
`improves the crystallinity of the extrudates no detailed
`work has been done in this study to examine the micros-
`tructural changes associated with
`the various
`mechanical-thermal
`treatments. This knowledge
`is
`mandatory if it is required to explain the experimental
`findings reported in this paper.
`
`70
`
`60
`
`so
`
`1.0
`
`ll
`
`20
`
`1()
`
`0
`a.
`~
`
`'0
`
`V\
`
`V\ w a:
`tii
`w
`:::> a:
`1-
`
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`TRUE STRAIN . €
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`KASHIV1041
`IPR of Patent No. 9,492,393
`
`

`

`Vol. 15 - N° 86 - Materiaux et Constructions
`
`REFERENCES
`
`(I] Wilchinsky Z. W. - Reduction of brittleness in poly-
`propylene by cold rolling, SPE Journal, Vol. 22, March,
`1966, pp. 46-49.
`(2] BROUTMAN L.J., KALPAKJIAN S. - Cold forming of
`plastics, SPE Journal, Vol. 25, October, 1969, pp. 46-52.
`(3] BROUTMAN L.J., PAT!L R.S. - Cold rolling of poly-
`mers. 1 -
`Influence of rolling on properties of amor-
`phous polymer, Poly. Eng. Sci., Vol. II, 1971, pp. 165-
`173.
`(4] CADDELL R.M., BATES Jr.T., YEH G.S.Y. - On the
`tensile behaviour of HDPE subjected to cold rolling,
`Mater. Sci. Eng., Vol. 9, 1973, pp. 223-230.
`Investigation of the ductility
`(5] BAHADUR S., HENKIN A. -
`of rolled polymers, Poly. Eng. Sci., Vol. 13, 1973, pp.
`422-428.
`(6] BROUTMAN L.J., KRISHNAKUMAR S.M. - Cold rolling
`of polymers. 2- Toughness enhancement in amorphous
`polycarbonates, Poly. Eng. Sci., Vol. 14, 1974, pp. 249-
`259.
`Impact strength of
`(7] THAKKAR B.S., BROUTMAN L.J. -
`polymers. 3 - The effect of annealing on cold worked
`polycarbonates, Poly. Eng. Sci., Vol. 21, 1981, pp. 155-
`162.
`- Deformation of
`[8] GEZOVICH D.M., GEIL P.H.
`polyoxymethylene by rolling, J. Mater. Sci., Vol. 6,
`1971, pp. 509-530.
`- Deformation of
`[9] GEZOVICH D.M., GEIL P .H.
`polyethylene oxide, nylon-11 and polyethylene tereph-
`zhalaze by rot'ting, J. Mater. Sci., Vat. 0, t971, pp . .511-
`536.
`(10] HOUTMAN L.J., KALPAKJIAN S., CHAWLA J. - Deep
`drawability of biaxially rolled thermoplastic sheets,
`Poly. Eng. Sci., Vol. 12, 1972, pp. 150-156.
`(II] Ll H.L., KOCH P.J., PREVORSEK D.C., OSWALD H.J.-
`Cold forming of plastics : draw forming of thermoplas-
`tic sheets, Poly. Eng. Sci., Vol. II, 1971, pp. 99-108.
`
`[12] BuCKLEY A., LONG H.A. - The extrusion of polymers
`below their melting temperatures by the application of
`high pressures, Technical Papers, 14, 664 (May, 1968),
`SPE 26th Annual Technical Conference, New York.
`Also in Poly. Eng. Sci., Vol. 9, 1969, pp. 115-120.
`[13] LEE C.S., CADDELL R.M., YEH G.S.Y. - Cold extru-
`sion and cold drawing of polymeric rod : the influence of
`subsequent tensile and compressive mechanical proper-
`ties, Mater. Sci. Eng., Vol. 10, 1972, pp. 241-248.
`(14] LEE C.S., CADDELL R.M., ATKINS A.G. - Heat treat-
`ment of cold extruded po!ycarbonate : some implica-
`tions for design engineers, Mater. Sci. Eng., Vol. 18,
`1975, pp. 213-220.
`[15] BAHADUR S. - The effect of cold and hot extrusion on
`the structure and mechanical properties of polypropy-
`lene, J. Mater. Sci., Vol. 10, 1975, pp. 1425-1433.
`Influence of the
`(16] CADDELL R.M., WOODLIFF A.R. -
`gradient in orientation on the compressive elastic modu-
`lus and yield strength of oriented polypropylene, Mater.
`Sci. Eng., Vol. 40, 1979, pp. 187-189.
`(17] SHAYOTA M., BABCOCK S.G. - Compressive behaviour
`of worked plastics, J. Appl. Poly. Sci., Vol. 18, 1974,
`pp. 2693-2702.
`(18] ELLIS D.T., BRAMLEY A.N., ATKINSON J.R. - The
`so/ide phase forming (or forging) of polypropylene,
`Proc. 18th Int. Machine Tool Design and Research Con-
`ference, London, England, 1977, pp. 283-288.
`[ 19] BAHADUR S. - The effect of annealing on the mechani-
`cal anisotropy of cold rolled polyoxymethylene, Poly.
`Eng. Sci., Vol. 18, 1978, pp. 255-259.
`(20] NADELLA H., SPRUIELL J.E., WHITE J.L. - Drawing
`and anneaT/ng of polypropylene fibres :structural chan-
`ges and mechanical properties, J. Appl. Poly. Sci., Vol.
`22, 1978, pp. 3121-3133.
`(21] PETERMANN J., SCHULTZ J.M. - Microstructure and
`annealing behaviour of cold-drawn isostatic polypropy-
`lene, J. Mater. Sci., Vol. 13, 1978, pp. 2188-2196.
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`Prentice-Hall, New Jersey, 1974.
`
`RESUME
`Effet de !'extrusion a froid et des traitements thermi-
`ques sur les proprit~tes mecaniques du polypropylene.
`- Les jones de polypropylene sont extrudes a froid a
`travers une filiere aux sections de reduction nominates
`de 18, 40 et 64 o/o. Les extrudants sont ensuite soumis a
`des traitements thermiques de 100, 120 et 140 oc de
`deux heures suivis par un refroidissement soit a /'air,
`soit par immersion dans l'eau. L 'extrusion a froid aug-
`mente Ia resistance en traction, les modules e/astiques
`en traction et en compression, ainsi que Ia capacite
`d'absorption de l'energie de choc. Cependant, Ia marge
`de 0,2 o/o de Ia limite e/astique en traction et en com-
`pression se trmtve legerement reduite. C'est un resultat
`de /'extrusion a froid que /e po!ymere so it mains dense,
`ce qui implique une diminution de Ia cristallinite. Le
`travail a froid sui vi par un traitement thermique reduit
`106
`
`les modules e/astiques mais augmente les limites elasti-
`ques. La resistance au choc monte rapidement avec Ia
`temperature de recuit. II ne semble pas qu 'if y a it de dif-
`ference notable dans /es proprif?tes mecaniques determi-
`nees par le refroidissement a /'air ou par immersion
`dr;ns l'eau. Cependant, les eprouvettes refroidies a /'air
`montrent une crista//inite un peu plus grande et des
`courbes contrainteldeformation en traction et en com-
`pression meil/eures au-de/a de Ia limite e/astique pour
`une temperature donnee de recuit. Les resu/tats de cette
`etude suggerent qu 'if est possible d'obtenir une combi-
`naison des proprietes mecaniques du polypropylene par
`une procedure appropriee d'extrusion suivie du traite-
`ment thermique. Une etude approfondie des micros-
`tructures du polypropylene affecte par les divers traite-
`ments mecaniques et thermiques permettra une com-
`prehension plus complete de Ia relation proprietel
`stru~ture.
`
`KASHIV1041
`IPR of Patent No. 9,492,393
`
`