7. Tubular Com

8/6/2019 7. Tubular Com

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TUBULAR CONSTRUCTION USING SINGLE POLYMER

COMPOSITE

Krishnendu Shaw, Debi Prasad Gon and Palash Paul

Panipat Institute of Engineering & Technology -Pattikalyana, Samalkha, Panipat, Haryana

ABSTRACT

Single polymer composite has been extensively used in various fields. Hot compaction is one of the techniques to make single polymer composite. Various different shapes and surface texturesare successfully made by hot compaction methods. So in this study it is tried to make cylindrical object by hot compaction of filaments in winded form. The advantage of this material over

conventional extruded pipe is it posses a very high strength in circumferential direction. Theaxial stress in the pipe or cylindrical construction is the half of the circumferential stresses when

an internal hydraulic pressure is applied to the thin wall of the pipe. Normally axial strength ishigher for extruded pipe or tubular elements because the macro molecular orientation during the

extrusion. So in order to improve the pressure endurance, strength in circumferential directionhas to be improved. Therefore to improve the strength in circumferential direction it is tried to

give preferred orientation of the molecules in the direction of stress. By filament winding process preferred orientation in the circumferential direction is created. The basic variables of hot compaction are temperature, pressure and time. In this study external pressure application is not necessary because pressure is automatically generated due to shrinkage of filaments during hot

compaction in winded form. It is found that higher temperature compacted material is superior inaxial compression strength. The material shows good resiliency in parallel plate compressiontest. It is observed that the crack generation is less at extreme loading condition in parallel platecompression test and very superior properties are obtained in circumferential direction. The

bending properties are also superior to extruded pipe.

Key words: Hot compaction, composite pipe, filament winding

1.0 Introduction

The technological advances in various sectors have created demand for newer materials, wherethey are required to perform in stringent conditions - high pressure & temperature, highlycorrosive environments, with high strength requirement, which the conventional materials failedto service. This has triggered the development needs for engineered materials to cater tocustomized needs. Industry has recognized the ability of composite materials to produce high-quality, durable, cost-effective products. At this moment, environmental legislation and waste

management regulations have been put in place that increase the pressure on manufacturers of materials and end-products to consider the environmental impact of their products at all stages of their life cycle, including recycling and ultimate disposal.

So there is a motivation to make materials which are fully recyclable. Single polymer thermoplastic composite by their nature be fully recyclable. Generally for this purpose

polypropylene is ideal thermoplastic material for its excellent recycling characteristics. Thecommercial pipes which are available in the market are isotropic in nature. So here is an approachto make anisotropic pipe made of single polymer composite which have a preferred orientation inthe direction of stress. The main advantage of this type of material is that it can withstand higher



pressure than isotropic material. Tubular composite made by filament winding is not a newconcept. In literature most of the work is carried out on resin based composite. But problem is

still exists in that case like recycling and interphase between the components. So in this project itis tried to make tubular parts by hot compaction technique. Flat surface, wavy surfaces, various

surface texture have been made by hot compaction, but making of single polymer tubular parts byfilament winding and hot-compaction process is a new concept. In the time of manufacturing any

composite material, temperature and pressure are very important variables. Temperature can beeasily monitored but in the case of tubular parts applying pressure is difficult. The idea which isapplied in this system is that when the filament is heated near to its melting point the filamentwill try to shrink but if the end point of the filament is anchored on a hard mandrel it can notshrink and due to its shrinkage force there is a generation of high pressure and thus external

pressure application is not required. Here polypropylene multifilament is used with polypropylene film. There are a large number of applications areas for this type of filamentwinded composite tube. The main advantage is that it can withstand a high internal pressure because orientation in the circumferential direction is very much high. By these technique pressure vessels, pipe, driving shaft can be made. Filament winding and hot compaction isrelatively cheap process, and thus this process may be industrially feasible for getting high

performance recyclable tubular composites.

It is seen in the literature that the hot compaction of the highly oriented polyethylene fibres andtapes is tried first, but this technique was applied only about six years ago with polypropylene. [1]

Hine et al. [2] investigated the compaction of unidirectional arrangement of high-tenacity polypropylene fibers. A combination of techniques, with the major emphasis being morphologicalstudies, showed that controllable "selective" surface melting was achieved at a high enough proportion to give substantial fibre to fibre good lateral strengths. The mechanical properties of the composite, made by introducing isotactic polypropylene fibre into the isotactic polypropylenematrix (by melting PP pellets) are as good as conventional glass fibre reinforced PP composite.There is a formation of epitaxial crystallization which is a result of the processing condition.These composites may show improved interfacial adhesion properties. In this literature it wasalso found that the melting point of the PP fibre increased substantially (almost 30°C) due to

constrain on the fibre by superior fibre-matrix interface. [3]The initial studies on polypropylene fibres it followed that hot compaction of woven polypropylene fabric can be economically successful. Although initial experiments of hotcompacted woven fabric involve both polyethylene[4,5,6,7] and polypropylene, these studiesshowed that the morphology of hot compacted polypropylene was very similar to that seen in polyethylene, with a matrix phase epitaxially recrystallised onto theoriented tapes. But there are some distinct difference between hot compacted woven polyethyleneand polypropylene sheets. [8,9]

2.0 Objective

By studying the literature it is observed that single polymer composite has been applied in variousways. The main advantage of this material is that it can be easily recycled and has reasonable

strength. Hot compaction is one of the techniques to make single polymer composite. There is a possibility to make cylindrical object by hot compaction technique. So the aim of this project is tomake single polymer tubular composite by filament winding process.1

• To make all polypropylene tubular composite by filament winding hot compaction process.

• To study and optimize the properties of the tubular composite.



3.0 MATERIALS

3.1.1 Yarn characterization

Polypropylene yarn was procured from Filaments India Ltd, Rajasthan. The polypropylene yarnis commercial grade multifilament type.

Table 3.1: Specifications of the yarn used Parameter Properties

Type Multi filament

Denier 2000

Melting Point (°C) 173

Crystallinity (%) 49

Tenacity (gpd) 6

Density 0.91

3.1.2 Film characterization

Cast polypropylene film was procured from Xpro India Pvt. Ltd., Faridabad.The specifications of the oriented PP film are given below:1 Thickness – 21 μmWidth – 220 mmWeight per linear metre – 3 gPeak Melting Point – 164°COnset melting temperature – 153Crstallinity – 31%

3.2 METHOD

The tubular composite sample preparation was first tried by winding the filaments on to thehollow metal mandrel and then, hot compacting the filaments in hot air woven. But after hot

compaction the shrinkage force was so high that the tube could not be withdrawn from thesurface of the hollow metal mandrel. So for efficient removal of the composite the inner mandrelshould be collapsed after hot compaction. Thus collapsible mandrel was necessary for efficient preparation of such type of sample. Therefore there was a need to develop a collapsible mandrelfor sample preparation.

3.2.1 Design of the collapsible mandrel

The collapsible mandrel is designed according to the size of the package of the winding machine.The mandrel is such that it can fit between the two holding point of the winding machine. Thematerial used for making the mandrel is hardened steel so that it retains the shape even after beingsubjected for high pressures repeatedly. The main winding zone of the mandrel is composed of two half of a solid cylinder. The total outer diameter of the cylinder is 40 mm and the spacing

between the two half is 2 mm. The two halves are joined by two disc type element in two extremeof the mandrel and separation between the two half part is maintained by inserting four bolts tothe disc. The total length of the mandrel is 213 mm. The separation between the two plates ismaintained by four bolts which are fixed on the disc of the two extreme portion of the mandrel.When these bolts are removed from the disc the inner portion will collapse and it will create somespace. The design and picture (Fig 3.1) of the collapsible mandrel is given below.



Fig 3.1: Design of the collapsible mandrel (schematic view & 3-D view)

3.3 SAMPLE PREPARATION

At first the collapsible mandrel is to be mounted on winding machine. Then filament package iskept on package holder near to the machine, and the filament is threaded through a tensiondevice. The tension device which is used here is disc type and spring loaded. After that it isthreaded through the traversing device which is mounted near to the mandrel and then thefilament is wrapped on to the mandrel. Before winding a Teflon fabric is winded on the surface of the metal mandrel it helps not to stick the material with the metal surface. Then film is wrappedover the Teflon fabric. The Advantage of using film is it has a smooth surface so the roughness of the inner layer of the pipe is easily covered by using film. And also the melting point of the filmis lower than the filament so it is easily adhere to the inner surface of the tube, and also it alsoacts like glue to suppress the delamination of the filaments. Then the filament is wound on to themandrel. The machine has an automatic counter which counts how much length is winded on tothe mandrel. The wind angle is 900. After winding the end portion of the filament is fixed byapplying knot, the knot is such that it should not be unraveled during heat treatment. After winding the whole arrangement is removed from the winding machine and then put it into the hotair oven.

Fig 3.2 Figure of composite structure

The compaction temperature was determined according to the melting point of the material. So toknow the melting point DSC is done initially. And it is observed that the melting point of thefilaments in the range of 170 – 173 oC. Different temperatures of the hot air oven are tried like180oC - 205oC .The set temperature of the oven is much higher than the melting point of thematerial because the material is heated by circulating hot air. It is not contact type of heating sosome amount of the heat lost is observed during heating. Different time is needed for partialmelting is about 10 min- 110 min according the temperature of the below (Table 3.2). Sixdifferent samples are made on six different temperatures. During sample preparation the mandrel



is rotated by hand after 5 min interval. After heat treatment the material is removed from the hotair chamber and the material is cooled by natural cooling. Then the bolt of the mandrel isremoved by rotating the bolt in reverse direction. And whenever the two discs are removed thentwo halves of the cylinder are collapsed automatically and sample is taken out over the surface of the mandrel. The schematic picture of the sample is given below (Fig 3.2). The various stepsduring preparation of sample are given (Fig 3.3).

Fig-3.3 Various steps for making tubular composite

Table 3.2: Sample code for samples prepared under different conditions

Serial No Sample Code Air oven Temperature(°C)

Time(min)

1 A205 205 10

2 B200 200 253 C195 195 45

4 D190 190 60

5 E185 185 75

6 F180 180 110

• The sample is prepared at different temperatures. Like A205 represents that thetemperature used during hot compaction is 205 °C.

• A, B, C, D, E, F represents samples prepared at six different temperatures.

3.4 TUBULAR COMPOSITE CHARACTERISATIONS

3.4.1 Thickness measurementThickness of the composite material was measured by electronic screw gauge.3.4.2 Density Measurement

The apparent density is calculated for both multifilament as well as the tubular compositeelement.3.4.3 MECHANICAL CHARACTERISATIONS

3.4.3.1 Axial Compression test of pipe



Compression test was done according to ASTM D1621 standard in INSTRON 1197. Beforetesting the sample was properly prepared. The sample was cut in circular wheel blade. Eachsample was 10 cm length, Inner diameter 40 mm; average outer diameter was 46 mm. The loadcell which was used for testing is 1 Ton. The cross head speed was 50 mm/min. The sample was placed on the flat platform and the upper cross head was lowered to touch the material, then thecrosshead was lowered further until the specimen breaks or delaminated in some portions. The

maximum breaking load of the specimen and corresponding displacement was observed.3.4.3.2 Three Point Bending Test of pipe

The bending strength is assessed according to the three-point loading system applied to a simplysupported beam. In standard testing procedure a bar of rectangular cross section rests on twosupports and is loaded by means of a loading nose midway between the supports. The specimen isdeflected until rupture occurs in the outer surface of the test specimen or until a maximum strainis reached.

Fig- 3.4 Experimental set-up for three point bending test

3.4.3.3 Parallel plate loading Test of pipe

This test was done according to the ASTM D2412 standard. This test method covers the loaddeflection behavior of the parallel plate loading. A short length of pipe was loaded between thetwo rigid parallel flat plates at a controlled rate of approach to one another. Load deflection datawas obtained. If cracking, crazing, delamination or rupture occurs then corresponding load anddeflection was observed.Pipe deflection

The ratio of the reduction in the pipe inside diameter to the initial inside diameter expressed asthe percentage of the initial inside diameter.Pipe stiffness (PS)The value obtained by dividing the force per unit length of the specimen by the resultingdeflection in the same unit at the prescribed percentage deflection. So pipe stiffness can becalculated by using this equation, PS = F/ ∆y

Fig-3.5 Experimental setup for parallel plate compression test of pipe

3.4.3.4 Tensile strength of composite pipe in axial direction

Tensile test of the composite pipe was done according ASTM D638, in INSTRON 5582 Tensiletesting machine. Here the tensile testing of whole tube was not possible in cylindrical form.That’s why tensile test was done by cutting strip from the tube. By this testing an idea about the



tensile strength along the axis of the tube could be obtained. The specification of the strip whichwas used for tensile testing wereWidth of the sample = 13 mmGauge length = 50 mmLoad cell used = 1000 kgCross head speed = 50 mm/min

The end part of the strip was flattened in compression molding machine for effectively gripping.If polypropylene is a thermoplastic material so it was easily flattened and the flat portion waseasily gripped between the jaws of the tensile testing machine.

3.4.3.5 Circumferential tensile strength test by split disk method

The circumferential tensile strength was done according to the ASTM D2290. Thecircumferential strength measurement is very much important for this type of tubular elements.For doing this test the tubular element was cut as a ring. The picture is given in Fig 3.6, the picture indicating the typical sample size for this type of test.

This sample was mounted on the tensile testing machine. For mounting this type of circular ringspecimen some attachment was needed. The attachment was designed in such a way that it canhold the circular ring. After mounting the sample, the cross head movement was started and gave

the stress to the sample until failure was not occurred.From the tensile testing graph we can calculate theThe Circumferential tensile strength (σa)σa = Pb / 2AmAm= Minimum cross section area of the two measurements, (b × d), mm2Pb = Maximum breaking load (Newton)σa = Ultimate tensile strength of the specimen in circumferential directiond = Thickness of the ring sample b = Width of the ring sample

Design of the attachment of Hoop Test of Pipe



Figure 3.7: Design of attachment for circumferential tensile test of pipe

Fig 3.6: Sample specification for circumferential tensile strength

Two symmetrical metal U shape materials were fabricated. The design of the U shape attachment isgiven in (Fig 3.7). The experimental set up for the test is given (Fig 3.8). The sample was insertedinto the two metal parts then the whole system was mounted on Instron Tensile testing machine. Thegauge length was the inner diameter of the ring. Here the gauge length is 40 mm. After the sample

mounting the cross head movement was started until the breakage occurred to the sample. Thecorresponding load elongation data was observed from the test



Figure 3.8: Experimental setup for circumferential test of ring specimen of pipe

3.4.3.6 Drop weight impact test of pipe

The standard tests for impact strength of a material include Charpy test, Izod test, drop weight impacttest, chip impactor test. The preference for drop weight impact test over the more conventionalmethods, for example, Charpy and Izod test is due to the limitations that are experienced while trying

to perform impact testing on composite materials. Another main advantage of using drop weightimpact test over other standard test is its ability to reproduce conditions under which real lifecomponent would be subject to impact loading.

3.4.4 Wide Angle X-Ray Diffraction

Xpert Pro – PAN Analytical X-ray unit is used for the assessment of crystallinity by wide anglediffraction studies. The unit is operated at 40KV and 30 mA. The unit has a Philips X-ray generator,equipped with nickel filtered CuKα (1.54Å) radiation source and Philips fibre goniometer. Intensity plots of powdered samples for both filaments and also the composite were obtained against 2θ, whereθ is the Bragg’s angle in wide angle X-ray diffractogram. The WAXD pattern was recorded for 2θrange of 10º - 35º, at the scanning rate of 2º per minute. Using the Xpert Pro-Data software providedwith the unit, the crystallinity was calculated after subtracting the area for amorphous contribution.

3.4.5 Differential Scanning Calorimetry

The samples were powdered and then the melting behavior of different samples for multifilament andtubular composite were obtained using a Perkin Elmer DSC7 differential scanning calorimeter at ascan rate of 20ºC per minute. A comparison of the areas under the melting endotherms for differentsamples prepared under different condition gave the idea of the amount of material melted during the process.3.4.6 Scanning Electron Microscopy (SEM)The surfaces and cross section of the tubular composite samples prepared in different temperaturewere studied with the help of ZEISS (Model: EVO 50) scanning electron microscope. The sampleswere first coated with a silver layer to provide surface conduction before their scanning and the effectof self generating pressure were observed by focusing at the edge of the cut sample.3.4.7 Optical MicroscopyThe samples prepared under different conditions were observed under the LEICA DMLP (Model TK-C1380E, Japan) microscope, attached with computer software “Leica”. The observation was made for different samples under transmission mode.

4.0 Results and Discussions

4.1 MECHANICAL PROPERTIES

4.1.1 Circumferential tensile strength test by split disk method



Circumferential tensile strength of the composite samples was tested and the values of circumferential breaking load and elongation are tabulated in (Table 4.1) and the circumferentialstrength values are tabulated in (Table 4.2). This test is done according to ASTM D2290 testing procedure. Special attachment is designed for this test. For each test 10 samples were tested.Circumferential strength is one of the important properties of any tubular type of material.Basically this test is done for assessment of strength in circumferential direction. Generally

circumferential strength is important because the stress is transferred in circumferential directionwhen internal pressure is exerted in cylindrical object.

Table 4.1: Load elongation data of circumferential tensile strength test

Serial No

Sampletype

Average BreakingLoad

(N × 102)

AverageElongation (%)

CV % Circumferentialstrength

(σa) (N/mm2)

1 A205 42.96 18 5.3 59.7

2 B200 46.89 24 4.1 65

3 C195 56.89 30 2.7 79

4 D190 58.66 32 3.3 81.5

5 E185 52.97 35 5.6 73.7

6 F180 50.03 37 4.4 69.5

It is observed that the strength is highest for D190 sample then the strength is lowered gradually.For the sample F180, E185 strength is lower because of matrix failure of the composite. In lower temperature the partial melting is much lower so impregnation is also lower so the stress is nottransferred properly and the local failure is initiated which indicates the low strength of thematerial. But in case of B200 more surfaces melting is occurred which lowers the reinforcement percentage, so strength bearing component is also low in case of B200 which reflects the value of lower strength of the material. The strength for A205 and F180 is not sufficient so rest of theexperiment was done by taking the rest four different samples.The strength of the material depends on the optimum ratio of reinforcement and matrix. It isobserved that at higher temperature the strength of the material is low because at higher

temperature the orientation of the molecule gone down so the ultimate stress bearing componentis also gone down which reflects the lower strength. And also it is observed that the sample whichwas made at higher temperature are stiff in nature so stress concentration is their and prematurefailure is observed at lower load.



It is also observed from (Table 4.1) that the sample which was made at higher temperature showslower elongation during the circumferential tensile test. The sample D190 shows the highest breaking load as well as circumferential tensile strength. From(Fig 4.1) we can get an idea about the trend of load elongation curve. From the (Fig 4.2) it isobserved that the sample which were made at lower temperature are quite fibrous in nature but athigher temperature the melting of fibre is so high that the flexibility or ductility of fibre is lost soat lower stress it was broken. From the (figure 4.3) it is clearly observed that the circumferentialtensile strength decreases after a certain temperature. It is highest at a temperature of 190°C after that it is decreased.

4.1.3 Axial Compression test of pipe

The axial compression tests for different samples were carried out and the average breaking load

and axial deformation values are tabulated in (Table 4.2). For each test five samples were taken.The best result is obtained for the samples prepared at 200°C. The value of axial compressivestrength is given below (Table 4.2). It is observed that Samples prepared at lower temperaturewere poor impregnation of the matrix and so breaking of the matrix is very easy and so easycrack generation. But as the temperature is increased the more amount of the fibre surface ismelted so better bond formation takes place due to fusing so compressive strength is increased.The compressive strength of the material mainly depends on the packing of the filaments inwinded form.



Table 4.2: Load Displacement data of axial compression Test of pipe

Serialno

Samplecode

Temperatur e

(°C)

AverageBreaking Load

(N × 102)

Average Axialdeformation

(mm)

CV % CompressiveStrength (MPa)

1 B200 200 59.35 13 2.2 14.6

2 C195 195 53.07 15 2.9 133 D190 190 50.03 18 3.5 12.4

4 E185 185 46.59 20 4.3 11

It is observed that at higher temperature the shrinkage force is much more so pressure generationdue to shrinkage is also more which improve the packing of filament in winded form, whichshows the increasing trend of compressive strength.

Fig –4.4 Axial compression failure sample picture of pipe

It is observed from the (Fig 4.5) that the samples which are made at higher temperature are higher modulus than the sample made at lower temperature. This can be easily understood by seeing theslope of the compression curve. A constant increase in slope is observed. The modulus of thematerial also increased due to increase in crystallinity. Compressive strength is increased withincreasing the temperature. From (Fig 4.4) it is observed the typical failure of axially compressedsample.



4.1.4 Parallel plate compression test of pipe

The load and deformation value for parallel plate compression test is given below (Table 4.3).The load deformation curve is given below (Fig 4.6). It is observed from compression test that thetube is in circular shape before experiment but as the tube is compressed by applying load itscircular shape is changed to oval shape (Fig 4.7). The failure is initiated at particular deformation.It is observed from (Table 4.3) that the samples which are made at temperature 185°C before

failure delamination was occurred in inside wall but the sample which are made subsequently190°C, 195°C no delamination was observed before cracking of the material. As the temperatureis increased the stiffness is increased accordingly because the crystallinity of the material isincreased due to heat treatment in higher temperature. The stiffness of the material is quite high because the filament is oriented in the circumferential direction.

Table 4.3: Parallel plate compression test of pipe

Serial No Sample code Average Load(N × 102)

AverageDeformation

(mm)

Pipe Stiffness(KPa)

CV%

1 B200 18.54 29 161.8 4.3

2 C195 20.30 32 174 2.83 D190 18.73 36 158.6 3.6

4 E185 17.85 37 150.4 5.5

It is observed (Table 4.3) that the stiffness is increased with increasing temperature but in case of sample B200 the breaking load is decreasing because the most of the reinforcement is melted atthis temperature and also material is much stiffer in nature. So during the compression test it cannot take much load due to load concentration in a same place and ductility is decreased whichmay be cause of earlier failure at a low deformation. It is also observed that the material is goodrecovery property after the test the material is recovered very much (Fig 4.8) shows the recoveryof the material. The material is failed in to the matrix region no reinforcement failure is observed.The samples C195 which are made in 195 °C are sufficient matrix than the others show the goodadhesion between the fibres and so the failure load is higher than the others.

Fig- 4.6 Deformation curve of parallel plate Fig-4.7 After parallel plate compression test 4.1.5 Three point Bending Test of pipe

Bending is one of the important property requirements for cylindrical construction. From the (Table 4.4) and(Fig 4.8) an idea about the bending load and deformation of the composite can be obtained. Bending load isincreasing up to temperature 195oC and then it is again decreasing. In this experiment the deflector puts the pressure on upper surface of the pipe and due to this it deflects. Due to orientation of the filament incircumferential direction it can take much load. It was early observed that the sample which is made at atemperature of 195oC have higher crystallinity.



After partial melting if the material is recrystallised in stressed condition so the modulus of the material isincreased. If the modulus is increased so bending strength is increased accordingly

Fig –4.8 Load deflection curve of composite pipe

Table 4.4: Three point bending Test of pipeSerial No Sample type Average BendingLoad

(N × 102)

AverageDeflection

(mm)

CV%

1 B200 8.9 14 4.2

2 C195 10.3 17 3.8

3 D190 9.8 22 5

4 E185 8.5 24 6.5

4.1.6 Impact Test of pipe

Impact test was carried out and the value of impact strength is tabulated in (Table 4.5). It is observed thatimpact strength is increasing and then again decreasing. It is observed that the samples which are made at

185oC are low impact strength and also the samples which are made at 200oC also show the same phenomena.The samples which are made at low temperature are flexible in nature but failure was observed due todelamination of structure.The delamination initiated for low surface melting and low compaction of the structure. But as thetemperature is increased, impact strength increases for the sample D190 and C195 but after that it againdecreased. This is due to the low ductility of the sample and the upper surface of the composite turns as a plastic material. The picture of impact failure sample is given below (Fig 4.10). The samples which are madeat higher temperature are more crystalline in nature. It is known that higher crystalline material are more rigidthan low crystalline material so in case of B200 ductility of the sample decreased and stress concentration ismore in one place. Due to lower ductility it can not dissipate the energy in larger area so impact strength ismuch lower.

Table 4.5: Impact strength test of pipeSerial No Sample type Average

Height(cm)

Average Energy to brake(Joule)

1 B200 15 3.67

2 C195 20 4.9

3 D190 16 3.92



4 E185 13 3.18

4.1.7 Comparison the properties of the composite pipe with extruded pipeTable 4.6: Comparison the properties of the composite pipe with extruded pipe

Sr No Type of Test B200 C195 D190 E185 Extruded PP pipe

1 Circumferential strength

(N/mm2)

65 79 81.5 73.7 19.6

2 Tensile strength in axialdirection (N/mm2)

14.6 13.4 9 7.5 22.6

3 Axial compressive strength(N/mm2)

14.6 13 12.4 11 14.7

4 Pipe stiffness (Kpa) 161.8 174 158.6 150.4 1245 Bending strength (N × 102) 8.9 10.3 9.8 8.5 6.8

6 Impact strength (Joule) 3.67 4.9 3.92 3.18 6.62From the above comparison (Table 4.6) it is observed that the circumferential tensile strength of composite material is very much higher than extruded material. The circumferential tensilestrength is higher in case of composite material because in filament winded material it has a preferred orientation in circumferential direction so strength is very high than normal extruded

material in this direction. This circumferential direction strength is very much important incylindrical object because the stress is applied in circumferential direction. From this data we cansay that filament wound composite tube can withstand four times higher pressure than normalextruded pipe in same thickness. But in axial direction the strength is not higher in comparison of extruded material because there is no orientation in axial direction and the strength in axialdirection mainly depends upon the interface strength between the filaments. It was observed thatthe axial compressive strength is nearly equal to each type of material. But the stiffness is more incase of filament wound material because of the preferred orientation in circumferential direction.So whenever the pipe is compressed between the two plates the oriented filament takes the loadso stiffness in case of filament wound material is much more than the extruded material. The bending strength is also high in case of filament winded material. The impact property of thismaterial is poor compared with extruded material because in this filament wound system the heat

is flowing from outside of the material so the more melting is occurred on the surface so ductilityof the surface is low compare to the core of material. So whenever the impactor hits the surfacethe stress is centralized and due to low ductility it can not distributed so failure takes place at alower energy compared to the extruded sample.

4.1.7 Effect of winding Angle:

Winding angle plays a major role in determining the orientation of polymer chains in resultantcomposite. In this study we wind the filament 90 degree with the axis of the collapsible mandrel.



We choose 90 degree as winding angle because in this study we want to study what is thedifference between the normal extruded pipe and filament winded pipe. Basically when we windthe filament in circumferential direction its strength in the circumferential direction increases butwe loose strength in axial direction, as we decrease the winding angle from 90 degree to lower wind angle side the strength in the circumferential direction decreases and the strength in theaxial direction will increase.

4.1.8 Effect of Thickness of Yarn:

Thickness of the yarn plays a major role in hot compactation. If thickness of the yarn decreasesthen packing fraction is increased substantially, so heat penetration is slow so their is a gradualchange of heat flux from outside to inside. It is also observed that their is substantially change of molecular structure along the cross section of the tube. The structure of the outside pipe is moredisoriented than the inner side. The orientation in less in outer side of the pipe but in inner side of pipe the structure of the filament is quite intact and the film helps it to integrate the structure. Soit forms a compacted material. The prepared sample thicknesses are same with the conventional pipe because we want to compare the properties between the extruded and winded pipe. The samethickness of the pipe is maintained by finishing the pipe in lathe machine after hot compactation, because during the hot compaction the surface is roughened so for smoothening purpose we have

to grind it in lathe.

4.2 THERMAL CHARACTERISATION

4.2.1 Differential Scanning Calorimetry

The two extreme samples like B200, E185 were chosen for thermal characterization bydifferential scanning calorimetry. From the (Fig 4.11) it is observed that there was a shift of melting point on the higher side for higher temperature compaction sample. This is due to meltingand recrystallisation of the samples during the heat treatment of the material. It may be due to thecrystal perfection which takes place during heat treatment. The smallimperfect crystal is melted and recrystallizes to form a more perfect crystal. It is known that tomelt a relatively crystal heat requirement is more than to melt an imperfect crystal. So with theincreased recrystallised fraction the melting point increases significantly. Under stressed

condition, the melting point of the fibre shifts to higher side. The change of enthalpy wasobserved in between sample B200 and E185. Also same phenomena were observed in case of C195, D190. For each sample there is some shifting of melting point to higher temperature.

It is observed that when the fibre is compacted near its melting point a high amount of shrinkageis observed but the filaments is not able to relax because it is fixed in the mandrel so a highamount of stress is developed in side the filament. So under stress condition the crystalinity isincreased and the heat flow during melting is increased accordingly. It is clearly observed from



(Table 4.7) that the crystallinity of the virgin multifilament sample is increased sufficient amountdue to hot compaction process.

Table 4.7: Melting point & crystallinity of different samples measured by DSC method

Sample code Melting Temperature (°C) Enthalpy ChangeΔH (J/g)

Crystalinity (%)

Onset Peak End

Multifilament(2000) 154 167 174 98 47

B200 170 177 182 135 65

C195 169 176 180 129 62

D190 167 174 178 125 60

E185 162 172 177 117 56

F180 158 168 175 105 50

4.3 WIDE ANGLE X-RAY DIFFRACTION (WAXD) STUDY

The samples chosen for WAXD were the same as for DSC and the crystallinity measured fromWAXD pattern showed a similar trend with the DSC crystallinity data (Table 4.8).From the (Fig 4.12) it is observed that the crystallinity and crystalline perfection increases withthe application temperature as can be observed from the area under the curves and the half widthof the peaks With higher temperature there is some stress induced crystallization because athigher temperature the shrinkage is more but the filaments are not allowed to shrink so a hugeamount of stress is developed which may be the reason behind the increase in stress inducedcrystallinity. For samples prepared at 185°C to 200°C the crystallinity goes up as well as thecrystal perfection as the width of the peak reduces.

Table 4.8: Crystallinity of different samples from X-ray diffractogram compared with DSC

Sample Code Temperature Crystallinity by X-Ray Crystallinity by DSC



( oC) (%) (%)

Multifilament 49 47B200 200 64 65C195 195 63 62D190 190 60 60

E185 185 55 56

Crystallinity study within the same material

It is observed that crystallinity of the material is changing at different temperature. But it is observedthat the crystallinity value is changing in the same material from surface to core. From the below (Table4.9) it is clearly observed the variation of crystallinity in the direction of thickness. The surfacecrystallinity is not increase much more than parent filament. But in inner layer there is a gradualincrease in crystallinity. The one cause of this variation is temperature between the surface and core of the material, because heat is flowing from outside. If at the surface heat is directly applied so on thesurface of the tube the polymer molecular chain in tries to relax in presence of more amount of heat. Soorientation is lost some amount so crystallinity of the material is not changed very high on the surfaceof this composite material. But in the middle of the tube the filament are much more stressed condition

because the upper layer filaments gives pressure on to it due to shrinkage force generated during hotcompaction. So under stress condition the crystallinity of the filament is increased.

Table 4.9: Crystallinity study of composite along the thickness

Sample Code Position Crystallinity (%)

Multifilament 52

C195Surface 53

Middle of the Tube 65Inner Layer of the Tube 68

Fig-4.13 Cross section of pipe E 185,D 190 at a magnification of 20X

Fig-4.14 Cross section of pipe B 195, B200 at a magnification of 20X

4.4 MORPHOLOGICAL STUDY

4.4.1 Optical microscopy

The optical study of the compacted samples under the microscope was done to know about the amount

of melting of the filaments and also to investigate how compaction takes place in winded form. It isclearly observed from (Fig 4.13(a)) that the fusing is occurring in between the two filaments. Thisfusing helps to make bond between the two filaments thus a good interface is created during hotcompaction. It is observed from (Fig 4.13 & Fig 4.14) that at higher temperatures more material ismelted. The cross section picture indicates a good interface formation. It is observed from the picturethat the samples which were made at 185 °C have good interface although the filaments is quite intact but as the temperature is increased the amount of melting is increased at 195°C. There is very little



difference in the two regions as most of the reinforcement has melted. The material is then rich inmatrix and behaves more like a plastic sheet.

4.4.2 Study the morphology of composite by SEM

It is observed from (Fig 4.15) during hot compaction the surface of the filaments are fused and joined

each other. It is also observed that at increase temperature the surface melting is high and percentage of matrix increases. The sample which was made at 200°C is rich in matrix than the other sample. It is alsoobserved (Fig 4.15) that for the sample E185 the filaments are quite intact and matrix percentage is lowso lower integrity is observed. The one of the cause of poor interface is pressure; if the pressure is lowthen the interface is also poor. In this process the external pressure is not applied and the pressure isgenerated due to shrinkage of filament. So the interface properties in this type of material mainlydepend on temperature of the compaction. At higher temperature the shrinkage force is high so pressuregeneration is also high and penetration of melted material between the filaments is also good. But a balance between the matrix and reinforcement is very much important in this type of composite becauseover heating of the fibre damage the whole mechanical properties of the composite. From the (fig 4.16)the same effect is observed. The picture shows that in the direction of winding compaction is also verygood, and it also shows each filament touch each other which make a good interface. It is also observed

that the surface which is created during hot compaction is quite void free. From (fig 4.17) it is observedthe fusing between the filaments and a very good interface is observed from this picture which makes avery strong interface.



.

5.0 CONCLUSION

The process parameter that means the compaction temperature is optimized at ~1950C. In thistemperature properties obtained is optimum. Below this temperature properties are not good dueto lower shrinkage and lower surface melting of the filaments and above this temperature meltingof reinforcement is so high that ultimate properties decreases. From SEM image it is observedthat interface between the two filaments are quite strong and also fusion is observed in betweenthe two filaments. At this processing temperature the filaments are quite intact after hotcompaction.From DSC study it is observed that, melting point of hot compacted sample is shifted to higher

side compared to parent filaments. Change in crystallinity is observed from X-ray study. Thecrystallinity of the material increases with increasing temperature. The hot compacted tubular composite gave only sufficient matrix by partial melting of the filament which helps in stresstransfer and giving the required structural integrity where as the retained reinforcement providethe strength.When compared to the properties of extruded polypropylene pipe it is observed that thecircumferential tensile strength i.e. strength in circumferential direction is four times higher thanextruded material. It can be say that this composite pipe can withstand four times more pressurethan extruded pipe in same thickness. The axial compressive strength is nearly equal to theextruded pipe. The stiffness is much more in case of composite pipe as compared to extruded pipe. The bending strength is also superior to extruded pipe. The impact property of hotcompacted material is inferior to extruded material.

6.0 References

1. Ward I.M, Hine PJ. Polymer 2004; 42: 14132. Maaty E, Bassett DC, Olley RH, Hine PJ, Ward IM, Journal of Materials Science, 1996;

31(5): 11573. Loos L, Schimanski T, Hofman J, Peijs T, Lemstra PJ. Polymer 2001; 42(8): 3824



4. Hine PJ, Ward I.M, Maaty E, Abo M.I, Olley RH, Bassett DC. Journal of MaterialsScience 2000; 35(20): 5091

5. Amornsakchai T, Bassett DC, Olley RH, Hine PJ, Journal of Applied Polymer Science,2000; 78(4): 787

6. Hine PJ, Ward IM, Jordan ND, Olley RH, Bassett D C,Journal of Macromolecular Science, Physics 2001; B40 (5): 959

7. Le Bozec.Y, Kaang. S, Hine PJ, Ward IM. Composites Science and Technology, 2000;60(3): 330

8. Amornsakchai T, Bassett D.C, Olley RH, Hine PJ, Ward IM. Journal of Applied,Polymer Science 2000; 78(4): 787

9. Hine PJ, Ward IM, Teckoe J. Journal of Materials Science 1998; 33(11): 2725

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