Effects of processing temperature, screw speed, and heating conditions on the mechanical properties of pure PVC (Polyvinyl chloride)

Harsh Bhalani | 2012ABPS552P Pankhuri Priya | 2012ABPS655 Radhika Gupta | 2012ABPS668P Sanjana Teje | 2012ABPS498P

TABLE OF CONTENTS
Title Page Table of Contents…………………………………………………………………………………………………1 Abstract……………………………………………………………………………………………………………….2 Introduction…………………………………………………………………………………………………………2 Literature Review………………………………………………………………………………………………..6 Materials & Equipment Required………………………………………………………………………..18 Design of Experiment…………………………………………………………………………………………..19 Methodology……………………………………………………………………………………………………….21 Lab Work……………………………………………………………………………………………………………..22 Analysis……………………………………………………………………………………………………………….29 Sources of Error…………………………………………………………………………………………………...32 Conclusions………………………………………………………………………………………………………….32 Verification of Hypothesis……………………………………………………………………………………33 References…………………………………………………………………………………………………………..33

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Abstract
The effects of the temperature of heating zones and the screw speed of the extruder on the tensile strength of the PVC sheets produced has been analysed in our report. In order to get a brief idea of the possible results, a literature review of some of the previous papers on similar topics was done. We designed our experiment based on CCRD, but due to time constraints and the shortage of raw material we had to use the full factorial method to vary parameters of our experiments.

Introduction
Polyvinyl chloride, commonly abbreviated PVC, is the third-most widely produced plastic after polyethylene and polypropylene. PVC is used in construction because it is more effective than traditional materials such as copper, iron or wood in pipe and profile applications. Its properties are often modified (it can be made softer and more flexible) by the addition of plasticizers during processing, such as phthalates. In this form, it is also used in plumbing, electrical cable insulation, inflatable products and many applications in which it replaces rubber. Most of the PVC products that we see have been made by injection molding or extrusion processes. Extrusion is a process used to create objects of a fixed cross section profile. A material is pushed or drawn through a die of the desired cross section. The extrusion of polymers begins by loading the PVC pellets in the hopper, following which the PVC is brought to a molten state by the combined effect of the heaters and the shear heating from the extrusion screw. The molten material is then passed through a die forming a sheet. In our project, we have analysed the effects of various extrusion parameters on the tensile strength of PVC sheets. The extruder used is a single screw extruder which uses a single screw to pass the material through the barrel. For measuring the tensile strength of the polymer sheets, we have used a UNITEK universal testing machine. The parameters varied during the processing of the various sheets are the temperatures of the four heating zones and the screw speed.

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PARAMETERS AFFECTING EXTRUSION
Temperature Maintenance Optimal temperature maximizes uniform fluidity of the plastic, and minimizes the possibility for stress and warping of the final product. The extrusion temperature does not remain constant because of a variation in pressure and temperature. Heaters must be monitored, lowered, raised, or shutoff as necessary to maintain constant heat within the extruder—cooling fans and cast-in heater jackets can also help maintain proper extrusion temperature. Smaller extruders – up to 3 inch diameter – usually have three or four heating and cooling zones each equipped with temperature sensors and a temperature controller. Temperature Profiles Modern extruders usually have three or more temperature control zones along the barrel length. Proper settings for other zones depend a great deal on the particular polymer being extruded and the screw design being used. We can describe different barrel profiles as being flat, reverse, or normal. A normal profile reflects a situation where the rear zone temperature is set significantly below the exit melt temperature. The temperatures of the intermediate zones gradually taper up to match the temperature of the final downstream zone. A reverse temperature profile describes the opposite situation: the rear zone is hotter than the final downstream temperature zone (which is sometimes set below the exit melt temperature). A flat temperature profile reflects a situation where all barrel zones are set at approximately the same temperature. Effect of Glass Transition on Properties Mechanical properties are frequently used as sensible and trustworthy criteria for determination of the technical quality of PVC materials. The most common measurements are tensile strength, elongation at break, modulus and impact strength. The effects of both physical and chemical ageing of PVC are generally reflected in its mechanical properties. Changes in elongation at break are the most sensitive measure of changes in the status of the material. This measurement, which is often neglected, is in many cases more important than the more common measurement of stress at yield. However, interpretation of the test results is very difficult owing to the large number of variables influencing mechanical properties.

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It is well established that conventional PVC is a partially crystalline polymer. In the amorphous state, polymer segments move by virtue of rotations around single bonds in the main chain of the polymer. The intensity of the motion increases with temperature. A segment moves in a concerted manner into holes adjacent to it and leaves at the same time a hole of similar dimensions behind. The local density on the molecular scale fluctuates to give an overall population of holes, which are often referred to as free volume. The glass transition temperature, Tg, is the temperature below which free rotations cease because of intramolecular energy barriers. Above Tg, the free volume reaches an equilibrium value, which depends on temperature but not on time. This state is frozen in by rapid cooling of the material from above Tg to below it, creating a non-equilibrium state. Commercial PVC is mainly atactic but with a small preference for syndiotactic configuration. The spaced arrangements of chlorine atoms along the hydrocarbon backbone of molecules results in rarity of long uninterrupted runs of stereospecific polymer. Thus, only about 50–70% of commercial polymer is syndiotactic. When sufficiently long syndiotactic sequences become close together, a crystalline region is formed, binding together different regions of the same or adjacent molecule. Covas found that, on processing in the temperature range 193–203 C, the primary particle structure is almost destroyed and converted into a network of entanglements and primary and secondary crystallinity. These crystallites, which vary in perfection, constitute about 7–10% of the polymer of which the structure is constituted. The crystallites are small and they do not form spherulites [9]. However, they have a decisive influence on the mechanical properties by way of acting as physical crosslinks, resulting in the formation of a network of polymer chains. Screw Design and Speed Since the heating rate, feed rate, and other integral extrusion factors are directly dependent on the only moving part in the plastic extruder—the screw—carefully consideration of the size and design of this component is necessary. In general, extrusion speed varies directly with metal temperature and pressure developed within the container. Extreme Conditions At excessively high billet temperatures and extrusion speeds, metal flow becomes more fluid. The metal, seeking the path of least resistance, tends to fill the larger voids in the die face, and resists entry into constricted areas. Under those conditions, shape dimensions tend to fall below allowable tolerances, particularly those of thin projections or ribs. Another result of excessive extrusion temperatures and speeds is tearing of metal at thin edges or sharp corners. This results from the metal's decrease in tensile strength at excessively high-generated 4|

temperatures. At such speeds and temperatures, contact between the metal and the die bearing surfaces is likely to be incomplete and uneven, and any tendency toward waves and twists in the shape is intensified. Cooling Process The goal of the cooling process is to bring the polymer from the molten state, leaving the die face, to a temperature that corresponds with the mechanical properties. Quenching is the rapid cooling preventing low-temperature processes, such as phase transformations, from occurring by only providing a narrow window of time in which the reaction is both thermodynamically favorable and kinetically accessible. For instance, it can reduce crystallinity and thereby increase toughness of both alloys and plastics (produced through polymerization). Extremely rapid cooling can prevent the formation of all crystal structure, resulting in amorphous metal or "metallic glass". Addition of Plasticizers Low-molecular-weight plasticizer is one of the major additives used in PVC compounding. The addition of plasticizers to a PVC formulation decreases many mechanical properties of the PVC product (hardness, tensile strength, modulus, etc.); however, low-temperature flexibility, elongation, and the ease of processing are all improved. The most widely used low-molecular-weight plasticizer is di-2-ethylhexyl phthalate (DOP). These types of blends present serious problems of high migration (permanence) and consequent loss of blend properties. One alternative to this kind of problem is the use of polymeric plasticizers. Polyester/PVC miscibility studies have shown that some polymeric polyester are to some extent miscible with PVC, and other studies have shown that some polyurethanes are also miscible with PVC. Polyester-based thermoplastic polyurethane (TPU) is commonly blended with plasticized PVC resulting in a PVC blend with improved abrasion and fatigue resistance. However, as with most PVC/thermoplastic blends, they are difficult to process on conventional PVC processing equipment because of their high melt viscosity and limited heat stability. The addition of TPU plasticizers to PVC to form a polymer blend can be accomplished in several ways, twin screw extrusion being a popular option.

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LITERATURE REVIEW
PAPER 1- Studies of processing properties of PVC/Wood Composites
The influence of processing temperature of polyvinyl chloride and its blends with wood filler (PVC/WF) is studied on characteristics of extrusion processes as well as on selected mechanical properties of obtained materials are studied. Materials Dry blends based on polyvinyl chloride S-58 (ANWIL S.A.) have been used. Compositions contain stabilizers and internal lubricants system facilitating processing of PVC/wood composites. Pine flour of fraction 0.25-0.5 has been applied as a wood filler. Methodology Granulate preparation PVC dry blend has been extruded using single-screw extruder with screw L/D ratio equaled 28 (D=32 mm) and screw revolutions were 9 min-1. Extrusion head with nozzle which L/D ratio equaled 30/5 has been used. Processing has been carried out with stable temperature in extruder controlled at four independent heating-cooling areas of extruder and two independent areas of head equaling respectively 140°C, 150°C, 160°C, 170°C, 185°C. Extrudates have then been grinded in an impact mill. Extrusion Process Temperature has been regulated at two heating areas on the cylinder and at one area on the cylinder-head connector. The extrusion process has been carried out in the temperature ranging 140°C÷185°C that corresponds to the temperature of PVC granulates preparation. The head with rectangle cross section equaling 10 mm x 4mm and length equaling 130 mm with Teflon covered internal surface has been used. Such type of a head allows to form a profile and its calibration simultaneously. Temperature of this head depended on processing temperature and was decreased with increasing distance from cylinder-head connector. The screw rotation speed equaling 20 min-1 has been established by the use of trial and error method. UTM Properties Mechanical properties have been determined during static extension by the use of universal testing machine TIRA test 2200. Research conditions were following: extension speed: 10 6|

mm/s, distance between grips: 100 mm. Length, width and height of samples equaled respectively 80 mm, 10 mm, 4 mm. Mechanical Properties The increase of extrusion temperature from 140oC to 185oC improves tensile strength of PVC samples from 13.9 MPa to 54.4 MPa. Tensile strength of extruded profiles is similar to the strength of molded pieces only for samples obtained at 185oC. Tensile strength of PVC normalized samples injected at temperature 140oC is considerably lower from these obtained at higher temperatures. The difference of strength between samples obtained at temperature 150oC and 185oC is not so significant. The increase of processing temperature also improves impact strength of both PVC and PVC/WF composites.

Conclusions The increase of processing temperature improves mechanical properties of PVC and PVC/WF composites obtained during both extrusion and injection molding processes.

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PAPER 2- Effect of screw rotating speed on polymer melt temperature profiles in twin screw extruder
The effect of screw rotating speed on two-dimensional temperature profiles of flowing polypropylene melt was investigated in the barrel of a counter-rotating twin screw extruder using a designed experimental apparatus and a thermocouple temperature sensing device, the experimental apparatus being connected to a high speed data logger and a computer. The flow patterns of the polymer melt in the barrel of the extruder were also revealed. The changes in melt temperature profiles with extruding time were discussed in terms of flow patterns of the polymer melt during the flow, the increase in melt temperature being closely associated with total flow length of the melt, and shear heating and heat conduction effects. Introduction The analysis of heat transfer of flowing polymer melts appears complex not only because of the significant frictional heat generation, but also because of the highly temperature sensitive, nonNewtonian rheological character of the fluid. In order to measure the melt temperature accurately in polymer processing, this experiment uses a thermo-coupled non-intrusive temperature sensor as it has a very fast response to a small change of the measurement, give an accurate and repeatable measurement and be very robust to withstand highly viscous polymer flow. Prior Research Sbarski [4] investigated the effect of screw rotating speed on the melt temperature change in the system and found that increasing screw rotating speed led to increased heat dissipation (greater melt temperature rise). Nietsch [5] conducted melt temperature measurements of a black filled polyethylene melt using an infrared thermometer during twin-screw extrusion. The changes in melt temperature were detected by the changing concentration of the black traced PE particles. The general findings were that the melt temperature decreased with time to a point where it had reached a minimum before increasing again. The increase in melt temperature was due to shear heating effect during the flow. Result Figs 2–6 show temperature profiles of PP melts flowing in the barrel, at each r=R position as a function of extrusion time, for different screw rotating speeds (from 3 to 140 rpm). The measuring time used was 500 seconds. 8|

Generally, it was found that the melt temperature in all cases (except for 3 rpm screw rotating speed) decreased slightly and then rapidly increased to reach a plateau value, which was higher than the initial melt temperature. At screw speed of 3 rpm, the melt temperature did not change with time due to the low flow rate of the melt, leading to small amount of shear heating occurring. The decrease in melt temperature at the initial stage of the flow was due to the heat conduction through the section that connected to the end of the barrel. The decrease in melt temperature at the initial stage of extrusion has also been found by Nietsch [5]. It can be seen that the width of the temperature minima became narrower as the screw rotating speed was increased. The sharp increase in melt temperature is caused by a considerable shear heating during the flow [6]. It was interesting to observe that the time the melt temperature has reached the plateau value for each screw speed was different, the greater the screw speed the faster the plateau time occurring. Considering the melt temperature at the plateau region, the cross duct temperature profiles were not uniform for each screw speed. The melt temperature at the duct center appeared to be higher than that of the other r=R positions. However, the differences in melt temperature at various r=R positions became less pronounced when increasing screw rotating speed. In terms of overall melt temperature fluctuation, for a given radial position, it can be observed that the higher the screw speed the greater the fluctuation in melt temperature, especially at screw rotating speed of 140 rpm.

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This was due to shear heating and heat conduction effects. In this particular case, the differences in melt temperature across the duct are explained by considering flow patterns occurring in the barrel of the extruder. Beyond the scope of this paper, the quantitative determinations of the flow patterns were not intended, the flow patterns being used only for describing the differences in melt temperatures at various r=R positions. Figs 7 and 8 show selected flow visualizations of the PP melt at various points along the barrel length (distances before and after the sensor position) for two screw rotating speeds, 30 rpm and 140 rpm respectively, the flow pattern samples being sections, transverse to the axis of flow, of the flows taken along the barrel. Observations of the radial flow patterns along the barrel length allowed us to follow the flow behavior, and to determine the changes in temperature profiles of the melt qualitatively. Generally, there were two components to the flow. The first was the flow near the barrel wall, this moving along the circumference of the barrel, this referred to as circumferential flow. The other flow, being referred to as central flow, was related to the melt that was circulating around (near) the center of the barrel.

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In the case of Fig. 7 (30 rpm screw rotating speed) the central flow was observed to be greater especially the distances near the screw tip. The central flow then tended to reduce when approaching the sensor position. In Fig. 8 (140 rpm screw rotating speed), it is clear that the circumferential flow was greater. An attempt to relate the above flow patterns to the changes in melt temperature profiles occurring in the barrel was made. The following should be noted: 1. Radial melt temperature profiles: From the flow patterns in Figs 7 and 8, it was thought that the flow having a large fraction of the circumferential flow would lead to more uniform in melt temperature across the flow channel than that having a great amount of the central flow. The increase in melt temperature due to the shear heating was suppressed by heat conduction occurring during the flow. As shown earlier, increasing screw rotating speed tended to generate a large amount of the circumferential flow, implying that the flow length of the circumferential flow has increased. This resulted in an increase in melt temperature around r=R positions of 0.4 and 0.8, thus the differences in melt temperatures at various r=R positions across the flow channel being less (more uniform radial melt temperature profiles).

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2. Relatively high melt temperature at the center: At lower screw speeds, greater differences in melt temperature across the flow channel were observed, the temperature around the duct center being relatively high. This may be associated with the flow occurring. In Fig. 7, the central flow circulated around half of the circumference of the barrel before flowing down along the centerline of the barrel crosssection. The flow length of this material was relatively long, and this led to increased shear heating and high temperature around the duct center. At higher screw rotating speeds, the flow length of the central flow reduced and was replaced by increased flow length of the circumferential flow (hence increased shear heating as mentioned earlier). As a consequence, the temperature distributions at higher screw speeds became more uniform. Maximum melt temperature rise Another aspect to consider was that the melt temperature rise, as compared to the initial melt temperature (190±C), during the flows for each screw rotating speed. It was found that the maximum temperature rise varied with screw rotating speed. The greater the screw speed the higher the maximum temperature rise, this being in good agreement with the results reported by Sbarski [4]. Thismay involve the two following reasons. Firstly, increasing the screw speed led to higher shear heating and thus increased melt temperature rise [7]. Secondly, considering the flow patterns for both low and high screw speeds, it was thought that the total flow length of the circumferential flow in the case of higher screw speed was greater than that of the circumferential flow with lower screw speed due to the larger radius of flow circulation, higher melt temperature rise being given for high screw rotating speed. It should be noted that after the sensor position the polymer flowed along its flow paths without any circumferential and circulating (central) flows, the flow patterns being similar to those reported in previous work [8] Comparison with theoretical temperature rise It was essential that the experimental results of melt temperature rise should be considered by comparing with those obtained theoretically. The expected temperature change of flowing polymer melt is determined by the sum of heat gain or loss by conduction and the rate of viscous dissipation within the polymer fluid [9]. In the case of a twin screw extruder, the maximum temperature rise (1Tmax) due to conversion of mechanical energy into heat during the flow can be quantitatively estimated using the following equation [9].

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Where Cp is the specific heat, Qh is the total rate of heat added to the extruder, ½ is the melt density, Q is the volumetric flow rate, N is the screw rotating speed, 0 is the torque, and 1P is the pressure drop at the die. In this work, it was assumed that no heat (Qh D0) added into the system (extruder) during the measurements. All the parameters used in the above equation were obtained simultaneously during the temperature measurements, except for the melt density and specific heat values which were obtained by literature [10, 11], the values being listed in Table I. Table II shows a comparison of experimental and theoretical temperature rise of PP melt at various screw rotating speeds. It was found that the values of melt temperature rise in both cases were considerably different, the theoretical temperature values being much greater than the experimental values. The differences in the temperature rise values may result from the following reasons. Firstly, the errors may arise due to flow components, in which the equation used did not take account of. From the results shown earlier, many flow components such as circumferential and central flows were found. Secondly, some parameters used in the calculations (Cp and ½) were given by independent methods from literature [10, 11], the conditions under which the polymer melt was being tested may be different. This would result in an error in the calculations. Finally, the errors may arise due to some assumptions made in the derivation of the above equation such as steady state and incompressible fluid which is unlikely in polymeric systems [9]. Conclusion A close relation between the melt temperature profiles and flow patterns was found, that is the greater the screw rotating speed the higher the melt temperature rise. At low screw rotating speed, melt temperature at the center appeared to be relatively high, and the melt temperature across the flow channel became more uniform as the screw speed was increased. The changes in melt temperature profiles were associated with shear heating and heat conduction effects, and the total flow length of the melt in the system. The experimental temperature results were found to be different from those obtained in theory.

PAPER 3- Influence of extrusion temperature and process parameter on microstructures and tensile properties of a particulate reinforced magnesium matrix nano-composite
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The application of secondary processing is necessary to further improve the specific properties. It has been shown that some improvement in strength can be achieved with the application of secondary processing techniques such as extrusion, rolling, etc. Among these, extrusion is the best processing route for achieving a combination of hot compaction and mechanical working. There have been limited studies on the effect of extrusion on microstructures. Experimental Procedures: A commercial AZ91 alloy with a nominal composition of Mg–9.07Al–0.68Zn–0.21Mn was employed as the matrix. SiC nanoparticles (SiCp) with an average size of 60 nm and volume fractions (vol.%) of 1% were selected as the reinforcement. The extrusion was carried out at different temperatures (250, 300 and 350 C) with an extrusion ratio of 12:1 and at a pressing speed of 15 mm/s, using a press with a 2000 kN load limit. The billets, pressure pad and dish-shaped die were put into the extrusion container. The extrusion container was heated to the given temperature in a muffle furnace. The temperature of the container was monitored using a K-type thermocouple inserted into a hole drilled in the container. Once the container attained the desired temperature, a period of 1 h was allowed to elapse before the extrusion was carried out. This time is long enough to allow the billet to reach a steady-state temperature, as determined from previous tests. A graphite-based mixture was used as high-temperature lubricant. Experiment and Equipment Optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the evolution of the matrix and the nanoparticles distribution introduced by extrusion. Samples for microstructure analysis were carried out in the central part of specimens parallel to the extrusion direction and prepared by the conventional mechanical polishing and etching using acetic picral [5 ml acetic acid + 6 g picric acid + 10 ml H2O + 100 ml ethanol (95%)]. In order to measure grain size of the matrix before and after extrusion, Image-Pro Plus(IPP) software was used to determine the linear intercept length of at least 200 grains of matrix in the SiCp/AZ91 nano-composites. Microstructural features of the SiCp/AZ91 nano-composites were identified using energy dispersive spectrophotometric (EDS) analysis. Specimens for TEM were prepared by grindingpolishing the sample to produce a foil of 50 lm thickness followed by punching 3 mm diameter disks. The disks were ion beam thinned. To determine the tensile properties, the samples were machined parallel to the extrusion direction. The tensile tests were carried out by Instron-1186 tension machine at room temperature and the tensile rate was 0.5 mm/min. The dimensions of the tensile test sample are given in Fig. 1. Three samples for repeat tensile tests were cut and the tensile strength reported in the work was averaged from the three tensile tests. 14 |

Results and Discussion With the extrusion temperature increasing from 250 to 350 C, the grain size of matrix in the nano-composites is gradually decreased and the scale of grain size distribution is reduced. This indicates that full dynamic recrystallization (DRX) occurs during extrusion. Two kinds of zones could be observed in the extruded nano-composites: SiC nanoparticle bands parallel to the extrusion direction and refined-grain zones between the SiC nanoparticle bands, as shown in Fig. 2. It can be also found that amount of SiC nanoparticle bands is decreased with increasing the extrusion temperature. Under higher extrusion temperature, the matrix of the nanocomposite can easily flow into the SiC nanoparticles clusters because that the flow velocity of matrix is faster than the SiC nanoparticles. Hence, the nanoparticle distribution of the nanocomposites has been improved and amount of the dispersed SiC nanoparticles has been increased with increasing the extrusion temperature. The dispersed SiC nanoparticles can introduce the larger strain resulting in the severer DRX and inhibit grain growth effectively. As a result, the grains of matrix in the nano-composites are gradually refined. Evolution of the tensile properties after extrusion Fig. 3 shows the yield strength (r0.2, 0.2% proof stress), ultimate tensile strength (UTS, the ultimate tensile strength) and elongation to fracture of SiCp/AZ91 nano-composites after extrusion with increasing the extrusion temperature. The yield strength and ultimate tensile strength of nano-composites are gradually improved with increasing the extrusion temperature, which indicates that higher extrusion temperature might be useful to enhance the mechanical properties of the nano-composites.

Fig 3. Tensile strength of SiCp/AZ91 nanocomposites extruded at different temperatures.

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This is the Hall-Petch equation. The Hall-Petch equation describes the change in the yield strength of a polycrystalline material with a change in the size of the grains. The reason for this inverse relation is that with smaller grain sizes, the polycrystalline material will have more grain

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boundaries per unit volume that can act as pinning centers to hold the dislocations in place.

The value of Ky is dependent on the number of slip systems. It is higher for HCP metals than for FCC and BCC metals [12]. Since Mg is HCP, the grain size affects the yield strength significantly. The grains of matrix in the extruded nano-composites are gradually refined with increasing the extrusion temperature (in Fig. 2) resulting in the increase of the tensile strength. The decrease of amount of SiC nanoparticle band can also contributes to the increase of elongation to fracture in the nano-composite. Wang et al. [13] has reported that it is necessary to employ high extrusion temperatures and ratios in order to eliminate particle clusters in the magnesium matrix composites reinforced with micro particles. So, it is expected that high extrusion temperatures is also necessary to further improve the distribution of SiC nanoparticle. Conclusions This experiment concluded with exhibiting that the scale of grain size distribution is reduced with the temperature increasing from 250 C to 350 C. It was also observed that the yield strength and ultimate tensile strength of the extruded nano-composites were gradually improved with increasing the extrusion temperature T.

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Our Experiment: Effects of processing temperature, screw speed, and heating conditions on the mechanical properties of pure PVC (Polyvinyl chloride)
Materials & Equipment Required
A single-screw extruder with four heating zones was used. The extruder had three independent heating areas and one independent area near the die. The material extruded was PVC pellets. Since there was a shortage of pure PVC pellets, a PVC sheet was pelletized by a pelletizer to make more of them. Tensile tests were conducted on a UNITEK Machine. Software Used for plotting graphs and finding the variation of parameters is DesignExpert. A Vernier Caliper and Ruler were used to measure the dimensions of the sheet for the Ultimate Tensile Machine. A roller was used to pass the PVC Sheet through it after the extruder operation to make the sheet more uniform. Emery Cloth was used to properly grip the piece of the PVC Sheet being tested in the UTM.

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Design of Experiment
The Centre Composite Design (CCD) has two important features - it is orthogonal and rotatable providing the correct spacing for the axial parameter (alpha ) is chosen. It can be shown that the design is rotatable if

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Temperature Speed 2nd Temperature Experiment Temperature 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Level 3 Level 4 Level 3 Level 4 Level 3 Level 4 Level 3 Level 4 Level 1 Level 5 Level 2 Level 2 Level 2 Level 2 Level 2 Level 2 Level 2 Level 2 Level 2 Level 2

130-170 C 70-90 rpm 100- 140 C Speed 2nd Temperature Speed 2nd Temperature Temperature 75 75 85 85 75 75 85 85 80 80 70 90 80 80 80 80 80 80 80 80 110 110 110 110 130 130 130 130 120 120 120 120 100 140 120 120 120 120 120 120 -1 1 -1 1 -1 1 -1 1 -1.682 1.682 0 0 0 0 0 0 0 0 0 0 -1 -1 1 1 -1 -1 1 1 0 0 1.682 1.682 0 0 0 0 0 0 0 0 -1 -1 -1 -1 1 1 1 1 0 0 0 0 -1.682 1.682 0 0 0 0 0 0

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Methodology
During our experiment, we did not vary the secondary temperature because it would be a much less contributing factor to the tensile strength. Because of time constraints, we did not consider the effect of this factor. Once we designed the experiment, we started the experiment in the lab under the supervision of Mr. Harish. Given the limitation of time, we manufactured 5 sheets. These sheets were made under various conditions wherein we varied the temperature and the screw speed. The details for each sheet are given below:

Heating Zone 1 Sheet 1 Sheet 2 Sheet 3 Sheet 4 Sheet 5 120 120 125 125 135

Heating Zone 2 126 126 130 130 140

Heating Zone 3 130 130 140 140 150

Heating Zone 4 145 145 150 150 160

Screw Speed 56.9 80 80 59.5 95

Tensile Strength (N/mm^2) 0.011 0.112 0.009 0.011 0.010

Keeping the Temperature constant at 120C we did not expect at drastic increase in strength as observed. In 125C we expected a slight increase in strength or a constant strength, what we see is a decrease. Keeping speed to be constant at 56.9rpm we expected an increase, what we see is a constant strength. At 80rpm we expected an increase but observe a decrease. We expected elevated strength at 135C and 95rpm, instead its lower than most strengths

Our first step was to pelletize an already prepared sheet using the pelletizer. The pellets were fed into a hopper which in turn fed the screw barrel, passed through the machine and then produced the sheets. The sheets were passed through a roller when still hot in order to produce sheets with a more uniform thickness. Next we determined tensile strength using the Unitek Tensile Machine(UTM). For this each sheet was cut into smaller parts so as to obtain a sheet of uniform thickness. It was imperative to have uniformly thick sample otherwise the sample sheet would slip off the clips and wouldn’t give accurate results. FIE software which accompanied the machine was simultaneously 21 |

plotting various graphs. The table below gives the dimensions of the sample sheets used for finding tensile strength. Sheet 1 2.07 79 42 Sheet 2 1.7 80 26 Sheet 3 2.05 70 45 Sheet 4 1.96 80 37.8 Sheet 5 1.84 82 47.02

Thickness (mm) Length (mm) Width (mm)

At the end of each experiment we obtained a load vs displacement curve and also stress vs. strain curve. The software itself calculated and produced the final results of tensile strength . The following section contains the results we obtained.

Lab Work

Sheet before failure

Sheet after failure

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A closer view of sheets after failure

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Sheet 1

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Sheet 2

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Sheet 3

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Sheet 4

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Sheet 5

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Analysis

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Sources of Error
1. The use of recycled PVC when there was a dearth of pure PVC. This can cause a change in the material properties of the sheet as some of the pellets had been previously used at different heating conditions. 2. The PVC sheets that were made by the UTM were uneven in cross-sectional thickness and other dimensions. Also in higher temperature ranges, sometimes the edges of the sheets were burnt. 3. Fluctuating Temperature regions. 4. A major problem that was faced is that the number of experiments conducted were not sufficient to draw conclusions. 5. The die of the extruder was not cleaned perfectly, which caused the PVC sheets that came out to be uneven and not 100% pure PVC. 6. The uneven thickness of the sheet caused the grip for UTM to be problematic as the sheet kept slipping and it was difficult to find the fracture point. 7. Since a particular heater takes a lot of time to reach a certain specified temperature, sufficient time may not have been given because the experiments were conducted successively, giving rise to discrepancies in the results. Minimizing errors 1. The above errors could have been minimized by a greater number of runs of the experiment. 2. Giving the heaters sufficient time to heat up and cool down rather than consecutive runs. 3. Having a preliminary experiment to familiarize with the material itself rather than expecting similar results from papers read before. 4. Tensile testing specially designed for flat PVC sheets.

Conclusions
Due to the smaller number of runs no concrete conclusion can be drawn from the experiment. However even with lesser runs the observed results do not comply with the theory (as seen in the fifth run). This could be due to the experimental errors mentioned above or due to the fact that theoretical basis for the experiment may not hold true for our experimental conditions. This design of experiment does give an insight on how to determine the relationship between experimental parameters before performing the experiment. It is essential to give an idea of how the experiment should be performed, that is at what levels we should look for data at.

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Verification of Hypothesis
Check if this is Verified 1. Extrusion Processing Temperature directly changes the strength 2. Screw Speed directly changes directly changes the tensile strength 3. Heating Temperature directly changes the tensile strength

References
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[13] Wang XJ, Xu L, Hu XS, Nie KB, Deng KK, Wu K, et al. Influences of extrusion parameters on microstructure and mechanical properties of particulate reinforced magnesium matrix composites. Mater Sci Eng A 2011;528:6387–92. [14] Maridass B., Gupta E.: Kautsch Gummi. Kunstst. 2003, 5, 232. [15]AdhikariB.,DeD.,MaitiS.: Prog.Polym. Sci. 2000, 25, 909. [16]Box G. E. P., Hunter W. G.,Hunter S. S.: “Statisticsfor experimenters”, John Wiley, New York 1978. [17]Montgomery D. C.: “Design and analysis of experi- ments”, John Wiley, New York 1984

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