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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgments
  8. ABBREVIATIONS
  9. REFERENCES

Blends of high-density polyethylene (HDPE) with chlorinated polyethylene (CPE) were generated using melt mixing. CPE of two different chlorination contents was used and its amount in the blends was varied from 1% till 30%. The rheological, thermal, mechanical, and morphological properties of the blends were characterized along with miscibility analysis. In general, better mixing of the CPE polymer in HDPE was observed at lower CPE concentration and reduced mixing or immiscibility occurred at higher concentration of CPE. However, the extent of immiscibility was different in both CPE25 and CPE35 systems. The rheological analysis of the data using Cole-Cole, Han-Chuang and van Gurp plots confirmed the miscibility of CPE25 blends (except for 30% CPE25 blend at lower frequency) whereas CPE35 blends with 10–30% CPE content were immiscible. Highest increase in the rheological properties (complex moduli) was observed at 2% CPE content. The mechanical properties of the CPE25 blends were superior than the corresponding CPE35 blends especially at higher CPE concentration where effects of immiscibility as well as matrix plasticization played a role. The morphology characterization using TEM indicated change in the crystalline features of the polymer in the case of CPE35 blends. The optical microscopy also confirmed the better mixing of CPE25 polymers in HDPE than CPE35. The CPE25 blends exhibited uniformly dispersed CPE phase which was also confirmed by the rheological analysis. However, the blends of CPE35 with 10% CPE content onwards had significant phase immiscibility. POLYM. ENG. SCI., 54:85–95, 2014. © 2013 Society of Plastics Engineers


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgments
  8. ABBREVIATIONS
  9. REFERENCES

The physical polymer-reinforcement means such as blending or filler incorporation have gained favorable position for acquiring new polymeric materials with altered properties [1, 2]. The properties of the resultant materials depend on features like interaction between the phases, compatibilization, processing conditions, composition, etc. The generation of polymer blends specially offers advantages such as property profile combinations, aid in processing, low capital costs as compared with development of new monomers and polymers of required properties.

Polyolefins are the largest group of industrial thermoplastics in terms of production and have superior rank among commodity plastics owing to their use in a large number of applications. The number of individual polyolefin members is limited and the number of applications based on such materials is constantly increasing. Various polyolefin-based blends and composites are thus required to meet the increasing demand of materials with required properties and processing suitable for specific applications [1, 3].

Chlorinated polyethylene (CPE) blends with different polymers have been reported for many purposes such as improvements in the toughening properties of host polymers [4], as a compatibilization agent through enhancement of interfacial interactions between two polymers [5, 6], improved processing properties [7], ameliorated adhesion properties [8], enhanced ignition resistance properties [9], and modified gas transport properties [10]. Based on the percentage of chlorination of the polymer, there are many classifications of CPE ranging from plastic (0–14%), thermo-elastoplast (15–30%), elastomer (31–46%), rigid polymer (47–61%), to friable resin (62–73%) [11]. Maksimov et al. blended CPE with 36 % chlorination content with high-density polyethylene (HDPE) and low-density polyethylene (LDPE) [12]. It was observed by using different models that the mechanical properties depended on morphological changes occurring at higher concentration of CPE36 in blends [12, 13]. Walsh et al. showed the compatibility of CPE with poly(methyl methacrylate) (PMMA) at around 50% chlorination content due to favorable heat of mixing at higher percentage of chlorination [14, 15]. Zhang et al. added CPE36 as an impact modifier for the blends of poly(vinyl chloride) (PVC)/poly (α-methylstyrene-acrylonitrile) which led to four-fold increments in the impact properties of ternary blends at 15 phr concentration [16]. However, a reduction in the modulus and strength of the blends was also observed. In a similar work, blends of CPE25 and CPE48 with epoxidized natural rubber were found to be miscible at higher degree of chlorination owing to the interactions involving chlorine atoms and oxirane groups [17]. Similarly, CPE blends with other polymer matrices have also been reported [18, 19]. Although incorporation of CPE has already been achieved in many polymer blends but in-depth morphological and rheological studies on the miscibility, structural properties and performance of blends of different types of CPE with polyolefins like polyethylene (PE) and polypropylene (PP) is still missing. The goal of this study was to achieve an optimum amount of two different CPE polymers in HDPE which generates miscible blends and does not have negative impact on the polymer mechanical and flow properties. The choice of more suitable CPE polymer was also necessary as the potential environmental hazards of CPE polymers limit the use of higher extents of these polymers in blends.

In this work, two type of CPE (with 25% and 35% chlorination content; i.e., from the thermoplastic and elastomer range, respectively) were used to generate blends with HDPE using melt blending. The content of CPE in PE was varied from 1% till 30% and the resulting impact on rheological, thermal, mechanical and morphological properties was studied.

EXPERIMENTAL

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgments
  8. ABBREVIATIONS
  9. REFERENCES

Materials

CPE grades Weipren® 6025 (25% chlorine content, named as CPE25) and CPE 135A (35% chorine content, named as CPE35) were obtained from Lianda Corporation and Weifang Xuran Chemicals, China, respectively. The melt flow index (190°C, 2.16 kg) for CPE25 and CPE35 was measured to be 1.8 and 1.9 g/10 min, respectively. HDPE BB2581 was supplied by Abu Dhabi Polymers Company Limited (Borouge), UAE. The specifications of the polymers as received from the suppliers are also reported in Table 1 [20]. The polymer materials were used as obtained.

Table 1. Specifications of the polymers as received from the suppliers
PropertyCPE25CPE35HDPE
AppearanceWhite granulesWhite powderTransparent pellets
Specific gravity, ASTM D7921.1–1.31.1–1.160.958
Melting point, °C, ASTM D7138147
Heat of fusion, J/g, ASTM D3418452
MFR 190°C/2.16 kg, g/10 min, ASTM D12380.35
Heat deflection temperature (0.45 N/mm2), °C, ASTM D64880

Generation of HDPE-CPE Blends

Polymer blends were prepared by melt mixing of CPE25 and CPE35 with HDPE using mini twin conical screw extruder (MiniLab HAAKE Rheomex CTW5, Germany). A mixing temperature of 170°C for 3 min at 80 rpm with batch size of 5 g was used. The screw length and screw diameter were 109.5 mm and 5/14 mm conical, respectively. Blends of CPE25 and CPE35 in weight percentages of 1%, 2%, 5%, 10%, 15%, 20%, and 30% were generated. The disc and dumbbell-shaped test samples were prepared by mini injection molding machine (HAAKE MiniJet, Germany) at a processing temperature of 170°C. The injection pressure was 700 bar for 6 s, whereas holding pressure was 400 bar for 3 s. The temperature of the mold was kept at 55°C.

Characterization Techniques

Thermal properties of the blends were recorded using Netzsch thermogravimetric analyzer (TGA). Nitrogen was used as a carrier gas and the scans were obtained from 50 to 700°C at a heating rate of 20°C/min. Calorimetric properties of blends were recorded on a Netzsch DSC under nitrogen atmosphere. The scans were obtained from 50–170–50°C using heating and cooling rates of 15°C/min and 5°C/min, respectively. The heat enthalpies used to calculate the extent of crystallinity were recorded in a narrow error range (±0.1%), which were also confirmed by repeated runs.

AR 2000 rheometer from TA Instruments was used to characterize the rheological properties of the blends such as storage modulus (G′), loss modulus (G″), viscosity (η′), and elasticity (η″). Disc shaped samples of 25-mm diameter and 2-mm thickness were measured at 185°C using a gap opening of 1.2 mm. Strain sweep scans were recorded at ω = 1 rad/s from 0.1 to 100% strain and the samples were observed to be shear stable up to 10% strain. For the comparison, frequency sweep scans (dynamic testing) of all the samples were recorded at 4% strain from ω = 0.1 to 100 rad/s.

The mechanical testing of the blends was performed on universal testing machine (Testometric, UK). The dumbbell-shaped samples with 53-mm length, 4-mm width, and 2-mm thickness were used. A loading rate of 5 mm/min was employed and the tests were carried out at room temperature. Win Test Analysis software was used for the calculation of tensile modulus and yield stress properties of the blends. An average of three values is reported.

Philips CM 20 (Philips/FEI, Eindhoven) electron microscope at 120 and 200 kV accelerating voltages was used for the bright field transmission electron microscopy analysis of the blend samples. Thin sections of 70–90 nm thickness were microtomed from the sample block and were supported on 100-mesh grids sputter coated with a 3-nm thick carbon layer. The macroscopic features of blends were also observed under an optical microscope Olympus BX 51. The cross-section of the samples was characterized at a magnification of 20× and both bright field and dark field reflection modes were used. Before the analysis, the surface of the block face of the samples was smoothened using a knife.

RESULTS AND DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgments
  8. ABBREVIATIONS
  9. REFERENCES

In this study, CPE with two different chlorination levels (Table 1) was blended with HDPE in different weight ratios using melt mixing process. The chlorination contents were differed to study their impact on miscibility with PE along with rheological, mechanical as well as thermal properties of the blends. The melt flow indices of the CPE samples were similar, however, they were higher than that of pure HDPE indicating their lower molecular weight. The processing conditions were kept unaltered to generate the various blends so as not to induce any variations in the material characteristics. A lower melt mixing temperature of 170°C was chosen in order not to thermally degrade the polymer, but it was still sufficient to have uniform polymer mixing.

Table 2 and Figs. 1 and 2 demonstrate the calorimetric properties of pure HDPE, pure CPE samples and HDPE–CPE blends. The heat of fusion of pure crystalline HDPE was taken as 293 J/g and was used to determine the extent of crystallinity in the polymer [21]. As shown in Fig. 1a, CPE25 was semicrystalline in nature as indicated by the crystalline melting peak in the DSC thermogram and a peak melting temperature of 130°C was recorded. CPE35 polymer, on the other hand, was amorphous in nature as no melting transition was observed in Fig. 2a. Hence, owing to the different extent of chlorination, CPE25 and CPE35 were different also in their structural morphology. The peak melting temperatures (Tm) of the blends decreased on adding the CPE polymers, though the magnitude of Tm reduction was less significant for blends till 10% CPE concentration (Table 2, Figs. 1a and 2a). Both the CPE polymers caused similar Tm reduction as compared with the pure HDPE. The crystallization transitions in the blends (Figs. 1b and 2b) almost overlapped and the peak crystallization temperature also remained fairly constant (Table 2). It confirmed that the CPE component did not act as a nucleating agent for the PE chains. In the case of blends with CPE25, the melt enthalpy remained unchanged for blends with 1% and 2% CPE content. For a CPE concentration of 5% onwards, the melt enthalpy started to decrease and the blend with 30% CPE25 content had a value of 119 J/g as compared with 151 J/g for pure polymer. It indicated that the CPE25 at lower concentrations did not hinder the crystallization of HDPE. On the other hand, in the case of blends with CPE35, the melt enthalpy gradually decreased with concentration of CPE35 due to its amorphous nature and the 30% CPE35 blend had significantly lower melt enthalpy value (normalized to actual PE content) of 102 J/g. The decrease was very significant at higher concentrations, indicating that the higher concentrations may have affected the crystallization ability of the HDPE chains. As compared with 52% crystallinity of pure polymer, the extent of crystallinity started to decrease in CPE25 containing blends when CPE25 content was beyond 2% and it was recorded to be 41% for the 30% CPE25 blend. On the other hand, the extent of crystallinity was even lower to 35% for the 30% CPE35 blend indicating that the initial morphology of the CPE component affected the final morphology of the blends.

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Figure 1. DSC thermograms of (a) melting behavior and (b) crystallization behavior of CPE25 blends as a function of CPE25 concentration in comparison with pure HDPE.

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Figure 2. DSC thermograms of (a) melting behavior and (b) crystallization behavior of CPE35 blends as a function of CPE35 concentration in comparison with pure HDPE.

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Table 2. Calorimetric analysis of pure polymers and polymer blends
CodeBlendΔH (J/g)Peak melting temperature (°C)Crystallinity, %Peak crystallization temperature (°C)
1HDPE15114052115
2CPE 25%47130
3CPE 35%
4HDPE/1%CPE2515313752116
5HDPE/2%CPE2514913751115
6HDPE/5%CPE2514013748115
7HDPE/10%CPE2513413746115
8HDPE/15%CPE2513013444115
9HDPE/20%CPE2512813444116
10HDPE/30%CPE2511913441116
11HDPE/1%CPE3513813847114
12HDPE/2%CPE3513713847115
13HDPE/5%CPE3513013744115
14HDPE/10%CPE3513213645115
15HDPE/15%CPE3511513439115
16HDPE/20%CPE3510313435114
17HDPE/30%CPE3510213435115

In Fig. 3, the comparison of the TGA thermograms of blends with pure CPE and HDPE polymers has been demonstrated. The thermograms of blends with 1%, 2%, and 5% CPE were indistinguishable from pure polymer. In the higher CPE concentration blends, the onset degradation temperature in the first degradation step coincided with that of the pure CPE polymers indicating that the CPE phase had independent signal. Moreover, the second degradation step in the blends was also observed to occur at higher peak temperatures (∼20°C) than the pure polymer due to the thermal stability in the presence of chlorine. In the case of CPE35 containing blends, the degradation temperature was observed to increase with increasing CPE 35 content probably due to higher extents of chlorine in this system.

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Figure 3. TGA thermograms of (a) CPE25 containing blends and (b) CPE35 containing blends in comparison with pure CPE and HDPE.

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Network structure of the polymer blends was evaluated with shear rheology and the storage and loss moduli of the samples as a function of angular frequency are demonstrated in Figs. 4 and 5. Strain sweep was conducted and samples were found to be safe up to 10% strain. Frequency sweep of the samples was performed with controlled shear strain of 4% using frequency range of 0.1–100 rad/s. All the samples exhibited gradual decline in the extent of modulus enhancement as a function of angular frequency due to shear thinning effect. In the case of CPE25 containing blends, the storage modulus increased on increasing the CPE concentration till 2%, after which a gradual decrease in the storage modulus was observed on increasing the CPE25 concentration. It indicated that the molecular mixing of the more stiff CPE chains to HDPE enhanced the shear behavior of the polymer. However, the modulus values for the blends till 15% CPE content were still higher than pure HDPE, confirming that the mixing of the phases was still optimum. For example, the shear modulus for pure HDPE at an angular frequency of 10 rad/s was measured to be 1,04,000 Pa which increased to its maximum value of 1,27,000 Pa for 2% CPE blend. The least value of modulus was observed for 30% CPE blend where the value of 92,000 Pa was observed for angular frequency of 10 rad/s due to matrix plasticization. The curves of shear modulus were also observed to converge with each other at higher frequency thus indicating concentration independence. In the case of CPE35 containing blends, the modulus similarly increased initially and the maximum enhancement was observed at 2% CPE35 blend. However, the reduction in the modulus beyond 5% CPE content was much more significant in this case and the 30% CPE blend had a modulus value of 53,470 Pa for angular frequency of 10 rad/s. It could have resulted due to the higher extent of immiscibility of the phases in CPE35 containing blends as compared with CPE25. The modulus vs. angular frequency curves also did not converge at higher frequency indicating concentration dependent morphological changes taking place in the blends. These findings were also reflected in oscillatory torque required to maintain the same strain in the samples during the rheological testing. The torque required to strain the samples was maximum at 2%CPE content. It remained same as HDPE till 15% CPE content for CPE25 system and 5% CPE content for CPE35 system followed by its decrease at higher CPE concentrations in the blends.

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Figure 4. Storage modulus (G′) of the (a) CPE25 and (b) CPE35 blends as a function of angular frequency as well as CPE concentration in the blends.

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Figure 5. Loss modulus (G″) of the (a) CPE25 and (b) CPE35 blends as a function of angular frequency as well as CPE concentration in the blends.

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Similar to storage modulus, the loss modulus of the blends (Fig. 5) increased initially as compared with pure HDPE with CPE concentration followed by decrease in its magnitude, which depended on the type of CPE added to HDPE. For example, the loss modulus of pure polymer at an angular frequency of 10 rad/s was observed to be 83,980 Pa which increased to 93,480 Pa for 2%CPE25 blend [12, 13]. Blends with 5% and 10% CPE content though had higher modulus than pure polymer, but the magnitude decreased with increasing the CPE content. 30% CPE25 blend at the same angular frequency was measured to have a value of 78,080 Pa. In the case of CPE35 containing blends, the modulus also showed maximum increase at 2% content. Higher concentration of CPE35, however, significantly deteriorated the polymer response as a value of 38,790 Pa was observed for blend with 30% CPE content. Similar to Fig. 4, the loss modulus curves for CPE25 blends converged with each other at higher frequency, thus, showing no dependency on CPE concentration. However, the blends with CPE35 showed convergence only for lower CPE concentration blends and significant concentration dependent behavior for higher CPE concentration blends.

Table 3 also shows the effect of percentage of CPE25 and CPE35 on transition point from liquid like to solid like viscoelastic behavior which is usually called gel point. At this point, polymer acts as true viscoelastic fluid (G′ = G″). This behavior could be referred to the lesser molecular flexibility and mobility due to forming of viscoelastic gel or solid. It can be seen that both CPE polymers showed opposite behavior as the percentage of CPE was increased in HDPE. For CPE35 blends, the transition point shifted to lower frequency as percentage of CPE35 was increased and showed lowest frequency of transition point of 0.8 rad/s (pure polymer 1.9 rad/s) at 30% of CPE35. This change could be attributed to the immiscibility of the CPE35 polymer in HDPE thus hindering the formation of gel structures, especially at higher percentage of CPE35 [21]. On the contrary, CPE25 addition initially decreased the transition point as compared with pure polymer but on average the behavior shifted to higher frequency values and the highest transition frequency of 3.4 rad/s was observed at 30% CPE content, which would have resulted because of better miscibility of the phases. It can also be inferred from the transition frequency values that in both of the cases that there was gradual change in magnitude of transition frequency point up to 15% CPE amount, but sudden changes occurred at 20% and 30%. These behaviors were also reflected in linear regression between ln G′ vs. ln ω of the samples by using equation:

  • display math

The linear regression is a power law relationship and states that true gel is characterized by zero slope of the power law model [22]. It can be inferred from the regression points in case of CPE25 blends that the slope (Table 3) was constant up to 15% but significant increment in slope could be observed when the CPE content was further increased. In the case of CPE35 blends, the slope was constant up to 10% CPE content, after which increase in the solid like characteristic was observed as the slope decreased. The slope reduced to 0.48 for 30% blend as compared with 0.54 for pure HDPE.

The miscibility of the blends was further studied using Cole-Cole viscosity plot which develops relationships between real (η′) and imaginary (η″) parts of complex viscosity [23-25]. A smooth, semi-circular shape of the graph would suggest miscible blends with homogenous phase. The deviation from this behavior indicates phase segregation due to immiscibility of the components in the blends. As can be seen in Fig. 6a (plots stacked vertically for clarity), 30% CPE25 blend showed deviation at higher viscosity (or lower frequency) values indicating presence of immiscibility in this region. Insignificant deviations of blends with 15% and 20% CPE content in the same region were also observed. All other blends followed a semi-circular shape indicating the miscible phase morphology in the blends. In the case of CPE35 blends (Fig. 6b), the blend with 30% CPE35 concentration showed significant deviation from the semi-circular path indicating immiscible phase morphology. Blends with 10%, 15% and 20% CPE35 concentration also had more straight curves indicating presence of incompatible phases in the blends. The blends with 1%, 2%, and 5% seemed to follow the semi-circular path suggesting phase miscibility in these blends. However, it is necessary to further support the findings from Cole–Cole plots as these findings could sometimes be misleading [26]. Figure 7 shows the analysis of the rheological data based on van Gurp plots representing the relationship between complex modulus (G*) and phase angle delta (δ) [21, 27]. The van Gurp plots confirmed the findings from Cole–Cole analysis. In the case of CPE25 blends, the time-temperature superposition principle was observed to hold (indicated by the merging of the curves into a common curve) for all the blends except the 30% blend at lower frequency (higher delta value) thus indicating their phase miscibility. Slight deviations at lower frequency were also observed for blends with 15 and 20% CPE content, but it was not significant. In the case of CPE35 blends, the pure HDPE, 1%, 2%, and 5% blends were observed to merge into a common curve thus confirming their miscibility. However, the blends with 10%, 15%, and 20% CPE content had significant deviation indicating the immiscible phases thus confirming the findings from Cole–Cole analysis. Most notable deviation was observed for 30% CPE35 blends indicating significant morphological changes occurring at higher concentration of CPE35.

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Figure 6. Cole–Cole plots of (a) CPE25 and (b) CPE35 blends.

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Figure 7. van Gurp plots of (a) CPE25 and (b) CPE35 blends.

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Table 3. Angular frequency at gel point as well as slope of the ln(G′) vs. ln (ω) plots in various HDPE–CPE blends
% of CPE in blendAngular frequency rad/s at G′ = GSlope of the ln (G′) vs. ln(ω) plot
CPE25CPE35CPE25CPE35
0 (pure polymer)1.9101.9100.540.54
12.0591.7030.550.54
21.6451.7000.540.54
51.7981.5560.540.53
101.9991.4790.550.55
152.2161.4050.550.50
203.3581.0770.590.48
303.4000.7730.570.46

The rheological behavior of the blends was also analyzed using criteria reported for compatibility of polymer blends by Han and Chuang [28, 29] as shown in Fig. 8. When G′ is plotted vs. G″, such analysis generated composition independent correlation for compatible blends, whereas the correlation is composition dependent for incompatible blends. For CPE25 blends, concentration independent correlation was observed except for 30% blend at lower frequency values indicating the miscibility of the system. However, the correlation was concentration dependent in the case of CPE35 blends beyond a CPE concentration of 5%. It indicated that the molecular mixing of the HDPE and CPE phases was absent when the concentration of CPE35 was increased. These findings fully correlated with the earlier analysis using Cole-Cole plots as well as van Gurp plots.

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Figure 8. Han-Chuang (G′ vs. G″) plots of (a) CPE25 and (b) CPE35 blends.

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Figure 9 reports the relative tensile properties of HDPE and its blends with CPE polymers. The tensile modulus for pure polymer was observed to be 1063 Mpa, which was observed to reduce as the CPE type and content was changed. As seen in Fig. 9a, in the case of 1% and 2% CPE25 blends, reduction in the modulus was <5% as compared with pure HDPE, confirming good mixing between the phases. The modulus reduced more significantly beyond these concentrations. It indicated that as CPE25 polymer was suggested to be well mixed with the HDPE phase by the rheological results, the decrease in modulus by increasing its concentration may have been primarily caused by matrix plasticization by the lower molecular weight CPE chains and secondarily by reduced mixing between the phases. CPE35 blends showed higher extent of modulus reduction and its magnitude increased with increasing CPE concentration. As a result, the blend with 30% CPE content had a modulus reduced to 40% of the pure HDPE. In the case of CPE35 blends, the presence of immiscibility (especially at higher CPE concentrations) would primarily result in reduced mechanical response. These findings further confirmed the different extent of immiscibility in the CPE25 and CE35 containing blends. The peak stress of the blends also reduced after 5% CPE content as shown in Fig. 9b. Though CPE25 blends had lower decrease in the peak strength as compared with CPE35 blends, the difference was less significant as compared with tensile modulus. However, similar to tensile modulus, the difference in the magnitude of strength reduction between the CPE25 and CPE35 blends increased on increasing CPE concentration.

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Figure 9. (a) Relative tensile modulus and (b) relative peak stress of the HDPE–CPE blends as a function of amount of CPE in the polymer blends.

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Morphology of the blends was also analyzed through transmission electron microscopy as shown in Fig. 10. The transmission electron micrographs represent morphological changes in the 5% CPE blends as compared with pure HDPE. The HDPE morphology (Fig. 10c) showed well defined features (organization of semi-crystalline domains) due to its semi-crystalline nature. A similar but modified morphology was also observed for 5% CPE25 blend (Fig. 10a). It also indicated that the crystalline morphology of the pure polymer may not have been affected by the addition of CPE25. This notion is also confirmed by DSC results which indicate that no significant change in the crystallinity of polymer was observed in this case. The morphology in the case of 5% CPE35 blend (Fig. 10b), on the other hand, was quite different and the nano-features observed in other two cases were observed to be diminished. These findings were also supported by DSC results as in this case a large decrease in percent crystallinity was measured. The miscibility of the blends could also be studied using optical microscopy as shown in Fig. 11. The miscibility of the CPE25 blends was much superior as compared with CPE35 blends thus confirming the earlier findings. The CPE25 blends with 1%, 2%, and 5% CPE concentration (Fig. 11b–d) were similar to pure HDPE (Fig. 11a) thus indicating molecular mixing of the two phases. The blends with 10%, 15%, 20%, and 30% CPE25 (Fig. 11e–h, respectively) had small whitish regions indicating CPE25 phase, but these were observed to be dispersed homogenously. In the case of CPE35 blends, the lower concentrations of CPE did lead to good mixing (Fig. 11i–k for 1%, 2%, and 5%, respectively) as confirmed earlier. However, beyond 5%, the immiscibility of the two phases was extensive and large domains of CPE35 (as black areas in the bright field images of Fig. 11l–o for 10%, 15%, 20%, and 30% CPE35 content) were clearly visible.

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Figure 10. Transmission electron micrographs of (a) 5% CPE25 blend, (b) 5% CPE35 blend, and (c) pure HDPE.

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Figure 11. Optical micrographs of (a) pure HDPE, (b) 1% CPE25, (c) 2% CPE25, (d) 5% CPE25, (e) 10% CPE25, (f) 15% CPE25, (g) 20% CPE25, (h) 30% CPE25, (i) 1% CPE35, (j) 2% CPE35, (k) 5% CPE35, (l) 10% CPE35, (m) 15% CPE35, (n) 20% CPE35, and (o) 30% CPE35 blends. The width of the images reads 500 μm. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

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CONCLUSIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgments
  8. ABBREVIATIONS
  9. REFERENCES

In this study, HDPE was blended with CPE grades of different chlorination levels in different weight ratios. The CPE polymer with 25% chlorination level was observed to be semi-crystalline, whereas the one with 35% chlorination was amorphous. The melting point of the blends decreased slightly till 10% CPE concentration, whereas at higher concentration, a decrease of 6°C was observed as compared with pure polymer. As compared with CPE25 blends, the blends with CPE35 polymers had significant reduction in the melt enthalpy as well as extent of crystallinity. The gel point frequency in the CPE25 blends increased as the content of CPE25 was enhanced, whereas the opposite behavior was observed for CPE35 containing blends. The G′ and G″ were observed to be maximum in blends with 2% CPE content followed by decrease in these values at higher CPE concentrations, however, the CPE35 system had much significant decrease. The regression of ln(G′) vs. ln(ω) also indicated that in CPE25 blends, the slope was constant initially followed by significant increment at higher CPE concentration. For CPE35 blends, the slope was constant up to 10% CPE content, after which the gel behavior of CPE35 blend significantly improved as the slope decreased. Cole-Cole, van Gurp as well as Han-Chuang analysis confirmed the miscibility in CPE25 blends (except 30% blend at lower viscosity) whereas the CPE35 blends with only 1–5% CPE35 content were miscible. The higher concentration blends showed significant deviations from the correlations for miscible behavior. The tensile properties of the blends were also significantly affected by the type as well as amount of the CPE used. The tensile modulus as well as the peak strength of the CPE25 blends had lower decrease in magnitude as compared with CPE35 blends. The decrease was observed only after 5% CPE content and the difference between the two systems enhanced on enhancing the CPE content. TEM characterization of the blends also revealed the changes in the microstructure of HDPE by the addition of amorphous CPE35, whereas the addition of the semi-crystalline CPE25 retained the features present in the semi-crystalline matrix. The optical microscopy also confirmed the earlier findings of miscibility in CPE25 blends even at higher CPE concentration, whereas the miscibility in CPE35 blends was observed only till 10% CPE35 content.

Acknowledgments

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgments
  8. ABBREVIATIONS
  9. REFERENCES

The authors are grateful to Dr. N. B. Matsko at Graz University of Technology for the transmission electron microscopy analysis.

ABBREVIATIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgments
  8. ABBREVIATIONS
  9. REFERENCES
CPE

Chlorinated polyethylene

HDPE

High density polyethylene

LDPE

Low density polyethylene

PE

Polyethylene

PMMA

Poly(methyl methacrylate)

PP

Polypropylene

PVC

Poly(vinyl chloride)

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgments
  8. ABBREVIATIONS
  9. REFERENCES