wax blends

Accepted Manuscript Title: Effect of expanded graphite on the phase change materials of high density polyethylene/wax blends Author: M.A. AlMaadeed Sami Labidi Igor Krupa Mustapha Karkri PII: DOI: Reference:

S0040-6031(14)00539-5 http://dx.doi.org/doi:10.1016/j.tca.2014.11.023 TCA 77080

To appear in:

Thermochimica Acta

Received date: Revised date: Accepted date:

2-6-2014 20-11-2014 21-11-2014

Please cite this article as: M.A.AlMaadeed, Sami Labidi, Igor Krupa, Mustapha Karkri, Effect of expanded graphite on the phase change materials of high density polyethylene/wax blends, Thermochimica Acta http://dx.doi.org/10.1016/j.tca.2014.11.023 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effect of expanded graphite on the phase change materials of high density polyethylene/wax blends M. A. AlMaadeed*1, Sami Labidi1, Igor Krupa1,a, Mustapha Karkri2 1

Center for Advanced Materials, Qatar University, 2713 Doha, Qatar

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QAPCO Polymer Chair, Center for Advanced Materials, Qatar University, P. O. Box

2713, Doha, Qatar 2

Université Paris-Est, CERTES, 61 avenue du Général de Gaulle, 94010 Créteil, France

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*Corresponding author: [email protected]

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Highlights

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Expanded graphite (EG) and low melting point (42.3 ⁰C) wax were added to HDPE to form phase change material.

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EG was well dispersed in the composites and did not affect the melting or crystallization

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of the HDPE matrix.

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EG increased the thermal stability of the composites by reducing chain mobility and

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inhibiting degradation.

The addition of a relatively small quantity of EG enhances the heat conduction in the

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composite.

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HDPE- 40% RT42 that contained up to 15% EG demonstrated excellent mechanical and

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thermal properties and can be used as PCM. Abstract

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Phase change materials fabricated from high density polyethylene (HDPE) blended with 40 or 50 wt % commercial wax (melting point of 43.08 °C) and up to 15 wt% expanded

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graphite (EG) were studied. Techniques including Scanning Electron Microscope (SEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and an experimental device to measure diffusivity and conductivity (DICO) were used to determine the microstructural, mechanical and thermal properties of the composites. The composites possessed good mechanical properties. Additionally, no leaching was

observed during material processing or characterization. Although the Young’s modulus increased with the addition of EG, no significant changes in tensile strength were detected. The maximum Young’s modulus achieved was 650 MPa for the HDPE/40% wax composite with 15 wt% EG. The EG was well dispersed within the composites and did not affect the melting or crystallization of the HDPE matrix. The incorporation of EG increased the thermal stability of the composites by reducing chain mobility and inhibiting degradation. The intensification of thermal conductivity occurred with increasing fractions of EG, which was attributed to the high thermal conductivity of

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graphite. The maximum quantity of heat stored by latent heat was found for the HDPE40% wax composite with EG. The addition of a relatively small quantity of EG enhances

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the heat conduction in the composite.

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Keywords: Phase change composites; DSC analysis; Thermophysical properties; Latent

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heat thermal energy storage.

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1. Introduction

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Phase change materials (PCMs) have recently attracted increased interest because of their

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efficient use and storage of thermal energy [1-5]. Latent heat storage is one of the most efficient ways of storing thermal energy. Because of their high storage density and the

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small temperature differential between stored and released heat, PCMs are effective and

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useful in thermal management applications [1-4]. Paraffin wax has many applications, although the widespread use of paraffin wax has low

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thermal conductivity [5-7]. However, thermal conductivity can be improved by a variety of methods [8-21]. Several studies have shown that phase change materials (PCMs) with

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a large thermal conductivity can be produced by using PCMs that contain a dispersion of highly conductive particles, such as metal additives [22-25]. Nevertheless, these additives

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can add significant weight and cost to the production of these storage systems and some are not compatible with PCMs. Recently, carbon-based materials, which are economical, stable and chemically inert with a high thermal conductivity and a low bulk density, have been investigated as attractive constituents to enhance the heat transfer of PCMs [11-21].

Porous carbon materials have an open cell structure that is interconnected with graphitic ligaments of high thermal conductivity (bulk thermal conductivity, 180 W/mK) that allow the rapid transport of heat throughout PCMs [13-21]. Therefore, many studies have examined the effect of graphite in PCMs on thermal conductivity [16-21]. Recently, polymer-based nanocomposites reinforced with expanded graphite (EG) [2627] have been shown to significantly improve the mechanical and thermophysical properties of PCMs, including the electrical and thermal conductivities. Expanded graphite is produced by reacting natural graphite flakes in sulfuric acid and subjecting the

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graphite to thermal shock, which causes a unidirectional expansion of the initial graphite platelets and produces highly porous worm-like accordions of graphite. EG is composed

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of hundreds of stacks of graphene nanosheets that have an enormous surface area (up to 2630 m2/g if both sides of the sheet are considered accessible) [28].

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Krupa et al. [29], AlMaadeed et al. [30] studied the polyethylene as a good matrix for the phase change materials. Zhang et al. previously developed a phase change composite

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(PCC) with a high density polyethylene matrix (HDPE), commercial paraffin wax

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(melting temperature of 51.22°C), 5% expanded graphite and flame retardants [31].

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In their investigation, they determined that the paraffin wax and EG were well dispersed

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within the HDPE matrix and that the thermal conductivity improved with the addition of EG. Other additives that can be used in PCC are graphite [31] which increased the

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mechanical properties.

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thermal conductivity and date palm fibre [32] which increased the stability and

In the current work, PCCs were developed with a HDPE matrix, a wax with a low

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melting temperature (melting temperature of 43.08 °C) and up to 15% wt% EG. The morphological, physical, mechanical and thermal properties of the composites were

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examined and are presented in this paper.

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2. Experimental details 2.1 Materials High density polyethylene (HDPE), with a melt flow index (MFI) of 0.35 g/10 min, and a density of 0.95 g/cm3, was obtained from QChem company in Qatar used to prepare the PCMs. Commercially available RT42 from Rubitherm Technologies (Germany), with a heat conductivity of 0.2 Wm-1K-1, a density of 0.88 Kg/l at 15 °C, a melting point of

43.08 °C, and an enthalpy of 133.832 J/G (heating rate of 10 °C), was used as the wax component. The expanded graphite (EG) (GFG200, SGL Carbon, Germany) consisted of 200 µm graphite platelets. 2.2 Methods 2.2.1 Sample preparation Composites formed by HDPE, wax (up to 50 wt %) and expanded graphite (up to 15 wt %) were fabricated using a lab scale Brabender twin screw extruder with screw diameter D of 20 mm and screw length of 40 D. The throughput of the extruder was programmed

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to 0.7 kg/h, and the screw speed was set to 110 rpm.

The extruder has five zones, zone one with 200 ⁰C while the other four zones have 180

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⁰C.

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To fabricate the final samples, the composites were dried for 30 minutes at 70 °C and then loaded into the injection molding machine at 180 °C.

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2.2.2. Morphology Analysis

The morphology of the HDPE/wax composites was characterized using an Environmental

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Scanning Electron Microscope (ESEM) FEI Quanta 200 (at 3.0 Kev). Thin surface of

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freeze-fractured samples in liquid nitrogen were analyzed.

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2.2.3 Differential scanning calorimetry (DSC)

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DSC analysis was performed under nitrogen gas using a Perkin Elmer DSC8500. To

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eliminate the effect of thermal history, results from DSC analysis were collected during the second heating cycle, which occurred from 20 to 170 °C at 10 °C/min. The total

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enthalpy of fusion was calculated by the following equations (1, 2): ∆Htotal = ∆HHDPE + ∆Hwax

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and

∆Htheo = wHDPE∆HHDPE + wwax∆Hwax

(1) (2)

where ∆HHDPE and ∆Hwax are the enthalpy of fusions for the HDPE matrix and the

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paraffin wax, respectively, and wHDPE and wwax are their fractional weight compositions. 2.2.4 Thermogravimetric analysis (TGA) TGA was performed using a Perkin Elmer TGA7 analyzer from 50 °C to 600 °C at a heating rate of 10 °C/min in a nitrogen-rich atmosphere (20 ml/min). 2.2.5 Tensile Tests

A tensile analyzer (LLOYD Instruments, 50 kN) was used to determine the mechanical properties of the composite materials at room temperature. Tensile testing was performed according to the ASTM D638 standard at a rate of 50 mm/min. Average values and standard deviations were obtained from the analysis of at least five measurements. 2.2.6 DICO device: Thermophysical property measurements A periodic method was used to simultaneously estimate the thermal conductivity, diffusivity and specific heat of the paraffin/graphite composite materials at room temperature. The composite sample being analyzed was fixed between two metallic

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plates. Efficient thermal exchange between the two plates and the sample was guaranteed by using heat conductive grease (figure 1). The front side of the first metallic plate was

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periodically heated using a sum of five sinusoidal signals. The temperature was measured using thermocouples placed inside both metallic plates [34]. The thermophysical

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parameters of the sample were identified by comparing experimental and theoretical heat transfer functions. The system being investigated is described by one dimensional

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quadrupole theory. The experimental heat transfer function was calculated at each

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excitation frequency as the ratio between the Fourier-transform temperatures of the front

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and rear plates [34]. A parameter estimation technique was then applied to

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simultaneously estimate the thermal conductivity ( λeff ) and diffusivity ( aeff ). The identification of the thermophysical parameters is a non-linear optimization problem that

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was iteratively solved. Starting with sufficiently accurate initial guesses for the unknown

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parameters, we successively refined the estimates using the previously developed Levenberg–Marquardt method [35-36].

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2.2.7 PCGT device: Latent heat thermal energy storage (LHTES) Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) are

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commonly used methods to determine the specific heat and latent heat of different materials [35]. These methods are well established, but they use only small micro-

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samples of the sample material. When evaluating material performance on a commercial scale, a test method that accommodates a larger sample region should be used that may provide additional information regarding long-term product stability. During long-term performance testing, large PCM specimens often settle or stratify and are typically not perfectly homogeneous, especially after undergoing multiple freezing/melting cycles.

Therefore, it is necessary to use noninvasive methods to determine the heat of fusion and specific heat of large samples. To determine the overall thermophysical properties of PCMs over several cycles of solidification and fusion, the design of a novel experimental device was required (figure 2). The sample is first positioned between two horizontal aluminum heat exchanger plates. Thermo-regulated baths supply heat to the plates and precisely regulate the injected H10 oil temperature with an accuracy of approximately 0.1°C. Heat flux sensors and thermocouples (type T) are placed on each side of composite, and the entire experimental set-up is maintained in place by a pneumatic jack.

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The flux-meters are approximately 0.2 mm thick and have a sensitivity of approximately 202 µV/Wm-2 for a 400 cm2 active surface area. The various sensors are connected to a

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Labview® program that was modified to measure temperature fluctuations and heat flux during fusion and solidification. Experimental data were recorded with regular and

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adjustable time steps (6 s). The lateral side faces, insulated by 11 mm thick polyethylene expanded foam (PE), reduced the multidimensional heat transfer system to 1D. In this

3. Results and discussion

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3.1 Morphology characterization

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study, the temperature was varied between 15 °C and 50 °C.

The SEM images of the HDPE/wax composites with wax mass fractions φ wax of 30 wt %,

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40 wt % and 50 wt. % are shown in figure 3. The composites maintained a solid state

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structure without apparent paraffin seepage. Additionally, the wax is homogeneously dispersed, which is similar to the distribution of wax observed in LDPE materials [29].

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This result indicates that the difference in microstructural branching did not affect the distribution of wax in the PE matrix. There is a clear separation between the HDPE and

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wax phases. Nevertheless, increased wax content produced a material with a less uniform distribution and greater wax agglomeration.

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The microstructure of EG (figure 4-a) is consistent with an irregular honeycomb network composed of graphite sheets. As shown in figures 4-b and 4-c, the solid state structure was also achieved with the addition of the EG mass fractions φ EG = 5 wt. % or φ EG = 15 wt. % to HDPE/50 wt. % or HDPE/40 wt. % wax composites, respectively. Phase

separation was more pronounced with the addition of EG, which was verified by DSC analysis. 3.2 Differential scanning calorimetry The DSC results of the HDPE/paraffin wax composites are presented in Table 1. The wax presented three endothermic peaks at 18, 30 and 45 °C. The first two peaks correspond to the solid-solid transition, and the third peak corresponds to the solid- liquid transition. The presence of these three peaks indicates that HDPE and wax are immiscible in the crystalline phase [2]. HDPE peak appears at 133 °C.

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The melting point of the HDPE matrix was affected by the amount of wax incorporated into the composite (Table 1). The melting point decreased from 133 °C for the neat

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polymer to 126, 124, and 123 °C for composites with 30%, 40% and 50% wax, respectively. This reduction indicates a decrease in lamellar thickness [1]. Nevertheless,

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the enthalpy significantly decreased from 169 J/g to 133.4, 119 J/g and 110 J/g for HDPE matrices with 30%, 40% and 50%, respectively (Table 1). This result indicates a similar

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reduction in the percent crystallinity of the composite, which is attributed to the

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plasticizing effect of the wax. Similar results were obtained by Molefi et al. [2] using a

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Fischer-Tropsch wax.

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The melting and cooling points of composites with 40 wt. % wax were not significantly affected by EG addition. However, a reduction in enthalpy content (for heating and

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cooling) was observed. The same results were observed for composites with 50 wt. % wax, indicating that EG does not affect the melting and crystallization of HDPE

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composites. The same conclusion was achieved by Mhike et al. [38] for a composite of LDPE, wax and various types of graphite.

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For all composites developed, only a small difference between the theoretical and

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experimental enthalpy was measured, which suggests that no leakage occurred during material transformation. 3.3 Thermogravimetric analysis

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Using TGA, two thermal degradation steps were observed for the HDPE/paraffin wax blends (figure 5). The first step at 220 °C corresponds to degradation of the wax, whereas the second step at 400 °C corresponds to the HDPE matrix.

In the first degradation step, the percentage of paraffin wax determined by TGA for blends with 30 and 40 wt. % wax matched the initial percentage of wax that was incorporated into the material during the extrusion phase. Nevertheless, the percentage of wax determined by TGA for the HDPE/50 wt. % wax blend was less than the amount of wax incorporated into the HDPE matrix during extrusion (~ 41 wt. %). This result confirms the DSC results and suggests that the HDPE matrix can only preserve a fraction of the wax if the wax is incorporated into the matrix at a high weight percentage. The same phenomenon is observed after the addition of expanded graphite. Because of the

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presence of EG, a char layer was formed above 500 °C.

The amount of EG determined during analysis of the residue at 600 °C was found to be

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the same as the initial amount of EG added into the composite. Same increase in char residue attributed to the addition of EG was reported by Zhang et. al [31]. The addition

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of EG increased the thermal stability of the composite by reducing chain mobility and inhibiting degradation.

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3.4 Mechanical results

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The Young’s modulus and tensile strength of the HDPE/wax blends are shown in figures

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6.a and 6.b. The addition of 30 wt. % wax to the HDPE matrix reduced the Young’s

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modulus of pure HDPE from 730 MPa to 360 MPa. This result may be attributed to the low molecular weight of the wax compared to that of the polyethylene matrix [15]. It may

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also be attributed to either the plasticizing effect of the paraffin wax or the low modulus

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of the wax compared to HDPE, which is also responsible for decreased tensile strength of the blends with additional wax. In addition to the HDPE/wax interface, wax domains,

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which present defects such as weak interfacial bonding between the wax and the polymer, also decreased the tensile strength of the composite.

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The addition of EG did not alter the tensile strength of the composites, as shown in figure 6-c; however, an increase in the Young’s modulus was observed. The maximum Young’s

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modulus achieved was 650 MPa for HDPE/40%RT4 with 15% wt. EG. This result indicates the following: (1) negligible aggregation in the composite, (2) effective interfacial interactions between EG and the blend, and (3) a high modulus of graphite (1 TPa) [39]. 3.5 Thermal conductivity and diffusivity results

The measured thermal conductivity and diffusivity properties of HDPE/RT42 composites with different wax loadings are shown in Table 2. When the wax load was increased, a significant decrease in the thermal diffusivity and conductivity of the composite was observed. For HDPE matrices with φwax = 30 % wt % and φ wax = 50 % wt %, thermal conductivity decreased from 0.477 W.m-1.K-1 to 0.293 and 0.2017 W .m −1 K −1 , respectively (at T=20°C). Therefore, with an increased wax load, a decrease in thermal conductivity was observed. This phenomenon is attributed to the molecular structure and thermal properties of RT42, which acts as an insulator. Thus, the addition of RT42 to the

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HDPE matrix composite decreases heat transport. This decrease is expected because the

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thermal conductivity of wax ( λ f = 0.2W.m−1K −1 ) is extremely low compared to that of the matrix ( λm = 0.477W .m−1K −1 ). To increase the thermal heat conductivity without

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significantly reducing energy storage, graphite particles were added to HDPE 40%RT42 and HDPE 50%RT42. The thermophysical properties and associated uncertainties of the

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HDPE/RT24/graphite composites are presented in Table 2. The addition of graphite

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significantly affected the experimental values obtained for the thermal conductivity and

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diffusivity of HDPE/RT42/graphite composites; increased graphite content enhanced the

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thermal conductivity and diffusivity. This increase is expected because graphite has a higher thermal conductivity than HDPE/RT42. In both cases we observed a non-linear

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increase in thermal conductivity with increasing graphite mass fraction. The thermal

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conductivity intensification Iλeff , obtained by the addition of graphite, was calculated using equation 3: λeff − λm λm

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I λeff =

(3)

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From Table 2, we observed that the intensification of HDPE /40%RT42/EG samples increased from 82.7% to 207.4% with increasing mass fractions of EG (from 5% to 15%). Similar behavior was observed for HDPE/50%RT42/EG, which exhibited a

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maximum I λeff = 230.6% . This result is attributed to the high thermal conductivity of EG. Latent heat thermal energy storage (LHTES) In a previous work [30], we demonstrated how to experimentally characterize phase change composites using the fluxmetric method (PCGT). This method is used to study

the behavior and heat storage capacity of various phase change composites. In this section, a temperature, Tinit °C, was applied to each face of the sample until the material reached an isothermal state. The flux measured on both sides of the sample was effectively zero at this time, t = 0s , which confirmed negligible lateral thermal loss. At this moment, the set temperature of the H10 oil in the heat exchanger plates suddenly changed. This resulted in the system, which was in a 'storage' phase, to switch to a second equilibrium state, Tend . Temperatures were measured at the center of the upper and lower

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faces of the composite. Different experiments were designed to evaluate the 'storage' process:

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(i) The temperature was varied from Tinit = 25°C to Tend = 35°C to determine the

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sensible heat and specific heat of the material in the solid state, Cp s .

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(ii) The temperature was varied from Tinit = 40°C to Tend = 50°C to determine the

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sensible heat and specific heat of the material in the liquid state, Cp l .

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(iii) The temperature was varied from Tinit = 25°C to Tend = 60°C to monitor the

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complete phase change cycle of the material as it transformed from the solid to the liquid state, which was used to determine the latent heat of fusion.

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(iv) The temperature was varied from Tinit = 60°C to Tend = 15°C to determine the

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sensible heat and specific heat of the material in the liquid and solid states, Q .

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This section utilized limited temperatures of 25°C and 60°C, which are sufficiently far from the melting point of the composite (38°C-42°C), to ensure that the material was

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indeed in either one or the other state. The total amount of energy per mass stored was

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then determined from the following expression: tend

Q =

1 ∫ ∆q.dt = C p eff .(Tend − Tinit ) [kJ/kg] ρ.e tinit

(2)

where ∆ q represents the cumulated heat rate entering the sample and C p eff is the apparent specific heat capacity of the composite (kJ/kg.°C). This quantity can also be expressed by the following equation: Q = Qsens + Lm = (Cps .∆Ts + Cpl .∆Tl ) + Lm

[kJ/kg]

(3) where Cp s and Cp l are the average specific heats of the material in the solid and liquid states, ∆Ts and ∆Tl are the temperature variations of the material in the solid and liquid

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phases, and Lm is the latent heat of fusion.

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Figure 7 compares the quantity of heat stored by latent heat in HDPE/40% RT42 and HDPE /50% RT42 composites at various EG concentrations. The latent heat was

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significantly greater in the composite with 40% RT42 compared to the composite without 50% paraffin. Specifically, the latent heat of HDPE /RT42 composites with 10 wt% EG

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decreased from 23.2 J to 12.6 J when the RT42 content was increased from 40% to 50

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wt%. It is interesting to note that the effective thermal conductivity only decreased

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slightly, from 0.6983 to 0.667 W/m.K (Table 2), which is a difference of less than 3%. Therefore, controlling the content of EG/RT42 will enable increased energy storage in

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the composites without reducing the effective thermal conductivity and enable a further

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understanding of the heat transfer behavior of the composites. The final weight ratio of

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the HDPE/RT42/EG composite used in this study was 50/40/10. During cooling, as the temperature decreased from 60°C to 15°C, the composite materials Various

heat

fluxes

were

measured

on

the

two

faces

of

the

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solidified.

HDPE/40%RT42/EG and HDPE/50%RT42/EG samples, as shown in figures 8 a and b. A

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typical change in heat flux, corresponding to the cooling of the liquid phase, was initially observed. At the end of this phase, when the surface temperatures were approximately

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42°C, the direction of the heat flux reversed. From this critical moment, the material slowly cooled and solidified until it approached equilibrium at 15°C. Generally, heat restitution is an extremely long process. At the beginning of solidification, a layer of solid PCC was formed on the planar surface in contact with the exchanging plate, creating a layer that “isolated” the liquid phase from the cooling source. Solidification continued

slowly because of the low thermal conductivity of the solid PCC (estimated at 0.2 W.m1

.K-1). It is important to note that compared to composites without graphite (PEHD-

G/wax), composites with graphite demonstrated intensified thermal conductivity and accelerated thermal discharge (figure 8b). Thus, the addition of a relatively small quantity of graphite as a thermal conductor reduced the crystallization time and therefore increased the latent heat storage capacity.

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Conclusions Phase change Materials fabricated from HDPE/wax blends and up to 15% wt EG were

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investigated in this paper. The composites possessed good mechanical properties. Additionally, no leaching was observed during material processing or characterization.

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Although the Young’s modulus increased with the addition of EG, no significant changes in tensile strength were detected. The EG was well dispersed in the composites and did

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not affect the melting or crystallization of the HDPE matrix. The incorporation of EG

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increased the thermal stability of the composites by reducing chain mobility and

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inhibiting degradation. The thermal conductivity intensification of HDPE-40%RT42/EG samples increased from 82.7% to 207.4% with increased mass fractions of EG (5% to

This result is attributed to the high thermal conductivity of graphite. The

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I λeff = 230.6% .

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15%). Similar behavior was observed for HDPE/50%RT42/EG, which had a maximum

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quantity of heat stored by latent heat for composites with EG, such as HDPE/40% RT42, was significantly greater than for HDPE/50% RT42, which lacked EG. The addition of a

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relatively small quantity of the thermal conductor graphite reduced the crystallization time and therefore increased the latent heat storage. Finally, composite materials of

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HDPE- 40% RT42 that contained up to 15% EG demonstrated excellent mechanical and thermal properties and therefore can be used as effective phase change composites. Acknowledgements

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This publication was made possible by NPRP grant # 4-465-2-173 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. The authors would like to thank Patrik Sobolciak for helping with the experiments.

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Figure captions:

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Figure 1: Experimental set-up of periodic method Figure 2: shows the quantity of heat stored by latent heat for the composites (HDPE /40% RT42) versus EG concentration Figure 3: SEM micrographs of HDPE/wax blends with concentration of wax (a) 30 wt. %, (b) 40 wt. % and (c) 50 wt. % Figure 4: SEM micrographs of HDPE/50 wt. % wax blends with concentration of 5 wt. % EG and (b) HDPE/40 wt. % with concentration of EG with 15 wt. % Figure 5: To draw 3-a TGA results of HDPE/wax blends and 3-b HDPE/40% wax/EG composites and 3-c HDPE/40% wax/EG composites

Figure 6: Mechanical results of HDPE/wax and HDPE/wax/EG blends Figure 7: Latent heat of composites: HDPE/RT42/EG Figure 8: Study of release of energy from 60°C to 25°C Table captions: Table 1: DSC results of HDPE/wax and HDPE/wax/EG blends

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Table 2: Conductivity and latent heat of the composites

HDPE HDPE/40%RT42/0% EG HDPE/40%RT42 /5% EG HDPE/40%RT42/10% EG

TE

D

HDPE/40%RT42/15% EG

EP

HDPE HDPE/50%RT42/0% EG

CC

HDPE/50%RT42/5% EG

A

HDPE/50% RT42/10% EG

Table 2.

∆Hc ∆Hctotal (J/g) (J/g) -14.2 / -137.8 -2.1 / 137.8

119.3 12.9 / 37.7 / 113.2 12.9 / 37.8 / 111.7 12.8 / 37.7 / 110.9

-170.2 -1.2 / 28.1 / 129.1 -2.4 / 39.8 / 112.6 -2.3 / 46.1 / 102.6

PT

-170.2 -157.2

-152.4

-148.7

119.3 12.9 / 37.8 / 111.7 12.4 / 37.5 / 111.2 12.3 / 37.5 / 111.3 12.3 / 37.6 / 112.8

-170.2 -2.4 / 39.8 / 112.6 -3 / 45.3 / 99.5 -2.9 / 46.3 / 89.9 -2.3 / 37.3 / 71

-170.2 -152.4

119.3 12.8 / 37.7 / 110.9 12.3 / 37.4 / 110.5 12.5 / 37.5 / 111.8

-170.2 -2.3 / 46.1 / 102.6 -4.1 / 51.9 / 90.2 -3.3 / 45.7 / 90.1

-170.2 -148.7

SC

HDPE/50%

U

HDPE/40%

N

HDPE HDPE/30%

A

RT42 wax

Tc ( C) 13.3 / 26.8 / 37.2 o

RI

∆Hm ∆Htotal ∆Htheo (J/g) (J/g) (J/g) 16.7 / 139.4 139.4 2.7 / 139.4 HDPE / RT42 133.3 169.5 169.5 169.5 17.7 / 1.3 / 162.4 160.47 43.9 / 29 / 126.5 133.4 18.2 / 3.3 / 160.2 157.46 44.6 / 40.9 / 124.8 119.3 18.3 / 3.9 / 158 154.45 44.6 / 47.3 / 123.4 110.7 HDPE / 40% RT42 / EG 133.3 169.5 169.5 169.5 18.2 / 3.3 / 160.2 157.4 44.6 / 40.9 / 124.8 119.3 17.3 / 3.5 / 147.1 148.9 43.7 / 46.6 / 122.5 100.5 17.4 / 3.5 / 141.6 140.5 43.8 / 47.4 / 122.5 94.2 17.6 / 2.6 / 125.5 132.1 43.9 / 47.2 / 123 78.3 HDPE /50% RT42 / EG 133.3 169.5 169.5 169.5 18.3 / 3.9 / 158 154.5 44.6 / 47.3 / 123.4 110.7 17.5 / 4.2 / 149.5 145.9 43.9 / 53.4 / 121.7 96.1 17.5 / 3.4 / 137.4 137.5 43.8 / 46.9 / 122.7 90.5

Tm (oC) 18.4 / 30 / 45

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Sample

-144.8

-136.2

-118.3

-142.1

-135.8

∆λeff

Expanded graphite φ (%) EG

(W.m .K 1 )

0 30 40

-

0.477 0.293 0.267

50 40

5

40

-1

-

a eff

I λeff

a eff

(%)

a*m

0.008 0.007 0.005

(m .s 1 ) .10-7 2.639 1.76 1.613

0.173 0.055 0.079

-38,5 -44

0,407 0,611

0.2017 0.488

0.004 0.012

1.486 2.324

0.122 0.183

-57,7 +82,7

0,563 1,440

10

0.698

0.021

2.730

0.225

1,692

40

15

0.821

0.006

3.190

0.08

50 50

5 10

0.221 0.667

0.001 0.004

1.327 2.530

+161, 4 +207, 4 +9,5 +230, 6

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∆aeff

2 -

SC

.10

-7

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HDPE /RT42/EG

HDPE /RT42

HDPE

λeff

RT42 ( wax %)

φ

RI

Samples

0.113 0.05

1,977 0,893 1,702