外文翻译--注塑成型中颗粒填充物聚丙烯的冷却情况

注塑成型中颗粒填充物聚丙烯的冷却情况摘要：聚丙烯复合材料的冷却情况被用于在同一注塑成型过程中，对影响散热性能的各种填料（磁铁矿，重晶石，铜，滑石，玻璃纤维和锶铁氧体）于不同比例下的调查。注塑成型期间，分别对室温和高温时热电偶在型腔模具表面的测量记录和对斜坡冷却曲线的热扩散分析中发现：该注射成型的工艺和该模具的填充材料使冷却曲线显示出不同的合并路段。所以说热扩散系数是个暂时性的系数。热扩散表明，最高值为30的滑石粉填充聚丙烯，在最短的冷却时间可以发现35铜填充聚丙烯。系统性变化的具有热传递性能的复合材料，在不同的填充材料和填充比例中使注塑过程优化，并以此 热 性能。此 ，滑石粉填充聚丙烯使 的复合材料 的最高热 ，是热传递的 。 ：聚丙烯 ；热性能；注塑成型； 填料1 . 用的塑料， 聚丙烯和聚 有一个 热系数。不过在 ， 传 ，要的材料具有高 热性。过currency1合“的填料，比 塑料，热 为聚合是可以变的。系统的热扩散fi于1.2 2fl /，0.22fl /为聚丙烯。 种填充聚合具有高的热 ，于”的用在电 成为一个 重要的。高的热 可以过使用一个合“的填料， ， 纤维和石，化磁铁矿 。此 ，在注塑模具的冷却，是聚合填料的热性能影响。 ，填充材料比能体现出热 的 值 。fi 比不同的材料，是 的， 可以说是不可能的。 此，聚丙烯 不同的填充 （ 氧化 铁， ，铜，玻璃纤维，滑石粉）的 出和注射成型用各种体分数（ 0-50 ） 表示 。磁铁矿重晶石一 是用 currency1重量的聚丙烯， ：为一 ，锶铁氧体是用聚合磁铁，玻璃纤维是用于材料，滑石粉是一种 。 ， 铜被 为 ， 为 具有高 的热 对于材料。 热性能， 注射成型 和注塑成型 为 调查和 的 和种填充材料。 2 . 的热量传递，在一维 出温 T ，时间t ， x和热扩散在一个均质体，热扩散A和热 L是 互 联的，具体密 r 和具体的热容量Cp根据假 一名注射成型工艺 恒温 浆期为聚合的温 TP和 对恒 的温 Tm及作为温 独的热扩散，解析解决式（ 1 ）果 在式（ 3 ） ,S是指壁厚注射模压部分和T的温 zai 时间t后注射。忽略高阶 算，式（ 3 ） 可以减少为式（ 4 ） 出的 系冷却速 和热扩散，在注射成型过程中，凡高热扩散致更高的冷却速 和短周期的过程。 3 .实验3.1 材料试验材料供合作编写RTP的有限公司（ 国）几种聚丙烯（ PP ）化合 各种填料（ 氧化 铁， ，铜，玻璃纤维，滑石粉）在 出过程中讲的类似在式 2 。填充材料是 用材料在工 产 。填料 不具备表面涂层可以影响热性能。一 的性能 材料列在表1图1.模具注塑成型实验。图 2 .模具 腔准备测试 本，在一个注塑。场 热电偶温 测量标志是一个箭头。3.2 热扩散测量热扩散的高分材料，是衡量一个瞬态 ， 雷射闪光实验有密切的 系。温 信号热电偶转移侧的抽 检验和注册,被转让温 信号启动一个热平衡过程该标本，记录热电偶作为区别 的背面和恒 温 ，用 为评 的热扩散。最小二乘算 是用 确 热扩散， 变系统地热扩散值在一个特别 差分 划。精确的测量于总量的3 。 为热扩散测量，小缸10fl 直径5-6fl 的身高，剪下的注射成型棒（参见图1 ） 。 3.3 注塑成型注塑标准 测量拉伸性能连同一棒热测量10fl 直径和130fl 的长分别准备在一模（参见图1 ） 。在腔的拉伸试验棒铬（ K型）热电偶中的用。 在注塑成型实验温 记录每0.5一个数字万用表和储存在一台个 电脑。热电偶sfi约0.2fl 成空腔。 此，一个良好的热之间的接触聚合和热电偶， 后缩的成型，是为了保证录得更好的温 时间。用过的注射 成型参数列于表2 。此时 特 的注塑成型周期 见表3 。4 果 图 3 比冷却曲线填聚丙烯 聚丙烯复合材料的各种填料 分的 氧化 铁。在图 3 中，聚丙烯的冷却过程在一个时间 在温 测量所热电偶最高值约 。 的时间 测温 下 。 过 在模具 ，冷却 为记录 热电偶变化， 为 是 长的接触 注射成型的材料。于以fi直径的棒， 个时间（ ） ，直模具是 及注射成型 对高，以确保该部分 。 可以 出，在图 3斜曲线变化显 后 ，对于时间 后，压 是 。此 ，图。 指出 种复合材料在腔 温 的磁铁矿分。要的温 -温 于 的 聚丙烯 ，在 实验的时， ， 冷却时间聚丙烯 的Fe3O4减 （参 表 ） 。减少冷却时间，是在好的所currency1的热扩散的磁铁矿填充复合材料于高的热扩散 （参见 表一） ，中的线，式（ 4 ） ，以一个currency1冷却速 。温 时间currency1性图。 3 不“一个的线性为 期温 -时间曲线式（ 4 ）在对数 。 为填聚丙烯实测值可fi 一个一的直线之间fi约15 和fl54的 路线 一个扩散（参见式（ 4 ） ） 。测量冷却曲线的聚丙烯复合材料的磁铁矿 有在每个个，直线，为高温fl 和 温 的地区。热扩散 斜坡的 直线算热扩散系数的 的温 高部分的冷却曲线有一 于扩散系数测量暂态， 算热扩散 的温 ，部分地区的冷却曲线”实测值扩散图 3 比冷却曲线填聚丙烯 聚丙烯复合材料的各种填料 分的 氧化 铁。该号字 间 直线（参见） 。图 4显示测得的热扩散数据的调查 本中可以 出， 该热扩散的磁铁矿-聚丙烯复合材料是 为填聚丙烯 currency1磁铁矿 。 此，冷却时间变短为高磁铁矿填料分（图 ） 。 之一，为变在坡的冷却曲线显示图3是变热扩散 温 的，中表现在是图 5 磁铁矿和重晶石聚丙烯复合材料 温 的高热扩散 。 此值 模实验小于测值的复合材料在室温。 热扩散的PP体中，要是所成的 ，是 系于 速 v和平均程长 L 据 温的影响PP体（约 ，测量的DSC ） ，热扩散的质减少，以致 了体 性模量k ， 减少了 速 ，并 平均程的长短 。此 ， 温 Ts 晶在聚丙烯是在 于Ts晶下在聚丙烯体中出现的。存在 晶影响体 性模量K和 的 路。是不同实验 是 压 在注塑成型过程和 温 的厚 的冷 过程，磁铁矿，重晶石，玻璃纤维， 滑石， 磁铁氧体和铜填料比空聚丙烯图 6 冷却的过程 铜填充聚丙烯存在差 。图 4 在室温下热扩散 值 注射成型聚丙烯 中不同填料和各种填料的比重 衡量暂态（参见）图 5 温 currency1性的热扩散的磁铁矿和重晶石填充聚丙烯的填料 量图 6聚丙烯复合材料的填料在30vol%后铜填充复合 温速 过调查材料。该温 的影响 聚丙烯是，在 个注射 成型工艺高于 温调查材料。冷 的过程 复合材料 有显示有fi的差别。该 温的磁铁矿 聚丙烯是一种比温 一的重晶石填充聚丙烯。 温的锶铁氧体聚丙烯复合材料， 是 于 该磁铁矿填充聚合。 测得的热扩散的滑石粉填充聚丙烯是 高于热扩散调查材料， 高于 对铜填充聚丙烯，冷却 为滑石粉是小调查材料。 出该滑石粉 的 填充复合一个对 的滑石粉。测量的热扩散是平于 个 的最高热 ， 温 测量在注塑成型过程中示扩散直 发。 ，该滑石粉填充聚丙烯 中有 各 性最高并在 动 直于 。 出现了高 热的铜（参 表1 ） 对于用于填充材料， 冷 是 对的测 温的。果表明： 是一个 对的 ，一个最 的互联 的高 电 在聚丙烯体， 于1 和差 比，互联磁铁矿55 互联的重晶石46 。 作 了影响 fi小和的聚丙烯 2,3 。图 7 各种聚丙烯复合材料的冷却时间（200下 60 ）冷却时间是线性currency1于填料量分数在聚丙烯体中，数据 算 系列于表6 。 可以 出，铜填充聚丙烯 温下 速 ， 过调查材料。冷却的情况，聚丙烯重晶石， 锶氧体和磁铁矿是 似的， 磁铁矿 温一速 比所有材料。5 冷 的过程中聚丙烯在注塑成型工艺可以减少所使用的磁铁矿重晶石，锶铁氧体，玻璃纤维，滑石粉和铜填料。 冷却过程中，于的currency1了传热和 热 温 ，所以不能 解 指数律 的 热传 。此 ，在注射成型周期，的注射 成型周期和热扩散的聚丙烯周期，冷却曲线显示不同的合并路段。 此 ，各 性的热传 性，例 ： 为滑石粉填充， 互联的影响冷却 为， 铜。 为使用的材料和在调查范围填料冷却时间冷却下 注射成型复合材料，温 200 60是线性currency1于填料。 铜在聚丙烯体中的冷却时间可缩短50.5 20，9。在 个过程“环中，具有高热传递性能的一 复合材料，可以用 优化模具进程 高冷却速 。献：1 Back E. Magnetite gives new recyclable dense polymers for the automotive industry Plastics Reborn in 21st Century Vehicles, Conference Proceedings. Rapra Technical Ltd； May 1999.2 Weidenfeller B, Hofer M, Schilling F. Thermal and electrical properties of magnetite filled polymers. Composites: Part A 2002；33:104153.3 Weidenfeller B, Hofer M, Schilling F. Thermal conductivity, thermal diffusivity, and specific heat capacity of particle filled polypropylene. Composites: Part A 2004；35:4239.4 Wong CP, Bollampally RS. Thermally conductivity, elastic modulus, and coefficient of thermal expansion of polymer composites filled with ceramic particles for electronic packaging. J Appl Polym Sci 1999；74:3396403.5 Lu X, Xu GJ. Thermally conductive polymer composites for electronic packaging. J Appl Polym Sci 1997；65:27338.6 Xu Y, Chung DDL, Mroz C. Thermally conducting aluminium nitride polymer-matrix composites. Composites: Part A 2001；32:174957.7 King JA, Tucker KW, Vogt BD, Weber EH, Quan C. Electrically and thermally conductive nylon 6.6. Polym Compos 1999；20(5):64354.8 Yu S, Hing P, Hu X. Thermal conductivity of polystyrene-aluminum nitride composite. Composites: Part A 2002；33:28992.9 Carslaw HS, Jaeger JC. Conduction of heat in solids. Oxford: Oxford University Press； 1986.10 Duifhuis P, Weidenfeller B, Ziegmann G. Funct Compd, Plast Eur 2001；11:424.11 Parker WJ, Jenkins RJ, Butler CP, Abbott GL. Flash method of determining thermal diffusivity, heat capacity, and thermal conductivity. J Appl Phys 1961；32:167983.12 Schilling FR. A transient technique to measure thermal diffusivity at elevated temperatures. Eur J Miner 1999；11:111524.13 Clauser C, Huenges E. Thermal conductivity of rocks and minerals. In: Ahrens TJ, editor. Rock physics and phase relations, a handbook of physical constants. American Geophysical Union Reference； 1995.14 Landolt-Bornstein. In: Madelung O, White GK, editors. Numerical data and functional relationships in science and technology, new series, group III: crystal and solid state physics, vol. 15. Metals: electronic transport phenomena, subvolume c: thermal conductivity of pure metals and alloys. Berlin: Springer； 1991.15 Gardon R. Thermal conductivity at low and moderated temperatures. In: Blazek A, editor. Review of thermal conductivity data in glass. International Commission on Glass； 1983.16 Weidenfeller B, Riehemann W, Lei Q. Mechanical spectroscopy of polymer-magnetite composites. Mater Sci Eng A 2004；370:Cooling behaviour of particle filled polypropylene during injection moulding processAbstractThe effects of thermal properties of various fillers (magnetite, barite, copper, talc, glass fibres and strontium ferrite) in various proportions on the cooling behaviour of polypropylene matrix composites are investigated in an injection moulding process. A thermocouple in the cavity of the mould records the temperatures at the surface of the composite during injection moulding. From the slope of the cooling curves the thermal diffusivities of the composites are estimated and compared with thermal diffusivities at room temperature and elevated temperatures measured with a transient technique. The cooling curves show different merging sections affected by the after pressure, the diffusivity of the composite and the diffusivity of polypropylene matrix. The cooling behaviour depends on the anisotropic thermal diffusivity of the used composite, which is caused by the alignment of filler material due to the injection moulding process and the interconnectivity of the filler particles. The thermal diffusivity shows the highest value for 30 vol% talc filled polypropylene, whereas the shortest cooling time was found for 35 vol% copper filled polypropylene. The knowledge of the systematic variation of thermal transport properties of composites due to different filler material andfiller proportionsallows to optimizethe mould process and tocustomize the heat flow properties. Furthermore,the strongly anisotropic thermal transport properties of talc filled polypropylene allow the design of composites with a predefined maximum heat flow capability to transport heat in a preferred direction.Keywords: A. Polymermatrix composites (PMCs)； B. Thermal properties； E. Injection moulding； Particulate filler1. IntroductionCommonly used plastics, such as polypropylene and polyamide, have a low thermal conductivity. However, new applications, mainly in automotive industries, e.g. for sensors or actuators, require new materials with an enhanced or high thermal conductivity 1. By the addition of suitable fillers to plastics, the thermal behaviour of polymers can be changed systematically up to significant higher thermal diffusivity of O1.2 mm2/s from 0.2 mm2/s for unfilled polypropylene 2,3. Such filled polymers with higher thermal conductivities than unfilled ones become more and more an important area of study because of the wide range of applications, e.g. in electronic packaging 46. The higher thermal conductivity can be achieved by the use of a suitable filler such as aluminium 1, carbon fibres and graphite 7, aluminium nitrides 6,8 or magnetite particles 2. Also, the cooling behaviour in the mould of the injection moulding machine is influenced by the thermal properties of the polymer-filler composite. However, published values of thermal conductivities of the same filler materials in different polymer matrices vary drastically and a comparison of different materials is difficult or at least impossible 2. Therefore, polypropylene samples with different com- mercially available fillers (Fe3O4, BaSO4, Cu, glass fibres, talcandSrFe12O19)werepreparedbyextrusionandinjection moulding using various volume fractions (050%). Magne- tite and barite are generally used to increase the weight ofpolypropylene, e.g. for bottle closures (cosmetics industry,cf. Ref. 10), strontium ferrite is used in polymer bonded magnets, glass fibres are used for the reinforcement of materials, and talc is an anti-blocking agent. However,copper was chosen as additional filler because of its high thermal conductivity compared to the other materials.The thermal properties of these injection mouldedsamples and the injection moulding behaviour were investigated and correlated to the amount and the kind of filler material.2. Theoretical considerationsThe Fourier law of heat transport in one dimension is given bywithtemperatureT,timet,positionxandthermaldiffusivitya.In an homogeneous body, thermal diffusivity a and thermal conductivity l are interrelated by specific density r and specific heat capacity cpaccording toAssuming an injection moulding process with an isothermal filling stage for a polymer with a temperature TPand a constant temperature of the mould TMas well as a temperature independent thermal diffusivity a, an analytical solution of Eq. (1) results in 9In Eq. (3), s denotes the wall thickness of the injection moulded part and T the temperature of the moulding after time t after injection. Neglecting higher order terms, Eq. (3) can be reduced for the position xZs/2 toEq. (4) gives a relation between cooling rate and thermal diffusivity in an injection moulding process, where high thermal diffusivities result in a higher cooling rate and shorter process cycles.3. Experimental3.1. MaterialsTest materials were supplied by Minelco B.V. (The Netherlands). Minelco B.V. prepared in cooperation with RTP s.a.r.l (France) several polypropylene (PP) compounds with various fillers (Fe3O4, BaSO4, Cu, glass fibres, talc and SrFe12O19) in an extrusion process similar to that described in Ref. 2. The filler materials are commonly used materials in industrial products. The filler particles do not have a surface coating which can affect thermal properties. Some selected properties of the filler materials are listed in Table 1.Fig. 1. Photograph of the used mould for the injection moulding experiments. The mould consists of a standard tensile test sample and a test bar for the measurement of thermal diffusivity.Fig. 2. Mold with cavity for preparing test samples in an injection moulding machine. The position of the thermocouple for temperature measurements is marked by an arrow.3.2. Thermal diffusivity measurementsThe thermal diffusivity of the polymers is measured by a transient method 12, closely related to laser-flash experi-ments 11. The used transient technique is especially optimized for measurements of polyphase aggregates. A temperature signal is transferred to the upper side of thesample and registered by a thermocouple. The transferred temperature signal starts a thermal equilibration process in the specimen, which is recorded by a thermocouple as the difference between samples rear surface and a constant temperature in a furnace and which is used for the evaluation of thermal diffusivity. A least squares algorithm is used to determine the thermal diffusivity, while varying systematically the thermal diffusivity value in an especially designed finite-difference scheme. A detailed description of the apparatus is given by Schilling 12. The accuracy of the measurements of the polyphase aggregates is 3%. For thermal diffusivity measurements, small cylinders of 10 mm diameter and 56 mm height were cut out of the injection-moulded rods (cf. Fig. 1).3.3. Injection mouldingWith an injection moulding machine (Allrounder 320C 600-250, Arburg, Germany) standard samples for measuring tensile properties together with a rod for thermal measure-ments of 10 mm diameter and 130 mm length were prepared in one mould (cf. Fig. 1). Inthe cavity of the tensile test bar a chromel alumel (Type K) thermocouple was applied.During injection moulding experiments the temperature was recorded every 0.5 s by a digital multimeter and stored in a personal computer. The position of the thermocouple at the sample surface and its position in the cavity of the ejector are shown in Figs. 1 and 2, respectively. The thermocouple submerges approximately 0.2 mm intothe cavity. Therefore, a good thermal contact between polymer and thermocouple even after shrinkage 10 of the moulding is ensured. For a better comparison of the recorded temperaturetime curves the same injection moulding parameters for all composite materials were chosen. The used injection moulding parameters are listed in Table 2. The resultantcharacteristic times of the injection moulding cycle are tabled in Table 3.4. Results and discussionIn Fig. 3, the cooling behaviour of polypropylene without and with various fractions of magnetite filler are presented.Fig. 3. Comparisonof coolingcurves ofunfilledpolypropylene with polypropylene compositeswith variousfillerfractionsof Fe3O4. The symbolsare measured values； the lines are regression lines (cf. text).At a time the temperature measured by the thermocouple reaches a maximum value around .With increasing time the observed temperature decreases.After the mould opens and the cooling behaviour recorded with the thermocouple changes because it is no longer in contact with the injection moulded material. Due to the large diameter of the rod, the time (54 s) until the mould is opened and the injection moulded parts are ejected is chosen relatively high to ensure that the parts are surely solidified.It can be seen in Fig. 3 that the slope of the curve changes significantly after , which corresponds to the time where the after pressure is removed. Additionally, Fig. 3 points out that the composite in the cavity cools down faster withincreasingmagnetitefraction.Toreachatemperatureof a temperature far below the solidification of the samplethe polypropylene needs in the described exper-iment a time of , whereas cooling time of polypropylene with Fe3O4is reduced to (cf. Table 4). The reduced cooling time is in good agreement with the increased thermal diffusivity of magnetite filled composites due to the high thermal diffusivity oftheparticles(cf.Table1)whichleads,regardingEq.(4),toan increased cooling rate. The temperature time dependence in Fig. 3 doesnotfollow asimplelinear behaviour expected for temperaturetime curves by Eq. (4) in a logarithmic plot. Only for the unfilled polypropylene the measured values can befittedwithasinglestraightlinebetweenapproximately15 and 54 s. The slope of this line leads to a diffusivity of (cf. Eq. (4). The other measured cooling curves of the polypropylene-magnetite composites are fitted in each case with two straight lines, for the high temperature and low temperature ( ) region. The thermal diffusiv-ities estimated from the slopes of the regression lines areIt is remarkable that the calculated thermal diffusivities of the higher temperature parts of the cooling curves are a little bit lower than the diffusivities measured with the transient technique, while the calculated thermal diffusivities of the lower temperature parts of the cooling curves meet the measured diffusivity valuesThe temperature values in parenthesis give the temperature region of the regression lines and the ambient temperature during the measurement with the transient technique.of unfilled polypropylene quite well (cf. Table 5 and Fig. 4).Fig. 4 shows the measured thermal diffusivity data of the investigated samples at ambient conditions. It can be seen that the thermal diffusivity of the magnetite-polypropylene composite is increased from for unfilled poly-propylene up to with increasing magnetite loading. Therefore, the cooling time becomes shorter for higher magnetite filler fractions(Fig. 3).One reason for the change in the slope of the cooling curves shown in Fig. 3 is a change of the thermal diffusivity with temperature which is shown in Fig. 5 for magnetite and barite polypropylene composites with filler fraction. With increasing temperature thermal diffusivity decreases. Therefore, the values derived from mould experiments should be smaller than the measured values of the composites at room tempera-tures. Thermal diffusivity of the PP matrix is mainly caused by phonons and is related to the mean sound velocity v and mean free path length l of phonons according toFig. 4. Thermal diffusivity values of injection moulded polypropylene samples with different fillers and various filler proportions measured by a transient technique at room temperature (cf. text). Solid lines are plotted to guide eyes. Above the solidification temperature of the PP matrix (around ,DSC measurements)the thermal diffusivity of the matrix is reduced due to the lowered bulk modulus K which results in a reduced phonon velocity and reduced mean free path length of phonons in a liquid (Einstein approximation). Furthermore, above solidification temperature TSno crystallites in the poly-propylene matrix are present, but below TSa crystallization in the polypropylene matrix appears, and the degree of crystallization as well as the bulk modulus of the composite is dependent on the amount of filler 16. The presence or absence of crystallites affects the bulk modulus K and the phonon free path. Other reasons for the discrepancy between diffusivity values of the different experiments are the non-isobaric conditions in the injection moulding process and the non-isothermal conditions along the samples thickness.The cooling behaviour of magnetite, barite, glass fibre,talc, hard ferrite and copper fillers in comparison with the unfilled polypropylene are plotted in Fig. 6. Only the cooling behaviour of the unfilled and the copper filled polypropylene show significant differences to the other composites.Fig. 5. Temperature dependence of thermal diffusivity of magnetite and barite filled polypropylene with a filler content of 45 vol%. The symbols represent measured values, the lines are deduced by linear regression.B. Weidenfeller et al. / Composites: Part A 36 (2005) 345351Fig. 6. Comparison of the cooling behaviour of polypropylene matrix composites filled with filler fraction of 30 vol% in the cavity of an injection moulding machine.The copper filled composite cools down much faster than the other investigated composites. The temperature of the unfilled polypropylene is during the whole injection moulding process higher than the temperature of the other investigated materials. The cooling behaviour of the other composite materials does not show large differences. The temperatures of the magnetite loaded PP is a little bit lower than the temperatures of the barite filled PP at the same cooling time. The temperatures of the strontium ferrite polypropylene composite again are a little bit lower than those of the magnetite filled polymers. While the measured thermal diffusivity of the talc filled polypropylene is much higher than the thermal diffusivity of the other investigated materials and even much higher than that of the copper filled polypropylene, the cooling behaviour of talc is smaller than that of the other investigated materials. Weidenfeller et al. 3 report in the talc filled composite an alignment of the talc particles oriented along their direction of highest thermal conduc-tivity in the direction of the flow, due to the moulding process. The measurements of thermal diffusivity are made parallel to this axis of highest thermal conductivity, whereas the temperature measurements in the injection moulding process reveal the diffusivity perpendicular to the flow direction. This implies that the talc filled PP samples have a strong anisotropy with a maximum in the flow direction and a minimum perpendicular to the flow. The anisotropy of the injection moulded specimens due to the geometry of the particles is shown in Ref. 3.In spite of the high thermal conductivity of the copper(cf. Table 1) compared to the other used filler materials,the cooling behaviour is relative poor and the measured temperatures in the cavity are not as significant different from those of the other composites as could be expected from the thermal conductivity which is approximately40 times higher than that of talc. This might be related to the poor interconnectivity of the particles in the composite,which was shown by Weidenfeller et al. 3. It was shown that the interconnectivity, which is a relative measure to anideally interconnected network of high conductivity par-ticles, is for copper in a polypropylene matrix lower than 1%and very poor compared to interconnectivity of magnetite with 55% or the interconnectivity of barite with 46% 3.The authors also discussed influences of particle size and shape on the interconnectivity in a polypropylene matrix 2,3.The necessary time to cool down the surface of the composite in the cavity to 60 8C is shown in Fig. 7.Fig. 7. Dependence of cooling time (from 200 down to 60 8C) from filler fraction for various polypropylene matrix composites. The symbols are measured values, the lines represent linear fits.Cooling time t represents the time span to cool down a polypropylene-filler composite with 30 vol% filler in the cavity of a mould from a mass temperature of TMZ200 down to 60 8C (333.15 K).The cooling time is linearly dependent on the filler volume fraction in the polypropylene matrix. The data of the calculated regression lines are listed in Table 6. It can be clearly seen that the copper filled polypropylene cools down much faster than the other investigated composites.The cooling behaviour of polypropylene with barite,strontium ferrite and magnetite is similar, whereas the magnetite cools down a little bit faster than all other materials.5. ConclusionsThe cooling behaviour of polypropylene in the injection moulding process can be reduced by the used magnetite,barite, strontium ferrite, glass fibre, talc and copper fillers.The cooling behaviour cannot solely be explained by a simple exponential law derived from the Fouriers law of heat conduction, due to the temperature dependence of the heat transfer and latent heat during solidification. Further-more, the cooling curves show different merging sections, which are affected by the after pressure at high temperatures and low times in the injection moulding cycle, thermal diffusivity of the composite at medium times of the injection moulding cycle and the thermal diffusivity of the poly-propylene matrix at the end of the injection moulding cycle. Additionally, an anisotropy of the thermal conductivity, e.g.for talc filler, or a low interconnectivity of particles, e.g.copper, influences the cooling behaviour.For the used materials and in the investigated range of filler fractions the cooling time for cooling down the injection moulded composite from a temperature of 200down to 60 8C is linearly dependent on the filler fraction.For 35 vol% copper in the polypropylene matrix the cooling time could be reduced from 50.5 (unfilled PP) to29.0 s.The strongly anisotropic thermal transport properties of talc filled polypropylene allow the design of composites with a predefined maximum heat flow direction which is capable to transport heat in a preferred direction.Besides the technical applications of higher conductingpolymers, the higher thermal transport properties of some composites can be used to optimize the mould process by enhancing the cooling of the composites during the process cycle