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材料导论_北京化工大学中国大学mooc课后章节答案期末考试题库2023年1.MSE involves the generation and application of knowledge relating _____ totheir _______ and uses, having interdisciplinary and multidisciplinarycharacteristics.答案:Composition, structure, and processing of materials, properties2. A concept that place recycling at the beginning or design stage of thematerials cycle to ensure that waste going into municipal landfills will beminimized.答案:Design for disassembly3.If there are components in the center of each face in addition to those at thecorners of the cube, then the unit cell is called.答案:Face Centered Cubic4.Which one typically has the largest thermal expansion?答案:Polymer5.Metals are good conductors of both_______________.答案:Electricity and heat6.The fiber reinforcement becomes more effective, when ____答案:the fiber length is larger than critical fiber length7.The hollow parts such as tanks can be produced by _______答案:Filament Winding8.Which one is the expression for the rule of mixture?答案:Ec=EmVm+EfVf9.________ experiment is carried out outside of the organism, usually in a testtube or petri dish.答案:In vitro10.Nanomaterials are generally defined as any particulate material with the sizeof __ nm in at least one dimension.答案:1-10011.The properties of crosslinked hydrogels depend on .答案:Crosslinking Density12.The cost of a finished piece includes _______.答案:The cost of raw materialsAny expense incurred during fabrication13.What are the characters of stiff materials?答案:High Bonding Energy within the MaterialHigh Elastic Modulus14.How to increase transition temperature range of brittle to ductile?答案:Increase grain sizeAdding certain elementsStrain hardening15.What are the factors influencing creep resistance of polycrystalline materials?答案:TemperatureStructures like Grain Types16.Sintering is a heat treatment applied to a powder compact toimpart _____________答案:IntegrityStrength17.LLDPE and LDPE have lower density than HDPE, because ______.答案:LLDPE and LDPE contains branchesHDPE is primarily a linear polymerThe formation of side branches will reduce the packing efficiency18. is an elastomer having physical cross-links in the “network” structure.答案:SISSBS19.Ceramics have the excellent properties as following:答案:Corrosion resistanceExtreme hardness20.Which can be selected as matrix materials for composites?答案:PolymerCeramicMetal21.The reinforcing effect of carbon black in tires is the result of the ______ of itsparticles.答案:Uniform DistributionGood adhesive bonding with the rubber molecules22.The additives used in polymer nanocomposites can be _____答案:NanofibersNanotubesNanoparticlesNanoclays23.Why fiberglass-reinforced composites are used extensively.答案:These composites have relatively high specific strengths.Glass fibers are very inexpensive to produce.They are chemically inert in a wide variety of environments.24.Materials science involves investigating the relationships that exist betweenthe structures and properties of materials.答案:正确25.Tensile strength can be estimated from the hardness reading.答案:正确26.Natural rubber usually is much stronger and harder than vulcanized rubber.答案:错误27.The modulus of crystalline polymers is higher than the modulus of anamorphous polymer答案:正确28.Viscoelasticity is a combination of elasticity and viscosity答案:正确29.Ceramics are crystalline compounds that combine metallic and nonmetallicelements.答案:正确30.Traditional ceramic materials include clays, refractories, glass, cement andabrasives.答案:正确31. A composite is composed of two (or more) individual materials, which comefrom metals, ceramics, and polymers.答案:正确32.Carbon-carbon composite is based on carbon fibers答案:正确33.Surface erosion could be characterized as zero order release.答案:正确。
Flow Induced Crystallization ofPolymersApplication to Injection MouldingChapter 1IntroductionThe final properties of a product, produced from semi-crystalline polymers, are to a great extend determined by the internal structure, which itself is established during processing of that product. For example,flow gradients act as a source for viscoelastic stresses, which can enhance nucleation and crystallization, not only accelerating the process, but also leading to different types of crystalline structures. A complete modeling, providing the means for pre-dicting the final product properties, is stillnot available. This study presents two important parts of that modeling; (i)a flow-induced crystallization model, based on the recoverable strain inthe melt and, (ii) a new experimental technique to determine the specific volume of semi-crystalline polymers, and its relation to cooling rate dependent crystallization kinet-ics. Both are implemented in a computercode for the numerical simulation of the injection moulding process, and validated by comparing the predicted results with well defined exper-iments (partly from literature). Applications are found in predicting internal structures (i) as resulting from the SCORIM process (which is a specific procedure (’push-pull’) to enhance mechanical properties like strength and stiffness), (ii) as present in a moulded strip (as a function of different processing conditions) and, finally, (iii) in their relation withlong-term dimensional stability.Crystallization of polymers is influenced by the thermo-mechanical history during pro-cessing. Dependent on the amount of strain experienced during flow, the number and type of the nuclei formed will be different, and so will be the final crystalline structure. For example,in the injection moulding process, the absence of shear in the center of a product results in a spherulitical structure, while in the highly strained regions atthe cavity walls an oriented structure (in polyolefins often referred toas ’shish-kebabs’)can be present (fig. 1.1). T o clarify the role of the processing conditions on the crystallization process (and, vice versa,therole of the growing crystal structure on processing behavior), a short overview will be presented concerning their mutual interactions.1.1 Crystallization of polymers related to processing: an overview 1.1.1 Molecular configuration, conformation and flowThe molecular configuration of polymer materials determines thematerials ability for order-ing. Three types of molecular structures are generally distinguished: isotactic, all side groups a re present at one side of the backbone of the polymer chain; syndiotactic, with alternating side groups; and atactic, with randomly positioned side groups. Crystallization is possible if the chain is symmetric or has only small side groups, which fit in a regularly packed confor-Fig. 1.1: A cross section of a product. After (44).mation; the polymer chain has to be linear and stereo specific. Therefore, isotactic polymers have the ability to crystallize; syndiotactic polymers might have this ability, depending on the side groups, while atactic polymers can not crystallize. The influence of isotacticity on the crystallization kinetics during quiescent crystallization has been studied by, for example,Janimak (41).Polymer molecules, in general, show a random configuration without any orientation,when in s olutions o r melts. However, t heir s tate (conformation a nd o rientation) c an b e a ltered by flow gradients, i.e. by stirring solutions or shearing melts. According to Keller ( 48)only two stages of orientation exist; the fully random and the fully stretched chain, with no stable intermediate stages. The trans ition from one stage to the other is assumed to be sharp, showing a molecular weight dependent coil-stretch transformation at a critical strain rate and temperature. Thus, with gradually increasing the elongational rate, first only s mall differences in the chain conformation will appear, but once a critical elongational rate has been reached, the chain will switch to the almost fully stretched stage of the conformation(‹˙θ> 1, with‹˙the deformation rate and θ= θ(M w, T , ...) the relaxation time). Moreover, not only has the critical elongational rate to be reached, it must be maintained for a certain time as well (‹˙t > 1, with t the deformation time). The structures observed in solutions or melts, all are the result of a c ombination o f b oth t hese s tages.1.1.2 CrystallizationThe crystallization behavior of polymers is determined by their ability to form ordered struc-tures; the configuration determines the conformation, which is influenced by the processing conditions. Crystallization under quiescent conditions is a phase transformation process,which is caused by a change in the thermodynamic state of the system. This change can be a lowering of the temperature or a change in the hydrostatic pressure. In flow, chain extension can occur as explained in the preceding section. Thermodynamically, chain extension will increase the opportunity of crystal formation by increasing the melting point, while kineti-cally the extended chain is closer to a crystal state than a random chain. By stretching the polymer chains, the rate of crystallization increases. Dependent on the conformation of thepolymer chain, two types of crystals can be formed; the random polymer chain will lead to lamellar, chain folded crystals that finally form spherulites, while the fully extended chain will lead to extended chain crystals, finally resulting in shish-kebab structures (Keller ( 48)).It has been shown, e.g. by Bashir (2) and Mackley (62), that the high end tail of the molecular weight distribution promotes the formation of extended chain crystals. Following Bashir ( 2),these high end tail molecules are stretched out while the rest remains practically unchanged;a stronger elongational rate results in a broader part of the molecular weight distribution to be extended. The elongational rate, therefore, determines the amount of oriented molecules(extended chain crystals) present. These extended chain crystals themselves are inadequate to influence the material properties, given their limited number. However, they serve as nuclei for lamellar crystallization of the not oriented lower molecular bulk, which will show lamel-lar over-growth at a later stage, perpendicular to the central core (Bashir ( 2)). The structure formed is called a shish-kebab. It has been shown by Petermann ( 67) that the number of core crystals, nucleated at a specific temperature, depends on the external strain. The core itself consists of a shish-kebab structure on a finer scale (Keller ( 48)).A certain strain and strain rate have to be present for shear flow to induce (noticeable)crystallization. After a nucleus has been formed, continuous crystallization of polymers is kinetically controlled, the motion involved refers to the transport of molecules from the dis-ordered liquid phase to the ordered solid phase, and to the rotation and rearrangement of the molecules at the surface of the crystal, similar to quiescent crystallization. The crystallization process can thus be subdivided into three stages:Nucleation: Nucleation can have different causes like overall nucleation from a nucleation agent, pressure induced nucleation, strain induced nucleation and cooling. The nuclei formed act as starting points forpolymer crystallization. There is no complete agreement on the physical background of the nucleation process. For example, Terrill et al. ( 81) considered,based on experimental evidence (WAXD and SAXS), the nucleation event during spinning of isotactic polypropylene to be the result of density fluctuations, although a repetition of old discussions on the true interpretation of combined WAXD and SAXS data 1 question these re-sults. Even without considering the basic underlying physics precisely, in case of flow, nuclei can be created by flow-induced o rdering phenomena in the melt, while the nucleation process for a quiescent melt can be described by a Poisson point process (Janeschitz-Kriegl ( 40)). For polymers containing nucleation agents, also clustered point processes have some importance.Growth: The nuclei grow, dependent on the thermo-mechanical history which they experi-ence; if the nuclei are sufficiently strained they will grow into threads, otherwise they stay spherical and will further grow radially. In these, so called spherulites, the lamellae are present like twisted spokes in a sphere, while thread-like nuclei grow mainly perpendicular to the thread(fig.1.2).Perfection: Perfectioning is the process of improvement of the interior crystalline structure of the crystalline regions. This is also referred to as secondary crystallization.Fig. 1.2: A schematic outline of the concept of crystallization. After (48) and (55).1.1.3 ModelingHistorically, crystallization transformations are described by using a phase diagram assuming the transformation to be in a quasi-equilibrium state,leading to a front model. An example of this approach is the description of the growth of the ice layer on the polar see (a Stefan-problem (78)). It has been shown by Berger (5), that the front model is inadequate in describ-ing solidification, if the process is governed by the kinetics of a phase change. For example,the occurrence of completely amorphous layers can never be understood using a front model.A zone model has to be used, were a phase change (crystallization) determines the solidifi-cation behavior. Crystallization in a moving zone takes place when the characteristic time of heat diffusion is less than the characteristic time of crystallization. In the limiting case of very fast crystallization, compared with the process of heat conduction, the zone model shows a transition into the front model.Quiescent crystallization: Describing the growth of the crystalline spherulites in case of quiescent crystallization has been done by representing the spherulites as spheres (Schultz ( 75)).Spherulitical growth is then accounted for by enlarging the sphere radius. However, the crys-tallizing medium is limited by free surfaces or other boundaries that induce truncations of crystalline entities and locally modify the crystallization kinetics. Benard ( 4) formulated a mathematical description for the growth of already existing nuclei and concluded that the ki-netics clearly are the controlling factor in the systems investigated.A more complete model for quiescent crystallization has been described by Janeschitz-Kriegl ( 39), which is based on the Kolmogoroff equation (Kolmogoroff ( 49)), who formulated the crystallization kinetics in terms of time dependent (bulk) nucleation and crystal growth rate. This formulation has b een extended for the influence of confining surfaces and surface nucleation processes by Eder (15; 16). A Poisson point process with special intensity measures for the description of the nucleation process and a deterministic law for crystal growth forms the basis. Using the method proposed by Schneider ( 74), this generalized Kolmogoroff equation can be trans-formed in a set of differential equations (Schneider’s rate equations), which give a complete description of the crystalline structure. These rate equations are coupled with the energy equation by the source term, which takes into account the latent heat when the polymer crys-tallizes (Eder (17)).Flow-induced crystallization: An onset for the description of flow-induced structures has been given by Eder et al. (19), who based their theory on the shear rate as the driving force for crystallization. Their model for flow-induced crystallization resembles their model for quiescent crystallization. It is assumed that the influence of the deformation on crystal-lization, is due to the formation of thread-likenuclei (shish), on which lamellae grow mainly perpendicular (kebabs). This model is described in chapter 3 of this thesis. Jerschow (45)used this model in analyzing the structure distribution found in isotactic polypropylene, after fast short term shear at low degrees of super-cooling. Besides a flow-induced (shi sh-kebab)structure at the surface and a spherulitical structure in the center, in between both layers a fine grained layer has been observed. It has been suggested that this layer consists of thread-like structures perpendicular to the flow direction. A model based on the conformation of the molecules in the melt has been proposed by Bushman ( 8) and Doufas (12), which includes a conformation tensor (the driving force, calculated using a viscoelastic model), an orienta-tion tensor and the degree of crystallinity. No description is available, however, of the final structure (size of structures, etc.). Other models have been proposed by Ito ( 37), based on the strain present in the melt, and by V erhoyen ( 86), based on the Cauchy stress. An iso-kinetic approach is used in models based on the Nakamura equations (Nakamura ( 66)) by Isayev (35)and Guo (29). The (dis)advantages of all these models are discussed in chapter 3.1.1.4 Relation with other material propertiesThe evolution of structure (spherulites and shish-kebabs) will influence the material proper-ties. The most severe effects are observed in the viscosity and the specific volume. Effects in other properties like the thermal conductivity and thermal capacity will not be discussed here.Viscosity: The coupling between the crystal structure and the viscosity of a polymer melt, is not fully clarified yet. For example, in startup flow experiments, it has been observed by Lagasse (52) that a sudden rise in the viscosity correlates with the appearance of crystal s in the sheared melt. Experiments by Vleeshouwers ( 87) showed the same kind of behavior.Initially, the melt still shows an amorphous behavior, since the amount of crystalline material(or the number of crystals) is very low. With increasing amount (or number) the influence on the viscosity will increase. Guo et al. (27) assumed that the melt loses its fluidity upon the occurrence of crystallization, i.e. a step-like change in the viscosity. They do not give a physical explanation although; one could assume that a network occurs in this stage. Another possibility could be, that the crystals form a separate phase in the amorphous melt. The rhe-ology will then be changed like is known from dispersion rheology (see for example Ito ( 36) and V erhoyen (85)).Specific volume: In polymer processing, the specific volume isinfluenced by process-ing characteristics like temperature, pressure and flow history, and it determines shrinkage which expresses itself by dimensional (in)stability. For amorphous polymers, the pressure and temperature history determine the specific volume and (frozen in) molecular orientation determines the anisotropic dimensional instability via (slow) relaxation processes below the glass transition temperature (Meijer (65)). For semi-crystalline polymers, however, the spe-cific volume is also influenced by the crystalline structure. This structure itself is influenced by the pressure and the temperature history, by the configuration of the polymer chains and flow induced ordering phenomena as well. Consequently, for semi-crystalline polymers the specific volume has to be related to pressure, temperature, cooling rate and the crystalline state (Zuidema (94)). For a correct modeling of the injection moulding of semi-crystalline polymers, accurate measurements and modeling of the specific volume have to be achieved not only in relation to the pressure and temperature, but al so to the cooling rate and ordered state of the molecules. This conclusion is subscribed by Fleischmann ( 22), regarding the influence of the processing conditions on the specific volume. The specific volume will be discussed in more detail in chapter 4.1.1.5 ProcessingFor polymer melts it has been observed (V an der V egt ( 83)) that the flow through a capillary die can become blocked by crystal formation, induced by the elongational flow at the con-striction. Bashir (2; 3) and Keller (48) explored these findings somewhat further and observed a macroscopical rheological effect in capillary flow of high molecular weight polyethylenes;a reduced flow resistance coupled with the absence of extrudate distortions when extruding a polymer melt in a specific processing window. Experiments by T as ( 80) showed that, dur-ing film blowing of LDPE films, the viscoelastic stresses at the freeze line determine the majority of the mechanical properties by directing the crystallization. Saiu ( 71) performed an experimental study on the influence of injection moulding conditions on product proper-ties for an isotactic polypropylene. Chiang ( 11) studied shrinkage, warpage and sink marks resulting from the injection moulding process, using semi-crystalline polymers. The effect of crystallization on the mechanical and physical properties has been studied, for isotactic polypropylenes with different molar masses. It has been observed (Guo ( 28)) that increasing the injection speed or the melt injection temperature leads to a decrease in the thickness of the flow-induced layer. The complicated thermo-mechanical history, in all these examples,requires a numericalanalysis. The effect of processing conditions will be discussed in more detail in chapter 5.1.1.6 Mechanical propertiesThe resulting morphology of the product is, together with the molecular composition, the factor determining the mechanical and dimensional properties. Because the solidification be-havior of amorphous polymers is quite well understood, prediction of warpage and shrinkage from ejection up to the complete life cycle of a product can be done (Caspers ( 9), Meijer (65)).This knowledge allows one to reduce shrinkage and warpage by choosing a different polymer(with different relaxation time/molecular weight (distribution)) by adjusting the processing conditions, or by improving the mould design. For semi-crystalline polymers, the different crystalline structures present (spherulites and/or shish-kebabs) have a different influence on secondary crystallization and physical aging. The mechanical properties of semi-crystalline polymers improve with increasing the amount of long polymer chains that function as ’tie-molecules’ between crystals. Also, a preferred molecular orientation in a product enhances the properties in the orientation direction, while perpendicular the properties reduce. An ex-treme example is the fiber spinning process of HPPE (High Performance Polyethylene fibers),where all molecules are aligned along the thread.An attempt to quantify the influence of injection moulding processing conditions on the mechanical properties has been performed by Fleischmann ( 23) who studied the effect of molecular orientation on the tensile behavior of an isotactic polypropylene. The application of packing pressure, the distance from the gate and the orientation of the testing direction relative to the chain orientation, all proved to influence the tensile behavior. Hsiung ( 34)showed that with decreasing the injection speed, the elongation to break, tensile strength and impact strength increase in injection moulded dumbbells. Gahleitner ( 25) investigated the influence of the molecular structure on the crystallinity and mechanical properties for two different polypropylene homopolymers, as influenced by their molar mass and heterogeneous nucleation, and he studied (24) the influence of processing on physical ageing. Additional to the generally observed correlation between mechanical properties and spherulite size, it has been shown that mechanical properties are influenced by the formation of highly ori-ented skin layers through shear induced crystallization. Based on these considerations, we conducted a number of, relatively extreme, experiments at the Borealis laboratory in Linz incooperation with Markus Gahleitner. Rectangular plates were injection moulded using an isotactic polypropylene. Different injection temperatures, mould temperatures and volume fluxes during filling were applied in order to study their influence on the resulting morphol-ogy and the mechanical properties. One of the conclusions was that the strongest effect on skin layer thickness and shrinkage resulted from a change in the melt temperature. Results are discussed in chapter 5. Generally, they are in line with previous examinations at the same polymer. Gahleitner (24) earlier also concluded that an increased melt temperature re-duces shrinkage. Moreover, he found that an increased wall temperature only weakly reduces shrinkage, while an increased volume flux during filling reduces shrinkage. Density near the injection gate was higher than far from the gate, while stiffness was higher in longitudinal compared to the transverse direction. Ageing has shown to follow a log-linear behavior, as was confirmed by Fiebig (21). Jansen (42) found that a variation of holding pressure affects both longitudinal and transverse shrinkage.1.1.2 Thesis’ objective and overviewThe main objective of this thesis is to predict the structure di stribution during injection mould-ing in dependence of polymer parameters and processing conditions of semi-crystalline poly-mers, given its direct relevance to dimensional stability and mechanical properties. Different models that describe (flow-induced) crystallization of semi-crystalline polymers are imple-mented in our software code VIp (Polymer Processing & Product Properties Prediction Pro-gram, Caspers (9)). A new model is proposed, based on the molecular conformation in the melt, i.e. the recoverable strain, as expressed by the highest relaxation time using the sec-ond invariant of the Finger tensor, and it replaces the until now used process parameter, the shear rate. The development and validation of thi s model for flow-induced crystallization is elucidated in chapter 3. Specific volume depends strongly on the crystalline structure and represents, therefore, an interesting material property. In chapter 4 the standard methods used to measure the specific volume are summarized and their deficiencies when used to charac-terize semi-crystalline polymers are discussed. A new experimental setup is proposed, able to measure specific volumes of semi-crystalline polymers dependent on both cooling rate and pressure applied. A model is proposed that relates structure distribution to specific vol-ume. Combining the set of equations that describe crystalline structure development, with the model for specific volume and using our injection moulding simulation software VIp, we are,finally, able to try to study the influence of processing variables, as they influence the struc-ture distribution (chapter 5). The thesis endswith a short discussion and recommendations for future research (chapter6).Hunan University of Arts and Science (118.239.51.229) - 2014/10/11Download。
Grivory GV经证实的金属替代材料该产品系列材料基于带部分芳香族含量的半结晶聚酰胺。
Grivory GV 以颗粒状供应，方便常规的市售设备和模具进行进一步注塑成型或挤出成型加工。
Grivory 用于制造具备以下特征的技术组件：∙较高的刚度和强度水平∙吸湿后特性值几乎无变化∙较低的吸湿性和吸水性∙良好的尺寸稳定性和低翘曲性∙典型聚酰胺的良好耐化学性∙良好的表面质量∙经济高效地进行生产提供以下 Grivory G 等级：Grivory GV：玻璃纤维增强，非常坚硬Grivory GVX：最高的刚度和强度值，极低的翘曲性Grivory GM：矿物增强，低翘曲性Grivory GVN：玻璃纤维增强，耐冲击性Grivory GC：碳增强，非常坚硬Grivory G4V：玻璃纤维增强，良好的表面质量Grivory GVS：玻璃纤维增强，卓越的流动特性Grivory GV FWA：玻璃纤维增强，用于接触食品和饮用水这些等级也适用于一系列不同的改性，根据所使用的增强剂、稳定剂和加工助剂的浓度而各不相同。
Grivory FWA产品对人体无害，并且还用于直接接触应用水和食品的敏感型应用领域。
Grivory GVX最高级别的金属替代我们的金属称为Grivory凭借高性能聚合物Grivory GV，EMS-GRIVORY 多年来一直是金属替代领域的市场领导者。
现在，新材料Grivory GVX 使我们更进一步。
该新材料大大提高了机械特性，显著扩大了金属替代应用的范围。
Grivory GVX 所提供的卓越性能在所有细节上均无可挑剔！Grivory GVX 尤其具备以下特性：∙最高的刚度和强度值∙极低的翘曲性∙加工过程简单Added performanceWith its exceptional property specification profile, Grivory GVX opens up a completely new chapter in the field of metal replacement.If all property values of Grivory GV-5H are compared with those of the new material Grivory GVX 5H, the consistent increase in performance is clearly apparent. The further development of Grivory GVX is particularly visible in its low warpage values, more isotropic material properties and flowability.Metal replacementDie-cast metals under pressureThe advantages of Grivory GVX compared to diecast metals are, above all, their lower density, simple processability and efficient production with up to 40% lower manufacturing costs.With a modulus of elasticity of up to 300 MPa, Grivory GVX is leader among thermoplastic materials and does not need to avoid direct comparison with property profiles of metals. At high temperatures for example, it exhibits much better performance than die-cast zinc. When combined with a component design suited for plastic materials, structural rigidity values, comparable to those of metal components, can be achieved.The future for metal replacementDue to its exceptional mechanical properties and simple processing, Grivory GVX expands the limits of metal replacement. The well-known advantages of weight reduction, freedom of design, functional integration and, above all cost savings, make polyamide materials much in demand as an alternative to more expensive metals. Grivory GVX - metal replacement at the highest level!Stiff and strongA significant increase in stiffness values - a new dimension for thermoplastic materials with glassfibre reinforcementGrivory GVX achieves modulus of elasticity values of nearly 30‘000 MPa. Compared to values for Grivory GV, this is an increase of more than 50%! These values also remain at the highest level for test bars in a conditioned state where conventional polyamides show a decrease of up to 35%.Significantly higher lateral stiffnessCompared to Grivory GV, Grivory GVX shows an increase of 26% in lateral stiffness for the same glassfibre content. This factor is particularly important in the manufacture of components exposed to internal pressure. The striking improvement is a great advantage for parts exposed to stress applied laterally to the direction of the fibres.WarpageAll semi-crystalline plastic materials are subject to the problem of warpage. With Grivory GVX, this warpage has been reduced by up to 50%. Due to an optimised interaction between the matrix and reinforcing glassfibres, 25% lower lateral shrinkage to the direction of alignment of the fibres has been achieved. This low transverse shrinkage results in the manufacture of components with greatly reduced warpage.The Moldflow analysis clearly shows the difference in warpage between Grivory GVX (A) and conventional products with the same amount of glassfibre reinforcement (B). This reduced warpage is not only Moldflow- Theory. Both test bars and daily applications confirm this lower warpage in an impressive manner.Grivory HT增强了高温下的性能Grivory® 是EMS-GRIVORY 所制造并销售的专用热塑性塑料商标名。
聚合物的结晶动力学本节主要内容：讨论结晶的过程和速度问题，即结晶的动力学问题。
目的：了解聚合物的结构和外界条件对结晶速度和结晶形态的影响，进而通过结晶过程去控制结晶度和结晶形态，以达到控制最终产品性能的目的。
一、高分子结构与结晶的能力聚合物结晶过程能否进行，必须具备两个条件：1、聚合物的分子链具有结晶能力，分子链需具有化学和几何结构的规整性，这是结晶的必要条件——热力学条件。
2、给予充分的条件－适宜的温度和充分的时间——动力学条件。
(一)链的对称性大分子链的化学结构对称性越好，就越易结晶。
例如：聚乙烯：主链上全部是碳原子，结构对称，故其结晶能高达95％；聚四氟乙烯：分子结构的对称性好，具有良好的结晶能力；聚氯乙烯：氯原子破坏了结构的对称性，失去了结晶能力；聚偏二氯乙烯：具有结晶能力。
主链含有杂原子的聚合物，如聚甲醛、聚酯、聚醚、聚酰胺、聚砜等，虽然对称性有所降低，但仍属对称结构，都具有不同程度的结晶能力。
(二)链的规整性主链含不对称碳原子分子链，如具有空间构型的规整性，则仍可结晶，否则就不能结晶。
如自由基聚合制得的聚丙烯、聚苯乙烯、聚甲基丙烯酸甲酯等为非晶聚合物，但由定向聚合得到的等规或间规立构聚合物则可结晶。
二烯类聚合物：全顺式或全反式结构的聚合物有结晶能力；顺式构型聚合物的结晶能力一般小于反式构型的聚合物。
反式对称性好的丁二烯最易结晶。
(三)共聚物的结晶能力无规共聚物：1、两种共聚单体的均聚物有相同类型的晶体结构，则能结晶，而晶胞参数随共聚物的组成而发生变化。
2、若两种共聚单元的均聚物有不同的晶体结构，但其中一种组分比例高很多时，仍可结晶；而两者比例相当时，则失去结晶能力，如乙丙共聚物。
嵌段共聚物：各嵌段基本上保持着相对独立性，能结晶的嵌段可形成自己的晶区。
例如，聚酯—聚丁二烯—聚酯嵌段共聚物中，聚酯段仍可结晶，起物理交联作用，而使共聚物成为良好的热塑性弹性体。
影响结晶能力的其它因素：1、分子链的柔性：聚对苯二甲酸乙二酯的结晶能力要比脂肪族聚酯低2、支化：高压聚乙烯由于支化，其结晶能力要低于低压法制得的线性聚乙烯3、交联：轻度交联聚合物尚能结晶，高度交联则完全失去结晶能力。
综述CHINA SYNTHETIC RESIN AND PLASTICS合 成 树 脂 及 塑 料 ， 2021， 38（3）： 59聚丙烯（PP）是半结晶的非极性材料，具有优异的耐热性、绝缘性、化学稳定性及力学性能，广泛用于电气绝缘材料和电容器电介质。
双向拉伸聚丙烯（BOPP）薄膜是电容器中重要的介质材料，占电容器成本的70%。
薄膜电容器常应用于消费类电子、节能灯具、家电、交流电机、电动汽车逆变器、电力等领域［1-2］。
电容器用PP薄膜有两种生产工艺，一种是目前主流的平膜法，另一种是管膜法。
按空隙率分类，PP薄膜分为可蒸镀薄膜（光膜）和油浸薄膜（粗化膜）。
光膜为表面光滑、空隙率小于5%的薄膜，经过金属蒸镀处理，主要应用于各种直流或高储能密度脉冲电容器等。
粗化膜为至少一面粗糙、空隙率大于等于5%的薄膜，常用来制造油浸箔式电容器，用于交流输电系统无功补偿等。
近年来，随着国家特高压柔性直流电网的发展、高铁的建设、新能源电动汽车的推广等［1］，对耐热性好、金属化薄膜电容器的需求快速增长。
日本东丽公司预测电动汽车的需求以每年20%的速度增长［2］。
因此，电容器薄膜用PP具有良好的市场前景和经济效益。
目前，电容器薄膜用国产BOPP已与国外产品质量基本持平，产能占世界的一半以上，但制备BOPP的原料仍被国外公司垄断。
本文对国内外相关产品、国内外生产情况和相关开发进展进行总结，为电容器薄膜用PP的国产化提供借鉴与参考。
1 电容器薄膜的主要性能1.1 击穿强度PP分子链中不含极性基团，因而其本征击穿电压值很高，BOPP薄膜局部击穿强度高达700 V/电容器薄膜用聚丙烯的生产现状张丕生1，孙福国2，徐 辉1，袁鹏辉1（1. 中国石化中原石油化工有限责任公司，河南 濮阳 457000；2. 中国石化化工销售有限公司华中分公司，湖北 武汉 430000）摘要：综述了电容器薄膜的主要性能特点、国内外生产现状，介绍了国内外生产工艺、产品牌号及性能。
链状大分子半结晶织态结构的调控Controlling the semi-crystalline texture ofchain-like macromolecules胡文兵南京大学链状大分子材料的微结构不同于常见的金属、陶瓷和氧化物玻璃,它的结晶和非晶相在几十纳米尺度上相互交错编织起来形成特殊的多相复合织态结构,如图1所示。
这样一来,一方面高分子的结晶相为塑料和纤维带来必要的强度和硬度,或者为热塑性弹性体带来较硬的物理交联点;另一方面,其非晶相中分子链可以发生大尺度的形变,为材料带来很好的柔韧性。
二者在纳米尺度上相互复合的结果使得大多数高分子材料表现出结构材料所需要的既强且韧的特点。
目前,不仅自然界中广泛存在的生物大分子材料如纤维素、淀粉、甲壳素、蚕丝和蜘蛛丝等具有半结晶性,而且全球总产量三分之二以上的合成高分子材料也具有半结晶性。
自然界已经进化出多种多样的生物品种可利用来制备具有不同化学和物理结构的半结晶性生物大分子材料。
但是,通过人工的方法改变高分子材料的半结晶性织态结构则为我们的选择提供了更大的灵活性,并带来大规模生产的低成本和高效率。
因此,通过物理和化学等人工手段来调控高分子材料的半结晶织态结构,是对高分子学科发展具有重大影响的基础性研究课题。
图1高分子半结晶织态结构示意图(1)物理手段研究进展柔性链高分子在结晶时自发地在几十纳米结晶片段处发生高频率的近邻折叠,从而形成热力学上处于亚稳态的折叠链片晶。
同时,不发生近邻折叠的地方则出现环圈(非晶片段另一端连在同一层片晶上)和连系分子(非晶片段另一端连在不同层片晶上),构成非晶相的主要成分。
这样的片晶结构通常在生长时进一步发生分枝从而组装成球晶,后者在普通的偏光显微镜下很容易被观察到。
这一结晶生长特点本身就决定了高分子的半结晶织态结构。
例如等规聚丙烯的α晶在较低温度生长时很容易发生大角度分枝,使得结晶度在隔离出的小区域中不能得到很好的发展,而相对较不稳定的同质β晶则可以避免这种情况的发生,从而提高最终产品的结晶度。
