Crystallization (polymer)

The crystallization of polymers can be observed in some thermoplastics . When the melt solidifies, the molecular chains in the polymer are partially ordered . Starting from crystallization nuclei , the molecular chains fold together and form so-called lamellae, which are separated by amorphous areas. The lamellas form superstructures such as B. spherulites . In addition to solidification, crystallization can also take place from a solution.

The crystallite formation depends on the cooling conditions, the additives and fillers in the polymer and the flow conditions during solidification. Subsequent stretching also changes the arrangement of the molecules and thus the properties of the material.

The crystallization affects the optical, mechanical, thermal and chemical properties of the polymer and its processing. The degree of crystallization can be measured using various analytical methods. The properties are not only determined by the degree of crystallization, but also by the size of the structural units or the molecular orientation.

Crystallization mechanisms

Many phenomena related to the crystallization of polymeric materials are still not finally understood or even proven. Various models were supported by experimental findings and have prevailed:

Crystallite formation when solidifying from the melt

Fig. 1: Schematic arrangement of the molecular chains in amorphous and crystalline areas

Polymers are made up of very long molecular chains. Thermoplastic polymers are characterized by the fact that they soften considerably when the temperature rises and finally become fluid. If there are crystalline areas, these melt. In the melt, the molecular chains are then arranged irregularly in the form of tangles (Fig. 1), which penetrate each other in many ways ( entanglement ). In the case of many thermoplastic polymers, this disorder remains as an amorphous structure in the solidified body when it cools.

If, on the other hand, the melt of a partially crystalline polymer (a subgroup of thermoplastics) is cooled, the chains move less and less and begin to arrange themselves regularly (crystallization). States of order (“crystallites”) with a typical size of 15–100 nm develop .

During the crystallization of polymers, sections of the molecular chains are deposited parallel to one another. It would be energetically most favorable if the molecules were arranged in parallel over the entire length of the molecular chain. However, since the molecular chains in the melt exist as tangled, intertwined coils, this order cannot be achieved in reality or only under very high pressure. Crystallites are therefore formed from folded molecular chains (Fig. 1), which form the basic structures of larger structural units such as B. form lamellar structures. The order is not to be regarded as complete. It can be on the folding sheets z. B. form smaller or larger loops. The chain ends can also be disordered. It is also common for a molecular chain to leave one crystallite and rejoin another. Each crystallite therefore consists of ordered (crystalline) and disordered (amorphous) parts. This is also the reason that even in the event that the polymer macroscopically does not have any amorphous areas, a polymer material can only be described as partially crystalline.

So far, it has not been possible to make tangled molecules in the solution or melt, nor folded molecular chains in solid polyethylene directly visible and document them photographically. However, there is compelling evidence of the correctness of the fold model in the case of polyethylene solidified from the melt, in that it was possible to mechanically tear the lamellae from a solid sample of low-pressure polyethylene (PEHD) with an average molar mass that was solidified by slow cooling from the melt separated from M = 100 kg / mol, made visible in the transmission electron microscope and documented photographically. This proves that the bond between the lamellae is smaller than the bond between the carbon atoms of the molecular chain inside the lamellae. The length of the molecules is many times greater than the thickness of the lamellae. This corresponds completely to the explanation of the founder of the folding model, A. Keller: "If the lamellae are isolated individual objects, as after crystallization from the solution, and the chains are arranged perpendicularly or at a large angle to the base, then the folding is a direct one Necessity because the chains cannot go anywhere else. This was the original basis of the chain folding postulate of 1957 and it remains as true now as it was then. "

Carbon imprint of a fracture surface of HDPE with adhering lamellae
Carbon imprint of a fracture surface of HDPE with adhering lamellae
Preparation steps for the detection of lamella separation with the electron microscope

Fig. 2a: isotactic polypropylene (PP)

Fig. 2b: atactic polypropylene (PP)

Whether plastics can crystallize depends on their molecular structure. Unbranched molecular chains with no or as few as possible, but regularly arranged side groups crystallize best. Examples of partially crystalline polymers are linear polyethylene (PE), polytetrafluoroethylene (PTFE) or isotactic polypropylene (PP).

Example: In isotactic polypropylene, the CH ₃ side groups are regularly all arranged on one side of the molecular chain (Fig. 2a). This makes it possible for two such chain parts to be superposed on one another in almost all positions. However, there are also polymers in which the side groups are attached to different sides of the chain. If there is also an irregular sequence of side chains (such as in the case of atactic polypropylene in Fig. 2b), the chains only come together if the sequence of the CH ₃ side groups corresponds to the neighboring chain. This makes crystallization much more difficult or even prevented. Atactic polymers only crystallize if the side groups ( substituents ) are very small, as is the case with polyvinyl fluoride .

Similar problems arise with the close parallel arrangement of the chains when larger side groups are present. In principle, the larger the side groups, the worse the polymer crystallizes. Thermosets or elastomers cannot arrange themselves in crystalline form due to the cross-linking of the chains. Even with highly branched polymers such as silicones , a parallel arrangement of the chains is impossible.

The conformation of the macromolecules in the crystal is basically determined by two structures: For example, in polyethylene , polyesters and polyamides, the molecules are in zigzag form according to the bond angle . In polyoxymethylene , polypropylene and isotactic polystyrene molecules have a spiral ( helical ) configuration. The molecules are stabilized by intermolecular forces which, in the case of a helical arrangement, also have an intramolecular effect.

Nucleation

The first crystallites form z. B. as a result of the thermal movements of the molecules, with chains or chain sections being in favorable positions to one another and lying parallel to one another (thermal or homogeneous nucleation ). For thermodynamic reasons, however, further growth is only possible if germs develop that have exceeded a critical minimum size. Otherwise the nuclei that have formed disintegrate again due to thermodynamic instability.

In real melts, however, nucleation due to impurities or unmelted crystals is more common than thermal nucleation . This is also known as heterogeneous nucleation. Processing aids, dyes, fillers or, of course, specially added nucleating agents ( nucleating agents ) can extremely promote the formation of nuclei. Although there has been a lot of work on the subject of nucleating agents, their effectiveness is largely not understood. Nucleating agents that have a major influence on one type of polymer are ineffective on other types of polymer. Many of the good nucleating agents known to date are metal salts of organic acids which are already in crystalline form at the crystallization temperatures of the polymer.

Crystal growth

Fig. 3: Principle of lamella formation during the crystallization of polymers

Fig. 4: Structural units in the formation of crystalline superstructures (spherulites)

Crystal growth occurs through the folded addition of further polymer chain sections (see previous section crystallite formation ). This takes place in a temperature range deep enough below the melting temperature T _m and above the glass transition temperature T _g . If the temperature is too high, the attached chains would be detached again by thermal movements. Below the glass transition temperature, the mobility of the chains is too low and the movement of the molecular chains is frozen.

Intermolecular forces act between the individual, parallel chain sections . Depending on the type of atoms involved, these can be dipole interactions or hydrogen bonds . In addition to the type of interaction, the magnitude of the forces also depends on the distance between the parallel chain sections and determines the mechanical and thermal properties of the polymer.

The crystalline areas prefer to grow in the direction of the greatest temperature gradient (Fig. 3). The side surfaces also act as a nucleus for crystallization; however, the rate of growth is significantly lower here. The amorphous folding arcs are located on the top and bottom of the crystallites, so that no growth can take place in this direction. The directional growth creates long, lamellar bands with high crystallinity, which grow from the crystallization nucleus and are called lamellae (Fig. 4).

The lamellae form the basic building block of further, larger crystalline superstructures. Under largely isotropic, static cooling conditions, spherulites (Fig. 4) are formed, which consist of lamellae arranged in a radial symmetry and are described in more detail in the main article spherulite .

If, on the other hand, there is a strong temperature gradient in the sample, the lamellae are arranged in a largely parallel manner and thus in a directed superstructure known as dendritic. Such structures are z. B. observed with polypropylene in the near-surface edge zones if the mold temperature is chosen relatively cold during injection molding.

Slow-flowing polymers form dumbbell-shaped structures when they cool, which are also described in the literature as so-called shish kebab structures. The inner part (soul) consists of parallel, largely stretched chains, while the dumbbells are made up of folded lamellas.

Components that were cooled very quickly (low mold temperature) did not have enough time to completely crystallize. Recrystallization can occur here at a later point in time (sometimes even over a period of years). During this secondary crystal growth, the mechanical component properties change. Since the chains are more densely packed in the crystalline state, there is also post-shrinkage , i.e. H. to a subsequent decrease in volume. This must be taken into account in the injection molding process.

In some cases, polymers are also stored for a longer time just below the melting point in order to increase their crystallinity. This process, known as annealing , allows the polymer chains to be aligned more closely and also prevents subsequent post-shrinkage during use.

Crystallization by stretching

Crystallization, as described above ( crystallite formation when solidifying from the melt ), is particularly important in the injection molding of plastic components. During the cooling process, the polymer can usually be viewed as a static, relaxed melt.

Fig. 5 Arrangement of the molecular chains after crystallization by stretching

Other conditions arise during extrusion . This method is z. B. used in the production of man-made fibers and plastic films. The polymer is pressed through a nozzle and the molecular chains are slightly pre-oriented.

Post-stretching (application of tensile stress) can significantly increase the orientation of the molecular chains. Fibers are z. B. drawn to a multiple of its original length. The chains are stretched and arranged in an oriented manner. This state corresponds to partial crystallization, with the crystalline areas additionally being aligned. The strength of the fiber in the longitudinal direction is greatly increased. Normally, a subsequent temperature treatment takes place under tension (heat setting ) in order to achieve a higher order and to reduce tension that could lead to subsequent relaxation (shrinkage). As a result, the fiber remains more dimensionally stable. The strong anisotropy of the fiber can also be measured in its optical properties ( birefringence ).

An increase in strength through subsequent stretching is also generated in the stretch-blow molding process. Here, the tempered PET blank (preform) is inflated in a forming process with compressed air to the size specified by the mold. Applications are e.g. B. petrol tanks or PET bottles. At the same time, the gas permeability can be significantly reduced by the biaxial (pointing in two directions) stretching.

Subsequent stretching can also be used to transform polymers that are actually amorphous into partially crystalline materials. Lamellar crystal structures are formed which, due to the strong stretching, do not form any spherulitic superstructures and thus remain completely optically transparent.

Crystallization from solution

Polymers can also be crystallized from solution or by evaporation of a solvent. Solutions are differentiated according to the degree of dilution. In dilute solutions, the molecular chains are not connected to one another and are present as separate polymer coils in the solution. If the concentration of the polymer in the solution is increased (concentrated solution), the chains penetrate each other more and more, and further reduction of the solvent (e.g. by evaporation) leads to an order of the polymer chains to form crystallites. The process largely corresponds to crystallization from the melt.

With the help of high-resolution magnetic nuclear magnetic resonance, only the dissolved portion of a supersaturated polymer solution is recorded. In this way, the decrease in the dissolved fraction during the crystallization from the solution and from this the crystallization rate can be determined.

A special form of crystallization can be observed when a few milliliters of a hot solution of polyethylene in xylene (90 ° C) is poured onto the surface of water at the same temperature. When the solvent evaporates, a thin skin (about 1 micrometer thick) with a honeycomb structure is created. When looking under the polarization microscope , crossed polarization filters show that they are spherulites with negative birefringence in the radial direction. This means: The refractive index is smaller for light oscillating in the radial direction than for the tangential direction of oscillation. In addition to the extinction cross, which is characteristic of spherulites, periodic dark rings are observed as geometric locations for places where the observer looks in the direction of the optical axis . The lamellae that make up the spherulites are twisted around the radius like a screw. When the skin is torn, the lamellae transform into fibers with positive birefringence without any transition.

Skin made of polyethylene, crystallizes at 90 degrees Celsius from a solution in xylene on the surface of water
Spärolithe in a skin made of polyethylene, polarizing microscope
Conversion of lamellae into fibers when a polyethylene skin is torn
Skin made of polyethylene, crystallized at 90 degrees Celsius from a solution in xylene on the surface of water, photo taken with an electron microscope

Crystallinity, degree of crystallinity, degree of crystallization

Polymer type	typical degree of crystallization
Polyamide (PA66 and PA6)	35… 45%
Polyoxymethylene (POM homopolymer)	90%
Polyoxymethylene (POM copolymer)	75%
Polyethylene terephthalate (PET)	30 ... 40%
Polybutylene terephthalate (PBT)	40 ... 50%
Polytetrafluoroethylene (PTFE)	60 ... 80%
Polypropylene (PP), isotactic	70 ... 80%
Polypropylene (PP), syndiotactic	≈ 30 ... 40%
Polypropylene (PP), atactic	≈ 0%
High density polyethylene (PE-HD)	70 ... 80%
Low density polyethylene (PE-LD)	45… 55%

The terms crystallinity, degree of crystallinity and degree of crystallization are used as synonyms in the literature and denote that portion of a partially crystalline solid that is crystalline. In the case of polymers, the degree of crystallization depends on the thermal history of the material.

Typically, degrees of crystallization of 10 to 80% are technically achieved. Achieving higher crystallinities is only possible with low molecular weight materials and / or specially tempered samples. In the first case, this makes the material brittle; in the latter, long storage at temperatures just below the melting point (tempering) means significant costs, which are only worthwhile in special cases. Crystallinities below 10% lead to an excessive tendency to creep if the application temperature of the component is above the glass transition temperature T _g .

The degree of crystallization is usually given as a mass fraction or mole fraction. Occasionally there is also an indication of a volume-related indication of the degree of crystallization.

Most evaluations of key figures for the degree of crystallization for semi-crystalline thermoplastics are based on a two-phase model in which there are perfect crystals and clear amorphous areas. The deviations due to imperfections and transition areas between amorphous and crystalline should be up to a few percent.

The most common methods for determining the degree of crystallization in polymers are density measurement , DSC , X-ray diffraction , IR spectroscopy or NMR . The measured value determined depends on the measurement method used. Therefore, the method should always be specified in addition to the degree of crystallization.

In addition to the above-mentioned integral methods, the distribution of crystalline and amorphous areas can be visualized using microscopic methods (especially polarization microscopy and transmission electron microscopy ).

Density measurements: Crystalline areas are generally more densely packed than amorphous areas. This results in a higher density, which typically differs by up to approx. 15% depending on the material (example polyamides 6: and ). The crystalline density is calculated from the crystalline structure, while the amorphous density is measured experimentally on quenched, amorphous material. The problem with density measurement to determine the density-crystallinity is that the density of the amorphous areas depends on the cooling conditions and the moisture present in the sample can influence the measured value. ${\ displaystyle \ rho _ {c} = 1 {,} 235 \, g / cm ^ {3}}$ ${\ displaystyle \ rho _ {a} = 1 {,} 084 \, g / cm ^ {3}}$ ${\ displaystyle \ rho _ {c}}$ ${\ displaystyle \ rho _ {a}}$

Calorimetry (DSC): When partially crystalline polymers are melted, additional energy must be used to convert the solid crystalline structures into an amorphous liquid state. The analyst speaks here of an endothermic change in enthalpy. The process extends over a wider temperature range. First, the smaller or less regular crystals melt. As the temperature rises, thicker and larger crystallites melt until the entire sample has melted.
The enthalpy of fusion (energy required to melt the crystals) can be measured with the help of dynamic differential calorimetry (DSC) . By comparing it with a literature value for completely crystalline material (degree of crystallization of 100%), the calorimetric degree of crystallization of the sample can be calculated.

X-ray diffraction: Recurring atomic distances generate signals at corresponding angles in the diffractogram . In amorphous substances there are very different distances between the molecular chains. This leads to a very broad distribution in the diagram in the form of a very broad bell curve (halo). The regular arrangements in crystalline areas, on the other hand, produce much narrower distributions in the form of peaks . In diffractograms of real polymers, halos and peaks are superimposed. The intensities of the peaks and the halo can be determined by a peak unfolding and the X-ray crystallinity can be calculated from this.

Infrared spectroscopy (IR): In the IR spectra of crystalline polymers, additional signals ( bands ) are found that are absent in amorphous materials of the same composition. These bands originate from deformation vibrations that are only made possible by the regular arrangement of the molecular chains. The infrared degree of crystallization can be calculated from the evaluation of these bands.

Nuclear Magnetic Resonance Spectroscopy (NMR): Crystalline and amorphous areas differ in their proton mobility. This shows effects in the line shape in the spectrum. Taking the structural model into account, statements about the crystallinity can be made from this.

Properties of partially crystalline polymers

Influence of increasing crystallinity
Properties increase	Properties decrease
Stiffness, modulus	Impact strength
density	strain
Yield stress	Thermal expansion
Chemical resistance	permeability
Glass and melting temperature	Swelling behavior
Abrasion resistance	Mechanical damping
Dimensional stability	Tendency to creep

The technical behavior and properties of plastics are determined by the chemical nature of the basic building blocks, the length, but also the arrangement of the macromolecules.

The crystallization of the macromolecules changes the properties of a material considerably. The properties of a partially crystalline material are determined by both the crystalline and amorphous areas of the polymer. This shows a certain connection with composite materials, which are also made up of several substances. Typical changes in properties with an increase in crystallization are summarized in the adjacent table and are described in more detail below.

Thermal properties

Below their glass transition temperature, amorphous polymer areas have brittle, hard-elastic properties. This is due to the immobility of the frozen chains. If the glass transition temperature (also known as the softening temperature) is exceeded, the molecular chains move against one another, and the typical rubber-elastic properties of the plastic arise. With increasing temperature, the mobility of the chains increases and the material becomes softer. The modulus of elasticity decreases significantly. With constant force acting on the component, a viscoelastic deformation occurs, ie the polymer begins to creep . Amorphous polymers therefore only have heat resistance below the glass transition temperature.

Between the chains of the crystalline areas, intermolecular forces act, which prevent softening. The modulus of elasticity is still relatively high above the glass transition temperature. The crystallites only melt at a significantly higher melting temperature with the addition of significant amounts of energy, which are necessary to overcome the regular arrangement of the chains (melting enthalpy). It is only at this transition to the viscous melt that there is a sharp drop in the modulus of elasticity. Partly crystalline polymers can therefore be used at significantly higher temperatures without the corresponding component changing its dimensions or shape.

In the case of quenched (not condensed) materials, post-condensation can occur, which causes the component to shrink (see section on crystal growth ).

Mechanical properties

The mechanical properties of the polymer are made up of the properties of the crystalline and amorphous areas. The higher the proportion of densely packed crystallites, the harder, but also more brittle, the component becomes. A certain crystallinity is therefore absolutely desirable for the production of plastic objects, since this is responsible for the stability of the plastic. The amorphous areas, on the other hand, are necessary to give the macromolecular materials a certain elasticity and impact strength.

Plastics are viscoelastic materials, which means that the behavior of the material when exposed to external stress is a function of time. With constant load, the deformation increases over time (creeping, retarding). With constant deformation, the stress decreases over time (recovery, relaxation). Stress-strain diagrams are therefore normally included to describe the mechanical properties. A distinction is made between short-term behavior (e.g. tensile test with typical times in the minute range), shock-like loading, behavior with long-term and static loading, as well as oscillating loading.

The plastic deformation of partially crystalline polymers is based on an orientation of the folded crystallites and an 'unwinding' or sliding off of previously folded molecular chains. The unwinding of the chains results in a plastic deformation in the area of the deformation zone in the form of a strong constriction (neck for neck) with simultaneous alignment of the molecular chains in the direction of pull. Stretched materials and thus aligned molecular chains can only be stretched very little. One makes this effect z. B. to use with synthetic fibers. The numerous molecular chains running in the direction of pull reinforce each other and ensure significantly increased strength in the direction of the fibers.

The molecular mass (chain length) also has an influence on the polymer properties. With increasing chain length, the contact areas increase, which leads to an increase in tensile strength and an increase in chemical resistance. At the same time, the number of entanglements increases, which improves the toughness at room temperature, but also has a negative impact on the flow behavior of the melt. If the intermolecular forces become stronger than the chain strength, the tensile strength no longer increases despite the increasing chain length.

Density and permeability

Fig. 7: Change in specific volume with temperature in amorphous and crystalline materials

If heat is withdrawn from a plastic melt, the mobility of the chains is reduced. In the case of amorphous materials, the volume initially reduces largely linearly with temperature. The chains are immobile below the glass transition temperature T _g . The coefficient of thermal expansion changes here, which results in the different slope of the red curve in Figure 7.

In the case of crystalline materials, below the melting temperature T _m there is a regular arrangement of the molecular chains (state of order) and thus a significant reduction in the distance between the chains due to intermolecular forces. This leads to an increase in the density or a reduction in the specific volume (light blue curve in Figure 7).

Due to the closer packing of the chains, gas can be let through more poorly, which leads to a reduction in permeability or, in other words, to an increase in gas tightness.

Optical properties

As a rule, partially crystalline polymers are opaque, i. H. cloudy. This is due to the refraction of light due to the different refractive indices of crystalline and amorphous areas. The degree of cloudiness increases with the crystallinity, but also depends on differences in the refractive index. So is z. B. syndiotactic polypropylene is almost completely transparent, while isotactic polypropylene with a comparable crystallinity of about 50% is highly opaque. This can be explained by the different crystal structure of these two modifications.

The subsequent staining takes place mainly through the amorphous phase. The dye molecules can better penetrate between the molecular chains of the polymer. Materials with a higher degree of crystallization can therefore be stained more poorly than materials with more amorphous areas but otherwise the same composition.

Influence of crystallization on processing properties in injection molding

When injection molding semi-crystalline thermoplastics, it must be ensured that the additional heat released by the crystallization process is dissipated, which increases the cycle time. In addition, the larger change in volume of the material (due to the change in density during crystallization) must be compensated for by longer holding pressure times.

The shrinkage of semi-crystalline thermoplastics is also greater than that of amorphous materials. The cooling conditions must be strictly adhered to, as the cooling process has a lasting effect on the degree of crystallization and thus on the properties of the material and molded part. Very rapid cooling allows the crystallization to be largely suppressed and an almost amorphous solidification to be forced, but in this case post-crystallization occurs over time, which means further shrinkage and warpage.

History and further crystallization models

Fig. 6: Arrangement of polymer chains in the form of fringe micelles

In 1925, Hermann Staudinger found out that certain chemical substances consist of long-chain molecules. X-ray structure examinations showed (depending on the material) diffraction spectra typical of crystals. More detailed investigations have shown that some polymers have to be built up from many small, crystalline structures. With the 'lattice constants' obtained from the X-ray examinations and the known chemical composition, the density of the material was calculated. However, the calculated density was always higher than the experimentally determined density of the polymer.

As a result, Abitz and Gerngroß developed the model of the fringed micelle (Fig. 6). Sections of the molecular chains are arranged parallel to one another as a crystal. The intermediate areas, however, are amorphous. A molecular chain (so the idea) runs through different crystals. After the smallest polymer single crystals were produced for the first time in 1957 , it turned out that the model of the fringed micelle for the description of single crystals could not be maintained. A. Keller postulated in the journal Nature in 1957 the structure of crystallites in the form of the folded molecular chains described above (Fig. 3), which run from one side of the lamella to the other side and back again.

With the contrasting method he developed in 1975, G. Kanig not only made the lamellar structure of polyethylene visible with an electron microscope, but was also able to observe its formation when the material was cooled down from the melt, or its melting when the material was heated.

literature

Bernd Tieke: Macromolecular Chemistry. An introduction. Wiley-VCH, Weinheim 2000. ISBN 978-3-527-29364-3 .
Georg Menges, Edmund Haberstroh, Walter Michaeli , Ernst Schmachtenberg: Materials science, plastics. Hanser Verlag, 2002, ISBN 3-446-21257-4 ( limited preview in Google book search).
Wolfgang Weißbach: Materials science and material testing. Vieweg + Teubner Verlag, 2007, ISBN 3-8348-0295-6 ( limited preview in Google book search).
Friedrich Johannaber, Walter Michaeli : Injection molding manual. Hanser Verlag, 2004, ISBN 3-446-22966-3 ( limited preview in Google book search).
GW Becker, Ludwig Bottenbruch, Rudolf Binsack, D. Braun: Technical thermoplastics. 4. polyamides. Hanser Verlag, 1998, ISBN 3-446-16486-3 ( limited preview in Google book search).
Wilbrand Woebcken, Klaus Stoeckhert, HBP Gupta: Plastic Lexicon. Hanser Verlag, 1998, ISBN 3-446-17969-0 ( limited preview in Google book search).
Michael Dröscher: States of Order in Polymers . In: Chemistry in Our Time . tape 10 , no. 4 , 1976, p. 106-113 , doi : 10.1002 / ciuz.19760100403 .

Individual evidence

↑ ^a ^b ^c ^d Martin Bonnet: Plastics in engineering applications: properties, processing and practical use of polymer materials. Vieweg + Teubner Verlag, 2008, ISBN 3-8348-0349-9 ( limited preview in Google book search).
↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Gottfried W. Ehrenstein: Polymer-Werkstoffe. Hanser Fachbuch, 1999, ISBN 3-446-21161-6 ( limited preview in Google book search).
↑ Andrew Keller: Crystalline Polymers; an Introduction . In: Faraday Discussion of the Royal Society of Chemistry 1979 . tape 68 . Faraday Division of the Royal Society of Chemistry, London 1979, p. 149 (English).
↑ ^a ^b ^c ^d ^e ^f ^g ^h Georg Menges, Edmund Haberstroh, Walter Michaeli , Ernst Schmachtenberg: Material science plastics. Hanser Verlag, 2002, ISBN 3-446-21257-4 ( limited preview in Google book search).
↑ ^a ^b ^c ^d ^e ^f ^g G.W. Becker, Ludwig Bottenbruch, Rudolf Binsack, D. Braun: Technical thermoplastics. 4. polyamides. Hanser Verlag, 1998, ISBN 3-446-16486-3 ( limited preview in Google book search).
↑ ^a ^b ^c ^d Wolfgang Weißbach: Material science and material testing. Vieweg + Teubner Verlag, 2007, ISBN 3-8348-0295-6 ( limited preview in Google book search).
^ Institute for Scientific Film , Klaus Peter Großkurth: Crystallization of Polypropylene, 1990, doi : 10.3203 / IWF / C-1699 (video with explanations on the dendritic crystallization of polypropylene).
↑ ^a ^b Wilbrand Woebcken, Klaus Stoeckhert, HBP Gupta: Kunststoff-Lexikon. Hanser Verlag, 1998, ISBN 3-446-17969-0 ( limited preview in Google book search).
↑ ^a ^b Burkhard Wulfhorst: Textile manufacturing processes. Hanser Verlag, 1998, ISBN 3-446-19187-9 ( limited preview in Google book search).
^ ^A ^b ^c Michael Thielen, Klaus Hartwig, Peter Gust: Blow molding of plastic hollow bodies. Hanser Verlag, 2006, ISBN 3-446-22671-0 , ( limited preview in Google book search).
↑ ^a ^b J. Lehmann: The observation of the crystallization of high polymer substances from the solution by nuclear magnetic resonance . In: Colloid & Polymer Science . tape 212 , no. 2 , 1966, p. 167-168 , doi : 10.1007 / BF01553085 .
↑ Heinz HW Preuß: fracture surface morphology and character of the fracture of polyethylene bodies , dissertation, Leipzig, 1963.
^ MD Lechner, K. Gehrke and EH Nordmeier: Makromolekulare Chemie , 4th edition, Birkhäuser Verlag, p. 355, ISBN 978-3-7643-8890-4 .
↑ Gottfried W. Ehrenstein, Gabriela Riedel, Pia Trawiel: Practice of thermal analysis of plastics. Hanser Verlag, 2003, ISBN 3-446-22340-1 ( limited preview in Google book search).
↑ ^a ^b Walter Michaeli : Introduction to plastics processing. Hanser Verlag, 2006, ISBN 3-446-40580-1 ( limited preview in Google book search).
↑ Joachim Nentwig: plastic films. Hanser Verlag, 2006, ISBN 3-446-40390-6 , ( limited preview in Google book search).
↑ ^a ^b ^c ^d Friedrich Johannaber, Walter Michaeli : Manual injection molding. Hanser Verlag, 2004, ISBN 3-446-22966-3 ( limited preview in Google book search).
^ ^A ^b Hans K. Felger, Hermann Amrehn, Alexander von Bassewitz, Gerhard W. Becker: Polyvinylchlorid. Hanser Verlag, 1986, ISBN 3-446-14416-1 ( limited preview in Google book search).

Web links

Video: Crystallization of Polypropylene . Institute for Scientific Film (IWF) 1988, made available by the Technical Information Library (TIB), doi : 10.3203 / IWF / C-1699 .

This article was added to the list of excellent articles on May 10, 2009 in this version .

[Bonnet-1] Martin Bonnet: Plastics in engineering applications: properties, processing and practical use of polymer materials. Vieweg + Teubner Verlag, 2008, ISBN 3-8348-0349-9 ( limited preview in Google book search).

[Ehrenstein-2] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Gottfried W. Ehrenstein: Polymer-Werkstoffe. Hanser Fachbuch, 1999, ISBN 3-446-21161-6 ( limited preview in Google book search).

[3] Andrew Keller: Crystalline Polymers; an Introduction . In: Faraday Discussion of the Royal Society of Chemistry 1979 . tape 68 . Faraday Division of the Royal Society of Chemistry, London 1979, p. 149 (English).

[Menges-4] ↑ ^a ^b ^c ^d ^e ^f ^g ^h Georg Menges, Edmund Haberstroh, Walter Michaeli , Ernst Schmachtenberg: Material science plastics. Hanser Verlag, 2002, ISBN 3-446-21257-4 ( limited preview in Google book search).

[Becker-5] ↑ ^a ^b ^c ^d ^e ^f ^g G.W. Becker, Ludwig Bottenbruch, Rudolf Binsack, D. Braun: Technical thermoplastics. 4. polyamides. Hanser Verlag, 1998, ISBN 3-446-16486-3 ( limited preview in Google book search).

[Weißbach-6] Wolfgang Weißbach: Material science and material testing. Vieweg + Teubner Verlag, 2007, ISBN 3-8348-0295-6 ( limited preview in Google book search).

[IWF-7] Institute for Scientific Film , Klaus Peter Großkurth: Crystallization of Polypropylene, 1990, doi : 10.3203 / IWF / C-1699 (video with explanations on the dendritic crystallization of polypropylene).

[Woebcken-8] Wilbrand Woebcken, Klaus Stoeckhert, HBP Gupta: Kunststoff-Lexikon. Hanser Verlag, 1998, ISBN 3-446-17969-0 ( limited preview in Google book search).

[Wulfhorst-9] Burkhard Wulfhorst: Textile manufacturing processes. Hanser Verlag, 1998, ISBN 3-446-19187-9 ( limited preview in Google book search).

[Thielen-10] A ^b ^c Michael Thielen, Klaus Hartwig, Peter Gust: Blow molding of plastic hollow bodies. Hanser Verlag, 2006, ISBN 3-446-22671-0 , ( limited preview in Google book search).

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