Hot compaction of polyethylene naphthalate

In this article, we describe the production of single polymer composites from polyethylene naphthalate (PEN) multifilaments by using the hot compaction process. In this process, developed at Leeds University, highly oriented tapes or fibers are processed at a critical temperature such that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the composite. This process is, therefore, a way to produce novel high‐volume fraction polymer/polymer composites where the two phases are chemically the same material. A variety of experimental techniques, including mechanical tests and differential scanning calorimetry, were used to examine the mechanical properties and morphology of the compacted PEN sheets. Bidirectional (0/90) samples were made at a range of compaction temperatures chosen to span the melting range of the PEN multifilaments (268–276°C). Measurement of the mechanical properties of these samples, specifically the in‐plane modulus and strength, allowed the optimum compaction temperature to be ascertained (～ 271°C), and hence, the optimum mechanical properties. The optimum compacted PEN sheets were found to have an initial modulus close to 10 GPa and a strength of just over 200 MPa. The glass transition temperature of the optimum compacted sheets was measured to be 150°C, nearly 40°C higher than compacted poly(ethylene terephthalate) (PET) sheets. In previous work on polypropylene and PET hot compacted materials, it proved instructive to envisage these materials as a composite where the original oriented multifilaments are regarded as the reinforcing phase, and the melted and recrystallized material are regarded as the matrix phase. Dynamic mechanical bending tests (DMTA) were used here to confirm this for PEN. DMTA tests were carried out on the original fibers and on a sample of completely melted material to determine the fiber and matrix properties, respectively. The composite properties were then predicted by using a simple rule of mixtures and this was found to be in excellent agreement with the magnitude and measured temperature dependence of the hot compacted PEN material. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 796–802, 2004     

Solid‐state compaction and drawing of nascent reactor powders of ultra‐high‐molecular‐weight polyethylene

The continuous production of ultra‐high‐molecular‐weight polyethylene (UHMWPE) filaments was studied by the direct roll forming of nascent reactor powders followed by subsequent multistage orientation drawing below their melting points. The UHMWPE reactor powders used in this study were prepared by the polymerization of ethylene in the presence of soluble magnesium complexes, and they exhibited high yield even at low reaction temperatures. The unique, microporous powder morphology contributed to the successful compaction of the UHMWPE powders into coherent tapes below their melting temperatures. The small‐angle X‐ray scattering study of the compacted tapes revealed that folded‐chain crystals with a relatively long‐range order were formed during the compaction and were transformed into extended‐chain crystals as the draw ratio increased. Our results also reveal that the drawability and tensile and thermal properties of the filaments depended sensitively on both the polymerization and solid‐state processing conditions. The fiber drawn to a total draw ratio of 90 in the study had a tensile strength of 2.5 GPa and a tensile modulus of 130 GPa. Finally, the solid‐state drawn UHMWPE filaments were treated with O₂ plasma, and the enhancement of the interfacial shear strength by the surface treatment is presented. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 718–730, 2005     

The development of morphology during hot compaction of Tensylon high-modulus polyethylene tapes and woven cloths

The development of morphology in tapes and woven cloths of oriented melt-spun Tensylon polyethylene has been studied both before and after hot compaction over a range of temperatures below and above the optimum. For both the unidirectional fibres and the woven cloths, the optimum temperature was found to be where approximately 30% of the original structure was lost which, for Tensylon tapes, was ∼2 K below the point of major crystalline melting, giving a processing window roughly twice as wide as for other previously studied polyethylene materials. Transverse sections show a two-component morphology after etching of cratered ribbons emerging from a flat, relatively featureless landscape. This morphology disappears at the highest temperature studied when the longitudinal morphology consists of oriented walls from which transcrystalline units have grown during cooling. Morphological comparison with other polyethylenes and their compactions places Tensylon behaviour alongside Dyneema, Spectra and Tekmilon rather than the melt-spun Certran.     

Crystallization and melting behavior in syndiotactic polypropylene: Origin of multiple melting phenomenon

The melting behavior of syndiotactic polypropylene (s‐PP) after isothermal crystallization from the melt state was studied using differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) techniques. Three melting endotherms were observed for isothermal crystallization at high degrees of undercooling. The minor endotherm, located closed to the corresponding crystallization temperature, was postulated to be the melting of the secondary crystallites formed at the crystallization temperature. The low‐temperature melting peak was found to be the melting of the primary crystallites formed, and the high‐temperature melting peak was a result of the melting of the crystallites recrystallized during a heating scan. The triple‐melting behavior observed in subsequent melting endotherms of s‐PP was therefore described as contributions from melting of the secondary crystallites and their recrystallization, partial melting of the less stable fraction of the primary crystallites and their recrystallization, melting of the primary crystallites, and remelting of the recrystallized crystallites formed during the heating scan. In addition, determination of the equilibrium melting temperature for this s‐PP resin according to the linear and nonlinear Hoffman–Weeks extrapolations provided values of 143.1 and 185.6°C, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1083–1097, 2001     

Technique development and measurement of Poisson's ratio,lateral creep behavior,and thermal and hygroscopic expansion of individual layers in magnetic tapes

An experimental technique was developed to measure the Poisson's ratio (lateral contraction over longitudinal elongation), lateral creep, and both thermal and hygroscopic expansion of thin polymeric films. A so‐called profile‐matching method was developed to measure the lateral and longitudinal deformation with the help of a laser scan micrometer. A thermomechanical analyzer was used to measure the coefficient of thermal expansion (CTE). The laser scan technique was also used to measure the coefficient of hygroscopic expansion (CHE). The measurements were performed on magnetic tapes, substrates, and tapes with front coat or back coat, or with both coats stripped. A model based on the rule of mixtures was developed to determine the Poisson's ratio, lateral and longitudinal deformation behavior, and thermal expansion of the front coat and back coat. To investigate the mechanical degradation of the substrates during tape manufacturing, the data for substrate with the front and back coats removed from the tape, were compared with the data for the never‐coated virgin film. The relationship between the molecular structure and the degradation mechanism of the substrates is discussed. The magnetic tapes used in this research include two metal particle (MP) tapes and two metal evaporated (ME) tapes that use polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) substrates. Longitudinal and lateral deformation tests were performed at 25 ± 0.5°C and 50 ± 2%RH, and thermal expansion was measured from 15 to 70°C. The CHE was measured at 25 ± 0.5°C and 15–80%RH. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2082–2096, 2003     

Study of multiple melting behaviour of syndiotactic polystyrene in β‐crystalline form

A series of syndiotactic polystyrene (SPS) samples in β‐crystalline form were prepared by cooling from the melt at various rates. The effects of cooling rate from the melt, DSC heating rate and annealing on the multiple melting behaviours of β crystals were investigated by differential scanning calorimetry (DSC) and temperature modulated differential scanning calorimetry (TMDSC), from which the nature of the multiple melting behaviour was determined. The two melting endotherms of β‐form crystals were considered to arise from the occurrence of simultaneous melting, recrystallization and remelting processes in the melting region. It is suggested that the lower melting endotherm is due to the melting of imperfect β crystals originally present in the sample, whereas the higher melting endotherm comes from the melting of recrystallized SPS crystals, ie more perfect β crystals that formed during the DSC scanning process. © 2000 Society of Chemical Industry     

Study of modified polypropylene nonwoven cloth. I. graft copolymerization of 4‐vinylpyridine onto polypropylene nonwoven cloth by preirradiation method

Polypropylene (PP) nonwoven cloth was grafted with 4‐vinylpyridine (4‐VP) by a preirradiation method. The effects of preirradiation conditions on the mechanical properties of preirradiated PP nonwoven cloth and the percentage of grafting (Pg) of 4‐VP onto the preirradiated PP nonwoven cloth were systematically investigated. The results indicated that the mechanical properties of preirradiated PP nonwoven cloth decreased with increasing irradiation dose and that the Pg was greatly affected by the concentration of monomer, irradiation dose, grafting reaction temperature, and the addition of inhibitor and inorganic acid in the grafting reaction system. The grafted nonwoven cloth samples were characterized using IR spectroscopy and SEM. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1861–1868, 2000     

Hot compaction of woven nylon 6,6 multifilaments

We describe a study of the hot compaction of woven nylon 6,6 multifilaments produced by a patented procedure, developed at the University of Leeds, for creating novel single‐polymer composites. In this process, an assembly of oriented elements, often in the form of a woven cloth, is held under pressure and taken to a critical temperature so that a small fraction of the surface of each oriented element is melted, which on cooling recrystallizes to form the matrix of the single‐polymer composite. This process is therefore a way of producing novel high‐volume‐fraction polymer/polymer composites in which the two phases are chemically the same material. Nylon is an obvious candidate material for this process because oriented nylon multifilaments are available on a commercial scale. The aim of this study was first to establish the conditions of temperature and pressure for the successful hot compaction of oriented nylon 6,6 fibers and second to assess the mechanical properties of the manufactured hot‐compacted nylon sheets. A crucial aspect of this work, not previously examined in hot‐compaction studies of other oriented polymers, was the sensitivity of the properties to absorbed water, with a significant change in the properties measured immediately after hot‐compaction processing and 2 weeks later when 2% water had been absorbed by the compacted nylon sheets. As expected, the water uptake had a greater effect on those properties that depended on local chain interactions (e.g., the modulus and yield strength) and less effect on those properties that depended on the large‐scale properties of the molecular network (e.g., strength). The only negative aspect of the properties of the hot‐compacted nylon sheets was the elevated‐temperature performance of the wet sample, with the modulus falling to a very low value at a temperature of 80°C. However, apart from the elevated‐temperature performance, the majority of the measured properties of the hot‐compacted nylon sheets were comparable to those of hot‐compacted polypropylene and poly(ethylene terephthalate). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 991–997, 2006     

Crystallization of low‐density polyethylene‐ and linear low‐density polyethylene‐rich blends

The crystallization of a series of low‐density polyethylene (LDPE)‐ and linear low‐density polyethylene (LLDPE)‐rich blends was examined using differential scanning calorimetry (DSC). DSC analysis after continuous slow cooling showed a broadening of the LLDPE melt peak and subsequent increase in the area of a second lower‐temperature peak with increasing concentration of LDPE. Melt endotherms following stepwise crystallization (thermal fractionation) detailed the effect of the addition of LDPE to LLDPE, showing a nonlinear broadening in the melting distribution of lamellae, across the temperature range 80–140°C, with increasing concentration of LDPE. An increase in the population of crystallites melting in the region between 110 and 120°C, a region where as a pure component LDPE does not melt, was observed. A decrease in the crystallite population over the temperature range where LDPE exhibits its primary melting peaks (90–110°C) was noted, indicating that a proportion of the lamellae in this temperature range (attributed to either LDPE or LLDPE) were shifted to a higher melt temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1009–1016, 2000     

The use of an interleaved film for optimising the properties of hot compacted polyethylene single polymer composites

It is shown that the incorporation of interleaved films has major advantages for the production of polyethylene single polymer composites by the process of selective melting (termed hot compaction). The key issue is to choose a compaction temperature which melts the minimum amount of the original oriented elements whilst achieving acceptable bonding within the compacted structure. Utilising an interleaved film, excellent interlayer peel strengths can be achieved at lower compaction temperatures giving greater retention of the oriented fraction of the original fibres or tapes and a wider processing window. For example, using a very high modulus, ultra-high molecular weight, polyethylene tape, together with an interleaved film, resulted in an in-plane modulus of 25 GPa, an in-plane strength of 500 MPa, and an interlayer strength of >10 N/10 mm. These are amongst the highest values reported for a single polymer composite. Other important factors have been investigated including fabric weave style and whether it is better to use fibres or tapes as the oriented reinforcement.     

Melting and crystallization behaviors of injection‐molded polypropylene

The melting and crystallization behaviors of the skin layer in an injection‐molded isotactic polypropylene (PP) have been studied, mainly in comparison with those of the core layer and subsidiarily in comparison with those of a compression‐molded PP and a nucleator (talc)–added PP. The skin layer contains about 5% crystals, which have a high melting point of up to 184°C. They thermally vanish by melting once. The subsequent melting history will scarcely affect the melting behaviors. On the other hand, crystallization behaviors are strongly affected by the melting history. The skin layer crystallizes in a wide temperature range at high temperature. This tendency weakens with increasing melting temperature, approaching a constant and that of the core layer above 230°C, which suggests that the memory effect of the residual structure of PP vanishes by melting above 230°C. In explaining these experimental results, it is assumed that the residual structure substance is a melt orientation of molecular chains that works as crystallization nuclei and that the vanishing of the residual structure is nothing but a relaxation of the melt orientation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1751–1762, 2000     

The morphological properties of PP coextruded tape fabrics

In the field of self‐reinforced composites many researchers have focused their attention on the coextruded tapes composed of polypropylene core and PP/PE copolymer skin. Two similar commercial fabrics (P and T) have been compared in respect of their peel resistance. For both materials, peel resistance has a periodic trend that regularly follows fabric weave style. T has demonstrated an average peel resistance and a well‐bonded area slightly greater than P. Skin/core interfacial properties have been investigated and a crosscheck between differential scanning calorimetry (DSC) and Raman spectroscopy has been adopted to understand the influence of skin structure on consolidated laminate. DSC curves exhibit three melting peaks during first heating for both fabrics, corresponding to copolymer, skin/core interface, and core melting. After consolidation at 140°C stretching‐induced superstructure and PP crystallinity degree are preserved. The presence of PP/PE copolymer + PE blend only in fabric P has been pointed out and PE content has been calculated. POLYM. ENG. SCI., 56:727–734, 2016. © 2016 Society of Plastics Engineers     

Effect of melting temperature,coupling agent,and width on properties of ABS+20%PC/al flake‐metallized plastics

Effects of different melting temperatures (270 and 210°C), Al flake widths (0.5 and 0.8 mm), and coupling agents (gamma aminopropyl triethoxy silane A1100 and gamma glycidoxy propyl trimethoxy silane A‐187) on the properties of ABS+20%PC/Al flake‐metallized plastics are discussed. According to experiments, it is found that the aspect ratio is larger with the 270°C melting temperature and 0.8 mm Al flake, but declines with the A‐187 coupling agent. The 0.5 mm Al flakes treated with the A‐1100 coupling agent at 270°C melting temperature has better distribution in the matrix and EMI shielding effectiveness, but has a lower volume resistance. With 0.8 mm Al flakes at 210°C melting temperature, and treatment with the A‐1100 coupling agent, it produces larger ultimate tensile strength and impact strength. There is no relation between HDT and melting temperatures, Al flake widths, or coupling agents. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1902–1909, 2000     

On the overdrawing of melt‐spun isotactic polypropylene tapes

The morphology and mechanical properties of melt‐spun and post‐drawn isotactic polypropylene (iPP) tapes have been studied in order to examine their dependence on the post‐draw ratio applied. Special attention is focused on the characterization of the so‐called overdrawing behavior of the tapes; at a certain draw ratio, a change of the optical appearance of the tape from transparent to opaque is observed. Overdrawing is accompanied with changes in the mechanical properties, surface, and morphology of the tapes. For post‐draw ratios without overdrawing, and for highly overdrawn tapes, the variation in the mechanical properties measured is very small, but for slightly overdrawn tapes, a large scattering of mechanical properties has been measured. In the latter case, this behavior is related to the start of internal delamination of the tapes during post drawing. It is shown that strongly overdrawn tapes have excellent mechanical properties, in particular, high specific stiffness and strength. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2920–2931, 2007     

The incorporation of carbon nanofibres to enhance the properties of self reinforced, single polymer composites

This paper describes the incorporation of carbon nanofibres (CNF) into polypropylene (PP) single polymer composites, materials where both the reinforcing phase and the matrix phase are PP. The CNF/PP composites were produced from an assembly of highly oriented tapes. The process of making the composites involves heating the tapes to a critical temperature such that a small fraction of the surface of each tape is melted; on cooling this recrystallises to form the matrix of the composite. The production of the composites required optimisation of three stages; incorporation of CNF into PP tapes, orientation of CNF/PP tapes by tensile drawing and hot compaction of the tapes. Results are presented to describe the research and findings in each of these key stages.Preliminary studies showed that the introduction of small amounts of carbon nanofibres (CNF) significantly improved the properties of isotropic PP. For example, 5% volume addition of CNF gave a 60% increase in the room temperature Young's modulus and a reduction of 35% in the thermal expansion coefficient. Moreover, the percentage enhancement of properties was greater at high temperatures where the stiffness of the PP is much reduced. These results can be very well understood in terms of conventional composite modelling.In unidirectional CNF/PP hot compacted composites the major improvements in mechanical behaviour are in the direction transverse to the orientation direction, where the CNF can make a proportionately greater contribution to the properties, and as shown by dynamic mechanical behaviour, this is most marked at high temperatures. Composite modelling based on uniform strain with appropriate allowance for the CNF aspect ratio predicts the behaviour extremely well. A very interesting result is that the peel strength of composites produced by hot compaction of woven CNF/PP shows a four-fold increase over woven PP composites and this is increased by another factor of two by the addition of a maleic anhydride compatibiliser. A further interesting result, of some practical significance, is that although the incorporation of CNF into PP causes voiding and some loss of molecular orientation during drawing, the hot compaction process closes and seals the voids, so that the original PP density is recovered.     

Mechanical,hygroscopic, and thermal properties of metal particle and metal evaporated tapes and their individual layers

Mechanical and thermal properties of magnetic tapes and their individual layers strongly affect the tribology of magnetic head–tape interface and reliability of tape drives. Dynamic mechanical analysis, longitudinal creep, lateral creep, Poisson's ratio, the coefficient of hygroscopic expansion (CHE), and the coefficient of thermal expansion (CTE) tests were performed on magnetic tapes, tapes with front coat or back coat removed, substrates (with front and back coats removed), and never‐coated virgin films of the substrates. Storage modulus and loss tangent values were obtained at a frequency range from 0.016 to 28 Hz, and at a temperature range from ?50 to 150 or 210°C. Longitudinal creep tests were performed at 25°C/50% RH, 40°C/25% RH, and 55°C/10% RH for 50 h. The Poisson's ratio and lateral creep were measured at 25°C/50% RH. CHE was measured at 25°C/15–80% RH. CTE values of various samples were measured at a temperature range from 30 to 70°C. The tapes used in this research included two magnetic particle (MP) tapes and two metal evaporated (ME) tapes that were based on poly(ethylene terephthalate) and poly(ethylene naphthalate) substrates. The master curves of storage modulus and creep compliance for these samples were generated for a frequency range from 10^?20 to 10¹⁵ Hz. The effect of tape manufacturing process on the various mechanical properties of substrates was analyzed by comparing the data for the substrates (with front and back coats removed) and the never‐coated virgin films. A model based on the rule of mixtures was developed to determine the storage modulus, complex modulus, creep compliance, and CTE for the front coat and back coat of MP and ME tapes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1319–1345, 2004     

Effect of short chain‐branching distribution on crystallinity and modulus of metallocene‐based ethylene–butene copolymers

In this article, the short chain‐branching distribution (SCBD) of some metallocene‐based ethylene–butene copolymers was evaluated by DSC, and some conventional ethylene copolymers were also studied for the purpose of comparison. It is found that metallocene‐based ethylene copolymers have a relative narrower SCBD. These copolymers were crystallized under different modes, and the crystallinity and initial modulus of them were examined. The metallocene‐based ethylene copolymers contain less interfacial regions, and the melting temperatures of them decrease more rapidly with the decrease of density than those of conventional ethylene copolymers. Moreover, the metallocene‐based and conventional ethylene copolymers of similar density have close initial modulus when they are quenched or annealed at 100°C, but conventional ethylene copolymers show higher initial modulus when stepwise crystallized from 120°C. These differences in crystallinity and initial modulus were explained based on their differences in short‐chain branching distributions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1709–1715, 2000     

Investigation on the interaction between polyamide and lithium salts

FTIR spectroscopy and thermal analysis were applied to study the nylon 6–lithium salt systems. The DTA results show that lithium ions cause a significant reduction of the melting point of nylon–lithium salt samples. In addition, lithium salts can also prevent the crystallization of molten nylon in the cooling process. Temperature‐variable FTIR spectroscopy demonstrates that stronger hydrogen bonds form when nylon–lithium halide is molten. Such stronger hydrogen bonds in molten nylon lithium systems may account for the reduction of the melting point and delaying the crystallization of the amorphous nylon. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2685–2690, 2000     

Further study on double‐melting endotherms of isotactic polypropylene

The origins of the single‐ and double‐melting endotherms of isotactic polypropylene crystallized at different temperatures were studied carefully by differential scanning calorimetry, wide‐angle X‐ray diffraction, and small‐angle X‐ray scattering. The experimental data show that spontaneous crystallization occurs when the crystallization temperature is lower than 117°C; thus the lamellae formed are imperfect. At a lower heating rate, the recrystallization or reorganization of these imperfect lamellae leads to double endotherms. On the other hand, when the crystallization temperature is higher than 136°C, two major kinds of lamellae with different thickness are developed during the isothermal process, which also results in the double‐melting endotherms. In the intermediate temperature range the lamellae formed are perfect, and there is only a single peak in the distribution of lamellar thickness. This explains the origin of the single‐melting endotherm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 163–170, 2000     

Crystallization and melting behavior of blends comprising poly(3‐hydroxy butyrate‐co‐3‐hydroxy valerate) and poly(ethylene oxide)

Blends of poly(3‐hydroxy butyrate‐co‐3‐hydroxy valerate) (PHBV) and poly(ethylene oxide) (PEO) were prepared by casting from chloroform solutions. Crystallization kinetics and melting behavior of blends have been studied by differential scanning calorimetry and optical polarizing microscopy. Experimental results reveal that the constituents are miscible in the amorphous state. They form separated crystal structures in the solid state. Crystallization behavior of the blends was studied under isothermal and nonisothermal conditions. Owing to the large difference in melting temperatures, the constituents crystallize consecutively in blends; however, the process is affected by the respective second component. PHBV crystallizes from the amorphous mixture of the constituents, at temperatures where the PEO remains in the molten state. PEO, on the other hand, is surrounded during its crystallization process by crystalline PHBV regions. The degree of crystallinity in the blends stays constant for PHBV and decreases slightly for PEO, with ascending PHBV content. The rate of crystallization of PHBV decreases in blends as compared to the neat polymer. The opposite behavior is observed for PEO. Nonisothermal crystallization is discussed in terms of a quasi‐isothermal approach. Qualitatively, the results show the same tendencies as under isothermal conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2776–2783, 2006