Yes / Polypropylene has been oriented by solid-phase deformation processing to draw ratios up to ∼16, increasing tensile stiffness along the draw direction by factors up to 12. Nanoindentation of these materials showed that moduli obtained for indenter tip motion along the drawing direction (3) into to 1–2 plane (axial indentation) were up to 60% higher than for indenter tip motion along the 2 direction into the 1–3 plane (transverse indentation). In static tests, tensile and compressive determinations of elastic modulus gave results differing by factors up to ∼5 for strain along the draw direction. A material model incorporating both orthotropic elasticity and tension/compression asymmetry was developed for use with Finite Element simulations. Elastic constants for the oriented polypropylene were obtained by combining static testing and published ultrasonic data, and used as input for nanoindentation simulations that were quantitatively successful. The significance of the tension/compression asymmetry was demonstrated by comparing these predictions with those obtained using tensile data only, which gave predictions of indentation modulus higher by up to 70%.

Yes / Highly oriented long-chain-branched poly (lactic acid) (LCB-PLA) was prepared and the structure evolution was studied in the process of solid die drawing by compared with poly (lactic acid) (PLA). During drawing, samples underwent not only die drawing process but also free drawing process. Drawing speed presented a prominent effect on the free drawing process, while die thickness showed a more obvious influence on the die drawing process. For PLA, free drawing process mainly contributed to its final orientation degree and crystallinity, and thus the mechanical properties of PLA were greatly influenced by drawing speed. However, for LCB-PLA, die drawing process made a greater contribution to the final orientation degree and crystallinity, and its mechanical properties were mainly affected by die thickness. Under the same drawing condition, the tensile strength and modulus of LCB-PLA were always higher than those of PLA, and reached up to 228 MPa and 7.2 GPa, respectively, which basically met the requirement for born fixation materials. Samples which only underwent die drawing showed obvious “sandwich” structure, and the thickness of the oriented skin layer for LCB-PLA was thicker than that for PLA, suggesting that shear-induced orientation can be easily retained due to the enhanced entanglement between long branched chains. After drawing, LCB-PLA samples showed smaller lamellae size (Llateral) but larger long period (Lac) compared with PLA, suggesting that the low chain mobility restricted the motion of chain slipping of LCB-PLA and thus resulted in the fragmentation of neighboring crystal lamella by chain stretched-out.

Yes / Cavitation is an important phenomenon in solid-phase deformation of polymers, which either has potential adverse effects on physical properties or creates potential opportunities for new properties. In either case, it needs to be better understood to help achieve better control of cavitation and its effects. Cavitation associated with solid-phase deformation in a β-nucleated isotactic polypropylene was found to depend on the solid-phase deformation route employed. Compared with samples obtained by free tensile stretching, cavitation was suppressed in samples deformed via die-drawing, although an almost identical β-to α-phase transition was observed for both deformation routes. Even when die-drawn samples were subsequently deformed to large strains by free stretching, there was still no comparable cavitation compared with the single free tensile-stretching route. The die-drawing process appears to suppress cavitation by fundamentally diminishing the number of growable nuclei of cavities, rather than merely hindering the growth of cavities. A relationship between cavitation intensity and the fractions of lamellae along specific directions has been established. During subsequent free stretching of die-drawn samples, newly created cavities were suggested to be initiated within the crystalline layers. The reduction of the cavity nuclei in the die-drawing process originated from the stabilization of the connections between the crystalline blocks within the lamellae. / This work is supported by the National Natural Science Foundation of China (21704102 and 51525305), Newton Advanced Fellowship of the Royal Society, United Kingdom (NA 150222) and ExxonMobil.

Yes / The morphology distribution of isotactic-polypropylene (iPP) shaped through a die during hot stretching process was investigated via wide-angle X-ray diffraction technique. The evolution of micro-structures in the outer layer (layer closer to the die wall) and the inner layer (layer in the center of die) of die-drawn iPP were both recorded. It turned out that the difference of morphology distribution between outer and inner layers changes with the distance from the die entrance to exit. In general, a larger difference between outer and inner layers could be found at the intermediate deformation region inside the die while such difference disappeared at both of the entrance and exit regions of die. These behaviors could be interpreted as a result of the existence of a heterogeneous distribution of force field inside the die, which was caused by the die geometry and inclination of the drawing force. This work showed that the heterogeneous force field inside the die could be revealed through analyzing the morphology of a die-drawn sample.

Yes / The isotactic polypropylene (iPP) usually shows a unique parent-daughter lamellae structure in which the parent and daughter lamellae are against each other with a near perpendicular angle (80° or 100°). Inducing a high fraction of oriented cross-hatched structure in iPP during processing is desirable for designing the bi-oriented iPP products. We processed a commercial iPP via tensile-stretching and die-drawing to evaluate the structural evolution of oriented parent-daughter lamellae. It turned out that the die-drawing process had an advantage in attaining a high fraction of oriented cross-hatched structure of iPP, as compared to the free tensile stretching. Besides, the presence of α-nucleating agents affected the formation of oriented parent-daughter lamellae in the die-drawn samples whereas such influence diminished in the free stretched ones. It was found that the confined deformation inside the die led to the well-preserved oriented cross-hatched structure in the die-drawn iPP. / This work was financially supported by the National Natural Science Foundation of China (Nos. 21704102, U1832186, and 51525305), Newton Advanced Fellowship of the Royal Society, United Kingdom (No. NA150222) and ExxonMobil Asia Pacific Research & Development Co., Ltd.

As a preliminary starting point for the present study, physical and mechanical properties of polypropylene nanocomposites (PPNCs) for samples received from Queen's University Belfast have been evaluated. Subsequently, polymer/clay nanocomposite material has been produced at Bradford. Mixing and processing routes have been explored, and mechanical properties for the different compounded samples have been studied. Clay intercalation structure has received particular attention to support the ultimate objective of optimising tensile and fracture behaviour of isotropic and die-drawn PPNCs. Solid-state molecular orientation has been introduced to PPNCs by the die-drawing process. Tensile stress-strain measurements with video-extensometry and tensile fracture of double edge-notched tensile specimens have been used to evaluate the Young's modulus at three different strain rates and the total work of fracture toughness at three different notch lengths. The polymer composite was analyzed by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, wide angle x-ray diffraction, and transmission electron microscopy. 3% and 5% clay systems at various compatibilizer (PPMA) loadings were prepared by three different mixing routes for the isotropic sheets, produced by compression moulding, and tensile bars, produced by injection moulding process. Die-drawn oriented tensile bars were drawn to draw ratio of 2, 3 and 4. The results from the Queen's University Belfast samples showed a decrement in tensile strength at yield. This might be explained by poor bonding, which refers to poor dispersion. Voids that can be supported by intercalated PP/clay phases might be responsible for improvement of elongation at break. The use of PPMA and an intensive mixing regime with a two-step master batch process overcame the compatibility issue and achieved around 40% and 50% increase in modulus for 3% and 5% clay systems respectively. This improvement of the two systems was reduced after drawing to around 15% and 25% compared with drawn PP. The work of fracture is increased either by adding nanoclay or by drawing to low draw ratio, or both. At moderate and high draw ratios, PPNCs may undergo either an increase in the size of microvoids at low clay loading or coalescence of microvoids at high clay loading, eventually leading to an earlier failure than with neat PP. The adoption of PPMA loading using an appropriate mixing route and clay loading can create a balance between the PPMA stiffness effect and the degree of bonding between clay particles and isotropic or oriented polymer molecules. Spherulites size, d-spacing of silicate layers, and nanoparticles distribution of intercalated microtactoids with possible semi-exfoliated particles have been suggested to optimize the final PPNCs property.

The feasibility of using oriented polymer technology in the design and manufacture of mechanical power transmission belts has been investigated. Working from an initial selection of polymers a die-drawing technique for orienting the polymers was devised, and the static and dynamic mechanical properties of the oriented polymers were investigated. These results indicated that PP, PBT, PPS and PEEK were suitable for further research. Of these 4 materials PBT was selected as the most appropriate material for belt manufacture based on cost, processability (drawing temperature, natural draw ratio) and limitations of laboratory equipment. A technique based on free-tensile drawing combined with simultaneous rotational motion was designed and used to manufacture oriented PBT flat belts from cylindrical injection moulded preforms. The technique used a tensile machine with two pulley-clamps, a fitted heated chamber and an electric motor to provide rotational motion to the belt during drawing. Two types of oriented PBT flat belts with different cross sections were produced successfully, termed 'thick' and 'thin'. These belts were tested on a purpose-built rig comprising two equal diameter pulleys, one driven by an electric motor and the other connected to a generator to provide load. The belt life and power transmission performance was investigated at various conditions of speed, transmitted torque and tension, and the results indicated that despite their smaller cross section 'thin' flat belts demonstrated up to 3 times longer life. However life was only 100hours, which was very low compared with conventional flat belts that last for many thousands of hours at higher speeds and much greater power transmission capacity. Synchronous belts were then produced through the same manufacturing method used for flat belts. This aspect of the research concentrated on the initial pitch design and size, i.e. the timing. Initially a rectangular tooth profile was selected for its simplicity in terms of manufacture. The produced belts exhibited high pitch length variation as well as deformed teeth and were not usable for synchronous power transmission. An extra timing feature was included to control orientation; reducing the pitch length variation enabling consistent tooth production. It was observed that the areas between the extra timing feature and the tooth edges did not orient completely with some regions remaining undrawn. Finite Element Analysis (FEA) was used to predict the drawing behaviour of different shapes and dimensions of the timing features. The results suggested that a 4mm wide and 7mm long slot provided the highest possible extension and the minimum non-oriented regions on the groove. Whilst, the thickness and width of the drawn belt timing features showed differences to the FEA predictions, manufactured synchronous belts based on that design had much better controlled dimensions and the lowest achieved pitch length variation ( ±1%), compared to initial attempts. It is concluded that oriented polymers have the potential to be used in power transmission belts since they offer higher stiffness, tensile strength and creep resistance compared with isotropic polymers that are currently used in commercially available belts such as thermoplastic polyurethane (TPU) and polyvinyl chloride (PVC). The main disadvantages were the lack of dimensional stability and number of cycle to failure.

The aim of work is to present and analyse assessment of the current state and at the same time the proposal of adjustments to the technology or parameters, the introduction of the wire into the drawing machine. The problem arises when the introduction of wire with a diameter of 14 mm from the material CK 67 to the drawbenches Schumag. If we introduce the wire into the drawing machines with two primary beams leads to a buckling of the wire and pack between the drawing die and the boot device. For the introduction of wire are used hydraulic boot collets, which are controlled semi-automatically. In connection with professional studies and on the basis of the calculation, simulation and practical experiment have been identified the conditions allowing the current method of deployment of wire to use.

As a preliminary starting point for the present study, physical and mechanical properties of polypropylene nanocomposites (PPNCs) for samples received from Queen's University Belfast have been evaluated. Subsequently, polymer/clay nanocomposite material has been produced at Bradford. Mixing and processing routes have been explored, and mechanical properties for the different compounded samples have been studied. Clay intercalation structure has received particular attention to support the ultimate objective of optimising tensile and fracture behaviour of isotropic and die-drawn PPNCs. Solid-state molecular orientation has been introduced to PPNCs by the die-drawing process. Tensile stress-strain measurements with video-extensometry and tensile fracture of double edge-notched tensile specimens have been used to evaluate the Young¿s modulus at three different strain rates and the total work of fracture toughness at three different notch lengths. The polymer composite was analyzed by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, wide angle x-ray diffraction, and transmission electron microscopy. 3% and 5% clay systems at various compatibilizer (PPMA) loadings were prepared by three different mixing routes for the isotropic sheets, produced by compression moulding, and tensile bars, produced by injection moulding process. Die-drawn oriented tensile bars were drawn to draw ratio of 2, 3 and 4. The results from the Queen's University Belfast samples showed a decrement in tensile strength at yield. This might be explained by poor bonding, which refers to poor dispersion. Voids that can be supported by intercalated PP/clay phases might be responsible for improvement of elongation at break. The use of PPMA and an intensive mixing regime with a two-step master batch process overcame the compatibility issue and achieved around 40% and 50% increase in modulus for 3% and 5% clay systems respectively. This improvement of the two systems was reduced after drawing to around 15% and 25% compared with drawn PP. The work of fracture is increased either by adding nanoclay or by drawing to low draw ratio, or both. At moderate and high draw ratios, PPNCs may undergo either an increase in the size of microvoids at low clay loading or coalescence of microvoids at high clay loading, eventually leading to an earlier failure than with neat PP. The adoption of PPMA loading using an appropriate mixing route and clay loading can create a balance between the PPMA stiffness effect and the degree of bonding between clay particles and isotropic or oriented polymer molecules. Spherulites size, d-spacing of silicate layers, and nanoparticles distribution of intercalated microtactoids with possible semi-exfoliated particles have been suggested to optimize the final PPNCs property. / SABIC

The feasibility of using oriented polymer technology in the design and manufacture of mechanical power transmission belts has been investigated. Working from an initial selection of polymers a die-drawing technique for orienting the polymers was devised, and the static and dynamic mechanical properties of the oriented polymers were investigated. These results indicated that PP, PBT, PPS and PEEK were suitable for further research. Of these 4 materials PBT was selected as the most appropriate material for belt manufacture based on cost, processability (drawing temperature, natural draw ratio) and limitations of laboratory equipment. A technique based on free-tensile drawing combined with simultaneous rotational motion was designed and used to manufacture oriented PBT flat belts from cylindrical injection moulded preforms. The technique used a tensile machine with two pulley-clamps, a fitted heated chamber and an electric motor to provide rotational motion to the belt during drawing. Two types of oriented PBT flat belts with different cross sections were produced successfully, termed 'thick' and 'thin'. These belts were tested on a purpose-built rig comprising two equal diameter pulleys, one driven by an electric motor and the other connected to a generator to provide load. The belt life and power transmission performance was investigated at various conditions of speed, transmitted torque and tension, and the results indicated that despite their smaller cross section 'thin' flat belts demonstrated up to 3 times longer life. However life was only 100 hours, which was very low compared with conventional flat belts that last for many thousands of hours at higher speeds and much greater power transmission capacity. Synchronous belts were then produced through the same manufacturing method used for flat belts. This aspect of the research concentrated on the initial pitch design and size, i. e. the timing. Initially a rectangular tooth profile was selected for its simplicity in terms of manufacture. The produced belts exhibited high pitch length variation as well as deformed teeth and were not usable for synchronous power transmission. An extra timing feature was included to control orientation; reducing the pitch length variation enabling consistent tooth production. It was observed that the areas between the extra timing feature and the tooth edges did not orient completely with some regions remaining undrawn. Finite Element Analysis (FEA) was used to predict the drawing behaviour of different shapes and dimensions of the timing features. The results suggested that a 4mm wide and 7mm long slot provided the highest possible extension and the minimum non-oriented regions on the groove. Whilst, the thickness and width of the drawn belt timing features showed differences to the FEA predictions, manufactured synchronous belts based on that design had much better controlled dimensions and the lowest achieved pitch length variation ( ±1%), compared to initial attempts. It is concluded that oriented polymers have the potential to be used in power transmission belts since they offer higher stiffness, tensile strength and creep resistance compared with isotropic polymers that are currently used in commercially available belts such as thermoplastic polyurethane (TPU) and polyvinyl chloride (PVC). The main disadvantages were the lack of dimensional stability and number of cycle to failure. / Polymer IRC; The University of Bradford; The Gates Corporation