Increasing Draw Ratio Research Articles

Effect of the crystal orientation on the enzymatic degradation rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) fibers

In this study, the relationship between the crystal orientation and enzymatic degradation rate of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) was investigated. The enzymatic degradation rates of melt-spun PHBH fibers were quantified via PHB depolymerase from Ralstonia pickettii T1, and the degradation rate decreased with increasing drawing ratio. The solid structure was investigated via differential scanning calorimetry and small-angle X-ray scattering, and kinetic analysis was performed, indicating that the degradation rate was affected not only by crystallinity and lamellar thickness but also by highly ordered structure. The highly ordered structure was examined via wide-angle X-ray diffraction. The enzymatic degradation rate from the fiber cross-sections was then quantified for the first time, and it increased with drawing ratio and was larger than that from the fiber sides. This result showed that the degradation rate varied depending on the crystal orientation. Furthermore, an enzymatic degradation test of PHBH ring-banded spherulites was conducted, and it was found that the degradation rate of flat-on lamellar crystals was greater than that of edge-on lamellar crystals. This is the first study to quantitatively evaluate the relationship between the crystal orientation and the enzymatic degradation rate.

Hydro-mechanical deep drawing of conical components: Wrinkling behavior and process enhancement

This study explores the hydro-mechanical deep drawing process of a conical part through finite element simulations using ABAQUS software. The central focus is on investigating the occurrence of wrinkling during the forming process. Given the limitations in generalizing previous studies on wrinkling, there is a critical necessity to comprehensively comprehend and mitigate wrinkling behavior through an investigation into the interplay of various parameters. In response to the recognized challenge of minimizing wrinkles, an experimental setup with a hydro-mechanical deep drawing die was resented, aiming to validate and refine the simulation results. Additionally, a comprehensive study is conducted regarding the effect of fluid pressure, chamber pressure, pre-bulge height, friction coefficients, and sheet thickness on wrinkling behavior. The findings reveal that, at a pre-bulge pressure of 40 bar and a pre-bulge height of 2 mm, the minimum wrinkling height is observed to be merely 0.02 mm — the lowest recorded value. Notably, an increasing drawing ratio demands a 50% higher minimum chamber pressure to prevent wrinkling in the flange. Furthermore, a larger distance between the sheet and the die reduces the safe working range by approximately 57%, impacting the production of a wrinkle-free part. Conversely, elevating the pre-bulge pressure results in a 50% expansion in the safe working area for producing a wrinkle-free part. By explicitly stating the challenge of minimizing wrinkles, this study aims to contribute valuable insights into optimizing the hydro-mechanical deep drawing process for enhanced efficiency and improved product quality.

Novel method of mechanical alignment for chopped carbon fiber/high density polyethylene composites: Processing, modeling, and characterization

In this study, we investigated a novel method of mechanical alignment to enhance the tensile properties of chopped carbon fiber (CCF)/high-density polyethylene (HDPE) composites. By utilizing a novel extruder and take-up system based on the melt spinning technique, we successfully controlled the alignment of CCF at various thicknesses using mechanical tension. This facilitated the production of extruded profiles with controlled tensile conditions. Experimental measurements were conducted to evaluate the tensile strength and modulus of the composites. The results demonstrate the effectiveness of the proposed CCF alignment method, which involves adjusting the thickness of the extruded profiles, in controlling the mechanical properties of the composites. As a result, the ultimate tensile strength increased by 50%, and the tensile modulus increased by 130%. Additionally, we developed a numerical model that predicts the tensile modulus based on randomly generated fibers and the Mori-Tanaka model for property estimation. The fiber orientation distribution was influenced by the fiber shape and manufacturing conditions. Scanning electron microscope (SEM) images revealed that the fibers aligned more along the extrusion direction with increased draw ratio. The orientation distribution of the randomly generated fibers varied significantly based on the fiber length and draw ratio, indicating a narrowed distribution range along the extrusion direction with increased fiber length or draw ratio. These findings demonstrate that the proposed CCF alignment method, which involves changing the thickness of the extruded profiles, can effectively control the mechanical properties of the composite.

Combined effects of nanoparticle and stretch‐induced orientation on crystal structure and properties of UHMWPE/TiO2 composite microporous membranes

AbstractThe nanocomposite microporous membrane of ultra‐high molecular weight polyethylene (UHMWPE) and nano‐titanium dioxide (nano‐TiO2) system was prepared by combining the thermally induced phase separation (TIPS) technique with the extrusion‐casting process using liquid paraffin (LP) as the diluent. The effects of variations of TiO2 content and melt draw ratio on the properties of composite microporous membranes were studied and the optimal processing parameters were further investigated. ATR‐FTIR demonstrated that nanocomposite microporous membranes were successfully prepared. The crystallization behavior and morphological evolution of membranes were systematically investigated by WAXD, 2D‐SAXS, and SEM. It was found that the stretch‐induced orientation of UHMWPE was promoted and the shish‐kebab structure was formed for the reason of addition of TiO2. The mechanism of combined effects of nanoparticles and stretch‐induced orientation on the crystallization behavior of UHMWPE was further discussed and explained. Compared to pure UHMWPE film, the permeability of the optimum performance film was significantly improved, with porosity of 49% and pure water flux of about 193 L m−2 h−1. Mechanical studies showed that nanoparticles and DR have significant effects on tensile strength and elongation at break. In addition, the thermal stability of composite microporous membranes was found to be improved with the increase of TiO2 content and melt draw ratio. Thus, this investigation delivers inspiration for the expansion of excellent performance microporous membranes used for battery separators and filtration devices.

Construction of fully biodegradable poly(L-lactic acid)/poly(D-lactic acid)-poly(lactide-co-caprolactone) block polymer films: Viscoelasticity, processability and flexibility

Development of biodegradable polymer films is essential for sustainable energy conservation and ecological protection. In this work, to improve the processability and toughness of poly(lactic acid) (PLA) films, poly(lactide-co-caprolactone) (PLCL) segments were introduced into poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA) chains via chain branching reactions during reactive processing, and fully biodegradable/flexible PLLA/D-PLCL block polymer with long-chain branches and stereocomplex (SC) crystalline structure was prepared. Compared with neat PLLA, PLLA/D-PLCL exhibited much higher complex viscosity/storage modulus, lower tanδ values in terminal region and obvious strain-hardening behavior. Through biaxial drawing, PLLA/D-PLCL films were prepared, which showed improved uniformity and non-preferred orientation. With increasing draw ratio, the total crystallinity (Xc) and Xc for SC crystal both increased. By introduction of PDLA, the two phases of PLLA and PLCL penetrated and entangled with each other, and the phase structure transformed from “sea-island” structure to “co-continuous network” structure, which was beneficial for exerting the toughening effect of flexible PLCL molecules on PLA matrix. The tensile strength and elongation at break of PLLA/D-PLCL films increased from 51.87 MPa and 28.22 % of neat PLLA film to 70.82 MPa and 148.28 %. This work provided a new strategy for developing fully biodegradable polymer films with high performance.

Construction of a Highly Oriented Poly(lactic acid)-Based Block Polymer Foam and Its Self-Reinforcing Mechanism

Developing poly(lactic acid) (PLA)-based biodegradable polymer foams with high performance is crucial for sustainable energy conservation and the ecological environment. In this work, by applying poly(lactide-co-caprolactone) (PLCL) as a compatibilizer, the block polymer of poly(l-lactic) acid (PLLA)-b-polycaprolactone (PCL) with a long-chain branched structure was prepared by reactive processing. By utilizing the difference between the glass-transition temperature (Tg) and melting temperature (Tm) of PLA and PCL, PLLA-b-PCL-PLCL foams with a PCL chain as the foaming phase and an oriented PLLA chain as the enhancing phase were prepared by establishing a solid-phase hot drawing@supercritical CO2 foaming method. The incorporation of PLCL links significantly improved the interfacial compatibility between PLLA and PCL phases and chain entanglements, exhibiting strain-hardening behavior and leading to an improvement in the stretchability of the block polymer. In the hot drawing process in the range of Tg(PLA)–Tm(PLA), both PLLA and PCL phases were elongated along the drawing direction, and with an increasing draw ratio, the orientation factor and the crystallinity of the two phases increased evidently, accompanied by the formation of a shish–kebab crystalline structure. In the subsequent foaming process in the range of Tg(PCL)–Tm(PCL), the molecular chains of the PLLA phase were frozen and the retention of the orientation factor reached over 90%, while under CO2, crystallinity and crystallite size increased and a more perfect crystalline structure formed for the PCL phase. With an increasing draw ratio, the saturated dissolved amount of CO2 increased and the cell density and cell size of foam reached 5.13 × 109 cells/cm3 and 4.06 μm, respectively. The fibrillar structures of the PLLA phase appeared on the cell wall, while the tensile strength and modulus of foam reached as high as 65.9 MPa and 1.01 GPa, respectively. As a result, a super-strong PLA-based microcellular foam with dense micropores and highly oriented microfibrillar structures was constructed.

Optimization of thermoelectric properties of carbon nanotube veils by defect engineering.

Carbon nanotubes (CNTs), with their combination of excellent electrical conductivity, Seebeck coefficient, mechanical robustness and environmental stability are highly desired as thermoelectric (TE) materials for a wide range of fields including Internet of Things, health monitoring and environmental remediation solutions. However, their high thermal conductivity (κ) is an obstacle to practical TE applications. Herein, we present a novel method to reduce the κ of CNT veils, by introducing defects, while preserving their Seebeck coefficient and electrical conductivity. Solid-state drawing of a CNT veil embedded within two polycarbonate films generates CNT veil fragments of reducing size with increasing draw ratio. A successive heat treatment, at above the polycarbonate glass-to-rubber transition temperature, spontaneously reconnects the CNT veils fragments electrically but not thermally. Stretching to a draw ratio of 1.5 and heat repairing at 170 °C leads to a dramatic 3.5-fold decrease in κ (from 46 to 13 W m-1 K-1), in contrast with a decrease in electrical conductivity of only 26% and an increase in Seebeck coefficient of 10%. To clarify the mechanism of reduction in thermal conductivity, a large-scale mesoscopic simulation of CNT veils under uniaxial stretching has also been used. This work shows that defect engineering can be a valuable strategy to optimize TE properties of CNT veils and, potentially, other thermoelectric materials.

Influence of drawing and annealing on the structure and properties of bio‐based polyamide 56 fibers

AbstractThe influences of drawing and annealing parameters on the structure and mechanical properties of melt spinning polyamide 56 (PA56) fibers were investigated and discussed in details. The as‐spun PA56 fibers have the relatively low crystallinity and rather low orientation. The crystalline phase in as‐spun PA56 fibers is mainly in γ phase. PA56 α‐like crystalline phase develops from the amorphous phase with the increase in chain orientation upon drawing of the as‐spun PA56 fibers. The crystallinity of PA56 fiber increases with rising draw ratio, which accompanies the increase in thickness of the crystalline lamella. The increase in draw ratio leads to the increase in tensile strength and the decrease in elongation at break of the resultant fibers. Tension annealing of the full‐drawn PA56 fibers at specific temperatures has obvious influences on the structure and properties of the fibers. The crystallinity and orientation increase with rising annealing temperature in the range of 150–210°C, during which the content of PA56 α‐like phase increases with the rising annealing temperature. Annealed the fibers at 230°C results in the increase in the content of PA56 γ phase with a tremendous decrease in the content of α‐like phase due to Brill transition. The optimum annealing temperature is around 170°C, at which the tenacity of the PA56 fibers is the highest. These results can provide valuable information for the production of PA56 fibers.

Tribological properties of oriented polytetrafluoroethylene at room temperature and cryogenic temperature

AbstractIn this study, the tribological properties of drawn PTFE were tested on a CSM tribometer at room temperature and cryogenic temperature. The orientation degree and worn surface morphology of drawn PTFE were studied and correlated with the friction and wear behaviors. It was found that the sample with low friction coefficient corresponded to high orientation degree in the parallel direction at room temperature, while the friction coefficient barely changed with increasing draw ratio in the perpendicular direction. The friction coefficient of drawn PTFE at liquid nitrogen temperature is higher than that at room temperature in the perpendicular direction, while the two values are almost undistinguishable within error range in the parallel direction. The wear volume of drawn PTFE at liquid nitrogen temperature is lower than that at room temperature in both perpendicular and parallel directions due to the mitigation of adhesive wear of drawn PTFE under liquid nitrogen temperature.

Zero–Zero Birefringence Cellulose Acetate-Based Optical Films by Benzoylation

Zero–zero birefringence film is one of the key components in optical displays, and its design and preparation remain a challenge nowadays. Here, we report the synthesis of benzoylated cellulose acetate (BCA), the preparation of BCA films by solution casting, and the birefringent properties of unstretched and stretched BCA films. It is found that zero–zero birefringence films can be fabricated using both unstretched and stretched BCA films. As the degree of substitution of benzoyl (DSBz) increases, the out-of-plane birefringence (Δnth) gradually decreases and changes from positive to negative. Particularly, for DSBz = 0.511, both the in-plane birefringence (Δnin) and out-of-plane birefringence (Δnth) of stretched BCA films are close to zero. The orientations of the acetyl and benzoyl groups under stretching are measured to interpret the underlying compensation mechanisms. Finally, we show that the wavelength dispersion of BCA films with DSBz = 0.511 varies significantly with the increase in draw ratio, and formulize the normalized birefringence with the relative orientation degree of the benzoyl and acetyl groups. Our results suggest that the birefringence and wavelength dispersion of cellulose acetate-based optical films can be well regulated by a combination of chemical modification and stretching, and have potential significance to the industrial production of zero–zero birefringence films.

Fabrication of high-performance HDPE/CWPF blend film via the assistance of OBC and solid-state drawing

To achieving highly efficient reuse of commingled waste plastic films (CWPF) in high-density polyethylene (HDPE), elastomer-olefin block copolymer (OBC) was adopted to improve the compatibility between CWPF and HDPE, and solid-state drawing was further used to improve the mechanical properties of the blends. The results showed that OBC could form core-shell structure with CWPF, as a bridge layer to simultaneously connect CWPF and HDPE, and form epitaxial crystallization induced by HDPE crystals, thereby greatly enhancing the compatibility between CWPF and HDPE, and improving the tensile strength, elongation at break and impact strength of HDPE/CWPF blend. In the subsequent solid-state drawing, depending on the fluidity of OBC at the drawing temperature of 100 °C, more CWPF were covered, efficiently reducing the defects caused by CWPF along the transverse direction (TD) and increasing the elongation at break of the stretched sheet along this direction. With the increase of draw ratio, lamellae in fibril along TD and shish-kebab-like structure along the flow direction (FD) formed, greatly improving the tensile strength of the blend along both TD and FD. And the long period (Lp), amorphous region (La) and lateral dimension (Llateral) decreased, but lamella thickness (Lc) increased. This work provides good bases for obtaining novel and low-cost HDPE based material as well as high-effect recycling of CWPF.

Structural evolution and related physical properties of machine direction oriented poly(butylene succinate-co-adipate) films

This study sheds light on the microstructural change of uniaxially oriented poly(butylene succinate-co-adipate) (PBSA) copolymer, and the consequent gas permeabilities, as well as tensile and optical properties. Uniaxial stretching at 62 °C takes place by means of a machine direction orientation (MDO) with varied draw ratios and annealing near the melting temperature. The PBSA precursor sheet favorably melt-crystallizes in the form of α-PBS crystals with isotropic in-plane orientation. MDO-PBSA films with and without annealing exhibit preferential orientation of the α-PBS crystal parallel to the stretching direction (MD), with an increased degree of crystallinity according to the increased draw ratio and applied annealing. This was evident from two-dimensional wide-angle X-ray diffraction patterns and X-ray diffraction profiles. Additionally, MDO stretching above the crystallization temperature simultaneously induces rigid amorphous fraction, in particular, by a high draw ratio (5 × ) and chain relaxation during annealing near the melting temperature. From the determined Herman's orientation function, the c-axis of the α-PBS crystal is parallel to the MD, thereby resulting in decreased diffusion path tortuosity. Consequently, oxygen and water vapor permeation are promoted. Furthermore, Young's modulus and tensile strength of MDO-PBSA films drastically increase with high ductility, and are approximately two and four times higher than those of non-oriented PBSA, respectively. MDO-PBSA films exhibit high clarities above 94% while yielding low haze values.

The effect of melt drawing ratio on the crystal structural change and performance of polyketone extrusion cast film

In this paper, the polyketone (POK) extrusion cast film is manufactured by melt stretching method, and the evolution process of the crystal morphology and mechanical properties with the increase of melt drawing ratio (MDR) are followed. The results show that the melt stretching process produces many micro shish-kebab crystals in the POK. The length of the shish crystal and the thickness of the kebab crystal hardly increase with MDR, but the lateral length of the kebab crystal shows linear growth when MDR exceeds 40. The crystalline morphology of POK is mainly affected by melt relaxation. The molecular chain has sufficient relaxation during cooling at a low MDR (20–40). At this time, micro shish-kebab crystals are mainly randomly arranged. When MDR exceeds 40, the rapid melt stretching shortens the relaxation time of the tie chain between the neighborhood shish crystal, and the atomic force microscopy image shows a typical shish-kebab structure. This experimental result indicates that the formation of the oriented lamella structure may be related to the relaxation of the molecular chains between the micro-shish. When the length of the shish axis and the thickness of the kebab lamellae are similar, it is difficult to distinguish the two.

The effect of acetylene flow rate on the uniform deposition of thick DLC coatings on the inner surface of pipes with different draw ratios

Thick multilayered DLC coatings were deposited on the inner surface of pipes with different draw ratios by hollow cathode plasma immersion ion processing (PIIP). By tuning the acetylene (C2H2) flow rate, the change of plasma density caused by different draw ratios can be compensated to fulfill the uniform deposition of thick DLC coatings along the pipes. The influence of C2H2 flow rate on the mechanical and tribological properties of the DLC coatings were investigated. With the increase of draw ratio, the deposition temperature and gas pressure declined, and the plasma density became more asymmetrical in the axial direction. Increasing the flow rate can timely replenish the plasma inside the pipe and resolve the mass depletion problem, resulting in better thickness and structure uniformity of the DLC coatings. The greatest deposition rate of 28.6 μm/h was obtained at the 250 sccm C2H2 flow with a draw ratio of 5:1. The results of Raman spectrum and XPS indicated that the content of sp2-carbon bonds decreased with the increasing draw ratio for lower impact energies of ions. The higher sp3 carbon bonds content contributed to the formation of carbonaceous transfer layers, which resulted in the lower friction coefficient and wear rate.

Effect of draw ratio on the mechanical properties of polypropylene self-reinforced composite

Polypropylene self-reinforced composites (PP-SRCs) are advantageous in terms of recycling, impact resistance, and price; however, a deeper understanding of their mechanical properties is required to expand their commercialization. Here, an in-depth study was conducted to understand the effect of changing PP-tape as a function of the draw ratio on the mechanical properties of PP-SRC. As the draw ratio increased, PP-tape showed higher orientation and thus significantly improved the tensile strength and Young's modulus. The tensile properties of PP-SRC showed the same trend; this was successfully predicted by employing the rule of mixtures as they were dominated by the reinforcing effect of PP-tape. Meanwhile, the impact resistance of PP-SRC improved with increasing draw ratio, but the T-peel adhesion deteriorated. This occurred because the failure mode at higher draw ratios transitioned from tape fracture to delamination, resulting in enhanced energy absorption ability, and the decrease in polymer chain mobility hindered interfacial inter-diffusion.

Highly Oriented Thermoplastic Poly (vinyl alcohol) Films by Uniaxial Drawing: Effect of Stretching Temperature and Draw Ratio

With the advantages of excellent processability and biodegradability, polyvinyl alcohol (PVA) becomes an environmentally friendly and biocompatible material in many fields currently. To further improve the mechanical properties of thermoplastic PVA films, the orientation was adopted and studied. In this work, the uniaxial stretched PVA films with ethylene glycol as plasticizer were prepared to explore the influence of stretching temperature and draw ratio on the structure and properties of oriented PVA films. The introduction of ethylene glycol improves the thermoplastic processing capacity of PVA. When the stretching temperature was lower than 100 °C, the strength of the film increased with the increase of temperature. However, as the temperature continued to increase, the strength decreased since the process of disorientation accelerated. In addition, with the increase of draw ratio, an increase in the tensile strength and Young’s modulus of the films and a decrease in the elongation at break were observed. When the draw ratio at 5, the tensile strength and Young’s modulus of the PVA films reached the maximum of 219.7 MPa and 219.6 MPa respectively. Thus through controlling the orientation conditions and plasticizers, the PVA films with enhanced performance could be obtained.

Highly reinforcing effect of polycarbonate/poly(ethylene terephthalate) blends by formation of orientation microfibrillar structure

AbstractHighly oriented microfibrillar polycarbonate/poly(ethylene terephthalate) (PC/PET) blends were prepared. Before orientation, the molecular chains of the blends were mostly randomly arranged with a low crystallinity, and low mechanical properties were obtained. Under stress, it was difficult for molecular chains of the amorphous PC phase in blends to form an oriented crystalline structure. With increasing draw ratio, the crystallinity and orientation degree of the PET phase increased, forming a dense lamellar structure with reduced crystalline and amorphous layer thickness, while with increasing PET content the crystalline orientation degree of the PET phase increased with larger sized lamellae. Moreover, the cross‐section of the oriented sample showed an obvious ordered microfibrillar bundle structure, which arranged compactly and orderly along the drawing direction. The tensile strength and modulus of the oriented PC/20 wt% PET sample were up to 126.01 and 7170.10 MPa, which were 66.48% and 317.49% respectively higher than those of pure PC. Therefore, the stress‐induced oriented microfibrillar structure of the PET phase exhibited a highly reinforcing effect on the PC phase and the blend. © 2021 Society of Industrial Chemistry.

Strain-sensing fiber with a core–sheath structure based on carbon black/polyurethane composites for smart textiles

Fiber-shaped sensors have great potential for real-time monitoring of human physiological signals thanks to the merging of electronic and textile technologies. This work reports on the fabrication of a core–sheath structured strain-sensing fiber based on the wet-spinning method. The sensing fiber is composed of a core of non-conducting polyurethane and a conducting sheath of carbon black in a polyurethane matrix. Microscopic observation reveals the irregular shape or scattered appearance of the core as well as the porous structure of the fiber, the diameter of which is in the range 200–500 μm. The electro-mechanical properties and their dependence on carbon black concentration in the sheath and draw ratio between the spinneret and first drafting roller are experimentally investigated. It has been found that the percolation threshold of the fiber is in the range 15–16 wt%. The resistance of the fiber rises stably as the fiber is stretched up to a strain of 120% and increases with the increase of draw ratio between the spinneret and first drafting roller. In the cyclic tensile tests, the resistance of the fiber exhibits good repeatability in subsequent loading–unloading cycles after pre-stretching, despite partial recovery of the resistance in the first few cycles. The integration of the strain-sensing fiber into textiles is demonstrated by the core-spun yarn fabricated based on a modified vortex spinning method. The results of this study indicate the fiber could be a promising candidate for a sensor for smart textiles.

Orientation of Poly(ε-caprolactone) in Its Poly(vinyl chloride) Blends Crystallized under Strain: The Role of Strain Rate.

The blends of high and low molecular weights poly(ε-caprolactone) (PCL) with poly(vinyl chloride (PVC) were prepared. The samples before and after the crystallization of PCL were uniaxially stretched to different draw ratios. The orientation features of PCL in a stretched crystalline PCL/PVC blend and crystallized from the amorphous PCL/PVC blends under varied strains were studied by wide-angle X-ray diffraction (WAXD). It was found that a uniaxial stretching of crystalline PCL/PVC blend with high molecular weight PCL results in the c-axis orientation along the stretching direction, as is usually done for the PCL bulk sample. For the stretched amorphous PCL/PVC blend samples, the crystallization of high molecular weight PCL in the blends under a draw ratio of λ = 3 with a strain rate of 6 mm/min leads to a ring-fiber orientation. In the samples with draw ratios of λ = 4 and 5, the uniaxial orientation of a-, b-, and c-axes along the strain direction coexist after crystallization of high molecular weight PCL. With a draw ratio of λ = 6, mainly the b-axis orientation of high molecular weight PCL is identified. For the low molecular weight PCL, on the contrary, the ring-fiber and a-axis orientations coexist under a draw ratio of λ = 3. The a-axis orientation decreases with the increase of draw ratio. When the λ reaches 5, only a poorly oriented ring-fiber pattern has been recognized. These results are different from the similar samples stretched at a higher strain rate as reported in the literatures and demonstrate the important role of strain rate on the crystallization behavior of PCL in its blend with PVC under strain.

Effect of die structure on the properties of self-reinforced polypropylene/noil ramie fiber composites prepared by solid-state extrusion

In this work, the self-reinforced polypropylene (PP)/noil ramie fiber (NRF) composites were prepared by the solid-state extrusion method. And the effect of die structure such as draw ratio and conical angle on the morphology, thermal and mechanical properties of samples was investigated. The results indicated that the solid-state deformation of PP/NRF composites conducted below the melt transition promoted the formation of the orderly arranged microfibrils inside the samples, which arranged along the extrusion direction and could be observed by scanning electron microscopy (SEM). Besides, the increased draw ratio and conical angle both contributed to the higher degree of orientation, which was obvious observed inside the sample prepared at the draw ratio of 5 and conical angle of 20°. The thermal properties tested by differential scanning calorimetry (DSC) also suggested that the intensified orientation of microfibrillar structure not only demonstrated the transformation of the spherulitic crystal into the aligned chain crystals, but also resulted in the enhanced crystallinity and narrowed melting peak. Moreover, the highly oriented fibrillar bundle structure endowed the samples with the excellent tensile strength and flexural strength, which were up to 80.9 MPa and 83.5 MPa respectively and increased by 182.8% and 102.7% compared with the commonly extruded samples.