Study on the relationship between the mechanical properties and processing for self-reinforced polymers: A method for estimating the theoretical strength of UHMWPE fiber

In this paper, a method for estimating the theoretical strength of polymer fiber from experiments was developed. It is based on a kinetic equation for bond rupture of overstressed Taut tie molecules (TTM) and/or trapped entanglement chains (TEC) in the disordered domain and is established by using the coefficient of overstressed TTM and/or TEC in the disordered domain as a variable. After integration and simplification, a general correlation between the tensile strength with the primary molecular weight, the processing condition, the testing condition and durability was obtained. When the draw ratio of processing and the primary molecular weight are extrapolated to infinity, a general relation between the actual tensile strength and the theoretical strength, the fraction of TTM and/or TEC (X_e3) in the disordered domain and the thermal fluctuation was obtained. Based on the relation, a method for estimating the theoretical strength of the polymer chain from the measurement of the actual tensile strength and the fraction of TTM and/or TEC is proposed. The theoretical strength of a PE chain was estimated by the method to be 30–40 Gpa.     

Mechanism analysis of interface characteristics of sequential Co-injection self-reinforced parts

The mechanism analysis of the interface characteristics of sequential co-injection self-reinforced parts starts from the following three aspects. Firstly, the formation process of the bonding interface and the factors affecting the bonding strength were investigated in theory. A theoretical model of interface bonding degree, which explains the bonding degree of the interface by the penetration depth of polymer chains through the initial solid-melt interface, was proposed, and then combines the average critical penetration depth to analyze the influence of different molding parameters on the interface bonding degree. Then, the interface bonding strength of the prepared polypropylene sequential co-injection self-reinforced parts under different molding parameters (including melt temperature, mold temperature and injection speed, etc.) was studied experimentally, and the reliability of the model was verified. Finally, the interrelationship function between effective penetration degree of molecular chain diffusion and interface bonding degree on both sides of the interface is established, which provides a new theoretical basis for interfacial mechanism analysis of sequential co-injection self-reinforced parts. The results show that the interface bonding degree between experiment and theory has a good consistency, and the deviation between them is within 10%, which proves that the theoretical model is reliable. In addition, the theoretical critical penetration depth and the theoretical maximum degree of bonding sequential co-injection polypropylene products are 1.399 nm and 0.857, respectively. The performance test results of different molding parameters show that the temperature change of reinforced melt is the key factor affecting the interfacial fusion of sequential co-injection self-reinforced parts. The high temperature melt is beneficial to the diffusion and intertwining of molecular chains on both sides of the interface and to the improvement of the degree of interfacial bonding.     

On-line testing equipment of P–V–T properties of polymers based on an injection molding machine

In order to obtain more accurate prediction of the service performance and service life of polymers and the optimization of processing parameters, this paper presents a novel, on-line testing equipment for measuring P–V–T (Pressure–Volume–Temperature) relationships of polymers under processing conditions. This equipment is based on an injection molding machine (IMM), and it can be used to get P–V–T data of polymers directly with a special testing mold under normal processing conditions. P–V–T properties of five polymers (ABS, PS, LDPE, PA 6 and PP) were measured. The experimental results under industrial processing conditions were presented. The results were compared with those obtained by the confining fluid technique. The P–V–T curves were consistent, which proved that the new on-line measurement is feasible. The repeatability of the P–V–T measurement was within 0.3%. Consequently, a new P–V–T database on typical commercial materials could be established. Repeatability of IMM could be improved significantly.     

聚2,5-呋喃二甲酸乙二醇酯/聚丁二酸丁二醇酯共混物的制备与表征

通过熔融共混制备了聚2,5-呋喃二甲酸乙二醇酯(PEF)/聚丁二酸丁二醇酯(PBS)共混物,探究了制备PEF/PBS共混物的影响因素,考察了共混温度、共混时间、螺杆转速、共混比例对PEF/PBS共混物力学性能的影响因素,并用示差扫描量热仪、热失重、扫描电子显微镜等技术手段对其热性能和相容性进行了表征。 结果表明,当PBS的含量为15%、共混温度为230 ℃,共混时间为90 s、螺杆转速为150 r/min时,为最佳共混制备条件,此时相容性最好,热性能良好,冲击强度和拉伸强度最大,冲击强度相对纯PEF提高了6倍,拉伸强度提高了近20%,从而大幅提高了PEF的冲击强度,有效地增强了PEF的抗冲击韧性。 这些工作为这一生物基聚酯材料的应用提供了可能。     

Adaptation of the molecular imprinted polymers towards polar environment

A new simple method for the post-polymerisation treatment of molecularly imprinted polymers was proposed. A layer of mineral oil was deposited onto the surface of the polymer in order to create a hydrophobic environment in the binding sites and to improve the recognition properties of the polymer in polar solvents. The testing of polymers performed in acetonitrile showed that the modified polymers possessed significantly increased selectivity as compared with non-treated ones. The three-fold improvement of recognition of the template (cocaine) was achieved; the same time, for non-specific molecule (morphine) the improvement was only 1.3 times. The investigation of the stability of mineral oil coating on the polymer surface suggested that the effect produced is stable over a long period of time. This approach could be used to broaden the range of experimental conditions where molecularly imprinted polymers can perform successfully.     

复合应力场剪切诱导成型PP-R自增强管材的结构与性能研究

利用自行设计制造的剪切拉伸双向复合应力场挤管装置生产出了双向自增强的无规共聚聚丙烯(PP-R C180)管材,研究分析了该双向应力场的剪切诱导效应对PP-R C180管材的结晶熔融、取向和拉伸强度的影响.结果表明,剪切拉伸双向复合应力场的引入所带来的剪切诱导效应促进了PP-R C180分子有序性的增加,使PP-R C180体系分子更容易形成分别沿管材周向和轴向方向的取向,因而保持甚至提高了耐热性与结晶速率,降低了结晶度,改变了PP-R C180的结晶结构与形态,诱导出了全新的β晶,进而改善了管材的强度性能.与常规管材相比,自增强管材在保持其熔点不降低的前提下,使结晶度从常规管材的44.96%降至40.03%,降低了4.93%;轴向强度从常规管材的23.35 MPa最高增强到25.49 MPa,提高了9.2%;周向强度从常规管材的22.71 MPa最高增强到26.54 MPa,提高了16.9%,且增强之后管材的周向强度已经高于了轴向强度,更优化地配置了聚合物材料的性能,更充分地满足了受内压管材使用的现实需求.     

Preparation and properties of self-reinforced polypropylene/liquid crystalline polymer composites

A fast and potentially economic method for creating a composite material of polypropylene (PP) with liquid crystalline polymers (LCPs) was explored. The LCPs were dispersed in the PP matrix in a conventional extrusion process and subsequently drawn in order to obtain a highly uniaxially molecular orientation of the LCP fibres. The strongest mechanical properties were found after rapid cooling of the blend, which was optimally exploited in thin filaments where cooling was fast enough to prevent fibre break-up and/or orientation relaxation. To enable the production of extrudates which are thick enough to be cut into self-reinforced pellets, a fused multi-filament technology was developed. In this technology several thin filaments were extruded/drawn and rapidly cooled to a temperature between the crystallisation temperatures of the LCP and the PP. After solidification of the LCP, the single filaments were fused to a multifilament strand and further cooled to room temperature. The thick multifilament LCP reinforced PP strands were cut into pellets and used in injection-and compression-moulding processes. This processing took place between the melting temperature of the PP and the LCP, with retention of the aspect ratio and the molecular orientation of the LCP fibres.     

Mechanical properties of emulsion polymer blends

Polymer blend technology has been one of the most investigated areas in polymer science in the past 3 decades. The one area of polymer blends that has been virtually ignored involves simple emulsion blends, although several articles have recently appeared that address film formation and mechanical characteristics. In this study, we investigated the mechanical property behavior of emulsion blends composed of low/high‐glass‐transition‐temperature polymers (where low and high mean below and above the test temperature, respectively). The emulsions chosen for this study had similar particle sizes, and the mixtures were rheologically stable. Two conditions were chosen, a binary combination of polymers that were thermodynamically immiscible and another system that was thermodynamically miscible. The mechanical property results over the entire composition range were compared with the predictions of the equivalent box model (EBM) with the universal parameters predicted by percolation theory. An array of randomly mixed and equal‐size particles of differing moduli was expected to show excellent agreement with theory, and the emulsion blends provided an excellent experimental basis for testing the theory. For the immiscible blend, the EBM prediction for the modulus showed excellent agreement with experimental results. With tensile strength, the agreement between the modulus and theory was good if the yield strength for the higher glass‐transition‐temperature polymer was employed in comparison with the actual tensile strength. The phase inversion point (where both phases were equally continuous) was at a 0.50 volume fraction of each component (based on an analysis employing Kerner's equation), just as expected for a random mixture of equal‐size particles. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1093–1106, 2001     

Performance prediction of Co-injection self-reinforced composites parts based on temperature field

In this paper, polypropylene (PP) was used as raw material to prepare rectangular parts. The temperature change data of the reinforcement with different molding parameters during the filling process were collected by using the injection molding temperature visualization experimental analysis platform. The electronic universal mechanical testing machine (EMUTM) was used for mechanical testing, and the micro-morphology of co-injection self-reinforced composites(CI-SRCs) parts and conventional parts with different temperature fields was observed and analyzed by Polarizing microscope (PLM) and Wide angle X-ray diffraction (WAXD), and the dimensionless equations among four variables (including molding parameters, area ratio of critical temperature field, area ratio of skin layer and mechanical properties) were established. From the results, it was found that the tensile properties of CI-SRCs parts with different molding parameters are superior to that of conventional parts, with a maximum increase of 18.64%. The overall performance of CI-SRCs parts is positively correlated with the performance of the reinforcement, and the performance of reinforcement is mainly determined by the area ratio of skin layer. The difference in the micromorphology characteristics of the parts depends on the change in the temperature field. Therefore, through microscope observation and simulation software analysis, it was obtained that the theoretical critical temperature field forming the orientation skin of the parts was 154.88 °C, and the temperature visualization platform was used to correct the critical temperature field obtained by simulation, and the real critical temperature field was about 170 °C. In the randomized trials, the simulated and actual area ratio of skin layer were in good agreement, with a maximum deviation of 8.9%, which proved that it was reliable to estimate the skin layer area ratio based on theoretical critical temperature field through the change of molding parameters, and then to predict the performance change of the parts.     

The effect of orientation on the mechanism of deformation of polymers

The mechanical behavior of HDPE, medium-density PE, and amorphous and amorphous-crystalline PET after their preliminary orientation is studied. The polymers are oriented by rolling at room temperature on lab-scale rolls, tensile drawing at temperatures somewhat higher than their glass-transition temperatures, and extrusion at room temperature. At low degrees of rolling (below 1.5), the tensile yield stress does not actually increase. (In amorphous-crystalline PET, this parameter even decreases.) It seems that the absence of strain hardening at low draw ratios is a common feature of the behavior of polymers below their glass-transition temperatures. In contrast to the tensile yield stress, the engineering strength increases in proportion to the degree of rolling. A new procedure for construction of the dependence of true tensile yield stress on tensile strain is advanced. At low strains, the true tensile yield stress shows practically no increase. This conclusion is verified by theoretical calculations.     

Study on the concentration effects in size exclusion chromatography VII. A quantitative verification for the model theory of concentration and molecular mass dependences of hydrodynamic volumes for polydisperse polymers

A model theory of concentration effects for polydisperse polymers was proposed in 1988. It is successful in relating the concentration of the injected solution to the effective hydrodynamic volumes of peak, the retention volumes of peak and the polydispersity index (Dc = (Vhcw)/(Vhcn) of hydro-dynamic volume distribution for polydisperse polymers at a given concentration. The dependence of the concentration of injected polymer solution on the effective hydrodynamic volumes, the retention volumes of peak and the polydispersity index of hydrodynamic volume distribution for narrow disperse and polydisperse polystyrene, poly(dodecyl methacrylate), poly(tridecyl methacrylate) and poly(methyl methacrylate) in tetrahydrofuran solvent were studied. The proposed theory was verified by these experimental data. Results show that the proposed theory can predict the concentration effects in GPC for polydisperse polymers quantitatively and can provide a theoretical foundation for the two methods of calibrating the universal calibration curves with polydisperse polymers and of determining the second virial coefficients (A2) of polymers. It is found that the determined values of A2 for narrow disperse and polydisperse polymers by the proposed method are in agreement with those obtained by the LALLS method, and the two universal calibration curves with narrow disperse and polydisperse polymers are in excellent agreement.     

The brittle-ductile transition in rubber-filled polymers

Composites based on various polymers and rubber particles as a filler were studied. As the filler concentration was increased, the transition from necking to brittle fracture and then to uniform ductile yielding was observed. The criterion for the brittle-ductile transition, which is accompanied by an increase in the elongation at break, is equality between the tensile strength and the upper yield stress of the filled composite. Upon the brittle-ductile transition, the critical concentration of rubber particles is determined by two parameters: the height of the yield drop (difference between the upper and lower yield stresses of matrix polymer) and adhesive strength at the interface between the matrix polymer and filler particles (in the case of good adhesion, tensile strength of rubber particles). The larger the yield drop, the broader the concentration range corresponding to the polymer brittle fracture. The enhancement of adhesion between the matrix and the particles makes it possible to displace the brittle-ductile transition to lower filler contents and, hence, to narrow the region of brittle fracture of the composite.     

Recovered-voltage phenomenon and prospects for its use for assessment of the condition of polymers

A general theory of the phenomenon of recovered voltage in polymers was considered on the basis of representation of an actual poling process by a discrete set of Debye relaxators. Examples of numerical solution of the direct and inverse problems are given. A correlation expression between intentionally aged polymer specimens and recovered-voltage curves was proposed for use in the assessment of the material state of a polymer under actual service conditions. It was shown that it is sufficient to restrict consideration to three relaxation processes in analysis of the phenomenon.     

Processing,structure and properties of oriented polymers

The fabrication techniques now available for the production of highly oriented polymers are reviewed. These techniques include tensile drawing from both melt-spun and gel-spun polymers, extrusion under pressure from the melt, and hydrostatic extrusion, ram extrusion and die drawing in the solid phase. In addition, lyotropic and thermotropic liquid crystalline polymers offer new routes to very stiff and strong polymers. Following the review of processing methods, an account is given of low strain mechanical behaviour and its relationship to structure, thermal properties (including thermal conductivity and thermal expansion behaviour) and barrier properties (permeability to liquids and gases and solubility).     

Tensile strength of oriented polymers below the glass transition temperature

A theory of tensile strength, based on the observation of cracks in specimens strained to breaking, is formulated. The treatment involves the assumption that a crack grows to a critical size by a nucleation process. When this critical size is exceeded the crack becomes unstable and propagates spontaneously to produce rupture. By comparing the predicted and measured strength, one can estimate the magnitude of the stress concentration factor in fibers. An interpretative analysis of experimental data obtained at various strain rates indicates that the resulting changes in tensile strength are due primarily to the changes in modulus.     

Development of flame retarded self-reinforced composites from automotive shredder plastic waste

Multilayered self-reinforced composites were developed from a density-separated light fraction of automotive shredder waste of high polyolefin content, which can fulfil the current technical, safety and environmental requirements of structural materials. The significantly enhanced mechanical properties of the recycled composites were ensured by polypropylene fabric reinforcement; meanwhile, reduced flammability was obtained by modifying the matrix layers, made of secondary raw materials, with phosphorous-containing flame retardant additive. The results of the new flame retarded composite systems allowed the discussion of a novel mechanistic observation. The mechanical and flammability properties of the prepared self-reinforced composites are compared to conventional glass fabric reinforced composites and to compounds without reinforcement.     

自增强高密度聚乙烯的结构与性能

<正> 高分子材料的自增强与外增强不同,它是充分利用材料本身的潜力,改变其内部的聚态结构,形成内在的增强相,达到增强的目的。由于自增强材料的增强相和基体相具有完全相同的分子结构,因此增强相与基体相之间不存在外增强材料中普遍存在的界面问题,表现出整体结构的优异的比强度和比刚度,而且具有较高的冲击韧性和耐化学稳定性,热     

Solvent diffusion in amorphous glassy polymers

In this article, a mathematical model is proposed for predicting solvent self‐diffusion coefficients in amorphous glassy polymers based on free volume theory. The basis of this new model involves consideration of the plasticization effects induced by small molecular solvents to correctly estimate the hole‐free volume variation above and below the glass‐transition temperature. Solvent mutual‐diffusion coefficients are calculated using free volume parameters determined as in the original theory. Only one parameter, which can be predicted by thermodynamic theory, is introduced to express the plasticization effect. Thus, this model permits the prediction of diffusion coefficients without adjustable parameters. Comparison of the values calculated by this new model with the present experimental data, including benzene, toluene, ethyl benzene, methyl acetate, and methyl ethyl ketone (MEK) in polystyrene (PS) and poly(methyl methacrylate) (PMMA), has been performed, and the results show good agreement between the predicted and measured values. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 846–856, 2000     

A New Approach to the Determination of Adhesion Properties of Polymer Networks

Summary: A new approach for the determination and comparison of adhesion properties of polymer networks was proposed. One permits to optimize the choice of polymers for composite materials with inorganic fibers (at the absence of binder diffusion to the fiber). For the first time the works of adhesion of polymer to liquids simulating polar or non-polar phases were used for prediction of adhesive properties of network (binder, coupling agent) and for the choice of network provided the best tensile strength of composite material. The correctness of proposed approach was experimentally proved by measuring of tensile strength micro plastics.     

Reprocessability and melting behaviour of self-reinforced composites based on PP homo and copolymers

In our present study, the reprocessability of a self-reinforced PP composites (SRPPC) prepared by compression molding was studied. The composite materials (handled separately, based on the related matrix material) were ground, then extruded five times and injection molded after the first and fifth cycle in order to investigate the behaviour of the material during reprocessing. As a reference, the matrices of the composites were also reprocessed and injection molded similarly to the composites. On the manufactured specimens, static (tensile and flexural) and dynamic mechanical tests (Charpy) were performed. The melting and crystalline characteristics were studied by Differential Scanning Calorimetry (DSC). The probable decomposition caused by multiple extrusions was followed by the Melt Volume Rate (MVR). The results indicated that in case of commercial materials there is no significant degradation even after multiple reprocessing cycles; therefore, the reprocessability of SRPPC products has no hindrance. The presence of α-iPP reinforcement in the rPP-based composites after reprocessing results in increased inclination for crystallization and consequently leads to improved mechanical stiffness compared to rPP neat matrices.