Structure and morphology development during deformation of propylene based ethylene-propylene copolymer and its blends with isotactic polypropylene

The structure and morphology development during the deformation of metallocene based ethylene-propylene copolymers with dominant propylene moiety (C3 M-EP) and its isotactic polypropylene (M-iPP) blends were investigated by simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) using synchrotron radiation, high temperature tensile testing and differential scanning calorimetry (DSC). X-ray results showed that the structure and morphology in the blends of M-iPP/C3 M-EP are dictated by the M-iPP component. During stretching at room temperatures, both pure M-iPP and polymer blends exhibited the same transition from the α-form crystal to the mesophase. However, the α-form was found to be unchanged during the deformation of C3 M-EP copolymer, which indicated that the effect of local stress on the crystal domain in pure copolymer was too small to induce the phase transition. Although the DSC results showed that the blends in their isotropic state were immiscible with each other, the mechanical properties of the blends at high temperature (70 °C) indicated that they follow the conventional rule of mixing.     

Stretching induced phase separation in poly(vinylidene fluoride)/poly(butylene succinate) blends studied by in-situ X-ray scattering

The structure evolution of poly(vinylidene fluoride)/poly(butylene succinate) (PVDF/PBS) blends during stretching above the melting point of PBS is investigated by synchrotron-based simultaneous wide angle and small angle X-ray scattering (WAXS/SAXS). Before stretching, PVDF crystallizes into the α-form, whereas the chains of molten PBS locate at the inter-lamellar amorphous phase of PVDF. Crystal transition from α to β of PVDF is observed in all samples during stretching. The morphological transformation from a lamellar structure into a fibrillar structure occurs at low and intermediate strains. With further deformation, a “stretching induced phase separation” phenomenon is observed. The final microstructure of PVDF/PBS blends contains PVDF microfibrils with PBS chains preferentially distributed in the inter-fibrillar region. The PBS molecular weight influences the onset and end strain for the transition. A new “two-step model” is proposed to describe the deformation process.     

Electrical behavior and structure of polypropylene/ultrahigh molecular weight polyethylene/carbon black immiscible blends

This study investigates the electrical behavior, which is the positive temperature coefficient/negative temperature coefficient (PTC/NTC), and structure of polypropylene (PP)/ultrahigh molecular weight polyethylene (UHMWPE)/carbon black (CB) and PP/γ irradiated UHMWPE (XL‐UHMWPE)/CB blends. As‐received UHMWPE or XL‐UHMWPE particles are chosen as the dispersed phase because of their unusual structural and rheological properties (extremely high viscosity), which practically prevent CB particles penetration. Because of their stronger affinity to PE, CB particles initially form conductive networks in the UHMWPE phase, followed by distribution in the PP matrix, thus interconnecting the CB‐covered UHMWPE particles. This unusual CB distribution results in a reduced electrical percolation threshold and also a double‐PTC effect. The blends are also investigated as filaments for the effect of shear rate and processing temperature on their electrical properties using a capillary rheometer. Because of the different morphologies of the as‐received and XL‐UHMWPE particles in the filaments, the UHMWPE containing blends exhibit unpredictable resistivities with increasing shear rates, while their XL‐UHMWPE containing counterparts depict more stable trends. The different electrical properties of the produced filaments are also related to differences in the rheological behavior of PP/UHMWPE/CB and PP/XL‐UHMWPE/CB blends. Although the flow mechanism of the former blend is attributed to polymer viscous flow, the latter is attributed to particle slippage effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 104–115, 2001     

Short‐time fabrication of well‐mixed high‐density polyethylene/ultrahigh‐molecular‐weight polyethylene blends under elongational flow: morphology,mechanical properties and mechanism

As linear polyethylenes, ultrahigh‐molecular‐weight polyethylene (UHMWPE) and high‐density polyethylene (HDPE) have the same molecular structure, but the large difference in viscosity between them makes it difficult to obtain well‐mixed blends. An innovative eccentric rotor extruder (ERE) generating an elongational flow was used to prepare HDPE/UHMWPE blends within short processing times. Compared with the obvious two‐phase morphology of a sample from a twin‐screw extruder observed with a scanning electron microscope, few small UHMWPE particles were observed in the HDPE matrix for a sample from the ERE, indicating the good mixing on a molecular level of HDPE/UHMWPE blends achieved by the ERE during short processing times. The morphological changes of blends prepared using the ERE evidenced the good integration of HDPE and UHMWPE even though the UHMWPE content is up to 50 wt% in the blends. Moreover, all blends retained most of the intrinsic molecular weight. The good mixing was further confirmed from the thermal, crystallization and rheological behaviors determined using differential scanning calorimetry and dynamic rheological measurements. Importantly, the 50/50 blend presented improved mechanical properties, especially super‐impact strength of 151.9 kJ m^?2 with incomplete‐break fracture state. The strengthening and great toughening effects of UHMWPE on the blends were attributed to the addition of unwrapped UHMWPE long molecular chains. The effective disentanglement mechanism of UHMWPE chains under elongational flow was explained schematically by a non‐parallel three‐plate model. © 2019 Society of Chemical Industry     

High temperature melted,radiation cross-linked,vitamin E stabilized oxidation resistant UHMWPE with low wear and high impact strength

In a previous communication we showed improvement in the wear resistance and toughness of cross-linked ultrahigh molecular weight polyethylene (UHMWPE) for total joint implants by radiation cross-linking after high temperature melting (HTM). In this study, we hypothesized that introduction of vitamin E into UHMWPE before high temperature melting could improve the oxidative stability of these UHMWPEs with low wear and high toughness. Vitamin E was blended with UHMWPE powder at concentrations of 0.1 and 0.2 wt% and consolidated, followed by melting at 300 and 320 °C for 5 h, and subsequent irradiation with electron beam to 150 kGy. These vitamin E/UHMWPE blends showed improved tensile and impact toughness and good wear resistance in comparison with the radiation cross-linked vitamin E/UHMWPE blends. Aggressive accelerated aging with or without pro-oxidant lipids showed that vitamin E-blended, high temperature melted and subsequently irradiated UHMWPE had good oxidation resistance.     

Thermo‐electric behavior (PTC) of carbon black–containing PVDF/UHMWPE and PVDF/XL‐UHMWPE blends

This paper describes the structure and electrical performance of PTC/NTC (positive temperature coefficient/negative temperature coefficient) effects and their reproducibility upon healing/cooling cycles. The following three‐component blends were studied: PVDF/UHMWPE/CB, PVDF/XL‐UHMWPE/CB and γ‐irradiated compression molded plaques of these blends. Carbon black (CB) particles are attracted to the UHMWPE (ultra high molecular weight polyethylene) and XL (cross‐linked)UHMWPE particles, which constitute the dispersed phase in the PVDF (polyvinylidene fluoride) matrix, but practically cannot or only very slightly penetrate them because of their extremely high viscosity. A double‐PTC effect was exhibited by all unirradiated samples. Irradiation of compression molded PVDF/UHMWPE/CB plaques does not add to their already outstanding reproducibility, and it results In a wide single‐PTC effect. Irradiation of compression molded PVDF/XL‐UHMV/PE/CB plaque, slabilizes their structure upon heating/cooling cycles and thus makes them reproducible PTC/NTC materials, still exhibiting a double‐PTC effect. The carbon black concentrations studied in this report are extremely low (< 2 phr CB) in comparison to other literature reports.     

PA-6/UHMWP/EHDPE-g-MAH共混合金的形态结构与性能的研究

通过SEM观察和机械性能测试,研究了PA 6 UHMWPE HDPE g MAH共混合金的形态结构和性能。结果表明:加入HDPE g MAH可有效地改善共混物的相容性,增强两相界面间的粘结强度,降低分散相尺寸;同时还改善了共混物的机械性能,降低了熔体流动速率,提高了常温和低温冲击强度,降低了吸水率。     

Micro-phase separation and crystallization behavior of amorphous oriented PLLA/PVAc blends during heat treatment under strain

Amorphous oriented poly(l-lactide) (PLLA)/poly(vinyl acetate) (PVAc) 50/50 films were prepared by uniaxial drawing of melt-mixed blends at 65 °C. The morphology development and crystal organization of the blends during heat treatment under strain were investigated using small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). Equatorial scattering maxima in the SAXS patterns for samples annealed at 75 °C were observed before the appearance of crystal reflections. Further annealing of the samples at higher temperature induced two further discrete meridian scattering maxima. The observations indicated that homogenous oriented PLLA/PVAc film undergoes micro-phase separation first, followed by crystallization of PLLA in the PLLA-rich phase. The micro-phase separated PVAc nanodomains are aligned parallel to the stretching direction, whereas the crystallized PLLA lamellae are oriented perpendicular to the stretching direction (crystal c-axis along the stretching direction). Micro-phase separation was not observed when films were annealed at 120 °C, at which temperature the high crystallization rate of PLLA overwhelmed the micro-phase separation process.     

聚丙烯/超高摩尔质量聚乙烯共混物的结构与性能研究

研究了不同物料比和加工工艺对聚丙烯（PP）／超高摩尔质量聚乙烯（UHMWPE）共混体系性能的影响。结果表明，PP／UHMWPE共混体系具有比音一组分更高的冲击性能，当体系中UHMWPE的质量分数为60％时，共混物的冲击强度高达101kJ/m^2，分别是PP的1．8倍和UHMWPE的1．3倍，将UHMWPE加入PP中可明显降低PP的摩擦系数，提高其耐磨性，而适量UHMWPE加入PP中，对UHMWPE的耐磨性能无不良影响，对以PP为连续相的共混体系，混炼方式对共混物的性能影响大，偏光显微镜分析表明，当PP／UHMWPE共混体系中UHMWPE的质量分数大于40％时，就很难观察到明显的PP大球晶结构，DSC分析显示，PP／UHMWPE共混物出现了两纯组分熔点的结晶熔融峰，PP／UHMWPE为热力学不相容体系。     

Viscoelastic properties correlations to morphological and mechanical response of HDPE/UHMWPE blends

Melt-mixed and injection molded binary blends of high density polyethylene (HDPE)/ultra high molecular weight polyethylene (UHMWPE) were evaluated for their structural, thermal, rheological, morphological and mechanical attributes. X-ray diffraction (XRD) study has revealed the absence of any significant changes in the crystalline alignment/morphology of the two polyethylene components. Differential scanning calorimetry (DSC) studies revealed the increase in melting temperature, whereas the properties such as crystallization temperature and percentage crystallinity remained broadly unaffected. Dynamic rheological behavior revealed a transition from liquid like behavior (G′?<?G″) to solid like behavior (G′?>?G″) in the composition range of 20–30 wt% of UHMWPE. Scanning electron microscopy (SEM) of the cryo-fractured surface depicts two phase morphology along with very strong interface. The blending of UHMWPE with HDPE matrix has caused improvement in tensile, impact and flexural properties, whereas strain at break suffered a decrease. The analysis of tensile fractured surface morphology by SEM has proved to be useful in qualitatively understanding the underlying failure mechanisms. Eventually, a viscous-to-elastic transition in the rheological behavior has been observed and found to have a correspondence with structural, mechanical and morphological response in the similar composition window.     

UHMWPE/HDPE共混物的流动性及力学性能的研究

采用不同MFR的HDPE与UHMWPE进行熔体共混。结果表明UHMWPE／HDPE共混物流动性和力学性能的变化受体系组成、熔体粘度比等因素的影响较大。HDPE的MFR过高、过低或用量过多，均不利于共混物流动性及综合力学性能的改善。当HDPE作为分散相时，易于实现向UHMWPE高粘弹粒子的渗透、分散及结合，共混物的．MFR及拉伸屈服强度、断裂强度、断裂伸长率均比UHMWPE有提高，共混物表现出协同效应；当UHMWPE为分散相或二者熔体粘度比差异过大时，混合效果变差，共混物综合力学性能下降；在某些中间配比下，二者表现出增链缠结效应，共混物MFR明显降低。     

Shear-induced crystallization in isotactic polypropylene containing ultra-high molecular weight polyethylene oriented precursor domains

Melt blends of short ultra-high molecular weight polyethylene (UHMWPE) fibers and isotactic polypropylene (iPP) were subjected to shear at 145 °C, above the melting point of polyethylene (PE). Structural evolution and final morphology were examined by in situ synchrotron X-ray scattering/diffraction as well as ex situ microbeam X-ray diffraction and high resolution scanning electron microscopy, respectively. Results indicate that the presence of oriented UHMWPE molten domains significantly facilitated the crystallization of iPP and enhanced the initial ‘shish-kebab’ structure leading to the final cylindritic morphology. It is argued that shear flow aligns the fibrillar UHMWPE domains, where the interfacial frictions between PE and iPP effectively retards the relaxation of iPP chains, allowing the aligned iPP chains to create a shish-like structure. Nucleation on the iPP shish initiates the folded chain lamellae (kebabs), which grow perpendicularly to the iPP/PE interface.     

Rheological,thermal, and morphological properties of low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene and linear low‐density polyethylene/ultra‐high‐molecular‐weight polyethylene blends

The dynamic rheological behavior of low‐density polyethylene (LDPE)/ultra‐high‐molecular‐weight polyethylene (UHMWPE) blends and linear low‐density polyethylene (LLDPE)/UHMWPE blends was measured in a parallel‐plate rheometer at 180, 190, and 200°C. Analysis of the log–additivity rule, Cole–Cole plots, Han curves, and Van Gurp curves of the LDPE/UHMWPE blends indicated that the blends were miscible in the melt. In contrast, the rheological properties of LLDPE/UHMWPE showed that the miscibility of the blends was decided by the composition of LLDPE. The differential scanning calorimetry results and scanning electron microscopy photos of the LLDPE/UHMWPE blends were consistent with the rheological properties, whereas with regard to the thermal and morphological properties of LDPE/UHMWPE blends, the results reveal three endothermic peaks and phase separation, which indicated a liquid–solid phase separation in the LDPE/UHMWPE blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of solid‐state shear milling on structure and properties of HDPE/UHMWPE blends

The structure and properties of HDPE/UHMWPE blends prepared through a pan‐milling reactor in solid state at ambient temperature were compared with the blends made by melt mixing. The changes of structure and properties of the blends were investigated by FTIR, melt flow index, mechanical properties, dynamic rheological measurement, DSC, and WAXD. DSC measurement illustrated that after pan‐milling treatment, the half‐width of the melting temperature became smaller. The more content of UHMWPE added in the blend, the more evident change was observed. Combined with the dynamic rheological analysis, it was proved that, the pan‐milling treatment can improve the compatibility of the HDPE/UHMWPE blends. X‐ray diffraction analysis showed that after pan‐milling treatment some ordered structure could be induced, but after heat treatment, the induced crystalline structure disappeared. The tensile properties of pan‐milled HDPE/UHMWPE blends also achieved improvement after pan milling treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39916.     

Shear-induced crystallization of isotactic polypropylene within the oriented scaffold of noncrystalline ultrahigh molecular weight polyethylene

Shear-induced crystallization of isotactic polypropylene (iPP) within the oriented scaffolds of noncrystalline ultrahigh molecular weight polyethylene (UHMWPE) was investigated by means of in situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). The study was carried out using iPP/UHMWPE blends under isothermal crystallization at 145 °C (i.e., above the melting point of polyethylene) and step shear (shear rate=60 s⁻¹, duration=5 s) conditions. The oriented and isotropic iPP crystalline phases were extracted from the 2D WAXD pattern, and their kinetics data were evaluated with the Avrami equation. The dominant component in the oriented iPP phase was a kebab structure, whose nanostructure dimensions were determined by a novel SAXS analysis scheme. The minor non-crystalline but oriented UHMWPE component played a key role in the nucleation of iPP, which could be explained in terms of mutual diffusion at the interface, resulting in a significant increase in the relaxation time of iPP chains. As a result, after shear, the interfacial iPP chains could also retain their orientation and formed oriented nuclei to initiate the kebab growth.     

In-situ X-ray observation of phase transformation of rhombohedral boron nitride under static high pressure and high temperature

In-situ X-ray diffraction study for phase transformation of rhombohedral boron nitride (rBN) to a denser phase was performed under static high pressure (HP) and high temperature (HT) up to 9 GPa and 1600 °C. It was found that the layer stacking sequence of rBN structure began to change at less than 1 GPa, and the phase transformation to wurtzite structure (wBN) was observed at 6–7 GPa and room temperature. After conversion to wBN, further transformation to the zincblend type cubic structure (cubic BN) at 8 GPa and 1400 °C was observed, which is quenchable and the P-T conditions yielding cBN form were similar to that from hexagonal boron nitride. The observed behavior of the phase transformation of rBN by using in-situ X-ray diffraction study is well consistent with the results obtained from the quenching experiment from HP/HT by using belt type HP apparatus.

No structural change was observed at 600°C isothermal compression up t0 8GPa, while wBN formation was observed at room temperature compression at 7 GPa. This variation of the transformation behavior under HT isothermal compression may essentially be caused by the reduction of shear stress which affects the rotation and/or slip of hexagonal plane of rBN under HP.     

Structure and tensile properties change of LDPE/UHMWPE blends via solid state shear milling

LDPE/ultrahigh molecular weight polyethylene (UHMWPE) blends were prepared through a pan‐milling reactor in solid state at ambient temperature. The changes of structure and properties of LDPE/UHMWPE blends were investigated by melt flow index, mechanical properties, scanning electronic microscope (SEM), differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction. SEM photos showed that after pan‐milling treatment the dispersed approximately equiaxed UHMWPE particle became rodlike. DSC measurement illustrated that after pan‐milling treatment, the peaks of UHMWPE shift to lower temperatures while the peaks of LDPE kept stable. The more content of UHMWPE led to more evident shift. X‐ray diffraction analysis showed that the crystallinity of milled LDPE/UHMWPE blends decreased lightly, but the crystalline grain size decreased only for high content UHMWPE blends. The tensile properties of pan‐milled LDPE/UHMWPE blends also achieved significant improvement after pan milling treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2487–2493, 2013     

Tuning the water permeability of ultra-high molecular weight polyethylene microporous membrane by molecular self-assembly and flow field

We have systematically studied phase separation behavior in ultra-high molecular weight polyethylene/liquid paraffin/dibenzylidene sorbitol (UHMWPE/LP/DBS) ternary blends. The aim of this paper is to investigate the combined effect of DBS and flow field on the structure and water permeability of UHMWPE microporous membrane. The experimental results show that DBS molecules self-assemble into fibrils firstly during cooling and the blends exhibit a gel-like state before liquid–liquid phase transition. The relaxation time of DBS fibrils is quite long, which shows a great sensitivity to flow field as compared to UHMWPE chain. UHMWPE microporous membrane was prepared via thermally induced phase separation method. DBS fibrils, as in situ formed nucleating agent, decrease the pore size and water permeability and enhance mechanical properties of membrane remarkably. Shear flow can result in alignment of DBS fibrils, which facilitates the nucleation of UHMWPE and induces the lamellae aligned perpendicular to flow direction. This feature was used to design thermal and mechanical histories and obtained oriented UHMWPE microporous membrane. In comparison to the isotropic UHMWPE microporous membrane, the oriented UHMWPE microporous membrane provides low tortuous paths across the membrane and produces high water permeability.     

Carbon nanotube localization at interface in cocontinuous blends of polyethylene and polycarbonate

A new technique to show good electroconductivity was proposed using carbon nanotube (CNT) localization in cocontinuous immiscible polymer blends comprising ultrahigh-molecular-weight polyethylene (UHMWPE) and polycarbonate (PC). When UHMWPE was added to PC/CNT in the molten state in an internal mixer, CNTs started moving to the UHMWPE phase. However, CNTs require a long time to diffuse into the UHMWPE phase owing to a low diffusion constant. Consequently, they remain at the interface between PC and UHMWPE. When the blends have cocontinuous structure, the localized CNTs at the phase boundary act as a conductive path, leading to a good electroconductivity. Although a similar morphology is obtained by adjusting the balance of interfacial tensions among polymers and CNT, it is difficult to find a system showing appropriate interfacial tensions. As the present method is applicable to various polymer blends, it will be an important technique to prepare a conductive nanocomposite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48676.     

The Effect of Compatibilizer on Morphology and Mechanical Properties of PA6/UHMWPE Blends

Abstract

This work deal with the effect of compatibilizer on the morphological and mechanic properties of polyamide 6 and ultrahigh molecular weight polyethylene (PA6/UHMWPE) blends. The blends were prepared by means of a twin-screw extruder. The compatibilizer was produced by grafting maleic anhydride (MAH) onto high density polyethylene (HDPE). The resulting HDPE-g-MAH was used to prepare ternary blends of PA6/HDPE-g-MAH/UHMWPE by melt mixing. The size of domain of UHMWPE in PA6/HDPE-g-MAH/UHMWPE blends is much smaller than that in PA6/UHMWPE blends. It was found that mechanical properties of PA6/HDPE-g-MAH/UHMWPE blends obviously surpassed that of PA6/UHMWPE blends. These behavior could be attributed to chemical reactions between MAH in HDPE-g-MAH and terminal amino groups of PA6. Thermal analysis were performed to confirm the possible chemical reactions taken place during the blending process.