Self-assembly nucleators have been increasingly used to manipulate the crystallization of PLLA due to their strong intermolecular interaction with PLLA, while the molecular mechanism of such interaction is still unrevealed. In present work, one special self-assembly nucleator (TMC-300) with relatively high solubility in PLLA matrix, is chosen to investigate how the interaction works at molecular level to promote the crystallization of PLLA mainly through time-resolved spectroscopy. The results indicate that due to the dipole–dipole NH···O═C interaction between dissolved TMC-300 and PLLA, PLLA chains are transformed into gt conformer before TMC-300 phase-separating from PLLA melt, resulting in low energy barrier to pass for the following formation of PLLA α-crystal (α-crystal is consisted of gt conformer). Once the dissolved TMC-300 starts to self-assemble into frameworks upon cooling, the transformed PLLA chains with high population of gt conformer form the primary nuclei on the surface of such self-assembling TMC-300 frameworks. For the first time, not only the heterogeneous nucleation but also the conformational regulation of PLLA chains are proved to be responsible for the high efficiency of the self-assembly nucleators (TMC-300) in promoting the crystallization of PLLA. Therefore, conformational regulation is proposed for crystalline manipulation of PLLA, and this work brings new insight on promoting the crystallization of PLLA even other polymers by regulating their molecular conformation.

•The alternating multilayered composites with 2 to 32 layers were obtained.•The multilayered structure was constructed through the melt extrusion method.•The contradiction between antistatic property and electrical insulation was resolved.•Thermally conductive enhancement mechanism of structure was in-depth investigated.To fabricate thermally conductive while electrically insulating composites with excellent antistatic property is a huge challenge in the region of packaging materials of electronic devices due to the contradiction between the electrical insulation and the antistatic property. In the present work, the peculiar multilayer structures with alternating high efficiency thermally, electrically conductive layers and thermally conductive, electrically insulating layers were constructed successfully through a simple, one-step melt extrusion method. Such thermally conductive and electrically insulating composites possessed significant anisotropic electrical resistivity; for example, the in-plane electrical resistivities (parallel to the layer direction) were below 117 Ω × cm, while the through-plane electrical resistivities were over 5 × 1013 Ω × cm. Meanwhile, with increasing the layer number, thermal conductivity of the composite with the same filler loading was improved monotonously, and reached as high as 1.45 W/(m × K) in the composite with 32 layers. In addition, tensile strength and elongation at break of the composites were also enhanced due to the different deformation mechanisms of separate layers. Furthermore, to give a deep insight into the enhancement mechanism of thermally conductive property, finite element analysis was applied and the results indicated that high efficiency thermally, electrically conductive layers possessed magnified effects on the heat dissipation. Therefore, the multilayer structure with alternating high efficiency thermally, electrically conductive layers and thermally conductive, electrically insulating layers can endow the composite with excellent comprehensive properties effectively, and it also sheds light on the design and fabrication of high performance materials for the applications of thermal management or other energy harvesting fields.Download high-res image (265KB)Download full-size image

Neutron radiation is often encountered in a wide range of industries, such as aerospace, healthcare and nuclear power plants. It has been an arduous challenge to shield this neutron radiation to improve equipment safety and protect human health. In order to make an effective neutron shielding material, alternating multi-layered composites (high density polyethylene)/(high density polyethylene/boron nitride), (HDPE/(HDPE/BN)) and (HDPE/BN)/(HDPE/Barium sulfate (BaSO4)) were fabricated using a multi-layered co-extrusion system. The HDPE/BN layers in the alternating multilayered HDPE/(HDPE/BN) and (HDPE/BN)/(HDPE/BaSO4) composites had a continuous and layered distribution in their structure, with the BN particles oriented in the extrusion direction. The probability of collision between incident photons and flake-shaped particles is enhanced through alignment of the oriented BN particles. In this way, neutron transmittance noticeably decreased with an increasing number of layers. Compared to traditional polymer-blended materials, the alternating multilayered composites showed excellent shielding efficiency. In addition, the results of the dynamic rheological analysis showed that alternating multi-layered composites with more layers can weaken the cross-linking effects induced by secondary radiation. Furthermore, according to the Nano-TA analysis, BaSO4 was an effective shield of secondary radiation, so the average melting point, in nanoscale, can be represented as follows: (Nano-Tm¯) ((HDPE/BN)/(HDPE/BaSO4))> Nano-Tm¯ (HDPE/(HDPE/BN)).

The heat dissipation property of the thermally conductive and electrically insulating composites can be enhanced by constructing high efficiency thermally conductive pathways, while the mechanical properties of the final composites are always neglected. In this work, graphite (Gt), a typical carbon based filler with excellent thermal conductivity, was highly oriented and uniformly dispersed in polymer matrix to keep the electrical resistivity of the composite at a high level, even when the content of Gt was 33 wt%. Then, in order to further improve thermal conductivity, the consecutive and high efficiency thermally conductive yet electrically insulating pathways were constructed by adding silicon carbide (SiC) particles into the composites as junctions to release the thermally conductive potential of Gt via forming phonon transport channels. As a result, thermal conductivity reached 1.68 W/(m × K) when the content of SiC was 20 wt%. Meanwhile, the in-plane thermal conductivity (along the melt flow direction) was as high as 3.8 W/(m × K), which was over 5-fold larger than the through-plane thermal conductivity (along the thickness direction). Subsequently, Agari model and thermally conductive simulation based on the finite element analysis were also applied to give a deep insight into the effect of this special filler architecture on the heat dissipation performance of the composites. Furthermore, mechanical properties of such composites were also largely enhanced. Therefore, building up high efficiency thermally conductive and electrically insulating pathways through highly oriented and uniformly dispersed 1-D or 2-D anisotropic carbon based fillers close-packed with another kind of uniformly dispersed thermally conductive and electrically insulating fillers is a simple and effective method to endow the composites with excellent thermal conductivity, high electrical resistivity and great mechanical properties simultaneously.

The poor dispersion of graphene-based materials and the weak interfacial interaction between the nanofillers and polymer matrix greatly limit the reinforcing efficiency of graphene-based nanofillers on polymers. Moreover, the polymers reinforced with graphene usually tend to be brittle. In this paper, hybrid GO/CNT nanostructure was designed and cross-linked through amide bond, which can disperse and embed into the PI matrix commendably, providing strong interfacial interaction between the nanofillers and the PI matrix. Compared with neat PI, the amide bond hybrid GO/CNT (1.1 wt % in total) can endow the PI matrix with a dramatic increment on strength (118%), modulus (94%), fracture toughness (138%) and electrical conductivity (11 orders), due to the effective stress transfer at the interface between PI matrix and nanofillers as well as at the interface between GO and CNT. Furthermore, the over-all performance of the nanocomposites containing chemical amide bond hybrid GO/CNT is superior to those containing hydrogen bond hybrid GO/CNT and π-π stack hybrid GO/CNT, providing us with a framework to study the interfacial interactions (covalent bond, hydrogen bond and π-π stack) in hybrid GO/CNT nanomaterials and their influence on the performance of polymer nanocomposites.Download high-res image (289KB)Download full-size image

To simultaneously resolve an undesirable electromagnetic wave and heat emissions that were caused by an electronic device, an electromagnetic interference (EMI) shielding material with excellent electrical insulation and high thermal conductivity was urgently required. However, keeping the EMI shielding material on electrical insulation still remained a challenge due to the superior electrical conductive network in it. We fabricated an ordered multilayer film through casting layer (graphene oxide/poly(-hydroxybenzate-co-DOPO-benzenediol dihydrodiphenyl ether terephthalate)) by layer (boron nitride/(maleated styrene-ethylene/butylene-styrene)), and the special architecture of the film not only simultaneously built the superior electrical and thermal conductive network in-plane direction, but also effectively blocked the electrical conductive path through-plane direction. Moreover, the ordered multilayer film (11 layers) exhibited a good EMI shielding effectiveness (37.92 dB), excellent electrical insulation (breakdown strength was 1.52 MV/m) and high thermal conductivity (12.62 W/mK) in-plane direction, indicating that the ordered multilayer film was a novel promising candidate for an ideal EMI shielding material with excellent electrical insulation and high thermal conductivity in today's electronic devices.The ordered multilayer film simultaneously has superior electromagnetic interference shielding effectiveness, excellent electrical insulation and high thermal conductivity.

In this work, an advanced extrusion approach (MSEDC technique) was adopted to control crystalline structure and phase morphology in PP/POE blends. The results showed that PP matrix alternating shish-kebab crystalline structure with spherulites, and POE phase alternating micro-/nano-sheets with nano-fibrils and elongated spherical particles were introduced into PP/POE blends simultaneously. The as-obtained densely-stacked shish-kebab crystalline structure of the PP matrix can provide blends with greatly enhanced tensile yield strength, while the planar POE phase with micro-/nano-sheets can induce the deflection of crack, providing the blends with greatly increased toughness. Moreover, hierarchical interfacial entanglement, formed between PP molecules and POE molecules, can connect the matrix and dispersed phase effectively, which is helpful to obtain materials with simultaneously enhanced strength and toughness. Compared with neat PP, the notched impact strength and tensile yield strength of MSEDC PP/POE blends is enhanced 490% and 35%, respectively, which is the first report realizing simultaneous reinforcement and toughening in polypropylene based on a polypropylene/elastomer binary system.

In an attempt to correctly understand an extra weak exothermic peak (Th) (near the melting temperature of the polyethylene (PE)) of the PE in the PE/boron nitride (BN) composites, a new hypothesis was proposed and proved: Th was induced by PE crystallization. When the BN content was more than 10 wt%, the Th was observed. Simultaneously, beside the Th, another weak exothermic peak (T1h), was also found. Beside the main melting peak (Tm), an extra melting peak (Tmh) also appeared. The results of the local thermal analysis technique (nano-TA) showed that the local melting temperature (nano-Tm) of the PE near the BN aggregates was higher 4–8 °C than that in other areas, indicating that the meso-phase (meso-phase was also induced by PE crystallization) can be formed near the BN aggregates during the PE crystallization. Moreover, the appearance of the Th and T1h was attributed to the differently nucleated capability of the different BN aggregates in local areas during the PE crystallization. When the annealing time and temperature were 20 min and 130 °C, respectively, the thermal conductivity of the PE/BN composite was 16% higher than that of the unannealed PE/BN composites. In addition, the results of the wide angle X-ray diffraction (WAXD) showed that the BN particles had no influence on the PE crystal form in the PE/BN composites.

•The POE foam/film foaming sheet with alternating multilayered structure was successfully prepared through multilayer co-extrusion system.•This technique provided the new idea to obtain structure–foaming material with high sound absorption.•The foam/film alternating multilayered structure could be improved the sound absorption efficiency due to more reflection and friction loss of sound in layer interface. Meanwhile, the sound absorption efficiency of the foam/film foaming sheet with alternating multilayered structure increased with increasing of layer number.Poly (ethylene-co-octene) foaming materials with alternating multilayered structure were successfully prepared through multilayer co-extrusion. Poly (ethylene-co-octene) was micro-crosslinked and fully cured before and after the foaming process with co-extrusion. The effects of the layer number on foam morphology and density of poly (ethylene-co-octene) foaming materials were investigated. It was found that with increasing the layer number, the cell size was reduced while the density was not obviously changed. Meanwhile, this technique provided the new idea to obtain the poly (ethylene-co-octene) foaming material with excellent sound absorption. The results indicated that the foam/film alternating multilayered structure could improve the sound absorption efficiency of the foaming sheet, which was increased with increasing the layer number and decreasing of cell size.

The multilayered polypropylene (PP) and poly(ethylene-co-octene) (POE) sheets were prepared by the micro-layered co-extrusion system. The essential work of fracture (EWF) and the impact tensile methods have been successfully used to evaluate the toughening behaviors of the PP/POE multilayered blends under quasi-static and dynamic uniaxial tensile stress, respectively. The experimental results indicate that the multilayered structure plays a key role in the toughening behaviors. On increasing the layer number of the multilayered blends, the specific essential work of fracture, we, increases obviously. As for the βwp, there is no obvious variation in the multilayered blends with low POE content (6.79%), however, obvious enhancement is observed with increasing the layer number of the high POE content multilayered blends (16.57%). Compared with the conventional blends, the multilayered blends with 6.79% POE content are effective to increase the value of we. Additionally, the multilayered blends with high layer numbers present absolute advantage in improving the impact tensile values.

In this work, the effects of annealing conditions on the microstructure of polypropylene (PP) precursor films and further on the porous structure and permeability of stretched membranes were investigated. Combinations of WAXD, FTIR, DSC and DMA results clearly showed the crystalline orientation and crystallinity of the precursor film increased with annealing temperature, while the molecular chain entanglements in the amorphous phase decreased. Changes in the deformation behavior suggested more lamellar separation occurred for the films annealed at higher temperatures. Surface morphologies of the membranes examined by SEM revealed more pore number and uniform porous structure as the annealing temperature increased. In accordance with the SEM results, the permeability of the membranes increased with annealing temperature. On the other hand, it was found that 10 min was almost enough for the annealing process to obtain the microporous membranes with an optimal permeability.

In this study, a novel approach is proposed to significantly toughen polypropylene (PP) by fabricating PP and poly(ethylene-co-octene) (POE) into alternating multilayered blends instead of conventional blends. POM, SEM, polarized-FTIR, DSC and XRD were performed to investigate and characterize the microstructure of the alternating multilayered and conventional blends. The crack-initiation term, impact fracture surface and bulk morphologies beneath the fracture surface are inspected in order to understand the differences in the impact behaviors of the alternating multilayered blends and the conventional blends. The results show that the unique multilayered structure has a great advantage in toughening PP. The notable improvement of the toughness of the alternating multilayered blends is ascribed to the synergetic effects of the interfaces' delaminations, craze deflection, larger subcritical damage zone (stress whitening zone) and the combination of the voids and deformation during the fracture process. Moreover, the alternating multilayered blends exhibit high toughness with a low POE content; thus, this work also offers a new method to toughen the materials without an obvious sacrifice of their strength.

In this paper, polypropylene (PP) and polypropylene/poly(ethylene-co-octene) blends (PP/POE) were fabricated into alternating multilayered materials to improve the low-temperature toughness of PP efficiently compared with conventional PP/POE blends. POM, SEM, micro-FTIR and part-impact test were performed to characterize and investigate the alternating multilayered microstructure and its relationship with mechanical properties. The results showed that the unique alternating multilayered microstructure could generate a distinctive distribution of POE, resulting in the great change in both macro- and micro-morphology of the materials. Most interestingly, the morphological evolution of the dispersed POE phase before and after the impact showed that a brittle–ductile transition (BDT) layer was formed at the interlayer interface between the adjacent PP layer and the PP/POE layer during the impact process, which was the main reason for the great improvement of the low-temperature toughness. Moreover, the rigidity of alternating multilayered materials was maintained very well because of the existence of the rigid PP layer, indicating that the alternating multilayered microstructure was very helpful to maintain a good balance between toughness and rigidity.

In this paper, SEM, POM, DSC, FTIR, polarized FTIR, and part-impact test were performed to investigate the effect of dispersed POE phase on crystallization kinetics behavior, molecular interaction, and impact-induced morphological evolution in polypropylene/poly(ethylene-co-octene) (PP/POE) blends. The main focus was to establish a systematic and deep toughening mechanism from microscopic molecular interaction to macroscopic deformation. The results showed that the existence of POE particles played the role of an obstacle during the crystallization process of a PP matrix, which could increase the growth path of PP lamellae or ordered PP molecules and reduce the growth space of spherulites, resulting in a slower spherulite growth rate and smaller spherulite size. This behavior was explained by a crystallization model. Most interestingly, a coated structure was formed in the interface, which was a transition state structure of molecules with different morphologies. The as-formed coated structure can be considered the origin of the cavitation effect and impact-induced morphology evolution of POE particles during the impact process. Moreover, micro-plastic deformation in PP/POE blends during the fracture process was a multi-stage mechanism, in which the POE content played a decisive role.

In this paper, effect of phase morphology on water diffusion in phosphorus-containing aromatic liquid crystalline copolyester (P-TLCP) named as poly(-hydroxybenzate-co-DOPO-benzenediol dihydrodiphenyl ether terephthalate) (PHDDT) was investigated by two-dimensional correlation infrared (2DIR) spectroscopy, in order to understand well the relationship between structure and properties of P-TLCP. The phase morphologies of the PHDDT films were observed by polarized light microscope. The experimental results showed that the clear nematic texture, which was observed for PHDDT film treated at 250 °C for 3 min under a nitrogen atmosphere. However, lots of bright spots were observed for untreated PHDDT film due to weak crystallization of PHDDT molecules. Moreover, the density of the untreated PHDDT film (1.1631 ± 0.0257 g/cm−3) was lower than that of the treated one (1.2969 ± 0.0134 g/cm−3), indicating that the arrangement of the molecules in treated PHDDT film was compact in comparison with that in untreated one. Therefore, the average diffusion coefficient of water in treated PHDDT film was lower than that in untreated one. The mechanisms of water diffusion into PHDDT films with different phase morphologies can be obtained through 2DIR analysis in OH stretching and bending bands. It was found that water diffused into the treated PHDDT film by forming moderate hydrogen bonds prior to forming strong and weak hydrogen bonds, while diffused into the untreated one by forming strong and weak hydrogen bonds prior to forming moderate hydrogen bonds. It was also found that the spectral intensity of PO varied prior to that of CO during water diffusion into untreated PHDDT film, which was reversed for treated PHDDT film.