Local process-dependent structural and mechanical properties of extrusion blow molded high-density polyethylene hollow parts

Although applied for several decades, production of hollow plastic parts by extrusion blow molding (EBM) is still over-dimensioned. To overcome this issue, a thorough investigation of the process-structure-property relationship is required. In this study, the local process-structure-property relationship for high-density polyethylene EBM containers is analyzed with differential scanning calorimetry and dynamic mechanic analysis microindentation. Local process-dependent crystallinity and complex modulus data at various processing conditions are supplemented with wide-angle X-ray diffraction and transmission electron microscopy (TEM). The crystallinities and the complex moduli clearly show lower values close to the mold side than at the inner side and the middle of the cross-section, which reflects the temperature gradient during processing. Additionally, the orientation of the polymer chain (c-axis) reveals a low level of biaxiality with a slight tendency towards transverse direction. The biaxiality increases for low mold temperature and high draw ratio. Finally, biaxiality is confirmed with TEM, which reveals no preferred lamellar orientation.     

Balancing the Crystallinity and Film Formation of Metal–Organic Framework Membranes through In Situ Modulation for Efficient Gas Separation

Polycrystalline metal–organic framework (MOF) layers hold great promise as molecular sieve membranes for efficient gas separation. Nevertheless, the high crystallinity tends to cause inter-crystalline defects/cracks in the nearby crystals, which makes crystalline porous materials face a great challenge in the fabrication of defect-free membranes. Herein, for the first time, we demonstrate the balance between crystallinity and film formation of MOF membrane through a facile in situ modulation strategy. Monocarboxylic acid was introduced as a modulator to regulate the crystallinity via competitive complexation and thus concomitantly control the film-forming state during membrane growth. Through adjusting the ratio of modulator acid/linker acid, an appropriate balance between this structural “trade-off” was achieved. The resulting MOF membrane with moderate crystallinity and coherent morphology exhibits molecular sieving for H₂/CO₂ separation with selectivity up to 82.5.     

Crystalline and spectroscopic characterization of poly(2-aminoethyl methacrylate hydrochloride) chains grafted onto poly[(R)-3-hydroxybutyric acid]

The present study is aimed to investigate the degree of crystallinity of poly(3-hydroxybutyrate) P(3HB) grafted with poly(2-aminoethyl methacrylate hydrochloride) (PAEMA) chains using WAXS, micro Raman, and FTIR spectroscopy. The samples were obtained by radiation induced graft polymerization of the monomer in the substrate using different solvents for comparison. The results of crystallinity are consistent with those obtained of lower crystallinity in grafting copolymer relative to the substrate P(3HB). The low crystallinity is directly related to the increase of the degree of grafting, meaning that although the P(3HB) amorphous region is grafted, the crystalline zone is also affected in some extent by the grafting process and the environment of the new molecule. Three different methods were surveyed to determine the variation of crystallinity degree with the grafting degree. It is shown that all methods provide linear relationships between these variables, but WAXS method was found more acceptable than the others (FTIR and Raman). A detailed characterization of the vibrational bands characteristic of amorphous and helical crystalline structure of the grafting copolymers are also highlighted.     

Effect of moisture content on the heat-sealing property of starch films from different botanical sources

In this study, we investigated the differences in the crystallinity of starch films (mung bean, water chestnut, sweet potato, and cassava starches) with different moisture contents stored in different humidity conditions (11%, 22%, 33%, 43%, 54%, 75%, and 84%) and evaluated their thermal adhesion and sealing properties. X-ray diffraction analysis revealed an association between the degree of crystallinity and the moisture content in starch films: crystallinity decreased with an increase in the moisture content. Field Emission Scanning Electron Microscopy (FE-SEM) analysis showed that films with low moisture content failed to completely adhere, but films with a high moisture content and lower crystallinity showed good adherence, with two films perfectly adhered at the same temperature because water molecules acted as a mobility enhancer. The peeling test demonstrated the failure modes of the heat-bound films. The cassava starch film, which had a low amylose content and crystallinity, showed better adhesion compared to other starch films.     

Achieving highly crystalline rate and crystallinity in Poly(l-lactide) via in-situ melting reaction with diisocyanate and benzohydrazine to form nucleating agents

The drawback of the application for poly(_l-lactide) (PLLA) is the low crystalline rate and crystallinity obtaining via normal processing methods. Modifying crystallization of PLLA has been found to be an efficient way to improve its mechanical and heat resistance properties. In this wok, 4, 4′-diphenylmethane diisocyanate (M) and benzohydrazine (P) were employed into PLLA melt to in-situ form nucleating agents. The in-situ melting reaction was confirmed by a nuclear magnetic resonance spectroscopy. The crystallization behavior and crystalline morphology were investigated by a differential scanning calorimetry, a polarized optical microscopy and a field emission scanning electron microscope. The crystalline rate of PLLA was abruptly enhanced by adding (M+P) and melting reaction with PLLA. The crystallization half-time of PLLA dramatically decreased from 42.0 to 1.1 min at 130 °C by the in-situ formation of nucleating agents. The crystallinity of PLLA increased from 10.3 to 42.1 by adding 0.25% (M+P) and melting reaction for 8 min. Furthermore, the size of PLLA crystals was dramatically reduced because of the nucleating effect. Accompanied with improvement on crystallinity, the Vicat softening temperature of PLLA shifted from 57.4 °C to 93.7 °C by the in-situ reaction with 6.00% (M+P), and indicating heat resistance enhancement.     

Alkali treatment of lignocellulosic fibers extracted from sugarcane bagasse: Composition,structure, properties

Lignocellulosic fibers extracted from sugarcane bagasse were treated with NaOH solutions of different concentration (0-40 wt%) to study the effect of alkali treatment on the composition, structure and properties of the fibers. Composition was determined by the van Soest method, structure was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), while mechanical properties by tensile testing. Hemicellulose and lignin content decrease, while cellulose content goes through a maximum as a function of alkali concentration. Crystallinity changes only slightly and microfibril angle (MFA) remains constant thus structural effects and especially MFA are not the primary reasons for changing properties. The Young's modulus of the fibers shows a slight maximum at around 2-4 wt% NaOH content, while tensile strength goes through a much more pronounced one at around 5-8 wt%. Direct correlation between structure and mechanical properties was not found indicating that composition is more important in the determination of properties than structure. Regression analysis proved that the combination of several compositional variables determines mechanical properties in a non-linear manner. The improvement in fiber properties was explained with the dissolution of weak amorphous fractions and the relative increase of cellulose content.     

Electrospinning of nylon-6,6 solutions into nanofibers: Rheology and morphology relationships

The relationship between the rheological properties of nylon-6,6 solutions and the morphology of their electrospun nanofibers was established. The viscosity of nylon-6,6 in formic acid(90%) was measured in the concentration range of 5 wt%-25 wt% using a programmable viscometer. Electrospinning of nylon-6,6 solutions was carried out under controlled parameters. The chemical structure, morphology and thermal properties of the obtained nanofibers were investigated using Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM) and differential scanning calorimetry(DSC), respectively. Entanglement concentration(ce) was found to be 15 wt% and a power law relationship between specific viscosity and solution concentration was observed with exponents of 2.0 and 3.3 for semi-dilute unentangled(c ce) and semi-dilute entangled(c ce) regimes, respectively. The diameter and uniformity of the nanofibers were found to be dependent on the viscosity. Moreover, the average diameter of electrospun nanofibers was found to be dependent on zero shear rate viscosity and normalized concentration(c/ce) in a power law relationship with exponents of 0.298 and 0.816, respectively. For nylon-6,6 solutions, the entanglement concentration(ce = 15 wt%) provides the threshold viscosity required for the formation of a stable polymeric jet during electrospinning and producing uniform beadless fibers. For concentrations less than ce, beaded fibers with some irregularities are formed. DSC analysis showed an increase in crystallinity of all electrospun samples compared to original polymer. Furthermore, Based on FTIR spectroscopy, α phase is dominant in electrospun nanofibers and minor amount of β and γ phases is also available.     

Surface bio-modification of poly(hydroxybutyrate-co-hydroxyhexanoate) and its aging effect

In this work, poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) film was fabricated by a solution-casting method and subsequently was modified by NaOH treatment to improve the surface hydrophilic property. Surface properties including hydrophilicity, surface appearance and functional groups were characterized by water contact angle measurement, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results showed the hydrophilicity of PHBHHx film was obviously improved by the NaOH treatment due to the topography changes promoted by the NaOH-etching and the introduction of polar groups included hydroxyl and carboxyl on the topmost surface layers. However, the modified film exhibited an aging effect: the hydrophilicity decreases with time elapsed during storage. It was found that the aging rate was strongly dependent on the crystallinity of the film and the storage environment. The sample with high-crystallinity lost hydrophilic property slower than that with low-crystallinity. Hydrophilic and low-temperature environment also prevented the modified PHBHHx from fast losing of the hydrophilicity.     

PET/PTT双组分弹性长丝的结晶取向结构和卷曲性能

为研制军官礼服用PET/PTT双组分弹性长丝,在纺丝加工工艺研究的基础上,通过声速法、WAXD、DSC、Instron5566对典型工艺下的弹性长丝进行了结晶和取向结构及卷曲性能的测试分析.在可纺的前提下,PET/PTT两组分复合纺丝中,PET组分优先结晶,具有高于其单组分纤维的拉伸诱导取向和结晶;而PTT组分只有形变,其结晶度和晶区取向均低于其对应的单组分纤维.在实验条件范围内,两组分粘度差异越大,纤维的卷曲伸长率和收缩率越大、声速取向因子增加、各单组分结晶度增加;两组分质量比为50/50时,纤维有最大的卷曲伸长率和收缩率,且各单组分结晶度随该两组分含量差异的增加而减少,而声速取向变化相反;随牵伸比的增加,纤维的整体取向、各组分结晶度均有所增加,卷曲伸长和收缩率也增加.牵伸温度和定型温度对双组分纤维的结构和卷曲性能影响较小.