Volume 36, Issue 4

Polypropylene (PP) is one of the most used polymers for microporous membrane fabrication due to its good thermal stability, chemical resistance, mechanical strength, and low cost. There have been numerous studies reporting the developments and applications of PP membranes. However, PP membrane with high performance is still a challenge. Thus, this article presents a comprehensive overview of the advances in the preparation, modification and application of PP membrane. The preparation methods of PP membrane are firstly reviewed, followed by the modification approaches of PP membrane. The modifications includes hydrophilic and superhydrophobic modification so that the PP membranes become more suitable to be applied either in aqueous applications or in non-aqueous ones. The fouling resistant of hydrophilized PP membrane and the wetting resistant of superhydrophobized PP membrane are then reviewed. Finally, special attention is given to the various potential applications and industrial outlook of the PP membranes.

Sodium alginate was provided with good processibility according to physical and chemical characterization of itself. Alginate scaffold has been used for preparation of soft or hard tissue engineering, but the structure of the scaffold needs to be improved for better performance for skin tissue engineering. In this study, highly porous alginate membrane was formed with ionic crosslinking. High molecular weight (M w =3.0×10 5 ) alginate showed the best film-forming property. Therefore, the appropriate molecular weight should be selected for improving its performance. With freeze-drying technology and pre-freezing at -10°C, we have built the honeycomb materials (porosity=92.06%). Changing the pre-freezing temperature can regulate pore structure to some extent. With the increased dosage of sodium alginate, the porosity and the pore size of the materials were reduced, whereas tensile strength and elongation at break increased. Water absorption performance of the materials was good. The above studies lay a foundation for construction of skin tissue engineering scaffold.

Triethyl citrate (TEC) and acetyl tributyl citrate (ATBC) were used as plasticizer for poly(lactic acid) (PLA). The treated and plasticized PLA at various concentrations were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and opacity. DSC was used to evaluate the crystallinity and thermal property of all the samples. It was found that the glass transition temperature (T g ) and the melting temperature (T m ) decreased as the amount of citrate esters increased. Additionally, the presence of TEC or ATBC tended to increase the crystallinity of PLA. This result was supported by XRD. DMA of plasticized PLA indicates that a decrease in T g is obtained with increasing plasticizer content. FTIR spectra indicate that there are some molecular interactions by intermolecular hydrogen bonds between PLA and citrate esters. The effect of the concentration of plasticizer on the opacity of the films was negligible.

In this paper, high-heat-resistant polymeric composite products were prepared via the traditional melt blending process by incorporating N , N ′-bis(benzoyl) adipic acid dihydrazide (BAAD) into poly( l -lactic acid) (PLLA), which acted as an organic nucleating agent. The heat distortion temperature (HDT) of the PLLA/BAAD composite samples was measured by an HDT apparatus, and a high value of 96.2°C was achieved at a BAAD loading fraction of 0.5 wt.%, whereas, at the same processing conditions, the HDT of PLLA/talc specimens reached a similar value at a talc content of 20 wt.%, which was much higher than the BAAD content. Differential scanning calorimetry and X-ray diffraction analyses were applied to determine the melting and crystallization behavior of the PLLA/BAAD blends. Polarized optical microscopy was used to observe the crystalline morphologies. Thermogravimetric analysis was employed to study the effect of BAAD on the thermal stability of PLLA. Measurement of the mechanical property confirmed that the addition of BAAD was beneficial to the enhancement of the mechanical properties of the resulting blends. However, the tensile strength of the PLLA/talc composites decreased with increasing weight fraction of talc.

A comparison study between carbon black (CB) filled thermoset (epoxy) and thermoplastic, polymethylmethacrylate (PMMA), was done in this research. CB was introduced as the conductive filler in epoxy and PMMA at different filler loading, which ranged from 5 vol.% to 20 vol.%. The physical, mechanical, electrical and thermal stability properties were investigated. The incorporation of CB into both epoxy and PMMA increased the density, improved the thermal stability and electrical conductivity of the composites, reduced the coefficient of thermal expansion and weakened the flexural and fracture toughness properties of the composites.

Large area graphene oxide sheets were synthesized, dispersed in water and used as nanofiller for mechanical improvement in terms of Young’s modulus and ultimate tensile strength (UTS) of polyvinyl alcohol (PVA) at low loading. The molecular level dispersion and interfacial interactions between the graphene oxides and polymeric matrix PVA were the real challenges. An excellent improvement in mechanical properties at 0.35 wt% loading was observed. Modulus improved from 1.58 GPa to 2.72 GPa (~71% improvement), UTS improved from 120 MPa to 197 MPa (~65% improvement), and in spite of these improvements, interestingly, there was no fall in elongation at break at this loading.

Epoxy nanocomposites that are produced in a solvent-free environment suffer from the inadequate dispersion of nanofiller and poor interfacial interaction between the nanofiller and polymer matrix. In this work, the effect of replacing a portion of the epoxy resin with a viscosity reducing agent (VRA) on the structure, electrical and mechanical properties of carbon nanotube (CNT)/epoxy nanocomposite have been investigated. Optical microscopy (OM) and transmission electron microscopy (TEM) were used to characterize the structure of the nanocomposite at the microscale and nanoscale, respectively. For nanocomposites without VRA, it was found that the addition of CNT degrades the tensile strength and toughness; meanwhile, it enhances the flexural modulus, Young’s modulus and electrical conductivity of the nanocomposite. However, the addition of VRA retained the tensile strength of the epoxy system and maintained the improvements in flexural strength and electrical conductivity that have been achieved due to CNT addition.

Heat generation mechanism in processes of ultrasonic welding of plastics was not fully solved. Experiment results showed that increasing the amplitude increased the energy dissipated with the exception of low amplitudes, but no detailed analysis can be found in explaining this problem. This study proposed to investigate the heat-generating processes in such a condition with a new physically based model by solving the N-S equations. The increasing mean temperature profiles and the final temperature patterns are well agreed with previous researches. The results predicted that the distribution of heat generated in the welding zone was non-uniform. The highest temperature area changed its position with the variation of time and the amplitude of vibration. In low amplitude conditions, energy dissipation was found to firstly increase with a slight fluctuation, then decreased when the driven amplitude was larger than 5 μm. And different temperature distribution patterns were observed at these turning points.

Textile techniques can be applied to create two-dimensional or three-dimensional tubular fabrics. Three-dimensional tubular knits can be used in many fields, such as for medical textiles, conductive textile, composites, and tissue engineering. This study aimed to examine the effects of different yarn types on various fabrics and of different temperatures on the variations in the properties of textiles. Four types of wrapped yarn (P150, P75, S140, and S70) were made into tubular braids and knits, after which the products were thermally treated at various temperatures (120°C, 140°C, and 160°C). A shrinkage measurement, a porosity test, a braid angle test, and a tensile test were performed to evaluate the tubular braids and knits. The test results indicated that the thermal treatment temperature did not affect the porosity of the tubular braids and tubular knits. The porosity of the tubular braids was between 40.32% and 48.27%, while that of the tubular knits was between 10.15% and 35.57%. In addition, the tensile strength of both fabric types increased by 40–50%, while their displacement increased by 200–250%. In the future, the efficacy of tubular braids and tubular knits for use as vascular grafts will be examined.

The aim of this work is to determine which of the techniques that allow to measure the strain induced in polymer composites by the chemical shrinkage of resin is most appropriate for predicting process-induced deformations. There are two approaches to determine the chemical strain: measurements in-plane and through-the-thickness of composite. In the following study, two methods were used for the measurement of unidirectional carbon/epoxy composite: novel one that employs a dynamic mechanical analyzer to measure through-the-thickness strain and one designed previously to measure in-plane strain. As the results of the methods were different, finite element simulation of process-induced deformation of C-sectioned composite element was carried out in order to verify the results. Comparison of numerical results with the real part deformation showed that the measurement of through-the-thickness chemical strain is the more accurate approach in the case of the prediction of deformation and that the novel method gives valid results.