Search

Polyelectrolytes (PEs) are a class of polymers with ionizable groups on molecular chains and could dissociate into a highly charged polymeric molecule in ionizing solvent. According to their surface charges, PEs can be classified into three groups: cationic PEs, anionic PEs and amphoteric PEs. PEs have received the attention of scientists for nearly a century ever since the discovery that some natural PEs could interact in water to form colloidal complexes known as polyelectrolyte complexes (PECs). PECs with three-dimensional macromolecule structure can be formed by mixing opposite charged PEs in solution. Formation of PECs will significantly influence the solubility, rheology, turbidity and conductivity of polymer solution and as-formed PECs contain the feature of stimulus responsiveness to change of external environment. Layer-by-layer self-assembly (LBL) of multilayers based on alternately adsorbing opposite charged PEs or multi-charged molecules on solid surfaces is a simple and multifunctional interface supramolecular self-assembly technology that developed in 1990 s. With the application of LBL technology, PECs with certain structures and properties are designed and are widely used in different kinds of industry. This review focuses on the preparation method, formation mechanism, influencing factors of PECs based on LBL technology. In addition, applications of PECs in nanoreactors, drug release, biosensor and fabric flame retardant fields were also summarized. Finally, it was pointed out that future research will focus on simplifying the production process, accurately controlling over the structure and realizing the multi-function of PECs.

Cellulose nanocrystal (CNC) plays a more and more important role in the process of designing and assembly of functional materials, due to its high strength and modulus, controllable structure, feasible modification, biocompatibility and biodegradability. As a kind of macromolecule system with "intelligent" behavior, the stimuli-responsively functional materials make a sensitive response when stimulated by the external environment, and show the corresponding function. With the addition of CNCs, not only the mechanical properties of CNC-based functional materials are greatly improved, but also the hydroxyl and carboxyl groups on the surface of CNCs provide a convenient way to enrich the stimulus response source of these functional materials. Herein, combining with the chemical structure of CNC, the synthesis of CNC-based stimuli-responsive functional materials was comprehensively summarized. Meanwhile, the recent developments of single or multiple stimuli-responsive functional materials based on CNCs, such as water-, thermal-, pH-, light-responsive functional materials were summarized, with the stimulate switch taken as the main line. Finally, it was pointed out that future research would focus on improving the surface-modification efficiency of CNC, and broadening multi-stimulus responsiveness of CNC-based functional materials. The preparation of CNC-based functional materials with high performances will be significant in the future research as well.

Rice straw fiber-high density polyethylene (HDPE) composites were prepared to investigate the effects of rice straw fiber morphology (rice straw refined fiber, rice straw pellet, rice straw strand), fiber content (20 and 40 wt %), and maleic anhydride polyethylene (MAPE) concentration (5 wt %) on the mechanical and thermal properties of the rice straw fiber-HDPE composites in this study. Rice straw refined fiber exhibited more variability in length and width, and have a higher aspect ratio of 16.3. Compared to the composites filled of rice straw pellet, the composites made of the refined fiber and strand had a slightly higher tensile strength and lower tensile elongation at break. The tensile and flexural strength of the composites increased slightly with increasing rice straw fiber content up to 40 wt %, while the tensile elongation at break decreased. With addition MAPE, the composites filled with 20 wt % rice straw fiber showed an increase in tensile, flexural and impact strength and a decrease in tensile elongation at break. Differential scanning calorimetry showed that the fiber addition and morphology had no appreciable effect on the crystallization temperature of the composites but decreased the crystallinity. The scanning electron microscopy observation on the fracture surface of the composites indicated that introduction of MAPE to the system resulted in promotion in fiber dispersion, and an increase in interfacial bonding strength. Fiber breakage occurred significantly in the composites filled with refined fiber and strand after extruding and injection processing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

The article discusses a study which investigated the impact of alkalization, acetylation and maleic anhydride grafted polypropylene (MAPP) treatments on the thermal and chemical properties of wheat straw fiber. It notes the use of thermogravimetric analysis, infrared spectrophotometer, X-ray diffraction and scanning electric microscopy techniques. Results of the study showed that relative cellulose content has increased due to alkalization.

The article discusses a study to determine the tensile, static, and dynamic flexural mechanical properties of the wheat straw fiber-polypropylene (PP) composites. It was noted that the addition of wheat straw fiber into PP matrix increases the tensile modulus and strength of the composites, but decreases the tensile elongation at break. As maleic anhydride grafted poly-propylene (MAPP) concentration increases, the tensile strength of PP composites also increases.