Both cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are nanoscale cellulose fibers that have shown reinforcing effects in polymer nanocomposites. CNCs and CNFs are different in shape, size and composition. This study systematically compared their morphologies, crystalline structure, dispersion properties in polyethylene oxide (PEO) matrix, interactions with matrix, and the resulting reinforcing effects on the matrix polymer. Transparent PEO/CNC and PEO/CNF nanocomposites comprising up to 10 wt % nanofibers were obtained via solution casting. Scanning electron microscopy (SEM), wide-angle X-ray diffraction (WXRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analyzer (DMA), and tensile testing were used to examine the above-mentioned properties of nanocellulose fibers and composites. At the same nanocellulose concentration, CNFs led to higher strength and modulus than did CNCs due to CNFs' larger aspect ratio and fiber entanglement, but lower strain-at-failure because of their relatively large fiber agglomerates. The Halpin-Kardos and Ouali models were used to simulate the modulus of the composites and good agreements were found between the predicted and experimental values. This type of systematic comparative study can help to develop the criteria for selecting proper nanocellulose as a biobased nano-reinforcement material in polymer nanocomposites.

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The physiological mechanisms causing fall dormancy (FD)‐induced differences in alfalfa (Medicago sativa L.) shoot growth in autumn and winter hardiness are not understood. The objective of this research was to examine root physiology of experimental germplasms selected for decreased FD that also were selected simultaneously for high winter hardiness. Dormant and semi‐dormant cultivars and germplasms had high root sugar concentrations that were positively associated with winter hardiness. Root amino N and protein levels in December were greater for germplasms selected for decreased FD and increased winter hardiness than for cultivars with comparable levels of winter hardiness. Among the five most fall dormant cultivars Vernal incurred the greatest amount of winter injury and it had lower root amino‐N concentrations when compared with three of the other four dormant cultivars and germplasms. Germplasm 98‐132 with an intermediate FD, incurred relatively low winter injury, similar to that of fall dormant Vernal, when compared with other intermediate dormancy cultivars and germplasms. This germplasm had root sugar concentrations that were similar to plants with FD ratings of 1 to 3. Creation of even less FD germplasms that possess high winter hardiness would facilitate our understanding of the physiological and molecular mechanisms controlling these two very important agronomic traits of alfalfa.

before a killing freeze was imperative for winter survival and plant persistence. Cutting during cold hardening Harvesting alfalfa (Medicago sativa L.) after mid-September in lowered both plant persistence and root total nonstructhe North-Central USA often reduces plant winter survival, but the physiological mechanisms associated with poor winter survival are not tural carbohydrate (TNC) concentrations. However, understood. Our objective was to determine how autumn harvesting other research has shown that cutting during this critical affects alfalfa root physiology, gene expression, and plant winter sur-

Interest in polymers from renewable sources, as alternatives to petroleum‐based polymers, remains strong; however, their performance must be acceptable. To improve performance of epoxidized vegetable oils (EVO) in composite matrix applications, five amine curing agents were evaluated and compared with an anhydride agent used previously. Curing agents were tested in matrices for composites containing a petroleum‐based epoxy resin plus 0% or 30% epoxidized oil from canola (ECO) and soybean (ESO). The two amines with the highest glass transition temperature, determined by differential scanning calorimetry, were selected for characterization by dynamic mechanical analysis; bis (p‐aminocyclohexyl) methane (PACM) showed the highest performance. Amine: epoxy ratios 0.6 to 1.6 were then evaluated; ratios of 0.8 and 1.0 showed superior performance. E‐glass fiber reinforced composites with PACM/EVO showed thermal and mechanical performance slightly lower than the composites with 0% EVO and comparable with those of the anhydride curing agent. Therefore, ECO or ESO blended with petroleum‐based epoxy resins cured with PACM are recommended for its application in E‐glass reinforced composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers