In the present study, novel bionanocomposite materials with tunable properties were successfully prepared using a poly(lactic acid) (PLA) matrix and acetylated microfibrillated cellulose (MFC) as reinforcing agent. The acetylation of MFC was confirmed by FTIR and (13)C CP-MAS NMR spectroscopies. The grafting of acetyl moieties on the cellulose surface not only prevented MFC hornification upon drying but also dramatically improved redispersibility of the powdered nanofibers in chloroform, a PLA solvent of low polarity. Moreover, we demonstrate that the properties of the resulting PLA nanocomposites could be tailored by adjusting both the acetyl content (Ac%) and the amount of MFC. These nanomaterials showed improved filler dispersion, higher thermal stability, and reduced hygroscopicity with respect to those prepared with unmodified MFC. Dynamic mechanical analysis (DMA) highlighted the reinforcing potential of both the unmodified and the acetylated MFC on the viscoelastic properties of the neat PLA. But more interesting, an increase in the PLA glass transition temperature was detected when using the 8.5% acetylated MFC at 17 wt %, indicating an improved compatibility at the fiber-matrix interface. These findings suggest that the final properties of nanocomposite materials can be controlled by adjusting the %Ac of MFC.

Water-redispersible, nanofibrillated cellulose (NFC) in powder form was prepared from refined, bleached beech pulp (RBP) by carboxymethylation (c) and mechanical disintegration (m). Two routes were examined by altering the sequence of the chemical and mechanical treatment, leading to four different products: RBP-m and RBP-mc (route 1), and RBP-c and RBP-cm (route 2). The occurrence of the carboxymethylation reaction was confirmed by FT-IR spectrometry and 13 C solid state NMR ( 13 C CP-MAS) spectroscopy with the appearance of characteristic signals for the carboxylate group at 1,595 cm -1 and 180 ppm, respectively. The chemical modification reduced the crystallinity of the products, especially for those of route 2, as shown by XRD experiments. Also, TGA showed a decrease in the thermal stability of the carboxymethylated products. However, sedimentation tests revealed that carboxymethylation was critical to obtain water-redispersible powders: the products of route 2 were easier to redisperse in water and their aqueous suspensions were more stable and transparent than those from route 1. SEM images of freeze-dried suspensions from redispersed RBP powders confirmed that carboxymethylation prevented irreversible agglomeration of cellulose fibrils during drying. These results suggest that carboxymethylated and mechanically disintegrated RBP in dry form is a very attractive alternative to conventional NFC aqueous suspensions as starting material for derivatization and compounding with (bio)polymers.

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Objective-Evaluate the effects of core structure and storage conditions on the mechanical properties of acid-resin modified composites and a control material by three-point bending and conversion measurements 15 min and 24 h after curing.Methods-The monomers pyromellitic dimethacrylate (PMDM), biphenyldicarboxylic-acid dimethacrylate (BPDM), (isopropylidene-diphenoxy)bis(phthalic-acid) dimethacrylate (IPDM), oxydiphthalic-acid dimethacrylate (ODPDM), and Bis-GMA were mixed with triethyleneglycol dimethacrylate (TEGDMA) in a 40/60 molar ratio, and photo-activated. Composite bars (Bariumoxide-glass/resin = 3/1 mass ratio, (2 × 2 × 25) mm, n = 5) were light-cured for 1 min per side. Flexural strength (FS), elastic modulus (E), and work-of-fracture (WoF) were determined in threepoint bending after 15 min (stored dry); and after 24 h under dry and wet storage conditions at 37 °C . Corresponding degrees of conversion (DC) were evaluated by Fourier transform infrared spectroscopy. Data was statistically analyzed (2-way analysis of variance, ANOVA, Holm-Sidak, p < 0.05).Results-Post-curing significantly increased FS, E and DC in nearly all cases. WoF did not change, or even decreased with time. For all properties ANOVA found significant differences and interactions of time and material. Wet storage reduced the moduli and the other properties measured with the exception of FS and WoF of ODPDM; DC only decreased in BPDM and IPDM composites.Significance-Differences in core structure resulted in significantly different physical properties of the composites studied with two phenyl rings connected by one ether linkage as in ODPDM having superior FS, WoF and DC especially after 24 h under wet conditions. As expected, post-curing significantly contributed to the final mechanical properties of the composites, while wet storage generally reduced the mechanical properties.

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