Viviana P. Cyras

Effect of Chemical Treatment on the Mechanical Properties of Starch-Based Blends Reinforced with Sisal Fibre

Biocomposites were produced using polycaprolactone (PCL) and starch as the matrix, and washed and treated sisal fibres as reinforcement. The matrix consists of a biodegradable product commercially known as MaterBi-Z®, which is based on a PCL, starch and additive. Alkaline and acetylation treatments were performed on the fibre in order to enhance the adhesion degree and the compatibility between the fibre and the matrix. The effect of chemical treatment on morphology, physical and chemical properties and tensile properties of fibres and composites were determined. Tensile properties of the biodegradable composite were improved by the presence of the fibre. However, the untreated fibres behaved as better reinforcement than the acetylated and alkalitreated fibres. This was attributed to an impairment of the mechanical properties of the acetylated fibres and incompatibility of the alkali-treated fibres. The results observed are supported by SEM analysis of fibres and the composite materials.

Influence of the Fiber Content and the Processing Conditions on the Flexural Creep Behavior of Sisal-PCL-Starch Composites

Flexural creep tests were performed on sisal-fiber-PCL (polycapro-lactone)-starch composites at different temperatures. The creep compliance increased with the increase of temperature and with the decrease of the fiber content. However, the fragmentation of the polymer macromolecules and the natural fiber fragmentation have influence on the creep behavior. The curves of compliance versus time were shifted along the logarithmic time scale to develop a creep master curve. Activation energy was determined from the shift factors. A four-parameter model was applied in order to quantify the viscoelastic behavior of the composites.

Biodegradable films from PHB-8HV copolymers and polyalcohols blends: crystallinity, dynamic mechanical analysis and tensile properties

Blends of poly(3-hydroxybutyrate)-poly(3-hydroxyvalerate) (PHB-HV) and polyalcohols have been prepared by solvent casting. The polyalcohols used were castor oil (CO) and polypropylene glycol (PPG400 and PPG1000). Thermal behaviour, crystallinity, morphology and dynamic mechanical properties of systems with various PPG1000 compositions have been studied. Crystallinity was determined by means of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. Final morphology was studied by means of scanning electron microscopy (SEM). Dynamical mechanical analysis showed two glass transition temperatures for the blends, corresponding to separate phases of PHB-HV and polyalcohols. Blend immiscibility was found. Polyalcohol addition enhances the crystallinity of PHB-HV. However, the storage modulus value decreases, upon the addition of amorphous compound.

Thermal stability of P(HB-co-HV) and its blends with polyalcohols

The thermal stability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-co-HV)] and its blends with poly(propylene glycol)s (PPGs) and castor oil (CO) is reported. The study includes the determination of the degradation kinetics of these materials and the analysis of the effects of the degradation on the mechanical properties and crystallization behavior. Spectroscopy (1H-NMR, FTIR), differential scanning calorimetry (DSC), thermogravimetry, and tensile testing techniques are used for the experimental analysis. A chain-scission degradation mechanism is confirmed by the formation of vinyl groups. Two temperature ranges are investigated. In the range closest to the melting point, 100–200°C, where the blend does not exhibit weight reduction, a fast and sensible loss of molecular weight and tensile strength was detected. The second temperature range, 200–400°C, is characterized by mass loss by pyrolysis. In this range, different kinetic models of the degradation process are proposed. Polyalcohol addition produces opposite effects, while the addition of PPG enhances the degradation of P(HB-co-HV). When CO is added, the thermal stability of the blend increases. Mechanical properties of the blends before and after degradation were determined. The tensile modulus increases at the first step of degradation and decreases with the degradation time.

Influence of Processing Conditions on Morphological, Thermal and Degradative Behavior of Nanocomposites Based on Plasticized Poly(3-hydroxybutyrate) and Organo-Modified Clay

Abstract The effect of processing conditions (casting and extrusion) and plasticization on the disintegrability in compost of organically modified clay poly(3-hydroxybutyrate) nanocomposites was studied. Tributylhexadecylphosphonium bromide (TBHP) was used as organic modifier. As revealed by WAXS and TEM observations, intercalated nanobiocomposites with clay stacks and some individually dispersed platelets were obtained. The melting temperature of the neat PHB diminished with the addition of plasticizer, thus broadening the processing window. Biodegradation test revealed that while the clay slows down the degradation rate, the plasticizer increases the degradation of the samples, reaching a similar final percentage of disintegrability when both plasticizer and clay were added in the formulation.

Starch/Clay Nano-Biocomposites

The aim of this chapter is to describe the main studies and results on starch-based nanocomposites reinforced with clay particles. This particular combination leads to the formation of a nanocomposite material with novel properties. However, a good knowledge about starch (structure, type, chemical and physical modification) and its rheological behaviour is necessary for developing these nanocomposites. Many factors and processing parameters affect the final properties of the starch based nano-biocomposites. The main factors which influence the mechanical properties of the nano-biocomposites will be analyzed such as the type of clay, the chemical modification of clay, the type of plasticizer, the water humidity test conditions, the use of chemically modified starches, the thermal stability and water absorption. In addition, the influence of different processing techniques and mixing methods will be studied.

Effect of Cellulose Nanocrystals and Bacterial Cellulose on Disintegrability in Composting Conditions of Plasticized PHB Nanocomposites

Poly(hydroxybutyrate) (PHB)-based films, reinforced with bacterial cellulose (BC) or cellulose nanocrystals (CNC) and plasticized using a molecular (tributyrin) or a polymeric plasticizer (poly(adipate diethylene)), were produced by solvent casting. Their morphological, thermal, wettability, and chemical properties were investigated. Furthermore, the effect of adding both plasticizers (20 wt % respect to the PHB content) and biobased selected nanofillers added at different contents (2 and 4 wt %) on disintegrability in composting conditions was studied. Results of contact angle measurements and calorimetric analysis validated the observed behavior during composting experiments, indicating how CNC aggregation, due to the hydrophilic nature of the filler, slows down the degradation rate but accelerates it in case of increasing content. In contrast, nanocomposites with BC presented an evolution in composting similar to neat PHB, possibly due to the lower hydrophilic character of this material. The addition of the two plasticizers contributed to a better dispersion of the nanoparticles by increasing the interaction between the cellulosic reinforcements and the matrix, whereas the increased crystallinity of the incubated samples in a second stage in composting provoked a reduction in the disintegration rate.

Extraction and Production of Cellulose Nanofibers

The chapter will content the review of different methodologies used for obtaining nanofibers of cellulose from lignocellulosic materials and bacterial cellulose. The first part of the chapter will deal with the extraction of cellulose. The classic methodology implies alkaline and acid treatment, but new ones include milder chemical conditions as well as chemo-enzymatic protocols. The second part deals with production of nanofibers from cellulose. Extraction of cellulose nanoparticles from lignocellulose materials has different routes: acid hydrolysis, mechanical, and enzymatic treatments. Strong acid hydrolysis promotes transversal cleavage of non-crystalline fractions of cellulose microfibrils, leading to the so-called cellulose nanocrystals or whiskers. Nanocrystals are characterized by high crystallinity and their aqueous suspensions display a colloidal behavior. On the other hand, strong mechanical treatment that imposes high shear forces to cellulose fibers allows the extraction of microfibrils and microfibril aggregates with high aspect ratio which form highly entangled networks. This kind of nanocellulose is called microfibrillated cellulose (MFC). Although widely used the mechanical process developed for the production of MFC has an important drawback which is the high energy input involved (several passes through high-pressure homogenizers which get blocked frequently). In the last years, enzymatic and chemical pretreatments have been proposed to reduce the energy input of the process. Moreover, microbially produced cellulose pellicles appear also as an attractive route of cellulose nanofibers, which will also be described in the chapter.