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Polyester and other synthetic fibres such as nylon are major contributors of microplastic pollution in the environment, say researchers and suggest switching to biosynthetic fibres may help prevent this. Synthetic fibres are petroleum-based products, unlike natural fibres such as wool, cotton and silk, which are recyclable and biodegradable. In the oceans, pieces of microscopic plastic are consumed by plants and animals and enter the human food chain through harvested fish. In the study, Mr.
Demirel suggested few things to prevent this: minimising the use of synthetic fibres and switching to natural fibres such as wool, cotton, silk and linen, even though synthetic fibres are less expensive and natural fibres have other environmental costs, such as water and land-use issues; large scale use of bacteria that could aid in biodegradation of the fibres for reuse; substituting synthetic fibres with biosynthetic fibres, that are both recyclable and biodegradable; and blending synthetic fibres with natural fibres to lend them durability and make them recyclable.
Bacteria that consume plastics do exist. However, they are currently at the academic research phase and will take some time to gain industrial momentum. The study was presented at the annual meeting of the American Association for the Advancement of Science. There are thousands of different fibers in the world and a few of them have been studied. All vegetable fibers wood or non-wood fibers are constituted by cellulose; hemicellulose and lignin combined to some extent as major constituents [ 6 ]. In fact, the so-called lignocellulosic fibers have cellulose as the main fraction of the fibers.
Cellulose is a semicrystalline polysaccharide made up of D-glucosidic bonds. Thus, they are hydrophilic in nature. Cellulose forms slender rodlike crystalline microfibrils that are embedded in a network of hemicellulose and lignin, i. Hemicellulose is a polysaccharide with lower molecular weight than cellulose. The main difference between cellulose and hemicellulose is that hemicellulose has much shorter chains and also has branches with short lateral chains consisting of different sugars while cellulose is a linear macromolecule [ 52 ]. Both are easily hydrolyzed by acids, but only hemicellulose is soluble in alkali solutions as well as lignin.
Lignin is a hydrocarbon polymer with a complex composition that presents hydroxyl, methoxyl and carbonyl functional groups [ 4 ]. Lignocellulosic fibers may be found in different parts of the plant like leaf, bast, seed and fruit. Climatic conditions, age of plant and the digestion process influence not only the structure of fibers but also their chemical composition [ 56 , 61 ].
Wood fibers have numerous types distributed in softwoods and hardwoods. Hardwoods are, in general, more complex and heterogeneous in structure than softwoods having a characteristic type of cell called vessel element or pore for water transport [ 64 ]. Table 4 shows the chemical composition of some non-wood vegetable fibers. The concentration of cellulose and other components of lignocellulosic fibers exhibit a considerable variation even for the same fiber. The references therein indicate concentration values all along the presented concentration range.
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The spiral angle of the cellulose microfibrils and the content of cellulose, determines generally the mechanical properties of the cellulose-based natural fibers [ 6 ]. For instance, these two structure parameters were used to calculate the Young's modulus of the fibers through models developed by Hearle et al [ 65 ] cited by Bledzski and Gassan [ 6 ]. As natural materials, vegetable fibers have nonuniformity such in dimensions as in mechanical properties when compared to synthetic fibers. These problems are well known and countless research has been developed to reduce them with reasonable success [ 66 , 67 ].
Nevertheless, vegetable fibers as fillers or reinforcements are the latest growing type of polymer additives [ 68 ]. Because of the low interfacial properties between vegetable fiber and polymer matrix which often reduce their potential as reinforcing agents due to fiber hydrophilic nature, chemical modifications are considered to optimize the interface of fibers.
Chemicals may activate hydroxyl groups or introduce new moieties that can effectively interlock with the matrix [ 69 ]. Over the last decade, many approaches towards enhancing interfacial adhesion have been pursued. Alkaline treatment or mercerization is one of the most used chemical treatments of natural fiber. The important modification done is the disruption of hydrogen bonding in the fiber network structure, increasing surface roughness. This treatment removes a certain amount of lignin, wax and oils covering the external surface of the fiber cell wall, depolymerizes cellulose and exposes the short length crystallites [ 69 , 70 ].
As a result; the adhesive characteristics of the fiber surface are enhanced [ 71 ]. Source: Authors. The efficiency of the alkali treatment depends on the type and concentration of the alkaline solution as well as time and temperature of the treatment. Different conditions for alkali treatment of vegetable fibers can be found in literature as well as combinations with other treatments [ 6 , 72 ]. Authors reported that alkali concentration and reaction time of mercerization has a significant effect on the surface modification [ 73 ].
Afterwards, the mercerization of C. Maximum mercerization observed in terms of weight loss of fiber polymer backbone was observed at min. This happens due to the removal of lignin, hemicelluloses, pectin and other surface impurities with NaOH. Campos et al. The authors observed strong adhesion fiber-matrix and interaction between carboxyl groups in PCL-starch and hydroxyl groups in sisal fibers.
When a chemical treatment is applied on synthetic fibers like glass fibers only fiber surface is modified. On the contrary, chemical treatments applied on vegetable fibers can produce important chemical and structural changes not only at fiber surface but also on the interphase between elementary fibers [ 66 ]. Furthermore, the orientation of microfibrils of cellulose within each elementary fiber plays an important role because it changes the crystallinity of the natural fiber [ 77 ].
A different variety of chemical treatments applied on sisal fibers resulted in greater extensibility and lower modulus. These phenomena must be related to the structural variation in the ultimate cells, that is, swelling and partial removal of lignin and hemicellulose [ 78 ]. Moraes et al. Acetylation of natural fibers is a well-known esterification method causing plasticization of cellulosic fibers. Acetylation reduces the hygroscopic nature of natural fibers and increases the dimensional stability of composites [ 54 ]. Acetylation is based on the reaction of cell wall hydroxyl groups of lignocellulosic materials with acetic or propionic anhydride at elevated temperature [ 70 ].
Other chemical treatments that have already used for fiber treatment are mainly benzoylation treatment, permanganate treatment, isocyanate treatment and peroxide treatment [ 69 ]. The use of coupling agents is also extensively used for chemical modification of synthetic and vegetable fibers.
Organosilanes and maleic anhydride are both coupling agents that not only produce surface modification but also can produce grafting polymers [ 63 , 79 ]. Acrylonitrile grafting has also been reported as fiber treatment for glass fibers as well as for vegetable fibers [ 69 ]. Coupling agents can be found inserted in polymer matrices grafted polymer matrices or in vegetable fibers or even introduced during reactive melt processing of the biocomposite. In work of Chang et al. The addition of Kenaf fiber up to 30 phr decreased the water absorption capacity of the maleated treated biocomposites with respect to non-treated biocomposites.
Besides, Kenaf fiber addition improved the mechanical properties of the maleated and non-maleated biocomposites. Nevertheless, tensile strength and modulus reached higher values for maleated biocomposites with higher Kenaf fiber loadings. The effective coupling mechanism of maleic anhydride between polymer matrix and Kenaf has been attributed to esterification reaction between the hydroxyl groups of the Kenaf and anhydride group to form ester linkages [ 69 , 80 ]. Different authors have applied different methods for silane treatment and have studied the effect of silane treatment on surface morphological and hygroscopic character of the natural fibers.
Some authors prepared bamboo fiber-reinforced polylactic acid PLA biocomposites using a film-stacking process [ 71 ]. Bamboo fibers were subjected to three different silane treatments: direct silane coupling, silane coupling after plasma treatment and silane coupling during UV irradiation. Biocomposites with silane coupling after plasma-treated fibers presented the highest increase in tensile strength with respect to biocomposites with untreated fibers and among all tested fiber treatments, showing a close adhesion between the PLA matrix and fibers.
The free silanols also adsorb and may react with each other forming rigid polysiloxane structures linked with a stable —Si-O-Si— bond and iv grafting under heating conditions since the hydrogen bonds between the silanols and the hydroxyl groups of fibers can be converted into the covalent —Si-O-C— bonds and liberating water.
The authors described the hypothetical reaction of silanol and the fiber: the ethoxy groups of APS hydrolyze in water or a solvent producing a silanol and next the silanol reacts with the OH group of the kenaf fiber which forms stable covalent bonds to the cell wall that are chemisorbed onto the fiber surface. In other work [ 83 ], ramie fibers were treated with permanganate acetone solution and with permanganate acetone solution followed by silane acetone solution to produce biocomposites with poly L-lactic acid PLLA matrix by hot press molding. The fiber surface-treatment with permanganate acetone solution followed by silane acetone solution improved the interfacial adhesion with PLLA matrix.
Both treatments accelerate the water permeation rate in PLLA biocomposites, which plays a critical role in the decline of interfacial adhesion strength. Also, physical treatments have been used. These treatments change structural and surface properties of the fiber and thus influence the mechanical bonding with the polymer matrix. Some pf these treatments envolve fibrillation and electric discharge Corona, cold plasma, sputtering and so on [ 72 ]. Nevertheless, the hydrophilic character of natural biobased polymers has contributed to the successful development of environmentally friendly composites, as most natural fibers and nanoclays are also hydrophilic in nature [ 85 ].
Most of the published studies on biocomposites with biodegradable polymers are with polyester matrix, such PHA, due to its polar character that provides better adhesion to lignocellusic fibers [ 86 ]. Cellulose is the most abundant renewable carbon resource on Earth.
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Thus, it can be obtained from many natural sources. Aside from occurring in wood, cotton and other plant-based materials derived from agricultural crops and by-products, cellulose is also produced by algae, some bacteria and tunics of marine animals — tunicates. The main difference between cellulose obtained by plants and bacteria is that plant-synthesised cellulose usually also contains hemicellulose, lignin and pectin while cellulose produced by bacteria on the other hand, is pure cellulose without foreign substances [ 90 ].
One of the more significant characteristics of nanofibers is the enormous availability of surface area per unit mass - 1 m 2 of them weighs only 0. Cellulose nanofibers are one class of natural fibers that have resulted in structures with remarkable mechanical properties. However, the full reinforcing potential of nanofibers has yet to be realized partly because of issues related to scaling manufacturing processes [ 94 ]. Cellulose nanofibers are nano-reinforcements from biomass that have been improved the biobased polymers properties such as thermal stability, mechanical toughness and barrier properties at much lower fiber fractions than those required in conventional vegetable fiber composites.
Biocomposite materials have been showed potential to be used in packaging with PLA matrix [ 95 ] and medical applications using polyurethane - PU - matrix [ 96 ]. Cellulosic materials intended for use as nano-reinforcements in biocomposites are usually subjected to hydrolysis by strong acids such as sulfuric or hydrochloric acid, yielding in a selective degradation of amorphous regions of cellulose and, consequently, the splitting of micro-fibril beams. As a result of cellulose hydrolysis, the disintegration of its hierarchical structure takes place to form crystalline nanofibers [ 89 ].
Usually the acid hydrolysis is combined with sonication [ 88 ]. The source of cellulose and hydrolysis conditions acid concentration, acid to cellulose ratio, temperature and reaction time directly affect the morphology of the nanocrystals [ 89 , 98 ]. The length of the so-produced nanocrystals generally ranges between and nm and width of nm [ 88 , 99 ]. Invariably these nanocrystals from plant fibers present a rod-like structure [ 91 ].
Cellulose nanoparticles are obtained as stable aqueous suspensions and thus the processing of cellulose nanocomposites was first limited to using hydrosoluble or at least hydrodispersible or latex-form polymers as nanocomposite matrices. After dissolution of the hydrosoluble or hydrodispersible polymer, the aqueous solution was mixed with the aqueous suspension of cellulosic nanoparticles to form a mixture that was cast and evaporated to obtain a solid nanocomposite film.
The use of the extrusion processing technique was hampered due to the hydrophilic nature of cellulose which causes irreversible agglomeration of the nanofibers in polymer matrices [ 3 ]. The development of newer industrially viable processing techniques as melt compounding is the focus currently. PLA nanocomposites reinforced by cellulose nanofibers separated from kenaf pulp were obtained using a two-step process: masterbatch preparation using a solvent mixture of acetone and chloroform followed by extrusion process and injection molding.
However, depending upon the raw material and the degree of processing, chemical treatments alkaline, enzimatic or oxidation treatments may be applied prior to mechanical fibrillation which aim to produce purified cellulose, such as bleached cellulose pulp, which can then be further processed [ ]. The major obstacle when producing cellulose based nanocomposites is to disperse the hydrophilic reinforcement in the hydrophobic polymer matrix without degradation of the biopolymer or the reinforcing phase.
In work of Wang and Drzal [ ], the solvent evaporation technique commonly used for drug microencapsulation was employed to suspend PLA in water as microparticles. The suspension of the PLA microparticles was mixed with high pressure homogenized cellulose nanofibers, producing nanocomposites with good fiber dispersion after water removal by membrane filtration followed by compression molding. A hierarchy structure of reinforcement was created with bamboo fiber as the primary reinforcement and cellulose creates an interphase in the PLA matrix around the bamboo fiber that prevents sudden crack growth.
In work of Cherian et al. This treatment was found to be effective in the depolymerization and defibrillation of the fiber to produce nanofibrils of these fibers. Figure 4 shows the cellulose nanofibers extracted through this treatment. These nanofibrils were used to reinforce the polyurethane PU by compression moulding [ 96 ]. The developed composites were utilized to fabricate various versatile medical implants. A new type of modification of vegetable fibers which consists in the deposition of a nanosized cellulose coating onto natural fibers or the dispersion of nanosized cellulose in natural fiber reinforced composites has been studied in order to develop hierarchical structures.
This fiber modification has great potential to improve the fiber-matrix interface and the overall mechanical performances of such composites. Nevertheless, the aspect ratio and alignment of the cellulose nanofiller need optimization as well as novel processing techniques need to be developed to take advantage of the potential use of cellulose nanocrystals [ ].
Transmission electron micrograph of cellulose nanofibers from pineapple fibers. Pothan, M. Kottaisamy Isolation of nanocellulose from pineapple leaf fibers by steam explosion, —, Copyright  with permission from Elsevier. Various inorganic nano-particles have been recognized as possible additives to enhance the polymer performance such as polymer nanofibers, the cellulose whiskers and the carbon nanotube. Among these, up to now only the layered inorganic solids like nanoclay have attracted some attention by the packaging industry. This is not only due to their availability and low cost but also due to their relative simple processability and significant improvements in some properties of the resulting polymer composites that include [ , ]:.
Most of synthetic bionanocomposites result from the assembly of biopolymers and silicates belonging to the clay mineral family. The effect of nanoclay minerals on polymer properties is mainly attributed to their high surface area and high aspect ratio as well as the combination of singular properties such as chemical inertness, low or null toxicity, good biocompatibility with high adsorption ability and cation exchange capacity [ ]. Montmorillonite MMT clays, part of the smectite family clays, are the clay minerals most used as fillers in polymer nanocomposites due to environmental and economic criteria [ ].
The chemical structure of MMT clays consist of two fused silica tetrahedral sheets sandwiching an edge-shared octahedral sheet of either magnesium or aluminum hydroxide establishing a nanometer scale platelets of magnesium aluminum silicate [ ]. Each platelet of MMT is about 1 nm in thickness and varies in lateral dimension from 50 nm to several micrometers, showing high aspect ratio.
Also, the platelet has a negative charge arising from isomorphous substitution in the lattice structure, which is compensated by naturally occurring cations that are located within the gallery or interlayer regions between the platelets [ 8 ]. MMT clays have hydrophilic nature due to the presence of inorganic cations on the basal planar surface of montmorillite layer [ ].
The hydrophilicity of the surface of MMT clays makes their dispersion in organic matrices difficult [ ]. Thus, MMT clays must be submitted to treatments which play an important role in the preparation of nanocomposites since it can affect their final properties. The most widely used treatments are the diverse functionalizations of clay by various organic cations through ion exchange where the inorganic cations are replaced by organic cations intercalated into the silicate layers.
Functionalization of MMT clay by means of the silylation reaction with 3-aminopropyltriethoxysilane and N -[3- trimethoxysilyl propyl]ethylene-diamine was also reported [ ]. There are three possible morphologies for polymer-clay nanocomposites that include: i immiscible, ii intercalated and iii exfoliated structures [ , ]. In the immiscible structure the polymer does not penetrate between the clay platelets and the interlayer space of the clay gallery does not expand due to its poor affinity with the polymer, so this structure is also known as phase separated morphology or tactoid morphology.
Intercalation is attained when polymer chains slightly penetrate within the gallery space and induce moderate expansion of the clay platelets. Exfoliation is characterized by a random distribution of the clay platelets due to extensive penetration of the polymer chains, resulting in the delamination of the clay platelets and the loss of the crystalline structure of the clay. This is due to a high affinity between polymer and clay.
The development of biocomposites started in the late s and most of the biodegradable polymers which are now available in the market do not yet satisfy each of the requirements for bio-composites. Although promising results were obtained, development of biocomposites is still in its preliminary stage. More data on properties of biocomposites are required to establish confidence in their use [ ]. Nanotechnologies promise many stimulating changes in composite materials in order to enhance health, wealth and quality of life, while reducing the environmental impact [ ].
Thus, many researches in the biocomposite area can be found in literature. Some of them are reported in the following items. One of the most studied biocomposites is PLA polylactide based biocomposite since PLA was the first commodity plastic produced from annually renewable resources [ ]. Lactid acid based polymers polylactides are polyesters made from lactic acid. The general term PLA polylactide is used for polymers without isomer specification.
PLA is brittle, so it needs modification for pratical applications. Bledzki and Jaszkiewicz [ ] reported that one of the main drawbacks concerning technical applications of biodegradable polymers, especially for PLA polymers, is their low impact strength. Most research on PLA biocomposite ultimately seeks to improve the mechanical properties to a level that satisfies a particular application [ ]. The mechanical properties of biocomposites depend on a number of parameters such as percentage of fiber content, interfacial characteristics between fiber and matrix, fiber aspect ratio, surface modification of fibers and addition of various additives coupling agents to enhance the compatibility between fiber and matrix [ ].
Huda et al. Although the introduction of treated kenaf fibers significantly improves flexural modulus compared to the neat PLA matrix, the flexural strength of the PLA composites decreases with the addition of Kenaf fibers. The notched Izod impact strength of surface-treated composites was higher than those of the neat PLA. The high toughness of this natural fiber laminated biocomposite places it in the category of tough engineering materials.
Other authors [ 63 ] used a carding process that provided a uniform blend of PLA fiber and Kenaf fiber that was followed by needle punching, pre-pressing and further hot-pressing in presence of silane coupling agent to form the biocomposite material. The flexural modulus and flexural strength of the treated fiber biocomposites increased with respect to neat PLA and untreated fiber biocomposites.
In other work, tensile strength and Charpy notched strength were evaluated for PLA biocomposites with a variety of types of natural fiber: abaca fibers, man-made cellulose, jute and flax fibers. The same improvement in mechanical properties was reported by Choie and Lee [ ] using ramie fibers and PLA resin as matrix. It was found that PLA could be reinforced with a maximum of 30 wt.
In Table 5 the best results of each reference for some mechanical properties of PLA biocomposites with vegetable fiber are summarized. As shown in Table 5 , PLA biocomposites have shown different mechanical properties. In this work, neat PLA showed a tensile strength of The same observation was achieved by Oksman et al. Different values for neat PLA mechanical properties were reported and they depend mainly on inherent PLA properties average molar mass, density, etc. Nevertheless, some authors have already observed an increase from a notched impact test for PLA biocomposites [ 82 , , , ] for different types of vegetable fibers.
Authors [ ] also reported PLA biocomposites with man-made cellulose that have shown good tensile and impact properties and they can be used in different fields of application like household appliances and in bumpers in the automobile industry. Biocomposites that show high tensile strength and stiffness as well as low impact strength could be used in manufacture of furniture, boardings or holders for grinding discs and so on which are not subjected to high impact stress.
Biocomposites that show the combination of properties as low tensile strength with high impact strength leads to application of these materials in interior parts in cars or safety helmets [ ]. The mechanical properties are thus among the most widely tested properties of natural fiber reinforced composites [ 2 ]. Compared with widespread research on mechanical properties of biocomposites, there are few reports on flame retardancy of biopolymers and biocomposites [ , ]. Other authors [ ] also studied PLA biocomposites using plasma-treated coconnut fiber and prepared using the commingled yarn method.
Generally, when the LOI value is greater than 26, materials can be considered to have flame retardancy [ ]. Nanoreinforcements were also tested in fully biodegradable biocomposites of PLA matrix. These biocomposites help to provide new food packaging materials with improved mechanical, barrier, antioxidant and antimicrobial properties [ ].
Moreover, the incorporation of organomodified mica-based clay to PLA matrix enhanced barrier properties to UV light; besides other barrier properties. This property is highly important for food packaging as protection against light which is a basic requirement to preserve the quality of many food products [ ]. The bionanocomposite reinforced by bentonite showed great improvements in tensile modulus and strength as well as a decrease in oxygen permeability whereas the bionanocomposite reinforced with microcrystalline cellulose only showed a tendency to improve strength as well as a reduction in elongation at break.
No changes for oxygen permeability were observed. This was attributed to the larger surface area of bentonite that allows interaction with a larger amount of PLA chains. In other work, the presence of a surfactant favoured the dispersion of cellulose nanocrystals in the PLA matrix, yielding bionanocomposites with higher tensile modulus and strength. The addition of silver nanoparticles to the bionanocomposite did not enhance these mechanical properties. Besides, an antibacterial activity against Staphylococcus aureus and Escherichia coli cells was detected for ternary systems, indicating that these bionanocomposites have great potencial to be applied in food packaging when an antibacterial effect is required [ 95 ].
Polylactides and their copolymers were been widely reported to be used in the fields of orthopedic and reconstructive surgery due to its biodegradability and better features for use in the human body nontoxicity [ , ]. According to Walker et al. PLLA constructs have a longer degradation time when compared to other polymers, having shown to be present at 3 years after implantation. Its structural characteristics have proven useful for the construction of orthopedic hardware.
Bionanocomposites of hydroxyapatite HPA nanospheres which is the main inorganic constituent of natural bone and PLLA microspheres were tested for biomedical application to produce scaffolds using a laser sintering process [ ]. The relative hydrophilicity of the clay layers has been shown to play a key role in the hydrolytic degradation of the PLA chains [ ]. Biodegradability of flax fiber reinforced PLA based biocomposites in presence of amphiphilic additives like benzilic acid, mandelic acid, dicumyl peroxide DCP and zein protein was investigated by soil burial test with farmland soil.
Authors reported that neat PLA films degraded rapidly compared to natural fiber reinforced biocomposites. But, regarding the use of amphiphilic additives, the higher loss in weight is obtained for flax reinforced PLA biocomposites in the presence of mandelic acid. In the presence of DCP, the biodegradability of the biocomposites was comparatively delayed. Depending on the end-uses of the biocomposites, suitable amphiphilic additives can be used as triggers for inducing controlled biodegradation [ ].
Besides, authors ascertained that coir fibers probably have no influence in the biodegradation process due to the slight differences in carbon dioxide produced for neat polymers and their biocomposites with coir fiber. Also, the presence of coupling agent decreased the percentage of evolved CO 2 compared to biocomposites without coupling agent [ ]. In other work, bacterial Burkholderia cepacia bacteria biodegradation studies were performed for biocomposites of PLA and mercerized banana fiber BF produced by melt blending followed by compression molding.
Banana fibers were also treated with various silanes to improve their compatibility with PLA matrix. Authors reported improvements in tensile and impact strength of the biocomposites with respect to neat PLA. While biocomposites with untreated and alkaline-treated BF degraded almost completely, silane-treated biocomposites degraded at lower rates.
Water absorption studies supported this evidence [ , ]. Poly hydroxyl-alkanoates PHAs. Biocomposites of PHBV with wood and bamboo fibers were fabricated using extrusion followed by injection molding. However, in other work biocomposites of PHBV and bamboo pulp fibers which were prepared by melt compounding and injection molding showed substantially increase of the impact strength by the addition of bamboo pulp fiber as well as increased tensile strength and modulus and flexural strength and modulus.
However, the toughness of the composites was substantially reduced due to the hindrance to fiber pullout [ ]. The most pronounced results were obtained with man-made cellulose. PHBV was blended with Moreover, tensile strength and modulus were increased. Nanoparticles also have already been incorporated into PHBV matrix. Well-dispersed cellulose nanocrystals into PHBV matrix were obtained with simultaneous enhancements on the mechanical property and thermal stability of PHBV. Lower concentrations of cellulose nanowhiskers 0—4.
The mechanical properties of the films increased with increasing cellulose nanowhiskers content until the content reached 2. Real permittivity of the composites also peaked at 2. These property transitions at 2. Nevertheless, rheological results of the bionanocomposites indicated a transition point lower than 2.
Furthermore, the PHBV processing behavior could be improved with addition of montmorillonite nanoclay since the processing temperature range enlarged by lowering melting temperature with the increasing clay content. Thus, in general many properties have been improved with the incorporation of fibers and mainly nanofibers and nanoclays into PHBV which are helpful to overcome many obstacles and enhance the efficiency in a diverse number of applications.
PHBV bionanocomposites were manufactured with various calcium phosphate-reinforcing phases for bone tissue regeneration while inducing a minimal inflammatory response. Authors showed that the addition of a mineral nano-sized reinforcing phase to PHBV reduced the proinflammatory response and also improved osteogenic properties with respect to pure PHBV [ ]. Soil biodegradation tests were carried out according to ASTM G with test exposures of up to 5 months. These voids allowed for enhanced water adsorption and greater internal access to the soil-borne degrader microorganisms.
Similarly, other authors found that biocomposites with PHBV and wood fiber have higher degradation rates than the neat polymer [ ]. On the other hand, some authors reported no significant difference between the degradability of PHBV and its composite with wheat straw using either Sturm tests or soil burial tests [ ].
Due to the high demand for environmental sustainable products, researchers continue to seek materials derived from renewable resources that can be applied in a wide range of applications. This overview provided a survey of some of the current researches on the biocomposites area. Within this context, this chapter showed that there have been many attempts to produce biocomposites using natural reinforcements and biobased polymers since improvements in their mechanical, barrier and other properties can be accomplished through the use of reinforcement agents like vegetable fibers and nanoparticles cellulose nanofiber or nanoclays.
Vegetable fibers are generally submitted to chemical treatments, mostly alkaline and acid treatments in order to favour interfacial adhesion between polymer matrices and the fiber. Also, the use of coupling agents enhance adhesion by surface modification as well as they can produce grafting reactions between matrix and fiber. Moreover, the presence of polar groups in most biobased poymers contributes to better affinity to cellulosic groups of vegetable fibers.
All these issues dramatically influence the mechanical properties of the biocomposites. With respect to nanoreinforcements, cellulose nanofibers and organic functionalized clays organoclays are the most used as fillers in bionanocomposites.