Hamida Boussehel* | DjamelEddine Mazouzi | Noureddine Belghar | Belhi Guerira | Mohamed Lachi
OPEN ACCESS
The use of natural resources in composite materials becomes more frequently, as they are low-cost and lightweight materials. In addition, industrial trends tend towards Eco-products, hence the importance of integrating natural products that are recyclable and easily degradable. Aim of this study is prepared polymer composites of polyvinyl chloride (PVC) using palm fibers at different loading (10 and 30 % by weight). Improving the interfacial adhesion between matrix- filler interfaces using chemical modification of date palm fibers (DPF) by two types of treatments (acetylation, alkali). The effect of chemical treatment and fiber content on morphological, thermal, mechanical and water absorption properties of composites have been studies. It was found that the use of treated fibers in PVC composites improves the mechanical properties and decomposition temperature, and reduce water absorption of the composites.
poly (vinyl chloride), palm fibers, acetylation, alkali, mechanical, thermal, water absorption
Composite materials are widely used all over the world in the manufacture of building materials, automobiles, naval parts and others. Composite materials consist of two constituents namely a matrix and reinforcement [1]. Synthetic materials have good mechanical properties and durability, but due to the environmental awareness, these materials have some criticisms because they are not easily biodegradable [2]. For Thus, efforts are being made to invent environmentally friendly composite materials to replace synthetic reinforcements such as glass, carbon, aramid fibers, etc., using natural cellulosic fibers like jute [3], coconut [4], sisal [5-7], bamboo [8-9], kenaf [10], sugar cane and rice [11-12]. The date palm (Phoenix dactylifera L) other source of cellulosic fibers with attractive morphology properties, has a fibrous structure can be extracted from different parts of plant such as: leaf fibers in the peduncle, bast fibers in the stem, wood fibers in the trunk and surface fibers around the trunk [13]. In Algeria, date palm is particularly abundant in Saharan oasis (more than 18.6 million date palms). The residual waste from these plants are incinerated or thrown every year after the harvest, generating more than 200,000 tonnes of waste causing major inconvenience in nature [14].
The effectiveness of composite materials depends to their ability to transfer stresses from the continuous phase (polymer matrix) to the dispersed phase (fillers). They are obtained when there is a good adhesion between surface of polymer and fibers with well dispersed in the matrix [15]. It is well known that the natural fillers are hydrophilic materials creates difficulties in achieving adhesion with polymer chains; generates voids around the fibers in composites, resulting in higher water uptake [16]. For thus, the treatment of natural fillers and some additives were used in the composite to improves charge-matrix compatibility, such as such as alkali treatment or mercerization, silanization, acetylation, benzoylation, acrylation, maleated coupling agents, isocyanates, permanganate treatment and plasma treatment [17-20].
Sodium hydroxide (Alkali treatment) is commonly used in Modification of the fiber, which decrease hydrogen bindings in cellulose and remove hydroxyl groups that tend to bind to water molecules to reducing the ability of fibers to absorb moisture [21]. In addition, acetylation is one of the most studied reactions for lignocellulosic materials. The principle of the method consists in reacting the hydroxyl groups (-OH) of the fibers components, i.e. lignin, hemicelluloses, and those of amorphous cellulose with acetyl groups (CH3CO-) [22]. A reduction of about 50% in moisture absorption for acetylated jute fibers and up to 65% for acetylated pine fibers with increasing in shear strength of acetylated fiber composites has been reported in the literature [23-25].
Polyvinyl chloride (PVC) is among of many polymers that have been used as matrix in composites material, it is a thermoplastic material widely used in the fields of automotive, housing and construction, due to their high mechanical strength, and corrosion resistance. In addition, it is easy to manufacture and suitable for engineering applications for its hardness and flexibility [26]. However, PVC is not biodegradable; it is a contaminant material due to the release of harmful substances into the atmosphere, such as hydrogen chloride and dioxins, during processing or decomposition [27-28]. The combination of PVC and natural fibers is an interesting because of the ecological friendliness of natural fibers.
The aim of this paper is to compare the impact of chemical treatment on the mechanical, water uptake and thermal properties of a palm date fiber-reinforced polyvinyl chloride (PVC) composites. The chemical treatments used in this work, alkali NaOH, and acetylation, have been chosen because they exhibit a different interaction mechanism with both fibers and polymer matrix. The properties of composites prepared with chemically-treated fibers will be compared to results obtained from untreated fibers composite as well as neat polymer.
The polymer used as matrix was polyvinyl chloride (PVC) also containing plasticizer, stabilizer, and lubricant provided by the national unity of cable industry, located in Biskra southeastern Algeria. The physical characteristics of the polymer are listed in Table 1.
Table 1. Properties of polyvinyl chloride (PVC)
|
Polymerization degree |
1250–1450 |
|
Density (g/cm3) |
0.43-0.50 |
|
Melt flow index at 200°C (g/s) |
≥10 |
|
Moisture content (%) |
≤0.3 |
|
Sulphate ash (%) |
≤0.1% |
The leaves of the date palm were collected from local agricultural resources (Biskra region, Algeria). They were washed several times with water to remove impurities and dried in the open air for 24 hours. After this, they are ground and sieved and stored in polyethylene bags for further compounding. Sodium hydroxide, ethanol, acetic acid, acetic anhydride, sulphuric acid and hydrochloric acid, were collected from reactive grade from Sigma-Aldrich, were used for the fiber surface treatments.
Palm fibers were subjected to the following surface treatments, in order to improve their interfacial adhesion with PVC matrix.
Palm fibers were treated with an aqueous solution of NaOH (5wt%). The fibers were immersed in the solution during 2 h at 50 °C temperature and then washed several times with distilled water containing acetic acid in order to neutralize the excess sodium hydroxide. After they are washed with distilled water until pH value of 7 was attained. The palm fibers were dried at 80 °C for 24 h in a vacuum oven.
Palm fibers are immersed in acetic acid solution at 25°C for 45 min, and then they are decanted and immersed in a solution of acetic anhydride with a few drops of sulfuric acid for 2 hours at 50 °C. The fibers are filtered and washed with distilled water to remove excess acetic acid, followed by drying in an oven at 80°C for 24 hours.
PVC powder and the various additives were placed in a mixer at a speed of 3000 rpm at 70 °C below the glass transition temperature of pure PVC powder. The different formulations obtained were used to prepare films by the calendering process at 160 °C in a "SCHWABENTHAN polymix 200 p" calender. After the addition of the matrix the palm fiber was added as soon as the polymer had reached a steady plastifying state. Before mixing, the fibers were dried in a vacuum oven at 75 °C for 24 h to prevent the formation of porous products by water evaporation during the composite preparation. The fiber content in the composites was 0, 10 and 30 wt %. The molten mix was transferred to a preheated press at 160 °C under a pressure of 300 bar in a hydrolical press "SWHWABENTHAN polystat 300s" for 5 min molder for specimen fabrication.
Fourier transform infrared spectroscopy (FTIR) spectra were recorded on SHIMADZU 8400S spectrometer to analysis the possible chemical bonding existing in the untreated and treated palm fibers using KBr pellets containing 1% of fibers finely ground at a range of 4000 – 400 cm–1.
The morphology of the virgin PVC and the composites were studied using a Quanta FEG250scanning electron microscope (SEM) operating at 15 kV. The specimens were carried out under liquid nitrogen. They were coated with a 50-100 µm layer of gold to avoid sample charging under the electron beam.
The different composite samples PVC/treated and untreated palm fibers were subjected to tensile tests according to ASTM D638, using Zwick / Roell Z50 testing machine at 1 mm/min crosshead speed preventing the viscoelastic effect. Five measurements were conducted for each sample, and the results were averaged to obtain a mean value.
Shore hardness A of the samples was evaluated by using a hardness tester type Zwick/Roell. Samples were placed on a horizontal surface. Tester was kept in vertical
In this paper, date palm fibers reinforced PVC composites with and without treatments were compounded and pressed into test samples with a loading rate of 10 and 30 wt%. The mechanical, thermal properties and water uptake of composites were compared and analyzed against neat PVC. The results show a change in structural of the fibers after treatments by the reduction of hydroxyl group band intensity of cellulose. The alkaline treatment leads to the partial disappearance of hemicellulose and lignin. The use of acetylated fibers in PVC composites improves the mechanical properties of the composite due to the chemical bonding between the fibers surface and the polymeric matrix.
The evaluation of the thermal properties of the composites shows the decomposition temperature of composites increase from 229 °C (untreated composites) to 231.3 °C and 228.1°C (acetylated and alkali composites, respectively), with fibers loading of 30 wt%. Water uptake test shows increase the absorption with the fiber content and the immersion time. The acetylated composites show the lowest rate of water absorption.
|
PVC |
Polyvinyl chloride |
|
DPF |
Date palm fibers |
|
PVC/UPF |
Polyvinyl chloride composite with untreated fibers |
|
PVC/APF |
Polyvinyl chloride composite with acetylated fibers |
|
PVC/NPF |
Polyvinyl chloride composite with acetylated fibers |