Effect of Addition of Dipersion Agent on Tensile Mechanical Strength of HDPE Water Hyacinth Composites

. Natural fiber-reinforced polymer composites are a solution to growing environmental threats. This research used water hyacinth natural fiber and HDPE thermoplastic polymer. Natural water hyacinth fiber contains cellulose which can be used to create environmentally friendly and high-strength composites. The uneven distribution of natural fibers in the composite causes a decrease in the quality of the composite, both in terms of mechanical strength and morphological structure. Clumping and agglomeration are caused due to the incorporation of regenerated cellulose fibers in the composite. The treatment of water hyacinth natural fiber using a dispersion agent is intended to improve fiber distribution so that it is more evenly distributed. The addition of 0.5 ml of Dispersion Agent to water hyacinth natural fiber created the highest tensile mechanical strength of 26.2 MPa. The lowest mechanical tensile strength occurred in natural fiber composites without Dispersion Agent treatment of 19.5 MPa. Water hyacinth natural fibers added with the concentration of the Dispersion Agent did not show an increase in the tensile strength of the water hyacinth-HDPE natural fiber composites.


Introduction
The limited amount of plastic raw materials from petroleum encourages the creation of alternative raw materials that are renewable [1].The technology of thermoplastic natural fiber composites is an alternative solution to the limited raw materials for petroleum plastic [2].Natural fibers act as reinforcement and thermoplastic binders to create composite panels that are strong, lightweight, economical and resistant to abrasives.
Cellulose in natural fibers can be used as a composite reinforcement which is environmentally friendly and high strength.Water hyacinth is a plant that has a high cellulose content and is very abundant in Indonesian waters [3].Water hyacinth fiber can provide good strength in mechanical properties and thermal properties.Water hyacinth fiber contains 60% water hyacinth hemicellulose, 19.1% lignin, and 32% alphacellulose [4].
The massive use of thermosetting in natural fiber polymer composites which are difficult to recycle has triggered the use of thermoplastic types which are more environmentally friendly.One type of plastic is HDPE (High Density Polyethylene).HDPE is a type of polyethylene (PE) polymer that is commonly used and is relatively inexpensive and has a low melting temperature [5].The melting point of HDPE is around 132 °C.The low melting point of HDPE can easily be adapted to composites without damaging the natural fibers as the reinforcement.
Research on water hyacinth natural fiber composites with HDPE has been carried out.Water hyacinth natural fibers with a concentration of 30% and 70% HDPE showed the highest average tensile strength of 28.83 MPa, and flexural strength of 36.31MPa [6].Differences in the properties of hydrophilic natural fibers and hydrophobic matrices can cause interfacial bonding problems [7].The properties of natural fiber polymer composites are also influenced by various factors such as the amount of fiber content, fiber distribution, fiber chemical treatment, treatment time and type of connecting agent, fiber extraction method, type of matrix material, composite fabrication method and fiber length [6].
The distribution of fibers in the matrix is one of the influences on the mechanical strength of the composite and its morphological structure (Karina et al., 2007) (Diani & Gall, 2006).Clumping and agglomeration are problems in the manufacture of composites.Dispersing agent is an effort to create a more even distribution of fibers in a composite (Ibrahim et al., 2021) (Lee, 2006).Previous studies have proven that adding a dispersing agent to the Stipa Tenacissima fiber composite matrix PLA can increase the flexural strength, which was originally 10 MPa without a dispersing agent to 30 MPa with a dispersing agent (Ibrahim et al., 2020).
Dispersion agent is proven to be able to increase dispersion by increasing the mechanical strength of natural fiber and polymer composites, therefore this is applied to water hyacinth natural fiber composites and

Materials
Natural water hyacinth fiber is used as reinforcement which is obtained from the Salatiga area.High-Density Polyethylene brand LOTTE HD 5740UA with a density of 0.955 g/cm3 and a melting point of 132°C.The Dispersion Agent used is from the BYK brand type W980 containing a Solution of salt of unsaturated polyamine amides and acidic polyesters with a flash point at 150°C obtained directly from BYK imported from Germany.The water hyacinth fibers used are short fibers with an average length of 2.35 mm.

Fiber treatment
In this study, the fiber was subjected to the Dispersion Agent immersion treatment process.Water hyacinth fiber was soaked in 20 ml of 100% ethanol alcohol, with the addition of 0.5 ml of Dispersion Agent; 1 ml; 2 ml for 1 hour.Water hyacinth fiber that has been soaked is done in an oven at 60°C for 12 hours.

Composite preparation
Composite samples were made by extrusion and hotpress processes.The fiber volume fraction is 30% and HDPE is 70%.Water hyacinth fiber is obtained by mechanical extraction process, which is then treated with Dispersion Agent immersion.HDPE is subjected to a crushing and screening process of 40 mesh size.The water hyacinth fiber that has gone through the treatment process is subjected to the crushing and screening process at a mesh size of 40.Both HDPE materials and fibers that have been filtered are mixed with the dry mixture at 75 rpm for 1 minute.The HDPE and water hyacinth mixture was then extruded at an extruder temperature of 160 o C. The extruder rotation used is 15 rpm.The pellets formed were hot pressed at a temperature of 180°C, holding time 25 minutes, and the pressure used was 0.34 MPa.

Mechanical testing
The tensile strength and modulus of elasticity of the composites were tested according to the ASTM D638 standard.The tensile test was carried out using a universal testing machine JTM-UTS 510.Tensile mechanical strength, 5 samples of each variation were collected.Density testing was carried out with an ACIS B-5000 digital scale with a maximum capacity of 500 grams.Density testing refers to ASTM D792.SEM testing used a photo SEM test tool with the Thermo Scientific ParticleX brand.The samples were coated with gold.The voltage used is 5 kV and 10 kV with a magnitude of 250x to 500x.

Density
The water hyacinth natural fiber composite without dispersion agent treatment has a very high porosity level of 16%.As shown in Figure 3, the dispersion agent treatment was able to reduce the porosity level.The lowest porosity of 8% was obtained by adding 0.5 ml of dispersion agent.The increase in porosity is due to better bonding at the fiber interface when the dispersion agent is added.This low porosity resulted in the density of the variations in the addition of 0.5ml dispersion agent being the highest at 0.96 gr/cm3.In Figure 2, it can be seen that the lowest density occurs in the HDPE water hyacinth composite without the addition of a dispersion agent of 0.87 gr/cm3.The low density of the water hyacinth HDPE composite without the addition of a dispersion agent is due to poor interfacial bonding.As evidenced by the results of the SEM test in Figure 6 (a), it can be seen that the addition of a dispersion agent affects the bonding of the fiber interface that occurs.So that a better bond occurs and affects the tensile mechanical strength of the composite.

Surface morphology
Figure 5 describes the surface of the composite tensile test results that have been carried out.Figure 6 (a) shows that water hyacinth fibers can be spread more evenly on the HDPE matrix and the voids that occur are very minimal.In Figure 6 (b) it is explained that fiber without dispersion agent treatment tends to agglomerate in one place.The fiber bonds in the matrix are also not very strong and some voids occur.the addition of a dispersion agent, the interfacial bond on the fiber is getting better.This can be seen from the polymer tensile test results where the loading is more even.The polymer binds better to the water hyacinth fiber which acts as a reinforcement.Water hyacinth fiber is compatible with HDPE polymer.This result is explained by the fact that the acidic groups of BYK W-980 bind to the hydroxyl groups of the fiber, which results in good wettability between the fiber and the polymer matrix [10].

Tensile strength
Improper interfacial bonds greatly affect the mechanical tensile strength of the composite.Good fiber distribution is also able to increase the mechanical strength of the composite [2].The mechanical tensile strength of the composite without the addition of dispersion agents is only around 19.5 MPa.Whereas the water hyacinth HDPE composite added with 0.5 ml of dispersion agent had the highest strength of around 26.22 MPa.The results of the composite tensile test are shown in Figure 1.The results of this tensile strength are similar to the 30% water hyacinth HDPE composite with 10% NaOH alkali treatment and 5% coupling agent, which is 27 MPa in the research reported by Robinson et al, 2021.[6].
The addition of the concentration of the dispersion agent also did not significantly affect the increase in the tensile strength of the water hyacinth-HDPE natural fiber composite.As can be seen in Figure 4, the addition of a dispersion agent can affect the tensile strength of the composite.The highest modulus of elasticity also occurs in the water hyacinth HDPE composite with the addition of 0.5 ml of dispersion agent, which can be seen in Figure 5. Water hyacinth natural fibers.The addition of the concentration of the Dispersion Agent also did not significantly affect the increase in the tensile strength of the water hyacinth-HDPE natural fiber composite.

Conclusion
The use of dispersion agents has been proven to increase the distribution of natural water hyacinth fibers in the HDPE matrix as shown in increased tensile mechanical strength.Visually, fiber distribution can be seen better with SEM testing.
/doi.org/10.1051/e3sconf/202346501009E3S Web of Conferences 465, 01009 (2023) HDPE polymers.The use of dispersion agents on water hyacinth natural fiber composites with HDPE matrices has never been used before.