This document discusses PLA/sisal fiber bio-composites developed through direct injection molding and extrusion injection molding. Mechanical testing showed that bio-composites produced via direct injection molding with short sisal fibers had 34.7% higher tensile strength and 15.9% higher flexural strength than those with long fibers. However, long fiber bio-composites had better impact strength. Both processes produced homogeneous, high strength materials but direct injection molding is better for short fibers while extrusion injection molding works for both short and long fibers. PLA/sisal fiber bio-composites have advantages of being renewable, biodegradable, and recyclable with applications

1. PLA/Sisal Fiber Bio-composites
MECHANICS OF COMPOSITE MATERIAL
Fahim Faisal Amio,
MS in Mechanical Engineering,
Spring’22
22240126
Sisal Plant
PLA

2. Contents • Introduction
• Manufacturing Process
• Direct injection Molding
• Extrusion Injection Molding
• Mechanical Characteristics
• Tensile and Flexural strength comparison
• Impact strength comparison
• Observations
• Advantages and disadvantages
• Applications

3. Introduction to
PLA/Sisal Fiber
Natural fibers have emerged as a potential alternative to glass and carbon fibers in
polymer composites due to their distinct advantages over the latter. Continuous
efforts are also being made to replace the petroleum derived polymers with
renewable resource derived fully degradable bio-polymers. Sisal fiber, Poly-lactic
acid (PLA) has emerged as a possible candidate for the same.
Sisal fiber is derived from an agave, Agave sisalana. The plant grows well all year
round in hot climate and in regions which are often unsuitable for other crops.
Polylactic acid (PLA) is biodegradable hydrolyzable aliphatic semicrystalline
polyester produced through the direct condensation reaction of its monomer,
lactic acid. PLA is a sustainable alternative to petrochemical-derived products,
since the lactides from which it is ultimately produced can be derived from the
fermentation of agricultural by-products such as corn starch or other
carbohydrate-rich substances like maize, sugar or wheat
Injection molding is acknowledged for being a precise and rapid processing route,
capable of producing small to medium sized plastic products having convoluted
profiles. It is one of the most widely used processing route for development of
plastic products. Injection molding process can be easily adapted to develop bio-
composites incorporating short natural fibers.

4. Manufacturing Process
The present experimental investigation explores the feasibility of using Direct-Injection molding (D-IM) process to
develop bio-composites in comparison to widely used Extrusion-Injection molding (E-IM) process.
 PLA (Ingeo™ 3260HP) in pellet form, having a density of 1.24 g/cm3 and melt flow rate of 65 g/10 min (210 ºC, 2.16
Kg), was used.
 Commercially available sisal fibers in strand form, were used. Fibers were manually chopped to the desired lengths
(3mm and 8mm). To remove undesired pith and dirt off the fiber surface, chopped sisal fibers were washed using
hot distilled water (70ºC). Chopped sisal fibers thus obtained were then dried in an air oven for 12 hours at a
temperature of 80 ºC.
 Prior to processing, hygroscopic PLA pellets were also dried in an air oven for 6 hours at 50 ºC.
Mechanical and morphological investigation of sisal fiber (30%) reinforced PLA bio-composites developed using both
the processes(D-IM, E-IM), was performed for comparative analysis.

5. Direct-Injection
Molding
• Chopped PLA pellets and sisal fibers mixed in a mechanical
agitator were directly fed into a commercial scale injection molding
machine (Endura-60, Electronica) for preparation of the test
specimens.
• A commercial scale injection molding machine is capable of both
compounding and injecting the fiber-matrix melt compound into
the mold. Sisal fibers and PLA pellets were melt compounded in-
situ at a screw speed and back pressure of 120 rpm and 5 MPa,
respectively.
• During processing, the injection barrel temperature profile was
fixed at 160 ºC, 185 ºC, 180 ºC and 195 ºC for feed zone,
compression zone, metering zone and nozzle, respectively. The
melt compound was then injected into the mold (mold
temperature: 30 ºC) with injection and holding pressure of 60 MPa
and 55 MPa, respectively.

6. Extrusion-Injection
Molding
• E-IM process in which, prior to injection molding, a
single screw extruder having screw length to diameter
ratio of 24, was used to melt blend sisal fibers and PLA
pellets. Sisal fiber and PLA pellet mixture was melted
blended at a temperature and screw speed of 185 ºC and 60
rpm, respectively.
• The extrudate obtained in the form of 4 mm diameter bio-
composite strand, was pulled through a water tank to cool
and subsequently pelletized using a pelletizer.
• These bio-composite pellets were then dried in an air oven
for 12 hours at 70 ºC. Dried, bio-composite pellets were then
injection molded into test specimens.

7. The mechanical behavior of the developed bio-composites was determined in terms of tensile, flexural, and impact
properties. Universal testing machine (Instron, USA) was employed to conduct tensile tests in accordance with ASTM
D3039M-14. The test speed and gauge length during tensile tests were kept as 1.5 mm/min and 50 mm, respectively.
An extensometer (Instron-5982, USA) was used to accurately record the tensile modulus. Flexural tests were
performed using a three-point bending fixture (ASTM D790-10), at test speed and span length of 2 mm/min and 64
mm, respectively. Notched Izod impact tests were conducted in accordance with ASTM D256-10. The tests were
performed using a low energy impact tester (Tinius Olsen-IT504)
Comparative bar graphs depicting tensile, flexural properties and impact strength of the developed bio-composites are
shown in figures 3, 4 and 5, respectively.
Mechanical Characteristics

8. Tensile and Flexural Strength Comparison
Figure 3. Tensile Strength Figure 4. Flexural Strength

9. Figure 5. Impact Strength
Impact Strength Comparison

10. From the above graphs it can be observed that:
The tensile and flexural strength of D-IM-SF bio-composites improved remarkably by 34.7% and 15.9% respectively,
compared to D-IM-LF bio-composites. Similar improvement in tensile and flexural modulus of D-IM-SF bio-composites
was observed which improved significantly by 92.5 % and 56.7% respectively, compared to D-IM-LF bio-composites.
However, D-IM process incorporating long fibers exhibit better impact properties.
 D-IM process is highly recommended for processing of bio-composites incorporating short fibers. While, E-IM
process was found suitable for both, long and short fibers.
 Both D-IM and E-IM processes ensured, uniform dispersion and orientation of short sisal fibers resulting in the
formation of homogenous bio-composites exhibiting superior tensile and flexural properties.
 Impact strength of the developed bio-composites declined with the incorporation of short fibers. D-IM-LF bio-
composites exhibited superior impact strength as compared to all the developed bio-composites
Observations

11. Advantages
and
Disadvantages
• Advantages:
• Consume less energy during processing
• Biodegradable
• Recyclable
• Does not pose environmental concerns after end of their useful life
• It has high strength and durability,
• Ability to stretch,
• Affinity for certain dyestuffs
• Resistant to deterioration in saltwater
• Disadvantages:
• Higher cost
• Low toughness compared to most utilized petroleum derived polymers
like polypropylene and
polyethylene
• Thermal degradation

12. Applications
Applications:
• Among 3D printing materials, PLA based bio-composites are
one of the most common feedstocks used for additive
manufacturing
• Since it is suitable for interaction with foods, this material is
used as a replacement for petroleum-based plastics for
packaging application, especially in the food industry
• It is exceptionally advantageous in manufacturing lightweight
with strong mechanical properties parts
• It is also seen as a potential substitution of glass fiber. Glass
fibers are hard to biodegrade and is detrimental to the
environment.
Reference:
https://doi.org/10.1080/10426914.2016.1198034

13. Thank You