MECHANICAL PROPERTIES OF ABACA FIBER BASED REINFORCED POLYURETHANE COMPOSITE E-Book

Dharmpal Deepak

• Herausgeber: BookRix
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2019

Beschreibung

From last few decades’ composite materials, ceramics and plastics has made a mark in the field of materials. Applications of these materials in engineering arespecially attributed to their low specific weight and comparatively high strength. Applications of composite materials vary from the basic daily needs to sophisticated luxury applications.

The demand of natural fiber in the composite materials has been increased owing to low density, low cost and biodegradable properties of natural fiber.But at the same time the natural fibers has certain disadvantages viz. they are hydrophilic in nature due to which there is poor incompatibility of natural fiber with the matrix. This intensity of this disadvantage can be reduced with the help of chemical treatment of natural fibers. Natural fiber has tendency of water absorption, which can also be reduced with chemical treatment.

There are number of factors which affect the properties of natural fiber reinforced composite viz. fabrication method, environment condition during fabrication, fiber and its quantity, matrix material. Any slight modification in the above said variables leads to change in the properties of the final composite material.

In the present work, the tensile and flexural properties of natural fiber (abaca fiber) reinforced TPU composites have been investigated. The content of natural fiber in composites has been varied from 0 to 30 wt%. The reinforced fibers were chemically treated with NaOH followed by treatment with maleic anhydride in acetone, prior to fabricating of samples by injection moulding. It is observed that the composite containing 10 wt% of abaca fiber has highest tensile strength among all the composites fabricated for this study, whereas the tensile strength of pure TPU sample has maximum among all the samples fabricated during this research work.Maximum flexural strength is observed ofthe composite containing 30 wt% of abaca fiber.SEM examinations of the fractured surface reveal that primary failure mechanisms in composite as fiber fracture and fiber pull-out.

Leseprobe

Pankaj Rana, Dharmpal Deepak

MECHANICAL PROPERTIES OF ABACA FIBER BASED REINFORCED POLYURETHANE COMPOSITE

Natural Fiber Based Polymer Composites

BookRix GmbH & Co. KG81371 Munich

Introduction

INTRODUCTION

1.1         Thermoplastic Polyurethane: Thermoplastic polyurethane is a category of plastic which is synthesized by polyadditon reaction between a diisocyanate and one or more diols (a chemical compound containing 2 hydroxyl groups (–OH groups)). Thermoplastic polyurethane (TPU) was first developed in the year of 1937. Upon heating, the polymer is soft and process able and upon cooling it is hard. This versatile polymer has capability to reprocess without losing its structural integrity. TPU can replace hard rubber and malleable engineering plastic. TPU has high elongation and tensile strength. It has ability to resist grease, oil, chemicals and abrasion (http://www.huntsman.com/polyurethanes/Media%20Library/global/files/guide_tpu.pdf). Above characteristics make TPU extremely popular across wide range of market applications. To create solid component, TPU can be extruded or injected on conventional thermoplastic manufacturing equipment. TPU is usually used for footwear, hose and tube, cable and wire, sheet and many more industrial products. 

1.1.1      Chemical Classification of TPU

Polyester TPUs: Polyester TPUs are unaffected by chemical and oils. They are offering value in the form of enhanced properties, provide excellent abrasion resistance. Polyester TPUs are compatible with PVC and other polar plastics; they also offer a good balance of physical properties.

Polyether TPUs

Polycaprolactone TPUs: They are an ideal raw material for pneumatic and hydraulic seals. Polycaprolactone TPUs exhibit inherent toughness and relatively high resistance to hydrolysis.

1.1.2 Classification of TPUs on the basis of aromatic and aliphatic varieties

(a)          Aromatic TPUs: They are based on isocyanates like MDI (Methylene diphenyl diisocyanate) which are workhorse products and can be used in the applications where flexibility, toughness and strength are required.

(b) Aliphatic TPUs: They are based on isocyanates like H12 MDI, HDI and IPDI (Iso Phorone Diisocynate) which are light stable and offer excellent optical clarity. They are usually used in automotive interior and exterior applications. They are also used in the areas where there are requirements of attributes like optical clarity, adhesion and surface protection.

1.1.3 Thermoplastic Polyurethane Chemistry: A TPU is multi-phase block copolymer. TPU is synthesized by three basic raw materials, which are combined together in a specific way. Individual component which is required to produce thermoplastic polyurethane are: Polyol or long-chain diol, Chain extender or short- chain diol, Diisocyanate

1.1.4 Performance characteristics of thermoplastic polyurethane: High abrasion resistance, High elasticity across the entire hardness range, Good range of flexibility over a wide range of temperature, Tactile properties, Excellent low temperature and impact strength,. Suitability for bonding and welding, Easy recyclability and ease of coloring, High energy radiation resistance

Physical properties of thermoplastic polyurethane

Shore hardness: It is an empirical measurement used to test the resistance offered by TPUs to penetration and indentation under the defined force. Two types of letters are used to categorize the TPU, these are: ‘A’ denotes flexible type and ‘D’ denote rigid type of TPU. Above categories may is overlap sometime. Both are measured on the scale from 0 to 100. Zero indicates very soft and 100 indicate very hard.

Tensile strength: It indicates TPU behavior when a specimen is placed under short term, uniaxial stress. 

Tear strength: Tear strength denotes the ability of TPU to counter break and distortion. Greater numbers of utilization option are present when tear strength is higher.

Compression set: A TPUs compression set can be defined as the permanent deformation that remains after the compressive stress has been released. It is calculated as a percentage of original deflection after the material has been allowed to recover at standard conditions for 30 minutes. TPU materials may have very best compression resistance after heat treatment like annealing.

Abrasion

Coarse paper is applied to a substrate under pressure via rotating cylinder, to measure the abrasion resistance of plastic material like TPU. Before and after the abrasion assessment, the weight of the specimen is measured. The original density of the material is considered alongside the roughness of the paper with results typically expressed in terms of volume loss of the substrate in mm3.

Shrinkage: There are different factors which influenced shrinkage of TPU such as part design, wall thickness, and gate design, processing condition, melt and mold temperature as well as injection and holding pressure.

Chemical Properties: The behavior of TPU is decided by its chemistry. It is very important to choose proper grade of TPU for its exposure to high temperature, water and other outdoor consideration.

Acids and alkaline solutions: TPU show its limited resistance for alkaline and acids. It can only withstand for short period of time with diluted acids and alkaline solutions at room temperature.

Saturated hydrocarbons: TPU expand slightly when exposed to saturated hydrocarbons and when exposed to isooctane and petroleum, moderate swelling will occur.

Aromatic hydrocarbons: When TPU come in contact with aromatic hydrocarbons such as benzene and toluene, it will swell resulting in reduction of mechanical properties. Scale of swelling will directly depend upon one type of hydrocarbon.