300+ REAL TIME Chemistry Notes PPT & Answers 2023

[Chemistry Class Notes] on Periodic Classification of Elements Pdf for Exam

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Need for Periodic Classification of Elements

Chemists discovered that all the substances are made up of atoms or elements. Slowly they discovered many elements. In 1789, Antoine Lavoisier published a list of 33 elements. With the discovery of many elements chemists felt the need of classification of elements for their easy understanding and comparison. So, Antoine Lavoisier attempted to group all 33 elements into gases, metals, nonmetals and earth metals. Slowly by 1865, 63 elements were discovered. By now, chemists felt the need of periodic classification of elements as now it was very difficult to study the properties of these chemical elements individually. Scientists were trying to classify elements in a periodic manner of the basis of their various properties.

In the year 1869, Dmitri Mendeleev arranged all 63 elements in rows or columns in order of their atomic weight. He left the space for corresponding elements in his periodic table which were not even discovered then. Although he was able to predict the properties of those elements through his periodic classification of elements.

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Mendeleev’s Periodic Table from his book-‘An attempt towards a chemical conception of the Ether’

By 1911, scientists discovered atomic structure and atomic nucleus. Now they know the terms like isotope, proton etc. Mendeleev’s periodic table was not able to describe all this and was not able to assign position to isotopes and a perfect position to hydrogen according to its properties. So, in 1913 Mendeleev’s periodic table was perfected by Henry Moseley. He arranged all the elements in order of their increasing atomic numbers. This improved all the flaws of the Mendeleev Periodic Table. Such a position of hydrogen was fixed as its atomic number 1, there was no need for a separate position for isotopes as the arrangement was according to the atomic number of elements.

Presently, 118 chemical elements are known and are arranged in the Modern Periodic table. Out of 118 elements 98 elements occur naturally while 20 elements are man made in laboratories.

Significance of the Periodic Classification of Elements

Periodic table is very important as they classify elements according to their properties and provide us a great deal of information about elements and how they relate to one another. The organized classification of chemical elements in the periodic table has following advantages:

It enables chemists to easily understand properties of elements.
It comes very handy while performing experiments.
It enables chemists to compare the properties of elements.
It gives systematic and orderly information about elements and their compounds as well.
It enables chemists to predict the properties of even those elements which have not yet been discovered.
It provides information which can be used to easily balance the chemical equations.
It gives a proper explanation of the difference and similarity between properties of elements in groups and rows.

You can get a free PDF of NCERT Solutions of all exercises of the chapter Classification of elements and periodicity by registering yourself on . To know more about the elements and pattern of board exams you can also download : Learning App for Class 6-10, IIT JEE & NEET.

[Chemistry Class Notes] on Phenol Formaldehyde Resin Pdf for Exam

Phenol formaldehyde resin (plastic) was the first commercial polymers used in the 20th century. We abbreviate the Phenol formaldehyde resin as PF. It is also known as the phenolic resin, one of the first synthetic polymers that we can obtain by the reaction of phenol or substituted phenol with formaldehyde.

What are Phenol and Formaldehyde?

Here, phenol is an aromatic alcohol that we can obtain from benzene. Bakelite is a phenolic plastic. Further, formaldehyde is reactive and can be derived from methane (CH₄).

Phenol formaldehyde resin chemical formula is C₈H₆O₂. It has various properties that we will discuss on this page.

Also, we will understand the phenol formaldehyde resin structure, phenol formaldehyde resin preparation, and phenol formaldehyde reaction.

What is Phenol Formaldehyde Resin?

Phenol formaldehyde Resin or PF are synthetic high polymers.

We can produce PF by the reaction with phenol and substituted phenol with formaldehyde.

Besides polyurethanes and polyesters, phenolic and epoxy resins are the widely known applications for technical lignins in thermosetting materials.

We produce phenolic resins by a step-growth polymerization reaction that can be either in the presence of acid or base (used as catalysts).

PFs are normally in liquid state and their specific gravity ranges from 1.12 to 1.16.

Now, let’s have a look at the Phenol Formaldehyde Resin Structure.

Phenol Formaldehyde Resin Structure

The Phenol formaldehyde resin structure looks like the following:

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Along with the structure, every chemical compound has several properties that we will understand below.

Phenol Formaldehyde Resin Properties

In Phenol formaldehyde, an exclusive range of molding powders is available in which the composition of the resin, fillers, etc, varies to provide moldings suitable for many purposes.

Here, the commonly used techniques for its preparation are compression and transfer processes.

The below table shows the illustration of the chemical and physical properties of Phenol Formaldehyde Resin or PF:

Parameters	Corresponding Value Structure
Phenol Formaldehyde Resin Structure (Chemical structure)	() Phenol Formaldehyde Polymer
Phenolic resin’s polarisability	10-24 cm3
Enthalpy of Vapourization	43.52 KJ/mol
Polar Surface Area	9.23 Å2
Bond donor	1 H bond donor
Bond acceptor	1 H bond acceptor
Flash Point	72.5 °C
Boiling Point at 760 mm of Hg	181.8 °C
Vapour Pressure at 0.614 mm of Hg	25°C
Phenolic resin colour	Amber coloured
Surface	Smooth and lustrous surface
Stability	Hard and rigid, with good dimensional stability
Strength	Brittle in thin sections Has low impact strength
Molding Efficiency	Easy to mold
Retaining properties	Retain properties at freezing temperatures
Strength	Improvised strength
Dimensional stability	Good dimensional stability on heating up to about 300 degrees F
Impact Resistance	Improved impact resistance
Colour	The Colour is good. It can be both normally transparent and colourless.
Electrical Property	Good electrical insulators
Type of plastic	Laminated Plastics

How Phenol Formaldehyde Resins are Produced?

The two following main production methods are:

The reaction of phenol with formaldehyde produces a thermosetting network polymer.
Another approach restricts the formaldehyde to produce a prepolymer known as a volcano.

A volcano can be molded, and therefore, cured with the addition of formaldehyde and heat.

There are many variations in both production and input materials that we use to produce a wide variety of resins for particular purposes.

Now, let’s understand the Phenol Formaldehyde Resin Preparation.

Phenol Formaldehyde Resin Preparation

A step-growth polymerization reaction that can be either acid – or base-catalysed method is used for Phenol-formaldehyde resins (as a group) preparation.

Since formaldehyde (a reactive derivative of methane) exists as a dynamic equilibrium of methylene glycol oligomers for the most part in the solution.

Further, the concentration of the reactive form of formaldehyde depends on the following two factors:

Temperature
pH

First Preparation Process

Phenol on reacting with formaldehyde at the ortho and para-sites, namely – 2, 4, and 6 sites permit up to 3 units of formaldehyde to associate with the ring.

The involvement of involves the formation of a hydroxymethyl phenol is crucial in all the cases of the initial reaction:

[C_6H_5OH + CH_20 rightarrow HOC_6H_4CH_2OH]

Phenol Formaldehyde 4 – Hydroxybenzyl alcohol

The hydroxymethyl group is capable of reacting with either of the following:

A free ortho or para-site or

With another hydroxymethyl group.

The first reaction produces a methylene bridge, and the second gi
ves an ether bridge in the following reactions:

Methylene Bridge: [HOC_6H_4CH_2OH + C_6H_5OH rightarrow (HOC_6H_4)^2CH_2 + H_2O]
Ether Bridge: [2 HOC_6H_4CH_2OH rightarrow (HOC_6H_4)2O + H_2O] PF Resin

Here, the diphenol a.k.a [(HOC_6H_4)2CH_2] is also known as “dimer”. Also, we call it the bisphenol F.

The bisphenol F is a crucial monomer in epoxy resin production. Further, Bisphenol-F links generate tri- and tetra-and higher phenolic oligomers.

Phenol Formaldehyde Resin Applications

Phenol formaldehyde Resin has several uses in industry. Besides this, it possesses the following applications:

1. In-Circuit Board Preparation

Phenolic resins are primarily used for making circuit boards like PCB.

Further, we find the applications of phenolic resins in Electrical equipment.

2. Day-to-Day Applications

Also, it is needed in the following areas:

We also find its use in Laminated Materials like Laminated sheets, rods, and tubes, made in great variety from fabric, paper, wood veneers, etc impregnated with phenolic resins providing a variety of materials of widely differing properties.

Industrial Applications of Phenol Formaldehyde Resin

In industrial practice, the two basic methods are used for transforming the polymer into useful resins:

1. First Method

An excess of formaldehyde is made to react with phenol in the presence of a base catalyst in water solution to produce a low-molecular-weight prepolymer called a resole.

Here, the resole frequently found in liquid form or solution, is cured to a solid thermosetting network polymer.

For instance, compressing it between layers of wood veneer, and therefore, heating this assembly under pressure to form plywood.

2. Second Method

This method involves the reaction of formaldehyde with an excess of phenol, in the presence of an acid catalyst.

The second process produces a solid prepolymer known as novolac (or novolak).

Here, novolak resembles the final polymer; however, it has a much lower molecular weight and is still thermoplastic. It means that we can soften it by reheating without undergoing chemical decomposition.

The curing process can be accomplished by grinding the novolac to a powder, therefore, mixing it with fillers such as wood flour, minerals, or glass fibres. Further, heating the mixture in a pressurized mold.

To obtain a thermosetting resin, novolacs need additional formaldehyde or, more commonly, compounds that decompose into formaldehyde upon heating.

[Chemistry Class Notes] on Phosphorus Pentachloride Pdf for Exam

Phosphorus pentachloride is a greenish-yellow crystalline solid, It is decomposed by water to form hydrochloric acid and phosphoric acid with the release of heat energy. It can also be prepared by the action of dry chlorine on phosphorus trichloride. The chemical formula for phosphorus pentachloride is PCl₅. In a solid state, it exists as PCl₄PCl₄⁺PCl₆PCl₆^–.

Phosphorus pentachloride vaporizes without dissociation in an atmosphere of phosphorus trichloride or chlorine gas. The dissociation equilibrium is shifted to the left side by the presence of the product.

Structure of Phosphorus Pentachloride

The hybridization in phosphorus pentachloride is sp³d and it has a trigonal bipyramidal geometry in gaseous and liquid states. It has two axial P−Cl bonds and three equatorial P−Cl bonds.

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Properties of Phosphorus Pentachloride

Formula of phosphorus pentachloride	PCl₅
Molecular Weight	208.24 g/mol
Density	2.1 g/cm³
Melting Point	160.5 ⁰C
Boiling Point	166.8 ⁰C
phosphorus pentachloride shape	Trigonal bipyramid
Odor	Irritating odor

Uses of Phosphorus Pentachloride (PCl₅)

It is used as a chlorinating agent.
It is used for the manufacture of penicillin and cephalosporin in the pharmaceutical industry.
Used to produce acid chlorides.
Used as a catalyst in the manufacture of acetyl cellulose and also a catalyst for condensation reactions and cyclization.

Methods of Preparation of Phosphorus Pentachloride (PCl₅)

Chemical Properties of Phosphorus Pentachloride (PCl₅)

Phosphorus pentachloride dissociates as: PCl₅ ⇌ PCl₃ + Cl₂
Reaction with water: PCl₅ + 4H₂O → H₃PO₄ + 5HCl
Reaction with metal: Zn + PCl₅ → ZnCl₂ + PCl₃
Reactions with phosphorus pentoxide: 6PCl₅ + P₄O₁₀ → 10POCl₃
Reactions with sulfur dioxide: SO₂ + PCl₅ → POCl₃ + SOCl₂

Harmful Effects of Phosphorus Pentachloride

Phosphorus Pentachloride is a Reactive Chemical. Direct exposure to Phosphorus Pentachloride can cause weakness, nausea, headache, dizziness, and vomiting. It may damage the liver and kidneys.

As a precaution, one must be able to identify Phosphorus Pentachloride. It’s a crystalline solid whose color can range from white to pale yellow with a pungent odor. Phosphorus Pentachloride is a manufacturing agent for other chemicals, aluminum metallurgy, and the pharmaceutical industry.

Some of the acute health hazards that can be caused by Phosphorus Pentachloride are mentioned below:

If an individual comes in contact with Phosphorus Pentachloride, one may experience severe irritation and burning of skin and eyes with possible chronic eye damage
Breathing in Phosphorus Pentachloride can lead to irritation in the nasal cavity and throat.
If inhaled deeply, it can cause intense irritation and damage to the lungs resulting in coughing and/or shortness of breath. A medical emergency can also be caused because of higher exposure to Phosphorus Pentachloride. This can lead to fluid build-up in the lungs called pulmonary oedema with severe shortness of breath.
Exposure to Phosphorus Pentachloride can cause the development of cough, phlegm in bronchitis.

[Chemistry Class Notes] on Physical Properties of Amines Pdf for Exam

Have you ever wondered why toilets smell so bad? Well, ammonia and compounds of ammonia called amines are responsible for that foul smell. These compounds have a pungent smell, but they have an enormous significance in chemistry and our everyday lives. Amines are an essential class of organic compounds. Amines are an exciting subject to study, and it also has a major application in biology. Nitrogen is the only famous product, but many other products of ammonia get derived by changing the hydrogen atoms. In this article, you can learn about the classification of amines, their structure, and their physical properties of amines.

What are Amines?

Amines are organic compounds, deriving from ammonia (NH₃). Amines get derived by replacing one or more hydrogen atoms with an alkyl or aryl group. Amines have a nitrogen atom with a lone pair of electrons. When you replace one or more hydrogen atoms with substituent groups like alkyl or aryl in ammonia, you get a new type of organic compound called amines. Amino acids, biogenic amine, trimethylamine, and aniline are some of the important amine structures.

Classification of Amines

Amines get classified into four categories, such as primary, secondary, tertiary, and cyclic. A primary amine is the one where you replace one of the three hydrogen atoms with an alkyl or aryl group. When you replace two of the three hydrogen atoms, then you get a secondary amine. Likewise, by replacing all three hydrogen atoms, tertiary amines get formed.

Keep in mind that only secondary or tertiary amines can be cyclic. Examples of primary amines are CH₃NH₂, methylamine, CH₃NHCH_3, and dimethylamine are examples of secondary amines. An example of tertiary amine is trimethylamine and 3 – member ring aziridine is an example of cyclic amine.

Physical Properties of Amines

The following are various amine physical properties that you should know.

General Properties:

Lower aliphatic amine often finds its gaseous state, and they have a fishy smell.
Primary amines having three or four carbon atoms are in the liquid state at room temperatures, and higher ones get found in the solid state.
Aniline and various arylamines are colorless. But, they do get colored due to atmospheric oxidation when you keep them in the open.

Solubility Characteristics:

Lower aliphatic amines can form hydrogen bonds with water molecules. And thus, such amines are soluble in water.
When there is an increase in the hydrophobic alkyl part of the amines, its molar mass goes up. As a result, such amines have a lower solubility in water.
Amines are soluble in organic solvents like alcohol, ether, and benzene because alcohols have high polarity as compared to amines.

Boiling Points of Amines:

Primary and secondary amines get engaged in intermolecular association because of the hydrogen bonding between the nitrogen of one molecule with the hydrogen of another molecule.
Such intermolecular association is more in primary amines as compared to secondary amines because there are two hydrogen atoms present for bond formation.
Tertiary amines don’t have an intermolecular association as they don’t have any hydrogen atoms available for hydrogen bond formation.
That’s why the order of boiling points for isomeric amines goes like primary > secondary > tertiary.

Those were some fundamental physical properties of amines.

Amines and Amino Acids

I am sure you must have come across the word”amino acid”. It is a compound that is a component of biological proteins. Amines are involved in the formation of amino acids while Amines are compounds that are derived from Ammonia. Amines chapter is studied in organic chemistry and they are basically classified as functional groups or organic nitrogen compounds containing nitrogen atoms with lone pairs of electrons. Many vitamins are made up of amino acids. Serotonin is an important amine that functions as one of the most important neurotransmitters in the brain. Amines are an important class of organic compounds found widely in plants and animals as proteins, vitamins, alkaloids, etc. Amine research is attractive in many ways. Amine chemistry is very important in biology. It is essential for all living things. Amines can be liquids, solids, or gases at room temperature.

Types of Amines

Amines are typically classified into- Aliphatic and Aromatic Amines.

Aliphatic Amines: Aliphatic amines are compounds where the nitrogen atom is directly bonded to one or more alkyl groups.
Aromatic Amines: Aromatic amines are compounds that are attached to aromatic hydrocarbons and have at least one benzene ring.

Aromatic Amines are further classified into-

Aryl amines
Aryl alkyl amines

Further Classification of Amine

Based on the number of alkyl or aryl groups attached to the nitrogen of the amine, further classification is as Primary, Secondary Tertiary, and cyclic.

Primary Amine: When one hydrogen atom in ammonia is replaced with alkyl or aromatic groups, that means it is a primary amine. Some examples of primary alkylamines include amino acids and methylamines, and primary aromatic amines include aniline.
Secondary Amine: Amines with two hydrogen atoms of ammonia are replaced with organic substituents, alkyl, and/or aryl substituents, forming secondary amine. Common examples include dimethylamine. Diphenylamine is also an example of aromatic amines.
Tertiary Amine: Amines are formed when all three hydrogen atoms of ammonia get replaced by organic substituents, Alkyl or aryl groups, forming Tertiary amine. Examples are trimethylamine and EDTA.

Keep in mind that only secondary or tertiary amines can be cyclic. Examples of primary amines are CH₃NH₂, methylamine, CH₃NHCH₃, and dimethylamine are examples of secondary amines. An example of tertiary amine is trimethylamine and 3 – member ring aziridine is an example of cyclic amine.

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[Chemistry Class Notes] on Plastics Pdf for Exam

Introduction:

In 1846, the renowned German chemist Christian Schonbein discovered plastic. Plastics have actually been mistakenly identified. In his kitchen, Christian was experimenting, and he accidentally spilled a mixture of nitric acid and sulphuric acid. He took a cloth to mop up the solution (a mixture of nitric and sulphuric acid) and placed it over the stove after moping. After some time, the fabric vanished and got name plastic. In this article, you will study what is plastic, different types of plastic, properties of plastic, and recycling of plastic.

What is Plastic?

Plastic is defined as a material that contains an organic substance of greater molecular weight as an important ingredient. It is also characterized as polymers with long chains of carbon. All plastics are said to be polymers.

The word plastic was derived in Greek from the word ‘Plastikos’ which means ‘to mold.’ Fossil fuels have hydrogen and carbon (hydrocarbon) containing compounds that act as building blocks for long polymer molecules. Such building blocks are referred to as monomers, which bind together to form long chains of carbon called polymers.

Types of Plastic and Their Uses

There are two different types of plastic

Thermoplastic:

plastics that are easy to bend when heated. Thermoplastics include linear polymers and a mixture of linear and cross-linked polymers. For instance, PVC, nylon, polythene, etc.

Thermosetting:

Plastics that, once molded, can not be softened again by heating. Heavily cross-linked polymers fall into the thermosetting plastics group. Bakelite, melamine, etc. Example: Bakelite is used to make electrical switches, while floor tiles use melamine.

Speaking about the variations between thermoplastic and thermosetting plastic, the key differentiating factor between the two is that thermoplastic products usually have low melting points, meaning they can be quickly remolded or recycled further.

The thermosetting plastic, on the other hand, is quite the contrary. They can withstand high temperatures and, even with the application of heat, can not be reformed or recycled once hardened. In any event, let’s take a look at some of the major differences below between these two compounds.

Thermoplastic	Thermosetting
Synthesized by the process known as addition polymerization	Synthesized by the process known as condensation polymer.
Thermoplastic is processed by injection molding, extrusion process, blow molding, thermoforming process, and rotational molding.	Thermosetting Plastic is processed by compression molding, reaction injection molding.
There are secondary bonds in thermoplastics between molecular chains.	There are primary bonds between molecular chains in thermosetting plastics and strong cross-links hold them together.
They have a low melting point and tensile strength	They have a high melting point and high tensile strength
They have low molecular weight.	They have high molecular weight.

Types of Plastic Materials

Examples of thermoplastics are listed below.

Polystyrene
Teflon
Acrylic
Nylon

Examples of thermosetting polymers include:

Vulcanized rubber
Bakelite
Polyurethane
Epoxy resin
Vinyl ester resin

Plastic Material Properties

Here are some plastic material properties-

They are light weighted.
They are highly resistant to chemicals.
They are high electrical strength.
They can easily be molded to desired shape and size.
They can be made transparent or colored.
Operations like drilling, sawing, and punching can be done on plastics.
They are cheap as compared to metals.
They are strong and ductile
They are poor conductors of electricity.
Plastic resists corrosion.

Recycling of Plastic

Plastic recycling is very significant. If they are not recycled at the right time, they are mixed with other chemicals or products, making them harder to recycle and a source of pollution.

They are non-biodegradable, and the microbial effect does not decompose them.

It is important to use biopolymers or biodegradable polymers to prevent this.

Did You Know?

In a landfill, plastic takes up to 1,000 years to decay. It takes 88 percent less energy to recycle plastic than to produce plastic from raw materials. Every year, enough plastic is thrown away to orbit the Earth four times. Each year, Americans throw 35 billion plastic bottles away.

[Chemistry Class Notes] on Polymers Pdf for Exam

Polymers are defined as chemical compounds whose molecules are large and often resembling long chains, which are made up of seemingly endless interconnected link series. The size of these molecules is remarkable, as explained in the Chemistry of Industrial Polymers, ranging from thousands to millions of atomic mass units (as opposed to the tens of atomic mass units generally found in the other chemical compounds). The primary causes of the peculiar properties associated with plastics are the size of the molecules, their physical state, and the structures that they follow.

Thermoplastic and Thermosetting

Polymers, which are classified as plastics, may be divided into two primary categories:

Thermoplastics
Thermosets.

Thermoplastics including polystyrene and polyethylene can be remoulded and moulded several times. Therefore, a foamed-polystyrene cup may be heated and also reshaped into a new form – for suppose, a dish. Individual molecules are separated from one another and flow past one another in the polymer structure that is associated with thermoplastics. The molecules can have either low or extremely high molecular weight, and they can be linear or branched in structure, but the important feature is that of consequent mobility and separability.

On the other hand, thermosets cannot be reprocessed upon reheating. Thermosetting resins undergo a chemical reaction that results in an infusible, insoluble network during their initial processing. Most importantly, the entire heated, finished article becomes a single large molecule. For example, the epoxy polymer, which is used in making a fibre-reinforced laminate for a golf club, undergoes a cross-linking reaction the time it is moulded at a high temperature. The subsequent application of heat, on the other hand, does not soften the material to the point that it can be reworked, and can even break it down.

Physical States and Molecular Morphologies

The morphology of polymers, or the arrangement of molecules on a wide scale, has an effect on their plastic behaviour. Simply stated, polymer morphologies are either crystalline or amorphous. Crystalline molecules can be organised tightly and in a discernible order, whereas amorphous molecules can be arranged arbitrarily and intertwined. The majority of thermosets are amorphous, while thermoplastics may be semicrystalline or amorphous. Crystallites, which are crystalline regions within an amorphous matrix, are visible in semicrystalline materials.

The figure shows amorphous and semicrystalline polymer morphologies on the left Volume-temperature diagram for the semicrystalline and amorphous polymers, representing the volume increasing with temperature. And the schematic diagram of the semicrystalline morphology, representing amorphous regions and crystallites on the right.

Properties

Polymer’s physical state and morphology hold a strong influence on its mechanical properties. A simple measure of the differences, which are produced in mechanical behaviour, is given as the elongation that takes place when plastic is loaded (or stressed) in tension. A glassy polymer like polystyrene is quite stiff, representing a high ratio of initial stress to initial elongation.

Processing and Fabrication of Plastics

The processing of the raw materials into a usable form is referred to as either conversion or fabrication. Plastic pellets can be converted into films or films can be converted into food containers, as an example from the plastics industry. There are also other processing techniques such as forming, mixing, finishing.

Extrusion

In the extrusion process, a melted polymer can be forced through an orifice with a specific cross-section (the die), and a continuous shape can be formed with a constant cross-section as same as that of the orifice. While thermosets can be extruded and cross-linked by heating the extrudate, thermoplastics are more common since they can be extruded and solidified by cooling. Among the products, which are produced by extrusion are film, tubing, sheet, insulation, pipes, and home siding. In every case, the profile can be determined by the die geometry, and solidification can be done by cooling.

Longitudinal section of the screw extruder of thermoplastic polymers. Plastic pellets can be fed into the extruder barrel from a hopper, where they are melted by mechanical energy provided gradually by a turning screw and distributed along the barrel by heaters. The molten polymer can be forced through a die that shapes the extrudate into a few products.

Most plastic grocery bags and similar items can be made by the continuous extrusion of the tubing. In the blow extrusion, the tube can be expanded prior to being cooled by being made to flow around a massive air bubble. Air can be prevented from escaping from the bubble by collapsing the film on the bubble’s other side.

Laminated structures can be made by extruding several materials at the same time via a single die or several dies for a few applications. Multilayer films can be useful since the outer layers may contribute strength and moisture resistance while the inner layer may control the oxygen permeability, which is an important factor in food packaging.