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NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 5

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 5

The history of polyurethanes

In 1937, the German chemist Dr. Otto Bayer (1902–1982) invented the versatile class of plastics we call polyurethanes. Polyurethanes are available in myriad forms—they are used in numerous products, from coatings and adhesives to shoe soles, mattresses, and foam insulation. Despite the variety in their characteristics, the underlying chemistry of these different forms is strikingly similar.

During World War II, the use of polyurethanes became popular as a replacement for rubber, which at the time was expensive and hard to obtain. Around the 1950s, polyurethanes began to be used in adhesives, elastomers, rigid foams, and flexible cushioning foams such as those used today.

Wallace Carothers, inventor of polyamide.
Dr. Otto Bayer was credited with inventing polyurethanes in 1937.

Nowadays, a life without polyurethane is difficult to imagine, as you can easily find it everywhere around you.

How is polyurethane created?

 

Polyurethanes are formed by reacting polyols (i.e., alcohols containing more than two reactive hydroxyl groups in each molecule) with di-isocyanates or polymeric isocyanates. Suitable catalysts and additives are used wherever necessary. Since both a variety of di-isocyanates and a wide range of polyols can be used to produce polyurethane, a large spectrum of polyurethane materials can be produced to meet the specific requirements for different applications. Polyurethanes can appear in a variety of forms including rigid foams, flexible foams, specialty adhesives, chemical-resistant coatings, sealants, and elastomers.

Figure 1. Molecular structures of isocyanates, polyols, and polyurethane.

Physical and chemical properties of polyurethanes

The properties of polyurethanes are highly dependent on their production process. When the polyol chain (Figure 1) is long and flexible, the final product will be soft and elastic. On the other hand, if the extent of cross-linking is very high, the final polyurethane product will be tough and rigid. The cross-linked structure of polyurethanes generally consists of three-dimensional networks which result in very high molecular weights. This structure also accounts for the thermosetting nature of the polymer since polyurethane typically does not soften or melt when exposed to heat.

One of the most popular forms of polyurethane is foam. This form is created by facilitating the production of carbon dioxide gas during the urethane polymerization process.

Typical applications of polyurethane

The primary application of polyurethane is in the production of foams (rigid and flexible). Other important applications and uses of polyurethane are listed below.

 

  • Low-density, flexible polyurethane foams are widely used in mattresses and automobile seats.
  • Bathroom and kitchen sponges are commonly made from polyurethane. It is also used in the manufacturing process of seat cushions and couches.
  • Polyurethane is also used to produce textiles used in some clothing and upholstery.
  • Due to its good insulating properties, polyurethane materials are commonly used in construction work.
  • Polyurethane moldings are also used in columns and door frames.
  • Flexible polyurethane is used in the manufacture of partially elastic straps and bands.
  • The low-density elastomers of polyurethane are widely used in the footwear industry.

In Table 1 a variety of polyurethane properties are compared to other conventional materials like rubber, metal, and plastic.

Table 1. Polyurethane in comparison with rubber, metal, and plastic.

PU vs. Rubber

PU vs. Metal

PU vs. Plastic

High abrasion resistance

Lightweight

High impact resistance

High cut and tear resistance

Noise reduction

Elastic memory

Superior load bearing

Abrasion resistance

Abrasion resistance

Thick section molding

Less expensive fabrication

Noise reduction

Colorability

Corrosion resistance

Variable coefficient of friction

Oil resistance

Resilience

Resilience

Ozone resistance

Impact resistance

Thick section molding

Radiation resistance

Flexibility

Lower cost tooling

Broader hardness range

Easily moldable

Low temperature resistance

Castable nature

Non-conductive

Cold flow resistance

Low pressure tooling

Non-sparking

Radiation resistance

Near-infrared spectroscopy as a tool to assess the quality of polyurethanes

Near-infrared spectroscopy (NIRS) has been an established method for both fast and reliable quality control within the polyurethane industry for more than 30 years. However, many companies still do not consistently consider the implementation of NIRS in their QA/QC labs. The reasons could be either limited experience regarding application possibilities or a general hesitation about implementing new methods.

There are several advantages of using NIRS over other conventional analytical technologies. For one, NIRS is able to measure multiple parameters in just 30 seconds without any sample preparation! The non-invasive light-matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes it an excellent method for the determination of both property types.

In the remainder of this post, a short overview of polyurethane applications is presented, followed by available turnkey solutions for polyurethane analysis developed according the NIRS implementations guidelines of ASTM E1655-17.

Did you miss the first parts in this series? Find them here!

For more detailed information about NIRS as a secondary technique, read our previous blog posts on this subject.

Applications and parameters for polyurethanes with NIRS

When producing different types of polyurethanes, it is important to check certain parameters to guarantee the quality of the finished products. Typical parameters include hydroxyl number, acid number, moisture, and color in polyols as well as the NCO (isocyanates) content, (total) acid number, and moisture content in polyurethanes. The most relevant applications for NIRS analysis in polyurethane production are listed later in this article in in Table 2.

Where can NIRS be used in the polyurethane production process?

Figure 2 shows the individual steps from plastic producer via plastic compounder and plastic converter to plastic parts and foam producer.

Figure 2. Illustration of the production chain for polyurethanes.

Easy implementation of NIR spectroscopy for plastic producers

Metrohm has extensive expertise with analysis of polyamides and offers a turnkey solution in the form of the DS2500 Polyol Analyzer. This instrument is a ready-to-use solution for the determination of multiple quality parameters in polyols and polyurethanes. For the analysis of polyurethane pellets and parts, the Metrohm DS2500 Solid Analyzer is recommended.

Figure 3. Turnkey solution for polyurethane analysis with the Metrohm DS2500 Polyol Analyzer.

Learn more about the possibilities of polymer analysis with Metrohm DS2500 Analyzers in our free brochure.

Application example:

Pre-calibrations and starter model for the PU industry on the DS2500 Polyol Analyzer

The determination of the parameters listed below in Table 2 is a lengthy and challenging process with conventional laboratory methods. To measure them all, several different techniques are required which takes a significant amount of time, not only to analyze the sample, but also for the instrument management and upkeep.

Table 2. Primary method vs. NIRS for the determination of various quality parameters in PU samples.
Parameter Primary method Time to result (primary method) Relevant NIRS Application Notes NIRS benefits
Hydroxyl number in Polyols

Titration

90 min. preparation + 1 min. Viscometer

AN-NIR-068

AN-NIR-065

AN-NIR-035

AN-NIR-007

All three parameters are measured simultaneously within a minute, without sample preparation or the need of any chemical reagents
NCO (Isocyanate) content in PU HPLC 20 min. preparation + 20 min. HPLC
Moisture content

Karl Fischer Titration

25 min. preparation + 5 min. KF Titration

 

The NIRS prediction models created for polyols are based on a large collection of real product spectra and are developed in accordance with ASTM E1655-17 Standard practices for Infrared Multivariate Quantitative Analysis. For more detailed information on this topic, download the free white paper.

To learn more about pre-calibrations for polyols, download our brochure and visit our website.

One example of a dedicated ASTM standard referring to NIRS is ASTM D6342-12 Standard Practice for Polyurethane Raw Materials: Determining Hydroxyl Number of Polyols by Near Infrared (NIR) Spectroscopy. The following application example demonstrates that the DS2500 Polyol Analyzer operating in the visible and near-infrared spectral region (Vis-NIR) provides a cost-efficient and fast solution for the determination of the hydroxyl number in polyols and the NCO (isocyanate) content in polyurethanes. With no sample preparation or chemicals required, Vis-NIR spectroscopy allows analysis of all three quality parameters listed in Table 2 in less than a minute. The results are shown in Figure 4 and Figure 5.

Figure 4. Turnkey solution for determination of hydroxyl number in polyols using the Metrohm DS2500 Polyol Analyzer. A: Sampling and analysis of polyols. B: NIRS results compared to a primary laboratory method along with the Figures of Merit (FOM).
Figure 5. Turnkey solution for determination of NCO content (Isocyanates) in polyurethane using the Metrohm DS2500 Polyol Analyzer. A: Sampling and analysis of polyurethane. B: NIRS results compared to a primary laboratory method along with the Figures of Merit (FOM).

This application example demonstrates that NIR spectroscopy is excellently suited for the analysis of multiple parameters in polyols and polyurethanes in less than one minute without sample preparation or using any chemical reagents. Visit our website to learn more about our variety of analytical solutions for the polymer industry!

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 4

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 4

Polyamide (Nylon): A brief introduction

Wallace Carothers (1896–1937), the creator of polyamide.

Polyamide, more commonly known as Nylon, was first synthesized by Wallace Hume Carothers, an American organic chemist working for the DuPont chemical company. In 1935, he developed the formula known as PA66, or Nylon 66.

Just a few years later in 1938, Paul Schlack, a German chemist working at IG Farben, developed PA6 (also known as Nylon 6), a different molecule based on the organic compound caprolactam. Both types of polyamides are well-suited for many kinds of applications. The use of PA6 or PA66 depends on the technical requirements needed as well as the economical constraints.

The two most widely used polyamides are by far PA66 and PA6. These polyamides are most often manufactured into fibers for the textile industry or blown into films used for the packaging industry. Polyamides are also used to produce parts for numerous industries.

Polyamides with the highest performances are PPA (Polyphthalamide or high-performance polyamide) and PA46. Polyamides with these qualities are often used as a replacement for metal materials or for very specific applications where the polymer is exposed to extreme conditions, e.g. automotive structural parts or safety helmets.

Differences between Polyamide 6 (PA6 / Nylon 6) and Polyamide 66 (PA66 / Nylon 66)

Polyamide 6 (PA6) is also known as Nylon 6 or Polycaprolactam. It is one of the most commonly used compounds in the polyamide family. PA6 is synthesized via the ring-opening polymerization of caprolactam.

Figure 1. Molecular structure of caprolactam.
Figure 2. Molecular structure of Polyamide 6.

Polyamide 66 (PA66), also known as Nylon 66, is one of the most popular thermoplastics for engineering purposes and is primarily used as a metal replacement for various applications. Nylon 66 is synthesized via the polycondensation of hexamethylenediamine and adipic acid (two monomers containing six carbon atoms each).

Figure 3. Molecular structure of Polyamide 66.

The differences between both PA6 and PA66 come down to a lot of little things. While both are cost effective, Nylon 6 is typically around 30% cheaper than Nylon 66. A comparison of different factors is made for the two polymers in Table 1.

Table 1. Comparison of PA6 and PA66
Parameter PA6 PA66
Machinability – low tool wear and surface finish Good Better
Mold shrinkage Lower Higher
Water absorption rate Higher Lower
Tensile strength 6.2 × 104 kPa (Good) 8.2 × 104 kPa (Better)
Crystalline melting point 225 °C 265 °C
Density 1.15 g/mL 1.2 g/mL
Typical molding shrinkage ratio 1.2 % 1.5 %
Key properties of PA66 and PA6

As stated earlier, Polyamide 66 (PA66) and Polyamide 6 (PA6) are used in so many different applications because of their excellent performance and relatively low cost. Some of the most important properties of these polyamides are listed below:

  • High strength and rigidity at high temperatures
  • Good impact strength, even at low temperatures
  • Good abrasion and wear resistance
  • Excellent resistance to fuels and oils
  • Good fatigue resistance
  • Very good flow for easy processing
  • PA6 has excellent surface appearance and better processability than PA66 due to its very low viscosity
  • Good electrical insulating properties
  • High affinity for water absorption can limit the applications and usage
  • Low dimensional stability (water absorption results in dimensional change)

Near-infrared spectroscopy as a tool to assess the quality of polyamides

Near-infrared spectroscopy (NIRS) has been an established method for both fast and reliable quality control within the polyamide industry for more than 30 years. However, many companies still do not consistently consider the implementation of NIRS in their QA/QC labs. The reasons could be either limited experience regarding application possibilities or a general hesitation about implementing new methods.

There are several advantages of using NIRS over other conventional analytical technologies. For one, NIRS is able to measure multiple parameters in just 30 seconds without any sample preparation! The non-invasive light-matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes it an excellent method for the determination of both property types.

In the remainder of this post, a short overview of polyamide applications is presented, followed by available turnkey solutions for polyamide analysis developed according the NIRS implementations guidelines of ASTM E1655-17.

Did you miss the first parts in this series? Find them here!

For more detailed information about NIRS as a secondary technique, read our previous blog posts on this subject.

Applications and parameters for polyamides with NIRS

Polyamide production requires that certain important quality parameters be checked on a regular basis. Typical parameters are relative viscosity as well as the amine and carboxylic end groups, and moisture content. Functional group and viscosity analysis of polyamides is normally a lengthy and challenging process due to the limited solubility of the sample and the need to use different analytical methods. Furthermore caprolactam, an important precursor for polyamide production, is very hygroscopic and water soluble—therefore it is crucial to have a reliable analysis technique for determination of water content. Otherwise the quality of the final product could be compromised.

The most relevant applications for NIRS analysis of PA quality parameters are indicated later in this article in Table 2.

Where can NIRS be used in the production process of polyamides?

Figure 4 shows the individual steps from plastic producer via plastic compounder and plastic converter to plastic parts and textile producer. The first step in which near-infrared lab instruments can be used is when the pure polymers like PA are produced, and their purity needs to be confirmed. NIRS is also a very useful technique during the next step where polymers are compounded into intermediate products to be used for further processing.

Figure 4. Illustration of the production chain for polyamides.

Easy implementation of NIR spectroscopy for plastic producers

Metrohm has extensive expertise with analysis of polyamides and offers a turnkey solution in the form of the DS2500 Polymer Analyzer. This instrument is a ready-to-use solution for the determination of multiple quality parameters in different polyamides.

Figure 5. Turnkey solution for PA analysis with the Metrohm DS2500 Polymer Analyzer.

Application example:

Pre-calibrations available for the polyamide industry on the DS2500 Polymer Analyzer

The determination of the parameters listed below in Table 2 is a lengthy and challenging process with conventional laboratory methods. To measure them all, several different techniques are required which takes a significant amount of time, not only to analyze the sample (which has limited solubility, further complicating the situation), but also for the instrument management and upkeep.

Table 2. Primary method vs. NIRS for the determination of various quality parameters in PA samples.
Parameter Primary method Time to result (primary method) Relevant NIRS Application Notes NIRS benefits
Relative viscosity

Viscosity

90 min. preparation + 1 min. Viscometer

AN-NIR-077

AN-NIR-060

AN-NIR-005

All four parameters are measured simultaneously within a minute, without sample preparation or the need of any chemical reagents
Carboxyl end groups

Titration

90 min. preparation + 20 min. Titration
Amine end groups

Titration

90 min. preparation + 20 min. Titration
Moisture content

Karl Fischer Titration (oven)

2 min. preparation + 15 min. KF Titration (oven)

 

The NIRS prediction models created for polyamides are based on a large collection of real product spectra and is developed in accordance with ASTM E1655-17 Standard practices for Infrared Multivariate Quantitative Analysis. For more detailed information on this topic, download the free white paper.

To learn more about pre-calibrations for polyamides, download our brochure and visit our website.

Figure 6 shows the results of the Metrohm turnkey solution for non-destructive determination of several quality parameters in PA listed in Table 2.

Figure 6. Turnkey solution for relative viscosity (RV), amine end groups, carboxyl end groups, and moisture in nylon (PA6) using the Metrohm DS2500 Polymer Analyzer. A: Sampling and analysis of PA6. B: Results of the four analyses from NIRS compared to a primary laboratory method along with the Figures of Merit (FOM) for each analysis.

This solution demonstrates that NIR spectroscopy is very suitable for the analysis of multiple parameters in polyamide in less than one minute without sample preparation or using any chemical reagents. Learn more about the procedure in our free Application Note!

The examples shown above refer to PA6 and PA66, but NIRS is undoubtedly a great tool for the rapid screening and QC of polyamides with different chain lengths.

Future installments in this series

This blog is a detailed overview of the use of NIR spectroscopy as the ideal QC tool for Polyamide 6 (PA6) and Polyamide 66 (PA66). The last installment of this blog series will be dedicated to:

 

  • Polyols and Isocyanates to produce Polyurethane (PU)

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.

Chemistry of Fireworks

Chemistry of Fireworks

Developed nearly two millennia ago in ancient China, fireworks are increasingly used in cultural celebrations around the world and enjoyed by nearly all ages. As one of the most entertaining forms of chemistry, fireworks appeal to our senses of sight and sound, offering a staggering variety of colors, sizes, shapes, sounds, and so on. We love to watch fireworks because they take our breath away with their magnificence and mystery.

However it is not all fun and games. The business of fireworks (and the field of pyrotechnics in general) is very serious since they should be made as safe as possible to use and also environmentally friendly. Beyond fireworks, other pyrotechnics are found in all kinds of entertainment, like in concerts, movies, and more serious applications for defense and security (e.g., safety measures like flares and signal lights).

What are fireworks made of?

Early fireworks were quite dangerous and were used for protection rather than for celebrations, and hardly resemble the ones we are now familiar with.

It all began back in Ancient China with the invention of gunpowder, which was created from a mixture of charcoal, sulfur, and saltpeter (potassium nitrate). Eventually, as new developments were made to increase the safety and predictability of using these early fireworks, experimentation with colors began and people started using them more for nonviolent purposes. Now there is an entire industry devoted to the development of all kinds of fireworks for consumers and professionals alike.

Learn more about the history of fireworks in the links below:

A firework, or aerial shell as it is also known, basically consists of three main parts aside from the housing: gunpowder and an igniter to make the rocket explode, and inside of the transported capsule on the top there are small garniture pods usually called «stars» (despite being shaped like spheres or cylinders) that include various chemicals for the desired effects. Stars consist of a colorant, a fuel, an oxidizer (oxygen providing substance, e.g., chlorates or nitrates), and a binder to hold the ingredient mixture together in a compact briquette.

The industry has spent a significant amount of time in development to make fireworks explode in shapes like stars and stripes, hearts, or even more complex forms like a cartoon figure, or letters and numbers if timed correctly.

Cross-sectional diagram of a firework capsule filled with star garnitures (72) and igniter (70). [1]

Forming a rainbow of colors

The vibrant colors of fireworks come from the combustion of metal ions which make up to 20% of the components. Metals have been used to color flames even before the invention of modern fireworks (e.g. Bengal fire). Chemically speaking, these metal ions change their electronic state by heating (addition of energy) and then going back to a lower energy state before emitting light of a certain color.

Table 1. List of metals used in pyrotechnics and their colors [2].

Color

Metal

Example compounds

Red

Strontium (intense red)

SrCO3 (strontium carbonate)

Lithium (medium red)

Li2CO3 (lithium carbonate)

LiCl (lithium chloride)

Orange

Calcium

CaCl2 (calcium chloride)

Yellow

Sodium

NaNO3 (sodium nitrate)

Green

Barium

BaCl2 (barium chloride)

B3N3 (boron nitride)

Blue

Copper halides

CuCl2 (copper chloride), at low temperature

Indigo

Cesium

CsNO3 (cesium nitrate)

Violet

Potassium

KNO3 (potassium nitrate)

Rubidium (violet-red)

RbNO3 (rubidium nitrate)

Gold

Charcoal, iron, or carbon black

 

White

Titanium, aluminum, beryllium, or magnesium powders

 

Very prominent here is the yellow color from sodium which is also seen in older street lightbulbs in some countries. Unfortunately, the most vibrant colors formed are also the most toxic for the environment, like strontium (red) and barium (green). These contaminants can be measured in the air, water, and even in the soil—but more on that later.

Find out more information about how fireworks get their colors in the links below:

Safety first

Safety is always a critical issue when discussing fireworks, whether concerning their construction, their use, or their storage. Too many serious accidents have happened over the years involving fireworks.

Learn more about how to handle fireworks in a safe manner here:

Among one of the largest fireworks disasters recorded in Europe was in Enschede (The Netherlands) in 2000. This explosion occurred in the warehouse of the S.E. Fireworks factory, which was located in the center of a residential area as the city grew and continued to build homes around it. An entire neighborhood was razed and the largest of the explosions was felt up to 30 kilometers away.

Because of this incident, sales of larger fireworks in most European countries is only allowed outdoors. Accumulating fireworks at home in preparation for celebrations should be avoided at least in confined environments like basements or apartments. It is better to store them in a ventilated shed or car parking to avoid problems in the case of a fire. Also do not store fireworks for long periods, since most of commercial fireworks are meant to be used within 3–6 months after production because the paper contents can get humid, ionic substances can dissolve and recrystallize, and therefore the likelihood of a failure increases.

In the event of a firework failure: Never have a look immediately! Wait at least 15 minutes at a proper distance and then use a tool to confine it afterwards—never touch it with your bare hands, especially when dealing with exploding fireworks or rockets.

Having said this, fireworks have integrated some safety features over the last several years to work more properly and reliably. For instance, the propellants have been modified from containing black powder to using technology from rockets such as plasticizers for better burning performance during launch, also resulting in less smoke and dust on the ground. A dedicated chain of reactions has to be followed, otherwise it will burn in a harmless way.

Knowledge is power: Prevent accidents with proper analytical testing

In order to help prevent fireworks accidents such as the one in Enschede and countless others, it is crucial to closely monitor different quality parameters including the water content of paper-based fireworks, grain size of the metal particles, and the purity and composition of the colorant, just to mention a few. Adequate quality control provides an entertaining, but safe fireworks experience even in the hands of the general public, when proper protocols are followed.

Metrohm offers several analytical technologies and related applications for this area of research. Analyses can be performed for a wide variety of substances and quality parameters as well as trace materials in the laboratory, on the street, and in the air either via wet chemical methods (e.g., Karl Fischer titration, ion chromatography, voltammetry) or spectroscopic techniques (e.g., near-infrared spectroscopy [NIRS] and Raman spectroscopy).

As mentioned earlier, moisture is an important quality parameter when discussing the safety of explosive materials. Metrohm offers two different techniques for accurate analysis of water content in a variety of matrices which are outlined in the following blog posts.

When it comes to determining the individual concentrations of the main constituents, some wet chemical techniques really stand out. Suppressed anion chromatography is ideal for measuring the ionic components of e.g., firecracker powder, other explosive material, and even in explosion residues for forensic purposes. Coupling an ion chromatograph to a mass spectrometer (IC-MS) opens up even more analysis possibilities. Read more about these studies (and more) by downloading our free Application Notes.

The use of several different metal salts to create the vibrant colors of fireworks can be beautiful but also harmful to our health and that of our environment. Voltammetry (VA) is an electrochemical method suitable for the determination of trace and ultratrace concentrations of heavy metals and other electrochemically active substances. Not only is VA excellent at determining these substances in the laboratory, but also in the field such as for measuring the after effects of a fireworks display or an undesired event. Check out our selection of VA instruments and applications on our website.

Spectroscopic techniques like Raman can help to determine the presence of dangerous explosive materials even when keeping a safe distance by using different instrument attachments. Read our free White Paper about how to use MIRA DS from Metrohm Raman for the purpose of identifying explosives safely.

Environmentally friendly fireworks – a contradiction?

Although fireworks are a very spectacular form of entertainment, there is quite an environmental impact after big cultural events or national holidays. The general atmospheric pollution after a fireworks display has been set off can be seen in an increase of dust and smoke, but also heavy metal content in the air as most contemporary fireworks use these for coloring.

The unburnt material still contains a significant amount of heavy metals. After falling to the ground, this material can dissolve and enter the ground water after it rains. Plastics materials that covered the fireworks for safety reasons are found again as broken shell shrapnel or as microplastics. The combustion of the compounds inside the fireworks leads to increased air pollution in form of aerosols that can be measured and evaluated resulting in heavy metals in the air, fine dust, and even nanoparticles which are extremely harmful for our lungs.

Metrohm Process Analytics has developed the 2060 MARGA (Monitor for AeRosols and Gases in ambient Air) which is used by official agencies and research bodies worldwide to monitor the air quality fully autonomously. This instrument is based on the analytical technique of ion chromatography and can be used as a dedicated continuous air monitoring device that can be left unattended for several weeks at a time, or as a research instrument that can be used for other projects when not monitoring the air quality.

Learn more about the 2060 MARGA and its capabilities in our blog post.

To find out more about the use of Metrohm instruments to monitor the air quality, check out this selection of peer-reviewed articles.

A new «green» firework generation is being developed for both professional and indoor use to try to minimize the heavy metal content and also reduce aerosol forming agents. This makes them more suitable for indoor pyrotechnic shows and for movie production. In regular outdoor shows (e.g. at theme parks), the gunpowder for transport of the capsule has mostly been substituted with an air pressure gun mechanism.

A significant amount of research has gone into substituting heavy metal-based colorants with more environmentally benign substances by increasing the luminosity of lithium derivatives by substituting them for strontium, or by using boron instead of barium or chlorinated compounds.

Finally, the plastic parts commonly used to surround fireworks are planned to be substituted by microcrystalline cellulose mixtures with better plasticizing binders. This leads to a similar stability compared to the current plastic materials, but the cellulose-based containers burn up completely and do not leave harmful materials scattered on the ground.

The future of fireworks shows

All safety measures increase the joy of fireworks not only during, but also after the event—being green and being safe. Foretelling the future, some of these celebrations may now use a cadre of lighted drones in a choreographed dance. This has been happening more steadily as drones fall in price and increase in their handling and programming capabilities. However, fireworks have already been with us for a couple of thousand years, and probably will not disappear any time soon.

Download our free Application Notes

and White Papers related to explosives and propellants

Post written by Dr. Norbert Mayr (Ph.D. in the field of HEDM, pyrotechnics, propellants, and oxidizers), Marketing Specialist & Product Training at Metrohm International Headquarters, Herisau, Switzerland.

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 3

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 3

Polyethylene terephthalate (PET): A brief introduction

PET is a very common plastic, mostly encountered in our lives as PET bottles and as a food packaging material. In this article you will learn how NIR spectroscopy can improve the efficiency of your PET analysis at different steps along the production cycle. Before getting into this, let’s introduce some background information about PET.

Polyethylene terephthalate (PET)

Polyethylene terephthalate (PET) is a general-purpose thermoplastic polymer which belongs to the polyester family. Polyester resins are known for their excellent combination of properties such as mechanical, thermal, and chemical resistance as well as dimensional stability.

PET is one of the most recycled thermoplastics and has the number 1 as its recycling symbol. Recycled PET can be converted into fibers, fabrics, sheets for packaging and for manufacturing automotive parts. PET is a highly flexible, colorless, and semi-crystalline resin in its natural state. Depending upon how it is processed, it can be semi-rigid to rigid. It exhibits good resistance to impact, moisture, alcohols, and solvents.

The chemical formula of PET is (C10H8O4)n and its molecular structure is shown in Figure 1.

Figure 1. Molecular structure of linear PET.

In addition to linear PET, there is also a branched version of the polymer. Branched PET is typically mixed with a small percent of isophthalic acid (C8H₆O4), because purified isophthalic acid (PIA, Figure 2) reduces the crystallinity of PET, serving to improve its clarity and increase the productivity of bottle manufacturing processes.

Diethylene glycol (DEG) as an additive also reduces the rate of crystallization of PET when crystallizing from the melt, isothermally and dynamically.

Figure 2. Molecular structure of isophthalic acid.
The key properties and advantages of PET resin are numerous:
  • very strong and lightweight, and therefore easy and efficient to transport
  • has good gas (oxygen, carbon dioxide) and moisture barrier properties, meaning low gas permeability (particularly against CO2)
  • exhibits excellent electrical insulating properties
  • broad range of use temperature (-60 to 130 °C)
  • high heat distortion temperature (HDT)
  • suitable for transparent application purposes
  • practically shatter-resistant – PET does not break or fracture and is used to replace glass in some applications
  • recyclable material
  • transparent to microwave radiation
  • very resistant to alcohols, aliphatic hydrocarbons, oils, greases, and diluted acids
  • moderately resistant to diluted alkalis, aromatic and halogenated hydrocarbons
  • PET is approved as safe for contact with foods and beverages by the FDA, Health Canada, EFSA, and other health agencies

What is polyethylene terephthalate (PET) used to make?

Polyethylene terephthalate is used in several types of packaging applications as shown in Figure 3. Due to its strength, light weight, and many other attractive properties, PET excels as a food packaging material.

Figure 3. PET is an ideal choice for many food packaging applications due to its strength to weight ratio.

Polyester makes up nearly two-thirds of synthetic fibers produced. There are many different types of polyester, but the type most often produced for use in textiles is PET. When used in a fabric, it is most often referred to as «polyester» or «poly» (Figure 4). This material costs very little to produce, which is the primary driver for its use in the textile industry.

Approximately 60% of the global PET production is used to make fibers for textiles while about 30% is used to make bottles for various purposes. Its ability to be recycled is especially attractive for manufacturers looking to save costs and operate in a greener manner.

Figure 4. PET makes up a significant portion of produced polyester fabric.

In the electronics industry, PET is chosen to replace less ideal materials due to its excellent electrical insulating properties and resistance to distortion even at high temperatures. PET is also used to manufacture many parts in the automotive industry (Figure 5).

Figure 5. PET is often used in the manufacturing of various automotive parts.

NIRS as a tool to assess the quality of PET

For over 30 years, near-infrared spectroscopy (NIRS) has been an established method for fast and reliable quality control within the PET industry. Despite this, many producers still do not consistently consider the implementation of NIRS in their QA/QC labs. Limited experience regarding application possibilities or a general hesitation about implementing new methods are some of the reasons behind this.

The advantages of using NIR spectroscopy for QA/QC are numerous. One major advantage of NIRS is the determination of multiple parameters in just 30 seconds with no sample preparation! The non-invasive light-matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes NIRS a suitable method for the determination of several critical quality parameters in these polymers and many more.

In the remainder of this article, a short overview of PET applications is presented, followed by available turnkey solutions for PET, developed according the NIRS implementation guidelines of ASTM E1655-17.

Did you miss the first parts in this series? Find them here!

For more detailed information about NIRS as a secondary technique, read our previous blog posts on this subject.

Applications and parameters for PET with NIRS

During production of PET it is important to check certain parameters to guarantee the quality. These parameters include the diethylene glycol content, isophthalic acid content, intrinsic viscosity (ASTM D4603), and the acid number (AN). Determination of these parameters is a lengthy and challenging process due to the limited solubility of the sample and the need to use different analytical methods.

The most relevant applications for NIRS analysis of PET are listed in Table 1.

Table 1Available application notes for use of NIR for PET
Polymer Parameter Related NIRS Application Notes
Polyethylene terephthalate (PET)

Diethylene glycol, Intrinsic Viscosity, Acid number, Isophthalic acid

AN-NIR-023

Where can NIRS be used in the production process of PET?

Figure 6 shows the individual production steps from the plastic producer via plastic compounder and plastic converter to the plastic parts producer. The first step in which near-infrared lab instruments can be used is when the pure polymers like PET are produced, and their purity needs to be confirmed. NIRS is also a very useful technique during the next step where polymers are compounded into intermediate products to be used for further processing.

Figure 6. Illustration of the polyethylene terephthalate production chain.

Easy implementation of NIR spectroscopy for plastic producers

Metrohm has extensive expertise with analysis of PET and offers a turnkey solution in the form of the DS2500 Polymer Analyzer. This instrument is a ready-to-use solution to determine multiple quality parameters in PET.

Figure 7. Turnkey solution for PET analysis with the Metrohm DS2500 Polymer Analyzer.

Application example:

Pre-calibrations available for the PET industry on the DS2500 Polymer Analyzer

Due to the limited solubility of polyethylene terephthalate and the need to use several different analytical methods, the determination of the parameters listed in Table 2 is a lengthy and challenging process with conventional laboratory techniques.

Table 2. Primary method vs. NIRS for the determination of various quality parameters in PET samples.
Parameter Primary method Time to result (primary method) NIRS benefits
Diethylene Glycol content

Extraction + HPLC-MS

45 min. preparation + 40 min. HPLC-MS All four parameters are measured simultaneously within a minute, without sample preparation or the need of any chemical reagents
Isophthalic acid content Dissolve + HPLC 45 min. preparation + 40 min. HPLC
Intrinsic viscosity Dissolve + Viscometer 90 min. preparation + 1 min. Viscometer
Acid number Dissolve + Titration 90 min. preparation + 10 min. Titrator

The NIRS prediction models created for PET are based on a large collection of real product spectra and is developed in accordance with ASTM E1655-17 Standard practices for Infrared Multivariate Quantitative Analysis. For more detailed information on this topic, download the free white paper.

To learn more about pre-calibrations for PET, download our brochure and visit our website.

The result of this turnkey solution for rapid non-destructive determination of the key quality parameters for PET listed in Table 2  is shown in Figure 8.

Figure 8. Turnkey solution for diethylene glycol, isophthalic acid, intrinsic viscosity and acid number in PET using the Metrohm DS2500 Polymer Analyzer. A: Sampling and analysis of PET granulate. B: Results of the four analyses from NIRS compared to a primary laboratory method along with the Figures of Merit (FOM) for each analysis.

This solution demonstrates the feasibility of NIR spectroscopy for the analysis of multiple parameters in PET in less than one minute without sample preparation or using any chemical reagents.  Learn more about the procedure in our free Application Note!

Future installments in this series

This article is a detailed overview of the use of NIR spectroscopy as the ideal QC tool for the analysis of polyethylene terephthalate (PET). Future installments in this series will be dedicated to:

 

  • Polyamide (PA)
  • Polyols and Isocyanates to produce Polyurethane (PU)

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 2

NIR spectroscopy in the polymer industry: The ideal tool for QC and product screening – Part 2

Polypropylene and polyethylene: A brief introduction

Did you know that polypropylene (PP) and polyethylene (PE) are the most produced plastics in the world? Products made out of PP and PE are so ubiquitous that every single one of us encounters them several times per day. In this article you will learn how NIR spectroscopy can improve the efficiency of your PP and PE analysis along different steps along the production cycle. But first, let’s get a little bit of background information about PP and PE.

Polypropylene (PP)

Polypropylene (also known as polypropene or PP) has a chemical formula of (C3H6)n. It is a thermoplastic polymer mainly produced from propylene monomers. PP is a versatile plastic commodity that also functions as a fiber. In 1954, it was first polymerized simultaneously by the Italian chemist, professor, and Nobel laureate Giulio Natta and Karl Rehn, a German chemist.

Polypropylene has the unique ability that it can be manufactured via several different methods and be utilized in many applications like packaging, injection molding, and fibers. This plastic commodity is the second most popular in the world, only preceded by polythene.

Polyethylene (PE)

Polyethylene (or polythene, PE) is also a polymer, but it is made from ethylene monomers and has the chemical formula (C2H4)n. The first synthesis of PE in 1898 by the German scientist Hans von Pechmann was accidental. Similar to PP, PE is also a thermoplastic.

PE is the most used plastic worldwide. Polythene is very stable and is a good electrical insulator. It has a very low melting point and is used in large amounts for the automotive and food packaging industries. Approximately 70% of PE is utilized in food packages, food containers, pallets, and even in crates and bottles.

Polyethylene is available in many different types:

  • Ultra-High-Molecular-Weight Polyethylene (UHMWPE)
  • Ultra-Low-Molecular-Weight Polyethylene (ULMWPE or PE-WAX)
  • High-Molecular-Weight Polyethylene (HMWPE)
  • High-Density Polyethylene (HDPE)
  • High-Density Cross-Linked Polyethylene (HDXLPE)
  • Cross-Linked Polyethylene (PEX or XLPE)
  • Medium-Density Polyethylene (MDPE)
  • Linear Low-Density Polyethylene (LLDPE)
  • Low-Density Polyethylene (LDPE)
  • Very-Low-Density Polyethylene (VLDPE)
  • Chlorinated Polyethylene (CPE)
Figure 1. Molecular structures of PE and PP.

Differences between polypropylene and polyethylene

Which is better, polypropylene or polyethylene? It all depends on the application! For what purpose are they being used? Both polymers are considered «commodity plastics». These are plastics that are used in high volumes for a wide range of applications.

Let’s compare some of the properties of each.

Table 1. Comparison chart of polypropylene vs. polyethylene.
Polypropylene (PP) Polyethylene (PE)
Chemical Properties

Semi-crystalline

Polypropylene bag

Inert, translucent

Polyethylene bag

Electrical Properties

High static charge

Poor insulator

Low static charge

Good insulator

Melting Point
130–171 °C 115–135 °C
Chemical Formula
(C3H6)n (C2H4)n
Uses
Fibers, films, caps, hinges, synthetic paper Plastic bags, bottles, food containers, pallets, geomembranes, films made of plastic, crates, etc.
Density

0.855 g/cm3 amorphous

0.946 g/cm3 crystalline

0.88–0.96 g/cm3
Relative Cost
Low Medium

NIRS as a tool to assess the quality of PP and PE

For over 30 years, near-infrared spectroscopy (NIRS) has been an established method for fast and reliable quality control within the PP/PE industry. Despite this, many producers still do not consistently consider the implementation of NIRS in their QA/QC labs. Limited experience regarding application possibilities or a general hesitation about implementing new methods are some of the reasons behind this.

The advantages of using NIR spectroscopy for QA/QC are numerous. One major advantage of NIRS is the determination of multiple parameters in just 30 seconds with no sample preparation! The non-invasive light-matter interaction used by NIRS, influenced by physical as well as chemical sample properties, makes NIRS a suitable method for the determination of several critical quality parameters in these polymers and many more.

In the remainder of this article, a short overview on PE and PP applications are presented, followed by available turnkey solutions for PE and PP, developed according the NIRS implementations guidelines of ASTM E1655-17.

Did you miss the first part in this series about NIRS as the ideal QC tool for the polymer industry? Find it here!

For more detailed information about NIRS as a secondary technique, read our previous blog posts on this subject.

Applications and parameters for PE and PP with NIRS

During production of PE and PP it is important to check certain parameters to guarantee the quality. These parameters include the density to classify the PE type, copolymer level to enhance certain properties like strength and solvent resistance, and melt flow rate to make sure PP can be formed to the intended shape.

The most relevant applications for NIRS analysis of PE and PP are listed in Table 2.

Table 2Available application notes for use of NIRS for PE and PP
Polymer Parameter Related NIRS Application Notes
Polyethylene (HDPE/LDPE)

Identification, Density, Melt Flow Index, Copolymer level

AN-NIR-083

AN-NIR-081

AN-NIR-034

AN-NIR-003

Polypropylene (PP)

Identification, Melt Flow Index, Additives

AN-NIR-083

AN-NIR-082

AN-NIR-034

AN-NIR-004

Where can NIRS be used in the production process of PE and PP?

Figure 2 shows the individual production steps from the plastic producer via plastic compounder and plastic converter to the plastic parts producer. The first step in which near-infrared lab instruments can be used is when the pure polymers like PE and PP are produced, and their purity needs to be confirmed. NIRS is also a very useful technique during the next step where polymers are compounded into intermediate products to be used for further processing.

Figure 2. Illustration of the polyethylene/polypropylene production chain.

Easy implementation of NIR spectroscopy for plastic producers

Metrohm has extensive expertise with analysis of PE and PP and offers a turnkey solution in the form of the DS2500 Polymer Analyzer. This instrument is a ready-to-use solution to determine multiple quality parameters in PE and PP.

Figure 3. Turnkey solutions for PE and PP analysis with the Metrohm DS2500 Polymer Analyzer.

Application example:

Turnkey solution for the determination of Melt Flow Rate (MFR) of PP

The Melt Flow Rate of polypropylene pellets is an important parameter to measure so that PP can be formed in the intended shape. The model created with the chemometric software is based on a large collection of real product spectra and is developed in accordance with ASTM E1655-17 Standard practices for Infrared Multivariate Quantitative Analysis. For more detailed information on this topic, download the free white paper.

To learn more about pre-calibrations for PP, download our brochure and visit our website.

The result of this turnkey solution for the non-destructive determination of Melt Flow Rate of PP without rheological tests is shown in Figure 4.

Figure 4. Turnkey solution for Melt Flow Rate of PP using the Metrohm DS2500 Polymer Analyzer. A: Sampling and analysis of PP pellets. B: Results of MFR from NIRS compared to a primary laboratory method along with the Figures of Merit (FOM) for this analysis.

This solution demonstrates the feasibility of NIR spectroscopy for the analysis of MFR in polypropylene samples. The standard procedure (ASTM D1238) requires a significant amount of work including packing the sample, preheating, and cleaning. With no sample preparation or chemicals needed, Vis-NIR spectroscopy allows the analysis of MFR in less than a minute.

Learn more about the procedure in our free Application Note!

Future installments in this series

This article is a detailed overview of the use of NIR spectroscopy as the ideal QC tool for the analysis of polypropylene and polyethylene. Future installments in this series will be dedicated to:

  • Polyamide (PA)
  • Polyols and Isocyanates to produce Polyurethane (PU)

For more information

About spectroscopy solutions provided by Metrohm, visit our website!

We offer NIRS for lab, NIRS for process, as well as Raman solutions

Post written by Wim Guns, International Sales Support Spectroscopy at Metrohm International Headquarters, Herisau, Switzerland.