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Applications – Polymers

Solution viscosity – Quality feature of plastics

Determining solution viscosity as a measure for the medium molecular mass of a polymer is one of the most tried-and-tested methods and the most sensitive method to evaluate the molecular identity of many plastics. Since the processing and usage properties of the plastic depend strongly on its molecular structure, the quality of the plastics can be easily monitored through the solution viscosity or most of them can be optimized and the necessary figure can be determined from this.

Binding standards for the practical execution of viscosity measurement exist for plastics. These determine, for example, solvents, concentration, sample preparation, viscometer type and size, measuring temperature, number and reproducibility of the processing time measurements as well as the type of evaluation. As the measurement result, the relative viscosity is always calculated from the ratio of viscosities of the polymer solution and of the solvent.

Application examples

  • Technical polymers, e.g. polyamides and polyurethane
  • Transparent polymers, e.g. PET, plexiglas and polycarbonate
  • Polyolefins, PE and PP, polyvinyl chloride and others
  • Medicinal polymers for surgery and hyaluronic acids
  • Cellulose and quality papers for transformers or similar


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  LAUDA solution viscometer advantages Your benefits
  • Intuitive measuring principle
  • LAUDA measuring systems with high degree of automation
  • Easy, affordable execution with stopwatch
  • Parallel measurement positions accelerate the process
  • Contact with solvents is reduced
  • Safe operation even by semi-skilled shift workers
  • Supplies important figures quickly for the chain lengths of polymers and their changes
  • Comparison of the specifications with current figures in the quality check
  • Production control in shift operation
  • Incoming components inspection of raw polymers
  • Outgoing components inspection of semi-finished products and compounds
  • Sample preparation and principle are determined in a few standards
  • High selectivity on properties of the polymer chain
  • Useful tool for polymer research
  • Worldwide comparability
  • Can be carried out everywhere with minimum effort
  • Results practically uninfluenced by filler materials or additives to the plastic, like, for example, with the melt flow index
  • High degree of flexibility
  • Applicable in many ways
  • Easy to implement
  • In some industries, e.g. automotive, the solution viscosity is required:
    • Along the entire value-added chain from raw granule to finished part
    • Selectively for aging and damage
  • Compensation for extra effort as competitive advantage
  • Continuous monitoring during product generation
  • Analysis of finished product over the entire life-span and recycling

Technical polymers

Viscosity number of polyamides (PA) and polybutylene terephthalates (PBT)

In the automotive industry in particular, the trend of replacing metal with high-quality technical plastics continues. Even mechanical motor parts subjected to high thermal stresses are now being manufactured, for example, from reinforced polyamides (PA) or polybutylene terephthalates (PBT).

One of the most important figures for the plastic quality is the viscosity number (reduced viscosity) as a measure for the chain length of basic polymers. The change to polymer chain lengths when manufacturing component parts, e.g. for injection molding or after continuous automobile operation, can be traced using viscosity measurements. The modular system of the automated LAUDA PVS viscosity measuring system offers tailored configurations according to current needs which minimize contact with naturally very aggressive or toxic solvents. The entire analysis process, from preparation to polymer solutions, to sample loading and measurement, all the way to the cleaning of the viscometers, is PC-controlled. The few remaining manual movements can even be performed by semi-skilled shift workers. For occasional inspections, e.g. after processing, there are affordable compact systems.

Typical configuration

Fully automatic measuring system for parallel measurement of reinforced PA and PBT for up to 100 samples a day

  • VAS 1/4 automatic sampler with four measuring stands S 5, two each for PA and PBT samples
  • Three VRM 4 S or VRM 4 cleaning modules for cleaning viscometers and dosing syringes
  • Sample frame for maximum 35 bottles
  • High-quality PV 24 viscothermostat with DLK 10 external cooler
  • Ubbelohde glass viscometer of sizes II and Ic (optionally in Micro-Ubbelohde version)
  • Online filter for separating glass fibers and undissolved sections (optionally centrifuges)
  • Automated sample preparation with filler material correction while using high-quality Mettler weighing balances and dosing units

Recommended standards

  • DIN EN ISO 307
    Plastics, polyamides – Determination of the viscosity number
  • DIN EN 1628-5
    Plastics – Determination of the viscosity of polymers in dilute solution using capillary viscometers – Part 5: Thermoplastic polyester (TP), homopolymers and copolymers

 

Transparent polymers

Viscosity number and IV value of polyesters (PC, PMMA, PET)

The mass worldwide pervasiveness of PET bottles and packaging makes recycling a necessity when it comes to protecting the environment and preserving resources. Here, the IV value, usually calculated according to the Billmeyer approximation, is the criterion for the quality of the recyclate and thus vital for further usage. Ideally, alignment with the original value of typically 80 cm³/g should be reached. With the mass-used plastics polycarbonate (e.g. CD-ROM), polymethylmethacrylate PMMA (e.g. Plexiglas) and others, the viscosity number (reduced viscosity) plays a similarly important role in production and re-use.

Even as early as in the production of the raw granule, e.g. polycondensation, the viscosity of the polymer solution is measured. Systems customized to operate in shifts have four to a maximum of eight measuring stations which are equipped with modules for automatic viscometer cleaning. Sample loading is done manually using a syringe or funnel. In 24-hour operation, these systems allow a sample rate of hundreds of samples. The restriction here is the time needed to dissolve the polymer which takes place in the magnetic stirrer at room temperature or at 80 or 130 °C. Here too there are affordable versions for just occasional measurements, e.g. for damage analyses and incoming and outgoing components inspections, which can be converted into fully automatic machines with samplers at later dates.

Typical configuration

Measuring system PVS 1/4 with four measuring stands and automatic viscometer cleaning for fast, precise measurement

  • PVS 1/4 control unit
  • Four measuring stands S 5
  • Two VRM 4 cleaning modules for viscometer cleaning
  • High-quality PV 24 viscothermostat with DLK 10 external cooler
  • Ubbelohde glass viscometer of sizes 0c, I, and Ic (optionally with aspirating tube or in Micro-Ubbelohde version)

Options

Automated sample preparation while using highquality Mettler weighing balances and dosing units

Recommended standards

  • DIN EN 1628-4/-5/-6
    Plastics – Determination of the viscosity of polymers in dilute solution using capillary viscometers – Part 4: Polycarbonate (PC) molding and extrusion materials, Part 5: Thermoplastic polyester (TP) homopolymers and copolymers, Part 6: Methylmethacrylate polymers

 

Polyolefins

Molar mass and IV value of polypropylene and polyethylene (UHMWPE))

Plastic wrap, e.g. for packaging and keeping food fresh, are usually made of polyethylene or polypropylene. Depending on the application, the molecular mass can vary quite strongly. As such, ultra-high molecular PE with molar mass >1,000 kg/mol is used in artificial limbs due to their outstanding gliding properties. The polyolefins are distinguished from most chemicals, solvents, and acids by their outstanding resistance to chemicals. For this reason, the solvents Decalin or Tetralin at 135 °C are usually used for solution viscometry. Since polymers quickly flocculate on cooling down, solutions previously were to be filled into the viscometer while hot, as was the solvent used for cleaning. A specially configured PVS system completely avoids contact with hot chemicals. In this case, the weighed samples are directly filled into an Ubbelohde dilution viscometer in the form of granules or powder using a funnel. Then, the PVS program initiates the loading of the exact solvent quantity via special dosing units. Afterwards, a magnetic stirrer which is integrated into the thermostat is used to dissolve the sample at 135 °C and measure it. This is followed by the automatic emptying, cleaning, and drying of the viscometer. Along with the calculation of the IV value according to the Schulz-Blaschke approximation, it can also be determined directly using a dilution series (linear serial regression).

Typical configuration

Measuring system PVS 1/2 with two measuring stands, integrated magnetic stirrer, and dosing units. Dissolving PE/PP samples directly in the glass viscometer – Automatic cleaning and recording of concentration series

  • PVS 1/2 control unit
  • Two measuring stands S 5
  • A VRM 4/HT cleaning module for viscometer cleaning with external pump
  • High-quality viscothermostat PV 15 operated with silicone oil at 135 °C
  • Special Ubbelohde viscometers of size I for dissolving and diluting samples, incl. filter frit
  • Integrated two-station magnetic stirrer with control console
  • Two dosing units for the solvents Decalin and Tetralin
  • Filling funnel for granulate and powder

Recommended standards

  • DIN EN 1628-3
    Plastics – Determination of the viscosity of polymers in dilute solution using capillary viscometers – Part 3: Polyethylenes and polypropylenes

 

Polyvinylchloride

Determining K-value according to Fickentscher

Monitoring the chain length of the basic polymers is essential in order to further improve the quality of PVC as a basic material for window housing, pipes, floor-coverings, containers, and foil as well as for a number of components in the electrics industry. The K-value according to Fickentscher based on the solution viscosity has become accepted as a measure for this. Here, the relatively harmless cyclohexanone serves as a solvent. From production of the rough polymer, to compounding and semi-finished products manufacture by injection-molding technology or extrusion, LAUDA offers PC-controlled K-value measurement, tailored to the current sample rates, from the affordable iVisc measuring system to the fully automated PVS measuring system with sampler.

One version for average sample rates with a good price-performance ratio and great ease-of-use is the two-station measuring system PVS 1/2 with cleaning module based on a Viscotemp 15 viscothermostat. This can easily measure up to four samples per hour. Using a syringe or funnel, the dissolved sample simply needs to be directly inserted into the Ubbelohde which stays in the thermostat. Measuring can then be started. Further process steps (viscometer cleaning and drying) are executed automatically. If desired, sample preparation can also be made automated.

Typical configuration

Measuring system PVS 1/2 with two measuring stands and automatic cleaning in the Viscotemp 15 viscothermostat

  • PVS 1/2 control unit
  • Two measuring stands S 5
  • A VRM 4 cleaning module for viscometer cleaning
  • Viscotemp 15 viscothermostat with DLK 10 through-flow cooler at 25 °C
  • Ubbelohde viscometer of size Ic with connections for emptying and rinsing
  • Sample preparation system including balance and dosing unit (see page 51)
  • Heated magnetic stirring block for dissolving PVC at 80 °C

Recommended standards

  • DIN EN 1628-2
    Plastics – Determination of the viscosity of polymers in dilute solution using capillary viscometers – Part 2: Poly(vinyl chloride) resins
  • DIN EN 922
    Piping and fittings of unplasticized polyvinylchloride (PVC-U) – Preparation of the samples for determining the viscosity number and calculating the K-value

 

Medicinal polymers

Molar mass and IV value of hyaluronic acid products and absorbable polymers according to pharmaceutical standards

Hyaluronic acid (HA) is a glycosaminoglycan produced naturally in the connective tissue of the body. Hyaluronic acid products serve as a lubricant for joints damaged by arthrosis and are used in nose sprays, eye drops, anti-wrinkle lotions, and in plastic surgery. Aconuresis and vesicoureteral reflux in infants can be treated with this.

Absorbable polymers are usually polylactides (PLA) which can be broken down into lactates through hydrolysis in the organism. They are used for surgical stitching material, screws, and plates for osteosynthesis and as carriers for medication. With both polymer classes, the molar mass expressed in the form of reduced or intrinsic viscosity is a decisive factor for application and life-span.

As a result of the flexibility and compatibility with GLP and FDA standards, e.g. of software (21-CFR-11), LAUDA PVS systems are used all over the world to check the quality of these products. The automatic control of concentration series and viscometer cleaning make sure of user-independent, reliable, and reproducible determining of the molar masses and their changes.

Typical configuration

Measuring system PVS 1/2 with two measuring stands and automatic cleaning. One measuring stand for HA with magnetic stirrer for dilution series, another for viscosity number of PLA in an ET 15 S viscothermostat

  • PVS 1/2 control unit
  • Two measuring stands S 5
  • A VRM 4 cleaning module for viscometer cleaning with chloroform (PLA) or water and acetone (HA)
  • ET 15 S DLK 10 through-flow cooler
  • Ubbelohde dilution viscometer of type 0a (HA) and viscometer of size 0c (PLA) with connections for emptying and rinsing
  • PC-controlled dosing unit with buffer solution for diluting the HA samples
  • Sample preparation system with dosing units and precision balances
  • Single-station magnetic stirrer (for positioning underneath)

Recommended standards

  • European Pharmacopeia
    Capillary viscometer method, Sodium Hyaluronate
  • DIN EN ISO 1628-1
    Plastics – Determination of the viscosity of polymers in dilute solution using capillary viscometers – Part 1: General principles

 

Cellulose and papers

Degree of polymerization of insulation paper using solution viscosity

Paper and cellulose consist of long chains of polymerized glucose rings. The degree of polymerization (DP value) is directly related to its mechanical strengths, e.g. tensile strength. The DP value of insulating papers is important to the mechanical resistance and, above all, to the short circuit load of transformers. A reduction in the DP value down to between 150 and 200 means the end of the transformer‘s life-span. The aging speed of the transformer oil is heavily dependent on the temperature and water content in the insulation. With insulating papers and textiles made from cellulose (e.g. cotton), the degree of polymerization is determined by the solution viscosity. Here, the intrinsic viscosity (IV value) correlates with the degree of polymerization (that is, with the chain length). Here, the solution, cupriethylendiamine (CED) is often used, as it caters for a gentle, that is, as non-destructive as possible, development of the cellulose molecules in the solvent.

With the modular PVS systems, the configuration can be tailored precisely to the needs of the user in regard to sample rate and automation requirements, e.g. automatic viscometer cleaning or sample loading. The INV-DLL software delivers the intrinsic viscosity according to the Martin formula, which is used to calculate the degree of polymerization. The systems can also work under extensive oxygen pulping so that the measurement of mildly oxidizing Cuoxam solutions and EWNN solutions is also possible.

Typical configuration

Measuring system PVS 1/2 with two measuring stands and automatic cleaning in an affordable ET 15 S viscothermostat

  • PVS 1/2 control unit
  • Two measuring stands S 5
  • A VRM 4 cleaning module for viscometer cleaning with water and acetone
  • ET 15 S with DLK 10 through-flow cooler
  • Micro-Ubbelohde of type Ic (recommended for reducing use of solvents and cleaning agents)
  • Viscometer of size I (IEC60450) with connections for emptying and rinsing
  • Sample preparation system with dosing units and precision balances

Recommended standards

  • IEC 60450
    Measuring of the average viscometric degree of polymerization of new and aged cellulosic electrically insulating materials
  • DIN 54270-1/-2/-3
    Testing of textiles – Determination of the limit-viscosity of celluloses – Part 1: Principles, Part 2: Cuen-procedure, Part 3: EWNNmod(NaCl)-procedure