1、 Application background: Difficult to measure polyolefins

Polyolefins typically include polyethylene and polypropylene. Unlike common polymer materials, polyolefin materials are difficult to dissolve in almost all common solvents at room temperature.Therefore, it is difficult to obtain a solution of polyolefin at room temperature, and viscosity measurement cannot be carried out at room temperature.

The sample particles must be at a very high temperature(ForPEandPPfor135°C)Dissolve the solution and transfer it to a viscometer. All operations must be carried out in contact with or using decahydronaphthalene or tetrahydronaphthalene(ForPEandPP)Under certain circumstances; And decahydronaphthalene or tetrahydronaphthalene itself is toxic and emits a strong odor. After the testing is completed, the viscometer must be manually removed from the high-temperature silicone oil bath and the viscosity tube cleaned.

With the increasing demand for safety in the working environment of laboratory operators, these routine steps are now almost impossible to be completed manually. This is extremely unfavorable for the viscosity measurement of polyolefin solutions, and more and more laboratories are turning to other quality control methods(For example, the melt index method）.During this process, people gradually overlooked but had to face the reality that capillary viscosity method has huge advantages such as high measurement accuracy and large information content, which other methods cannot match.

2、 LAUDA Viscometer Solution

LAUDA has developed and designed targeted solutions for measuring the viscosity of polyolefins, addressing the aforementioned characteristics and difficulties. Currently, it can provide a variety of mature matching and solutions.

plan1——Automatic sample preparation in viscosity tube integrated into constant temperature bath

LAUDAAt present, a special configuration can be provided thatPVSThe viscosity measurement system is the main body, and the PV series bath is a constant temperature device, using a dilution type Ubbelohde viscosity tube. The bottom of the bath is equipped with a magnetic stirrer and a high-temperature resistant VRM4HT automatic cleaner.

This system can overcome various problems mentioned at the beginning of the article and achieve135°CThe automatic measurement and cleaning of viscosity of polyethylene and polypropylene under high temperature conditions are easy to operate without any safety hazards.

PVSThe modular system has flexible scalability and can be applied to users with different requirements for sample processing quantities. Using two of themPVS1/2Matching, every day(press8hour calculation)Can test up to 6 samples; Using four digitsPVS1/4Supporting, it can test twice the sample size per day, that is, up to 12 samples for testing. To meet the demand for higher sample throughput,LAUDAIt can also provide a configuration with an automatic sampler, allowing the device to operate automatically even in unsupervised situations (such as during lunch breaks and at night). The configuration diagram is shown in Figure 1 below.

Unlike traditional methods of operation, plastic particles will dissolve inside the viscometer. Weigh the powdered or granular sample and pass it through a funnel(11,image1)From the injection port(8)Directly added to the diluted Ubbelohde viscometer(3)In the middle.PVSProgram-controlled burette(2)，By flushing the moduleVRM4HT(1)，Add a precise amount of solvent to one of the two dilution viscometers. The solvent will undergo a certain volume expansion between room temperature (20-30 ℃) and testing temperature (135 ℃), and the concentration change caused by this volume expansion can be calculated by software. Magnetic stirrer installed at the bottom of the constant temperature bath(4,5)It can accelerate the dissolution and constant temperature of polymer samples.

After a warm-up period (which can be selected and adjusted by the user), the software program starts to automatically run the measurement. The method used to measure intrinsic viscosity is the serial dilution method, also known as the dilution linear extrapolation method. *Measure the cycle, as it is undiluted, testing a high viscosity solution. Afterwards, the sample solution will be automatically diluted, preheated, and tested according to the pre-set concentration, repeating this process until the entire concentration series of samples is tested.

The detailed principles and calculation formulas for measuring characteristic viscosity can be found in various domestic and foreign literature, and will not be elaborated here.

image1:Equipped with an automatic burette and two dilution viscometersPVS1/2Schematic diagram of two measurement systems

Legend:

(1)Automatic cleaning moduleVRM4HT (2)Automatic burette(Swiss Wantong 765 model)

(3)Dilution type Ubbelohde viscometer with sintered glass sand filter(4)magnetic stir bar

(5)Built in magnetic stirrer(6) PTFEExtract tube, used to discharge samples and solvents

(7) VRM-liquid addition pipeline, cleaning solvent enters capillary tube(8)Manual sampling port

(9)Closed plug(10) VRM-Extract the tubing, sample, and cleaning solvent from the capillary tube

(11)Sample funnel(12)External controllable extraction pumpVRP

(13)Silicone tube - connecting suction pump and waste liquid bottle(14)Silicone rubber ventilation pipeline - steam exhaust

(15)Waste liquid bottle for storing samples and cleaning agents(16)bottle cap( GL45thread)

(17) PTFEPipeline - ConnectionVRM4HTAnd solvent bottle(18)Storage bottle for holding cleaning solvents

(19) PTFETube connection burette andVRM4HT(20)Valve unit for extracting hot polymer solution

(21)Valve unit for feeding solvent from burette

After the series of measurements were completed, LAUDA was equipped with a powerful and controllable suction pump(12)Pass the sample through an independent valve unit placed in a constant temperature bath(20)，Discharged into the waste liquid bottle(15)In the middle. and then throughVRM4HT(1)Clean the solvent(I.e. sample solvent)Feed into the viscometer for rinsing, and finally blow dry the viscometer. After completing a complete cleaning procedure, the viscometer can proceed to measure the viscosity of the next series of samples.

To complete the testing of a sample, it may usually require1.5Up to 2 hours of time. The main reason for the long testing time is that the dissolution process of the sample in the viscosity tube may take 1 hour or more. We have another configuration that uses an automatic sampler, which will be explained in detail in the next section.

The important characteristics of LAUDA viscometer in characterizing the viscosity of polyethylene and polypropylene are summarized as follows:

Add powdered or granular samples into a special dilution viscometer equipped with a sintered glass sand filter. The viscometer has a magnetic stirrer inside and is placed in135°CIn a high-temperature bath, the sample automatically dissolves and dilutes at this temperature without the need to transfer hot samples and solvents.

After the pre selected dissolution and constant temperature time by the user has ended，The system automatically starts the measurement, ensuring the reproducibility of the measurement and further simplifying the operation.

The specially designed valve unit can be used for liquid distribution, which allows two viscometers to only require one liquid dispenser.

passVRThe M4HT module and a high-power vacuum pump discharge the sample into a waste liquid bottle, and then add cleaning solvent to the viscosity tube to thoroughly clean and dry it, ensuring that there is no residual sample or cleaning agent in the viscometer.

The operation of the liquid dispenser and the filling and discharging of the cleaning solvent are all controlled by the program.

The measurement of two or four samples can run automatically.

plan2——Equipped with an automatic sampler and an integrated dissolution stationPVS

For users with a large sample size,LAUDAAnother higher version configuration can be provided, which is an upgrade based on the two or four bit configuration with automatic cleaning module mentioned earlier.

For this versionPVSSystem, additional functional modules required: one unitPALAutomatic sampler, an automatically heated feed injector, and a dissolution station that matches the injector. The dissolution station adopts electric heating method, and the high operating temperature can reach200°C，Can be placed simultaneously up to14aPE/PPDissolve the sample. The prepared sample solution is first drawn into a heated syringe and then automatically injected into a fixed sample135°CIn a glass viscometer in a constant temperature bath.

For the measurement of viscosity, or using an approximate formula (such as according toSchulz-BlaschkeMeasurement of intrinsic viscosity using formula，No dilution type Ubbelohde viscosity tube is required, so there is no need to install a magnetic stirrer under the constant temperature bath. For the above tests, standardDIN/ISO/ASTMUbbelohde viscometerI(k=0.01)Just enough. Since there is no sintered glass sand filter for this viscosity tube, the sample solution must be filtered before being added to avoid the dispersion of measured values, and at the same time avoid the blockage of narrow capillary tubes caused by undissolved polymer or gel particles in the solution.

LAUDAProvide a filter element made of corrosion-resistant stainless steel material(0.1mmaperture)，Insert this component into the sample bottle before injection. The sample injector of the automatic sampler will extract samples through this filtering element without the need for manual filtration. This filtering element can be called an "online filter". These filters are easy to clean, and the replacement of the filter mesh is also fast and simple.

There are a total of 15 workstations in the dissolution station, with 14 positions reserved for placing samples and 1 position reserved for placing cleaning bottles for syringes. Accurately measure and add solvent to the sample bottle，Place the sample bottle into the dissolution block. The subsequent operation loop will continue:

1. Users weigh using laboratory scalesPE/PPSample to50 mlsample vial(LAUDAattachment)Medium, and add an appropriate volume(about30-50 ml)The solvent. It can be manually added or added using a metering dispenser. At this point, it must be considered that the temperature at which the liquid is added is room temperature, while the measurement temperature is 135 ℃. The volume of the liquid at room temperature is much smaller than its volume at the temperature measured in the viscometer. The impact of this effect can be considered through the PC software of LAUDA viscometer, and a feasible solution at this time is to use mass concentration as the standard. ThereforeLAUDAA method has been developed that is based on commercial analytical scales and metrological dispensers (such as Metrohm 765), allowing for precise measurement of capacity and weight directlyPVSSoftware orLIMSCommunication.

2. After adding the solvent, place the magnetic stirrer, insert the online filter and seal the bottle with aluminum foil. Then place the sample bottle into a heating block with magnetic stirring function. The heater is used in conjunction with the automatic sampler. Subsequently, the user must immediatelyPVSSet the sample to "Ready for Testing" in the software interface and determine the dissolution time.

3. In135°CAfter the dissolution process begins in a mixer at a higher temperature, appropriate methods can be used(Such as stirring, shaking, or a combination of both)Accelerate the dissolution of the sample and achieve optimal homogenization effect.

4. After the sample preparation is completed, it is generally discharged into the mixer in the order of the numbers marked on the mixer. If a sample needs to be measured immediately, it can be achieved by setting priority for that sample number.

5. After the set dissolution time has elapsed, the automatic sampler starts processing * samples, which will enter the syringe through an online filter. The syringe can inject 5ml of the sample into the viscometer through the injection port driven by an electric motor each time. After the injection process is completed, the injector (or sampler) will automatically move to a specific position reserved on the dissolution station for cleaning and drying. If the dissolution of the next sample has been completed and any other measuring station is available, the sample will continue to run the automatic injection program.

6. Users can set the preheating time of the sample based on the temperature between the dissolution station and the constant temperature bath. After the preheating time is over, the measurement of flow time starts. The software will automatically calculate the average of multiple flow times, and then evaluate the viscosity or intrinsic viscosity based on the viscosity and sample concentration data of the polymer solvent that have been measured in advance.for example，according toSchulz-BlaschkeFormula calculation IV.

7. Once the measurement is completed, the sample in the viscosity tube will be drawn out into the waste liquid bottle through a heated valve block, and then the viscosity meter will be cleaned and dried. This process is carried out byVRMThe 4HT cleaning module is completed together with an external pump. After the automatic cleaning is completed, the measuring table returns to a usable state.

Conclusion

For the above two typesLAUDAThe configuration of the viscosity measurement system, as all steps such as sample preparation, measurement, dilution, and cleaning are carried out inside the device and controlled by a computer, greatly simplifies the actual operation process of viscosity measurement of polyethylene and polypropylene solutions, effectively avoiding direct contact between operators and toxic solvents and high-temperature media. On the basis of excellently completing all these tasks,PVThe accuracy, adaptability, and data integrity of the S system will not be affected in any way. LAUDA's current polyolefin application examples in China include Shanghai Petrochemical, SABIC, Yanshan Petrochemical, Maoming Petrochemical, Saico Petrochemical, Fushun Petrochemical, Dushanzi Petrochemical, and so on.