High Temperature Non Aqueous Volatile Acid Titration in Recycled Polyethylene
High temperature non-aqueous titration strips volatile carboxylic acids from hot PE melt into organic media to quantify corrosion risks and thermal stability.
Blown Film Defects
Meaning
Departures from specified quality or optical clarity occurring during the extrusion and cooling of thin plastic membranes represent a primary source of scrap in flexible packaging production. These blown film defects occur when processing parameters like melt temperature or blow-up ratio deviate from the stable window defined for a specific resin grade. Operators identify such issues through visual inspection or automated cameras to prevent the shipment of non-conforming rolls.
Visual Irregularity
Optical imperfections such as gels or fish eyes indicate unmelted resin or contamination within the melt stream. When blown film defects take the form of arrowheads or chevrons, the cause usually lies in localized stress or temperature gradients at the die lip. Heavy frost lines or hazy patches suggest insufficient cooling or incorrect air ring adjustment.
Correcting these surface issues requires a precise balance between internal bubble cooling and external airflow.
Thermal Instability
Temperature fluctuations in the extruder barrel or die often produce thickness variations known as gauge bands. These blown film defects cause uneven winding and can lead to telescope-shaped rolls that jam downstream converting equipment. Molten plastic that remains too hot upon leaving the die may suffer from bubble instability, leading to a total collapse of the production line.
Mechanical Failure
Physical weaknesses such as low dart impact or poor tear strength result from improper molecular orientation during the stretching phase. While some blown film defects are purely aesthetic, these structural failures render the final product unfit for containing heavy loads or sharp objects. Monitoring the blow up ratio and the draw down ratio ensures the film maintains the necessary strength in both the machine and transverse directions.
Because molecular alignment is determined early in the cooling process, any drift in the cooling rate will compromise the integrity of the entire production run.