Guide

PET Resin Drying: Dew Point, Temperature and Moisture

Check resin-specific drying requirements using measured dew point, temperature, airflow, residence time and moisture before investigating preform quality.

Direct answer

PET Resin Drying: Dew Point, Temperature and Moisture: key points

Use the processing instructions for the actual PET resin grade to set drying temperature, air dryness, airflow, residence time and residual-moisture limits. Moisture during melt processing can cause hydrolytic degradation and loss of molecular weight. Check resin and preform evidence when investigating a defect; a bottle appearance alone cannot establish that drying failed.

Blowing settings do not restore polymer chain length lost during melt processing, but an observed bottle defect still needs a confirmed cause.
Check air dryness, temperature and airflow together at the specified measurement locations.
Estimate nominal residence time from usable resin mass divided by mass throughput, then check actual hopper flow and startup conditions.
Do not substitute an as-packed moisture value for the required moisture before injection or deliberately relax the resin supplier limit.

Review status

What this page is reviewed against.

ClusterBlow machine selection

Last reviewed2026-07-15

Use this page forShortlisting, RFQ preparation and evidence-aware route selection

Factory and route evidence

Public references linked to this buying decision.

These links point to public route pages, reference media or downloadable worksheets that buyers can review before requesting a project-confirmed quote.

PET preform mold route Drying sits upstream of the preform mold, not on the blowing line. PET bottle defects and their causes Compare material evidence with alternative explanations for visible defects. Compressed air and cooling requirements Check measured utility conditions alongside the material investigation.

Decision table

Use this guide to avoid vague machine or mold quotes.

Each row converts a common buying question into the exact data engineering needs before final route selection.

Drying air dew point	Use the resin supplier limit and specified sensor location; compare measured delivery with the dryer display
Air and pellet temperatures	Identify which temperature the supplier specifies and where it is measured; check both during operation
Nominal residence time	Usable resin mass in kg / throughput in kg per hour gives hours; this average does not prove the residence of every pellet
Moisture acceptance	Use the resin-grade limit and approved test method at the specified point before injection
Sampling control	Record sampling time, location and handling so moisture results represent the resin entering the process
Intrinsic viscosity review	Use material test results if degradation is suspected; do not intentionally increase moisture to adjust IV without a validated specialist process
What happens when PET is wet	Hydrolysis splits the polymer chains, intrinsic viscosity falls, and the preform becomes weaker and more brittle
Startup and stoppages	Follow resin and dryer instructions for startup, interruptions and extended heating; do not infer readiness from elapsed time alone
Bottle observations	Appearance or strength changes may justify a material investigation but do not diagnose moisture or IV loss by themselves
Changing resin feed	Review incoming moisture, storage exposure, recycled-content specification and throughput when the feed changes
Engineering confirmation	Confirm dryer delivery, usable hopper capacity, residence and moisture acceptance for the actual resin and throughput

Workflow

Prepare the buyer-side data package.

01 Step 1

Confirm the dew point at the location specified by the resin and dryer instructions, and investigate delivery or regeneration problems if measured conditions differ.

02 Step 2

Check residence time against real throughput, not the hopper volume alone, because a faster line empties the hopper faster and shortens time at temperature.

03 Step 3

Sample resin at the specified pre-injection acceptance point using the approved handling and test method; record exposure during transfer from the dryer.

04 Step 4

Compare resin moisture and preform evidence with bottle symptoms, then review drying and blowing conditions without assuming one cause from appearance alone.

FAQ

Questions this guide answers.

What moisture level does PET need before injection?

Use the limit in the current processing instructions for the actual resin grade, together with the specified test method and sampling point. An as-packed moisture value or a limit for another resin is not a substitute.

Can a bottle defect from wet resin be fixed on the blowing machine?

Blowing adjustments do not restore molecular weight lost through hydrolysis during melting. However, do not assume that a visible defect proves this mechanism: check material measurements and trial evidence before attributing it to wet resin.

Why is dew point specified as well as temperature?

Temperature, air dryness and airflow all affect moisture removal. A temperature setpoint alone does not show that the delivered drying conditions meet the resin instructions; verify the specified measurements during operation.

How would I know the dryer is under-sized rather than faulty?

Compare usable resin mass and actual throughput with the specified residence time, then check airflow, temperatures, dew point and hopper flow. Insufficient nominal residence suggests a capacity problem, but measurements are still needed to separate it from delivery or control faults.

Does regrind change the drying requirement?

Review the actual recycled feed specification, moisture, particle form and processing history. Do not assume all recycled material has the same IV or drying behaviour; use the applicable supplier instructions and verify moisture at the acceptance point.