I would suggest use standard SAP delivered classes to dump the comments into NW. the following code might help you.
Data: lo_cmt_manager TYPE REF TO cl_ujc_cmtmanager.
DATA: ls_cmt_db TYPE ujc_s_compact_cmtbl,
lt_cmt_db TYPE ujc_t_compact_cmtbl.
TRY .
* create comment manager
CREATE OBJECT lo_cmt_manager
EXPORTING
i_appset_id = <XYZ>
i_appl_id = <ABC>
if_disable_security = abap_true.
CATCH cx_ujc_exception.
RAISE EXCEPTION TYPE cx_ujxc_cmt
EXPORTING
textid = cx_ujxc_cmt=>ex_cmt_mgr_err.
ENDTRY.
TRY.
CALL METHOD lo_cmt_manager->add_cmts_fast
EXPORTING
it_compact_cmtbl = lt_cmt_db
it_all_dim_mbr = lt_all_dim_mbr_collection
IMPORTING
ef_inserted = lf_success
et_error_cmtbl = lt_error_cmtbl
CHANGING
ct_message = lt_message.
CATCH cx_ujc_exception INTO lx_ujc_exp.
ENDTRY.